Patent Publication Number: US-2011059821-A1

Title: Infinitely variable transmission

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to, and the benefit of, U.S. Provisional Application Ser. No. 61/276,121, filed on Sep. 8, 2009 and entitled “INFINITELY VARIABLE TRANSMISSION,” to U.S. Provisional Application Ser. No. 61/240,646, filed on Sep. 8, 2009 and entitled “REVERSE DIFFERENTIAL WITH ENGAGED NEUTRAL,” to U.S. Provisional Application Ser. No. 61/281,460, filed on Nov. 18, 2009 and entitled “INFINITELY VARIABLE TRANSMISSION,” to U.S. Provisional Application Ser. No. 61/294,388, filed Jan. 12, 2010 and entitled “INFINITELY VARIABLE TRANSMISSION,” to U.S. Provisional Application Ser. No. 61/307,380, filed on Feb. 23, 2010, and entitled “CHAIN FOR INFINTELY VARIABLE TRANSMISSION,” to U.S. Provisional Application Ser. No. 61/323,795, filed on Apr. 13, 2010, and entitled “INFINITELY VARIABLE TRANSMISSION,” and to U.S. Provisional Application Ser. No. 61/378,875, filed on Aug. 31, 2010 and entitled “INFINITELY VARIABLE TRANSMISSION WITH SPROCKET CORRECTION MECHANISM.” The foregoing applications are each expressly incorporated herein by this reference, in their entireties. 
    
    
     BACKGROUND OF THE INVENTION 
     1. The Field of the Invention 
     The present application relates to the field of transmission systems. More particularly, embodiments within the scope of the application and claims relate to methods, systems, sub-systems, assemblies, and components for providing constant engagement during power transmission, and during changes of gear ratios in very small, and possibly infinitely small, increments. 
     2. Related Technology 
     From nearly the beginning of mechanical engines, the purpose and design of an engine has been focused, to at least some degree, on allowing a small engine to move a large load. As engines evolved and technology became more sophisticated, engines were developed having transmissions with multiple ratios to allow the engine to start moving the load with a low ratio and to incrementally step up to higher ratios as the load began moving. In this manner, a transmission can make more effective use of the engine&#39;s torque and keep the engine operating near an appropriate speed. Moreover, an engine can operate within a narrow range of speeds while providing a wider range of output speeds. 
     To effect an incremental change in gear ratio, a manual transmission uses various separate driven gears of different sizes in connection with one or more drive gears. As a gear ratio change is made, a drive gear disengages from the driven gear and re-engages with a different gear. For example, a clutch may disengage a drive gear from a driven gear and then re-engage the same or a different drive gear with a second driven gear having a different radius. As the newly engaged gears have different radii—or levers—the gear ratio is changed. To effect this gear ratio change, however, the drive gear must be temporarily disconnected from all driven gears, such that the power source is also temporarily disconnected from the load while the gear ratio change is made. 
     Automatic transmissions also make incremental changes in gear ratio by disconnecting the engine from the load. To do so, automatic transmissions typically use one or more planetary gear sets which are used in connection with a series of clutches and bands that are driven by hydraulic system. To change between gear ratios, valves within the hydraulic system are used to control hydraulic pressure which activates various clutches and bands so as to connect and disconnect the carriers and various gears of the automatic transmission from the engine. Based on the specific clutches and bands that engage and disengage, the transmission achieves a predetermined gear ratio change. 
     When the power source is disconnected or disengaged from the load, the engine coasts until the power source is reconnected to the load. As the engine coasts, however, a moving load begins to lose momentum. For instance, a semi-tractor trailer or other moving vehicle may be moving uphill when a gear change is required. By pushing in the clutch or otherwise disconnecting the power source from the load, the engine RPMs are decreased, turbos may be dumped, and torque can be lost. As a result, the driver often must shift two or three gears down because re-engaging the power source will not occur fast enough to maintain the engine RPMs at a drop of only one or two gears down. This results in an inefficient use of the engine horsepower and fuel. 
     Similarly, where a tractor is pulling a load such as a plow, disconnecting the engine from the load reduces the momentum of the tractor and the plow. While the tractor may be able to coast, the plow is less likely to coast. For example, when the plow loses momentum it may catch on the ground being plowed and thereby drag against and stop the tractor from coasting. The plow may catch and stop with a sudden movement that can damage the tractor and potentially injure the operator. Therefore, to avoid damage and injury, the tractor operator may drive the tractor and plow in a low gear to avoid the need to shift gears although a higher gear would allow the tractor to more quickly plow the field, consume fuel more efficiently, and make use of the momentum to obtain a draft of the plow. 
     In addition, many other applications have previously been unable to take advantage of the benefits of a variable speed transmission because disconnection of the power source from the load makes the application unsafe or impractical. For example, an elevator could benefit from gear ratio changes to change the speed of its ascent or descent. However, disconnecting the power source during ascent or descent would cause the elevator carriage to coast and could make the variable speed transmission unsafe for the elevator passengers. 
     A conveyor system such as those used in manufacturing or mining operations could also benefit from variable speeds. For example, as the system starts up, the conveyor belt could be started at a slow speed and the speed then increased for full operation. Many conveyor belts are, however, loaded with material and/or are miles long, thereby creating a large load that must be moved. If a gear ratio change is made by even temporarily disconnecting the power source, the material and conveyor belt lose momentum and can prevent an efficient gear ratio change. As a consequence, materials often have to be removed from the belt just to get the conveyor moving and/or the conveyor system must be operated at a constant speed. 
     While variable speed transmissions provide numerous benefits, the problems of the disconnection of the power source from the load has caused engine and transmission designers to search for methods and systems that minimize the time the power source is disconnected and a drive gear is disengaged. To at least some degree, automatic transmissions have improved this time by automating the shifting between gears and changing gear ratios, but the change has not been fundamental, although such automatic transmissions have at least reduced the time between disconnecting and reconnecting the power supply. However, even automatic transmissions disconnect the engine from the drive gears, thereby causing a loss in torque for a time and failing to make an efficient use of the horsepower. Moreover, by operating with only a small group of discrete gear ratios—each having only one or a very few speeds at which the engine operates at optimum efficiency—the engine operates mostly in an inefficient range. Consequently, the engine must be capable of providing more horsepower, and must thus be larger, than would otherwise be required if an engine was more frequently running at an efficient speed. The inefficient use of these engines, in turn, burns more fuel than would an engine run at more efficient speeds. 
     In low torque applications, the problems associated with disconnecting the power source from the load have been reduced, to some extent, by continuously variable transmissions (CVT). A CVT typically uses two pulleys which are connected by a belt. The pulleys can include two oppositely oriented cones that face each other and which can be pulled together or pushed further apart by hydraulic pressure, centrifugal force, or spring tension. As one pulley is moved to position the belt over a larger radius portion, the other pulley is moved to position the belt over a smaller radius to keep the belt tight. As the position of the belt changes to engage portions of pulleys with differing widths, various gear ratios can be created. A similar concept that may also be considered a CVT also makes use of similar, complementary pulleys and cones. Instead of a belt, however, the CVT uses a rolling member that is sandwiched between the cones. 
     Regardless of whether a belt or a rolling member is used, however, the CVT system generally relies on friction to facilitate adjustment of gear ratios and provide power output. Friction introduces heat into the system, however, and as a result the wrapping member and rolling members heat up and are susceptible to wear damage, thereby requiring that the user repair or replace the parts. To reduce the frequency of repair, the frictional wrapping or rolling members can be toughened, such as through the use of a thicker belt or impregnation of the belt with metals or other tougher materials. However, as the belt strength is increased, the part costs increase. Moreover, sufficiently tough materials can cause the cones or pulleys within the transmission to wear and fail. 
     Moreover, because these systems are friction-based, they are typically only suitable for low torque applications, as high torque applications could cause excessive heating within the transmission, thereby causing even greater wear and failure of the transmission components. As a result, CVT transmissions are not considered scalable for a wide variety of low and high torque applications. In fact, the application of torque to a CVT in a high torque or high horsepower system may cause near immediate failure as the rolling member or wrapping member can melt or otherwise deteriorate due to the friction-induced heat. 
     Because the CVT systems have been seen as unacceptable alternatives in high-torque applications, additional efforts have been made within high-torque applications in an attempt provide little to no time gap between disconnection and reconnection of the power source and load. For example, John Deere produces tractors with a PowerShift transmission that uses a complex design to automatically do the clutching and disconnect a clutch and reconnect the clutch at the same time such that there is no real time gap and little to no torque loss. The transmission is, however, much larger than a standard transmission, and can house a large number of hydraulic lines inside the transmission. As a result, maintenance of the lines may be difficult, and the size of the engine further increases the size of the equipment and the weight or load that must be carried. Moreover, because of the complexity and size of the transmission, it can be cost prohibitive for certain applications, and it is not scalable for low torque or smaller applications. 
     Accordingly, a need exists for an improved transmission which is scalable and which can move between multiple gear ratios without disconnecting the power source from the load. 
     BRIEF SUMMARY OF EXAMPLE EMBODIMENTS OF THE INVENTION 
     Exemplary embodiments of the present disclosure are directed to a transmission capable of operating over a large, possibly infinite, number of gear ratios. 
     In at least some aspects, a transmission includes an axially movable sheave, radially movable gears, and a chain engaged with the axially movable sheave and the radially movable gears. 
     In at least one aspect that can be combined with any other aspects herein, the radial movement of the radially movable gears is in an amount corresponding to axial movement of the axially movable sheave. 
     In at least one aspect that can be combined with any other aspects herein, the axially movable sheave is rotatable about an axis. 
     In at least one aspect that can be combined with any other aspects herein, the radially movable gears collectively orbit about a common axis. 
     In at least one aspect that can be combined with any other aspects herein, the radially movable gears are rotatable about respective internal axes; 
     In at least one aspect that can be combined with any other aspects herein, the chain orbits around an axis. 
     In at least one aspect that can be combined with any other aspects herein, a radius of the chain relative to an axis corresponds to a radial position of the radially movable gears. 
     In at least one aspect that can be combined with any other aspects herein, a radius of the chain relative to an axis corresponds to a position of a pair of angled surfaces of the sheave, the pair of angled surfaces being offset by a distance corresponding to a width of the chain. 
     In at least one aspect that can be combined with any other aspects herein, the radially movable gears are movable are movable in very small, and possibly infinitely small, increments within a range of radial positions. 
     In at least one aspect that can be combined with any other aspects herein, the sheave includes two halves, one or both of which are axially movable. 
     In at least one aspect that can be combined with any other aspects herein, the radially movable gears are at least partially disposed within the sheave. 
     In at least one aspect that can be combined with other aspects herein, a chain is rotatable around a sheave, and can engage each of the radially movable gears during a portion of the rotation of the chain. 
     In at least one aspect that can be combined with any other aspects herein, the chain is adapted to enter into and out of engagement with each of the radially movable gears. 
     In at least one aspect that can be combined with any other aspects herein, a sheave has a beveled internal surface and a chain has a plurality of links with an external surface inclined at an angle generally corresponding to the beveled internal surface of the sheave. 
     In at least one aspect that can be combined with any other aspects herein, a transmission includes a synchronization system configured to control at least radial movement of the radially movable gears. 
     In at least one aspect that can be combined with any other aspects herein, the synchronization system is configured to move the radially movable gears generally synchronously with axial movement of the sheave and radial movement of the chain. 
     In at least one aspect that can be combined with any other aspects herein, a correction system is coupled to the radially movable gears and can be used to selectively rotate the radially movable gears about their internal axes. 
     In at least one aspect that can be combined with any other aspects herein, radially movable gears are movable between at least one integer position and multiple non-integer positions. 
     In at least one aspect that can be combined with any other aspects herein, a correction system can cause selective rotation of radially movable gears only at non-integer positions. 
     In at least one aspect that can be combined with any other aspects herein, a correction system can rotate a radially movable gear independent of other of the radially movable gears. 
     In at least one aspect that can be combined with any other aspects herein, a correction system can rotate radially movable gears while disengaged with the chain. 
     In at least one aspect that can be combined with any other aspects herein, the transmission includes a locking system. 
     In at least one aspect that can be combined with any other aspects herein, a locking system can lock a radially movable gear over a period during which the radially movable gear is engaged with the chain. 
     In at least one aspect that can be combined with any other aspects herein, the locking system can lock the radially movable gear against rotation around its internal axis. 
     In at least one aspect that can be combined with any other aspects herein, a sheave is coupled to, and is rotatable around, a drive shaft. 
     In at least one aspect that can be combined with any other aspects herein, a transmission includes a transmission input that is configured to receive a rotational input. 
     In at least one aspect that can be combined with any other aspects herein, a chain is engaged with an output member, and the output member is linked to a transmission output. 
     In at least one aspect that can be combined with any other aspects herein, one or more actuators are coupled to an input assembly of a transmission. 
     In at least one aspect that can be combined with any other aspects herein, an actuator is configured to correct, synchronize, or lock radially movable gears, or moves a sheave in an axial direction. 
     In at least one aspect that can be combined with any other aspects herein, an actuator is a hydraulic actuator, an electrical actuator, a mechanical actuator, a controller, or a gear train. 
     In at least one aspect that can be combined with any other aspects herein, an actuator is configured to maintain constant tooth engagement between teeth of the radially movable gears and a chain during changes in gear ratio. 
     In at least one aspect that can be combined with any other aspects herein, gear ratio changes may occur from one or more of an integer position to a non-integer position, a non-integer position to an integer position, or a non-integer position to another non-integer position. 
     In at least one aspect that can be combined with any other aspects herein, at a non-integer position, a circumference of an effective circle around the sheave at a point of contact with the chain is not equally divisible by one or both of a pitch of the chain or a pitch of the radially movable gears. 
     In at least one aspect that can be combined with any other aspects herein, a radially movable gear is movable out of engagement with the chain while in-line with the chain and, but for a correction system, would be out-of-line with the chain at re-engagement with the chain. 
     In at least one aspect that can be combined with any other aspects herein, a transmission includes at least three radially movable gears. 
     In at least one aspect that can be combined with any other aspects herein, a transmission includes a differential adapted to receive two inputs and provide a single output. 
     In at least one aspect that can be combined with any other aspects herein, two inputs to a differential include a first input that is at least partially affected by a gear ratio involving an output system, and a second input that is independent of the output system. 
     In at least one aspect that can be combined with any other aspects herein, a correction system includes at least one of a set of hydraulic turbines, an off-center ring gear, a wheel-and-ball assembly having two pocket wheels and a set of balls between the two pocket wheels, a follower gear coupled to a chain and mechanically linked to a moon gear shaft for each radially movable gear, or a worm gear coupled at least indirectly to an actuator, rotation of the worm gear configured to rotate a respective radially movable gear about its own axis. 
     In at least one aspect that can be combined with any other aspects herein, a wheel-and-ball assembly includes a spring loaded mechanism coupled to at least one pocket wheel. 
     In at least one aspect that can be combined with any other aspects herein, a pitch of a pocket wheel corresponds to a pitch of one or both of a radially movable gear or a chain. 
     In at least one aspect that can be combined with any other aspects herein, a synchronization mechanism includes a linearly defined radial path, an arcuate radial path, a radial movement slot in a sheave, a worm gear coupled to an actuator and the worm gear rotating to move a radially movable gear in a radial direction, an outer ring gear with multiple inner gears, each inner gear linking to an arm coupled to a radially movable gear such that rotation of the inner gear rotates the arm and the radially movable gear, or a shifting arm coupled to a cam, where the shifting arm and cam are linked to radially movable gears and the shifting arm is rotatable independent of a drive shaft about which a sheave rotates. 
     In at least one aspect that can be combined with any other aspects herein, a shifting arm is configured to cause radial movement of radially movable gears by causing a relative difference in rotational speed between a drive shaft and a cam. 
     In at least one aspect that can be combined with any other aspects herein, a locking system includes a worm gear, cam ring, set of clutch disks compressed by a spring, a wedge and yoke, or any combination thereof. 
     In at least one aspect that can be combined with any other aspects herein, a transmission includes a tensioning system. 
     In at least one aspect that can be combined with any other aspects herein, the tensioning system includes some combination of a second axially movable sheave, a movable tensioning gear positioned between an input assembly and an output assembly, or a pivot and actuator coupled to an output or input member, wherein the actuator is arranged to cause the input or output member to orbit at least partially around the pivot. 
     In at least one aspect that can be combined with any other aspects herein, a chain is configured to engage an axially movable sheave of an input system and transfer power through a fixed-size output system. 
     In at least one aspect that can be combined with any other aspects herein, a chain is configured to engage a fixed-size input member and transfer power through an axially movable sheave of an output system. 
     In at least one aspect that can be combined with any other aspects herein, a chain link includes a fluid retention system. 
     In at least one aspect that can be combined with any other aspects herein, a chain link includes an angled roller. 
     In at least one aspect that can be combined with any other aspects herein, each link of a chain is identical. 
     These and other aspects of example embodiments of the present disclosure will become more fully apparent from the following description and appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To further clarify the aspects of embodiments of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
         FIG. 1  illustrates a schematic representation of a transmission according to one example embodiment of the present disclosure; 
         FIG. 2  illustrates a perspective view of an exemplary transmission according to another example embodiment of the present disclosure; 
         FIG. 3  illustrates a partial perspective view of the transmission of  FIG. 2 , including an exemplary embodiment of a synchronization system; 
         FIG. 4  illustrates a partial perspective view of the transmission of  FIG. 2 , including an exemplary embodiment of a correction system; 
         FIG. 5A  illustrates a perspective view of a differential system of the transmission of  FIG. 2 ; 
         FIG. 5B  illustrates a side view of the differential system of  FIG. 5A ; 
         FIGS. 6A-6D  illustrate components of the differential system of  FIGS. 5A and 5B  with exemplary rotational and linear velocity conditions; 
         FIGS. 7A and 7B  schematically illustrate exemplary embodiments of a transmission having primary and secondary power supplies to a reverse differential; 
         FIG. 8A  illustrates a perspective view of a portion of a chain according to one exemplary embodiment of the present disclosure; 
         FIG. 8B  illustrates a frontal view of the exemplary chain of  FIG. 8A ; 
         FIG. 9A  illustrates a perspective view of a transmission according to another example embodiment of the present disclosure; 
         FIG. 9B  illustrates a partial cross-sectional side view of the transmission of  FIG. 9A ; 
         FIG. 9C  illustrates an enlarged perspective view of a turbine disk correction mechanism in the transmission of  FIG. 9A ; 
         FIG. 10  illustrates an enlarged perspective view of a surface of a turbine disk in the transmission of  FIG. 9A ; 
         FIG. 11  illustrates an example hydraulic system usable to drive hydraulic actuators used in connection with embodiments of the present disclosure; 
         FIG. 12A  illustrates a perspective view of a chain link usable with transmissions according to some embodiments disclosed herein; 
         FIG. 12B  illustrates a frontal view of the chain link illustrated in  FIG. 12A ; 
         FIG. 13  illustrates a frontal view of a chain engaged with a transmission sprocket, according to some embodiments of the present disclosure; 
         FIG. 14A  illustrates a perspective view of a transmission according to another exemplary embodiment of the present disclosure; 
         FIG. 14B  illustrates a frontal view of the transmission of  FIG. 14A ; 
         FIG. 14C  illustrates a partial rear view of the transmission of  FIG. 14A ; 
         FIG. 15  illustrates a chain link usable in accordance with some embodiments of transmissions disclosed herein; 
         FIG. 16A  schematically illustrates an overhead cross-sectional view of a portion of a chain link engaging a sheave; 
         FIG. 16B  illustrates a side cross-sectional view of the portion of the chain link and sheave in  FIG. 16A ; 
         FIG. 17A  illustrates a perspective view of a transmission according to another exemplary embodiment of the present disclosure; 
         FIG. 17B  illustrates a rear view of the transmission of  FIG. 17A ; 
         FIG. 18  schematically illustrates an exemplary differential system usable in accordance with various transmissions; 
         FIG. 19A  illustrates a partial perspective view of a differential system of the transmission of  FIG. 17A ; 
         FIG. 19A  illustrates a partial frontal view of the differential system of the transmission of  FIG. 17A ; 
         FIG. 20  illustrates a perspective view of a transmission according to another embodiment of the present disclosure; 
         FIG. 21A  illustrates a rear perspective view of a synchronization system of the transmission of  FIG. 20 ; 
         FIG. 21B  illustrates a frontal perspective view of the synchronization system of the transmission of  FIG. 20 ; 
         FIG. 22A  illustrates a frontal view of a locking system of the transmission of  FIG. 20 ; 
         FIG. 22B  illustrates a side cross-sectional view of the locking system of the transmission of  FIG. 20 ; 
         FIG. 23  schematically illustrates a transmission according to an embodiment of the present disclosure; 
         FIG. 24A  illustrates a rear perspective view of a correction system of the transmission of  FIG. 20 ; 
         FIG. 25A  illustrates a perspective view of a transmission according to another embodiment of the present disclosure; 
         FIG. 25B  illustrates a rear view of a locking system of the transmission of  FIG. 25A ; 
         FIG. 25C  illustrates a side cross-sectional view of the transmission of  FIG. 25A ; and 
         FIG. 26  illustrates an exemplary method of designing a transmission according to the principles disclosed herein, with components and system being interchangeable. 
     
    
    
     DETAILED DESCRIPTION OF SOME EXAMPLE EMBODIMENTS 
     This description relates to transmission systems. More particularly, the description herein relates to transmission systems that can convey power from a source to a load using gear ratios that are changeable in very small, perhaps infinitely small, increments. More particularly still, the description relates to transmission systems usable with any of a variety of technologies, and which can in at least some embodiments operate with an engaged neutral and move in very small, perhaps infinitely small, increments either forward or reverse out of the engaged neutral. 
     Reference will now be made to the drawings to describe various aspects of example embodiments of the present disclosure. It is to be understood that the drawings are diagrammatic and schematic representations of such example embodiments, and are not limiting of the present disclosure. Moreover, while various drawings are provided at a scale that is considered functional for some embodiments, the drawings are not necessarily drawn to scale for all contemplated embodiments. The drawings thus represent an exemplary scale, but no inference should drawn from the drawings as to any required scale. 
     In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be obvious, however, to one skilled in the art that the present disclosure may be practiced without these specific details. In other instances, well-known aspects of transmission systems, including bearings, journals, manufacturing processes, and the like have not been described in particular detail in order to avoid unnecessarily obscuring aspects of the disclosed embodiments. 
     A. Infinitely Variable Transmission 
       FIG. 1  illustrates an example infinitely variable transmission  10  according to various aspects of the present disclosure. Briefly, transmission  10  illustrated in  FIG. 1  is configured in a manner that allows very small, and possibly infinitely small, variations in gear ratio without disconnection between a power source and an associated load. More particularly, power is input to the transmission  10  at a transmission input  12  and power is output from the transmission  10  at a transmission output  14 . The power input at the transmission input  12  and the power output at the transmission output  14  may be in the form of a rotational power, and other components of the transmission  10  can be used to determine the gear ratio between the transmission input  12  and the transmission output  14 . The gear ratio in the transmission  10  can change in very small increments. For instance, as discussed hereafter, power transfer members may slide between radial and/or axial positions, such that any position along a movement path can be used to produce a gear ratio. In some embodiments, the movement can be in infinitely small increments. In other embodiments, the movement may be in very small increments. A very small increment can include, for instance, where gear ratio changes are made between gear ratios that involve non-integer locations as described hereafter. 
     As described in greater detail herein, the components between the transmission input  12  and the transmission output  14  optionally remain engaged and maintain a physical connection between the power source that is coupled to the transmission input  12 , and the load that is coupled to the transmission output  14 . In some embodiments, the transmission  10  may even maintain engagement between the power source and the load while the power source is operating and supplying a power input to the transmission input  12 , while the transmission output  14  has a zero velocity output. Such an aspect is sometimes referred to herein as an engaged neutral. 
     In another aspect of the transmission  10 , the gear ratio of the transmission can be increased and/or decreased in very small, and possibly infinitely small, increments. The maximum and minimum gear ratios provided by the transmission  10  are a configurable aspect of the transmission  10 , and can be varied to suit any number of different applications. For instance, the transmission  10  may include various components as discussed hereafter. By adjusting the features of such components, including the number, size, type, shape, profile, or other feature, or any combination of the foregoing, of such components, the transmission  10  can be adapted to operate in a number of different environments and applications. For instance, the transmission  10  can be adapted to operate with land vehicles (e.g., conventional automobiles, electric automobiles, hybrid automobiles, motorcycles, scooters, etc.), marine vehicles (e.g., ships, barges, boats, etc.), power generating devices (e.g., wind and water based power generating devices), transport systems (e.g., conveyor belts, elevators, escalators, etc.), and in virtually any other industry or application. Indeed, according to one aspect of some embodiments of the present disclosure, the transmission  10  further has the capability of operating at a constant velocity to manage torque spikes, or is otherwise configured in a way that makes the transmission  10  particularly suited to use in high-torque applications (e.g., construction equipment, semi-tractor trailers, trains, etc.). Accordingly, at least some embodiments of the transmission  10  may effectively operate as a universal transmission suited for virtually any application where a gear ratio and/or output speed change is desired. 
     Gear ratio changes are made in the transmission  10  using a drive system  16 . The drive system includes an input system  18  and an output system  20 , and either or both of the input and output systems  18 ,  20  may be used to produce gear ratio changes. In practice, the input system  18  of the illustrated embodiment is coupled to the transmission input  12  and receives power therefrom. Power from the transmission input  12  passes through the input system  18 . The output system  20  is coupled to the input system  18 . Consequently, the power input to the input system  18  is conveyed to the output system  20 , and from the output system  20  to the transmission output  14 . Optionally, the output system  20  includes, or is coupled to, a differential system  22  that may also cooperate with the output system  20  to convey power to the transmission output  14 . In some embodiments, such as that disclosed in  FIG. 1 , the differential system  22  receives two inputs. For instance, the differential system  22  may receive a first power input from the transmission input  12  (e.g., a power input which bypasses the output system  20 ) and a second power input from the output system  20 . The two inputs can be combined to produce an output that is provided to the transmission output  14 . 
     The drive system  16  may facilitate implementation of gear ratio changes within the transmission  10 . According to one embodiment, gear ratio changes are produced in very small, and possibly infinitely small increments. For instance, as described in greater detail herein, the drive system  16  may use engaging members that can slide between different positions. In sliding between different positions, the transmission  10  can have gear ratios that change according to any location along the movement path of the engaging members, thereby producing a large, potentially infinite, number of gear ratios between maximum and minimum positions on the movement path. Further, the drive system  16  can maintain a connection between the power source and the load even during a gear ratio change, such that corresponding driving and driven members may collectively remain under load while a gear ratio change is made. 
     To illustrate an exemplary manner in which gear ratio changes can be made, a more particular discussion of the input system  18  will be provided. It should be appreciated that while such discussion regarding gear ratio changes is provided in relation to the input system  18 , the discussion could additionally or alternatively be made with respect to the output system  20 . In particular, the output system  20  could operate according to the same principles described hereafter in relation to the input system  18 , and may do so either in combination with the input system  18 , or instead of the input system  18 . 
     In  FIG. 1 , the input system  18  includes a drive shaft  24  coupled to the transmission input  12 . The drive shaft  24  may be in-line with the transmission input  12  although it need not be so aligned. For instance, the drive shaft  24  may be offset from the transmission input  12  and coupled thereto by using a belt, chain, gear, or other transfer mechanism, or a combination of the foregoing. 
     In  FIG. 1 , the transmission input  12  may be configured to receive and convey a rotational power input. The drive shaft  24  may also be adapted to rotate as the transmission input  12  rotates. The drive shaft  24  may be integral with the transmission input  12 , or otherwise connected, such that the rotational speed of the drive shaft  24  is the same as the rotational speed of the transmission input  12 , although the rotational speed of the drive shaft  24  may be greater or lesser than the rotational speed of the transmission input  12  where, for example, the drive shaft  24  is coupled to the transmission input  12  using a transfer mechanism that gears the drive shaft  24  up or down relative to the transmission input  12 . The drive shaft  24  may be adapted to rotate in any suitable manner. For instance, in one embodiment, the transmission  10  is contained at least partially within a housing (not shown) and the drive shaft  24  rotates relative to the housing and the drive shaft is supported by one or more bearings (not shown). 
     As also illustrated in  FIG. 1 , some embodiments according to the present disclosure may include a sheave  26  coupled to the drive shaft  24 . The sheave  26  of  FIG. 1  includes two sheave halves  26   a ,  26   b , and each of the sheave halves  26   a ,  26   b  is centered on the drive shaft  24  and configured to rotate around a longitudinal axis of the drive shaft  24 . The sheave halves  26   a ,  26   b  may also be coaxial and rotate around the same drive shaft  24 , rather than separate shafts. The sheave  26  may be rotated by the drive shaft  24 . For instance, using a spline or other suitable connection, the sheave  26  may be coupled to the drive shaft  24  such that the drive shaft  24  an sheave  26  maintain the same rotational speed, although this is merely exemplary. Regardless of the manner of connection between drive shaft  24  and the sheave  26 , rotation of the drive shaft  24  can also cause the sheave halves  26   a ,  26   b  to rotate at a same or different rotational speed. In this manner, power is transferred through input system  18  from the drive shaft  24  to the sheave  26 . 
     The sheave  26  can operate as one driving mechanism for conveying power from the input system  18  to the output system  20 . For example, in the illustrated embodiment, a wrapping member  28  is positioned in a groove within the sheave  26 , and between the sheave halves  26   a ,  26   b . For simplicity, the wrapping member  28  may be referred to herein as a chain. However, the wrapping member  28  can also be a belt, cable, or other member, and can be made of any number of different materials. For instance, the wrapping member may be made from metals, alloys, composites, polymers, metal reinforced polymers, rubber, or other materials, or combinations of the foregoing. 
     The wrapping member  28  of the illustrated embodiment is at least partially wrapped around the sheave  26 . The wrapping member  28  may frictionally engage the sheave halves  26   a ,  26   b , although such frictional engagement may be minimal as described herein. For instance, in some embodiments, the wrapping member  28  and sheave  26  may have metal-to-metal contact, and such contact may possibly also include a lubricant between the wrapping member  28  and the sheave  26 , such that friction between the sheave  26  and the wrapping member  28  is almost negligible. As discussed herein, the sheave  26  may also be movable to define variable radial positions of the wrapping member  28 . While the sheave  26  may, in some embodiments, be used for transferring power to the wrapping member, in other embodiments, the sheave  26  may be used for positioning of the wrapping member  28  and other components may primarily be used for power transfer and to reduce or prevent slippage between the wrapping member  28  and the sheave  26 . 
     As the sheave halves  26   a ,  26   b  rotate, the wrapping member  28  may also be rotated, and power from the sheave  26  can be transferred to the wrapping member  28 . Further, the wrapping member  28  may be connected to the output system  20  so as to convey power from the input system  18  to the output system  20 . In particular, in the illustrated embodiment, the output system  20  includes a driven member  30 . The wrapping member  28  may engage the driven member by wrapping around at least a portion of the driven member  30 . The driven member  30  may be, for instance, a gear, sheave, pulley, or other member, or a combination of the foregoing, and can be rotated by the wrapping member  28 . The wrapping member  28  may cause the driven member  30  to rotate, which can also result in a corresponding rotation of an output shaft (not shown). Such an output shaft can be directly or indirectly attached to the transmission output  14 . 
     The rotation of the output shaft (not shown) that is coupled to the driven member  30 , and the rotation of the transmission output  14 , can be related to the input at the transmission input  12  by a gear ratio. According to one aspect of the present disclosure, the gear ratio that relates the output of the driven member  30  to the input at the transmission input  12  is at least partially controlled by the wrapping member  28  being movable between different radial positions on the sheave  26 . For example, in the illustrated embodiment, the wrapping member  28  is positioned approximately midway along a beveled internal surface in the sheave  26 . This is merely exemplary, however, and the position of the wrapping member  26  can be varied as necessary to suit any particular application or to obtain a desired gear ratio. Indeed, in the illustrated embodiment, one or both of the sheave halves  26   a ,  26   b  are configured to be selectively moved axially inward (i.e., toward each other along the longitudinal axis of the drive shaft  24 ) and axially outward (i.e., away from each other along the longitudinal axis of the drive shaft  24 ). Thus, as the sheave halves  26   a ,  26   b  move axially inward, the beveled internal surfaces of the sheave halves  26 ,  26   b  also move axially inward. 
     The wrapping member  28  may have a fixed width. Due to axially inward movement, the width of the groove at the location of engagement with the wrapping member  28  decreases. In response to such reduction in size of the groove, the wrapping member  28  may move radially outward, and further from the longitudinal axis of the drive shaft  24 , to a location on the beveled internal surfaces which corresponds to the width of the wrapping member  28 . In contrast, as the sheave halves  26   a ,  26   b  move axially outward, the groove defined by the beveled internal surfaces of the sheave  26  may increase in width at a location of engagement with the wrapping member  28 , such that the wrapping member  28  may move radially inward, and towards the drive shaft  24 . As the wrapping member  28  moves in this manner, the gear ratio within transmission  10  is changed. In some embodiments, the wrapping member  28  may maintain a same axial position relative to the drive shaft  24  while the sheave halves  26   a ,  26   b  move. In other embodiments, the axial position of the wrapping member  28  may change. For instance, if only a single sheave half  26   a ,  26   b  moves, or if the sheave halves  26   a ,  26   b  move different amounts, the groove within the sheave  26  may move axially relative to the drive shaft  24 . 
     To facilitate the movement of the wrapping member  28  within the sheave  26 , the sheave halves  26   a ,  26   b  each have a beveled interior surface. As described in greater detail hereafter, the wrapping member  28  can be positioned against such beveled interior surfaces, and the wrapping member  28  may also have an angled outer surfaces generally corresponding to the angle on the beveled sheave halves  26   a ,  26   b . In embodiments in which the wrapping member  28  is a chain, the chain may include links that have one or more angled exterior surfaces corresponding generally to the beveled interior surfaces of the sheave  26 . Each sheave half  26   a ,  26   b  may have a beveled internal surface although in other embodiments only one of the sheave halves  26   a ,  26   b  may have a beveled surface. 
     As will be appreciated by one skilled in the art in view of the disclosure herein, the ability to move the sheave halves  26   a ,  26   b  axially provides a capability to change a radial position of the wrapping member  28 , and further provides a range of gear ratios for the transmission  10 . In some embodiments, the driven member  30  of the output system  20  may include a sheave, sprocket, or pulley that has a fixed size. In other embodiments, the driven member  30  includes a sheave that is at least partially axially movable. Indeed, by having selectively movable sheaves on the input and output systems  18 ,  20 , an even greater range of ratios can potentially be provided. 
     The range of gear ratios provided by the input and/or output systems  18 ,  20  can also be modified based on other parameters in the transmission  10 . For example, the angle of the beveled interior surfaces of the sheave halves  26   a ,  26   b  can be varied. In particular, when one or both of the sheave halves  26   a ,  26   b  move axially, the wrapping member  28  can be moved radially outward or inward in a plane perpendicular to the longitudinal axis of the drive shaft  24 . The distance the wrapping member  28  moves in the radial direction will, however, be different in embodiments that have different bevel angles on the sheave halves  26   a ,  26   b . For instance, for a specific distance the sheave halves  26   a ,  26   b  move in an axial direction, a steeper bevel angle on the sheave halves  26   a ,  26   b  can cause the wrapping member  28  to move a greater distance than would an embodiment that has the sheave halves  26   a ,  26   b  with a more shallow bevel angle. The width of the wrapping member  28  can also be varied as a wider wrapping member  28  can potentially remain positioned between beveled surfaces of the sheave  26  over a greater range of axial movement by the sheave halves  26   a ,  26   b , and may thus also allow for a greater range of gear ratios within the transmission  10 . 
     The movement of the sheave halves  26   a ,  26   b  can be effected in any suitable manner. For instance, in  FIG. 1 , a synchronization system  38  may be used to move the sheave  26 . In the illustrated embodiment, two sheave actuators  32  are provided, with each one being configured to control a respective one of the sheave halves  26   a ,  26   b . The sheave actuators  32  may be any suitable device that can be used to facilitate inward and outward movement of the sheave halves  26   a ,  26   b . For instance, in one example, the sheave actuators  32  include hydraulic or pneumatic pistons that are journaled around the drive shaft  24 . When a gear ratio change is desired, the sheave actuators  32  can be activated to exert a force on a portion of a sheave half  26   a ,  26   b  and thereby move sheave halves  26   a ,  26   b  closer together. By reducing the force exerted on the sheave halves  26   a ,  26   b , the sheave actuators  32  can retract and allow the sheave halves  26   a ,  26   b  to separate. 
     The sheave actuators  32  of  FIG. 1  also represent sheave actuators other than hydraulic or pneumatic actuators. For example, in another embodiment, a mechanical actuator may include a worm gear that advances a compression plate. Such a worm gear may be actuated by an electronic, hydraulic, pneumatic, mechanical, or electro-mechanical device, and can advance the compression plate to cause a sheave half  26   a ,  26   b  to move axially inward, or can be used to back-off the compression plate to cause or allow one or both of the sheave halves  26   a ,  26   b  to move axially outward relative to each other. In still other embodiments, the sheave actuator  32  may include an electrical motor such as a stepper or servo motor. Further, while the illustrated embodiment illustrates two sheave actuators  32 —one for each of the sheave halves  26   a ,  26   b —this arrangement is merely exemplary. In some embodiments, one of the sheave halves  26   a ,  26   b  may be fixed at an axial position relative to the drive shaft  24 . In such an embodiment, a single actuator can potentially be used to move a movable one of the sheave halves  26   a ,  26   b  relative to the fixed sheave half. 
     In  FIG. 1 , the diameter of the portion of the sheave  26  at which the wrapping member  28  is engaged is less than a diameter of the driven member  30  about which the wrapping member  28  is engaged. Accordingly, the wrapping member  28  may extend in a direction generally perpendicular to the drive axis between the sheave  26  and the driven member  30 , and angle upward from the sheave  26  and towards the driven member  30 . In particular, the radius of rotation of the wrapping member  28  increases as the wrapping member  28  gets closer to the driven member  30 , and decreases as the wrapping member  28  approaches the sheave  26 . However, this is merely exemplary. For instance, the size of the driven member  30  may be reduced such that a radius of rotation of the wrapping member  28  decreases or stays the same as the wrapping member  28  approaches the driven member  30 . Moreover, in embodiments in which the sheave halves  26   a ,  26   b  are movable, the sheave  26  may move the wrapping member  26  to a position that is radially larger or smaller than the radius of rotation of the wrapping member  28  about the driven member  30 . 
     It should be appreciated in view of the disclosure herein that the wrapping member  28  of  FIG. 1  can wrap around at least a portion of the exterior surface of the sheave  26 . For instance, the wrapping member  28  may extend between the driven member  30 , engage the sheave  26  at a first point, wrap around the sheave  26  and disengage at a second point on the sheave  26 , and extend towards the driven member  30 . In one embodiment, the portion of the sheave  26  between points of engagement and disengagement range between about one-hundred thirty-five and two-hundred forty degrees of the exterior of the wrapping member  28 , although such range is exemplary only. Further, the amount of wrapping may also be varied as the sheave  26  moves. For instance, as the sheave  26  moves axially inward (e.g., by reducing a width of the sheave  26  as sheave halves  26   a ,  26   b  move axially inward) and the wrapping member  28  moves radially outward, the wrapping member  28  may wrap around an increasingly larger portion of the sheave  26 . 
     In some embodiments, a tensioning system  44  may be included. The tensioning system  44  may include one or more gears, rollers, rails, or other members that engage the wrapping member  28  between the sheave  26  and the driven member  30 . Such a tensioning system  44  may provide a mechanism to maintain a desired tension and/or a substantially constant tension in the wrapping member  28 . In some embodiments, the tensioning system  44  may also change an angle at which the wrapping member  28  enters or exits engagement with the sheave  26 . Thus, the tensioning system  44  can also change the amount of engagement between the wrapping member and the sheave  26  and/or on the driven member  30 . 
     In  FIG. 1 , the wrapping member  28  is illustrated as being cross-sectioned so as to illustrate the interior of the sheave  26 . In the illustrated embodiment, the wrapping member  28  is shown as engaging the sheave  26 , or being in near engagement with the sheave  26 . In the illustrated embodiment, the wrapping member also engages a set of driving moons  34 . The driving moons  34  may be radially movable members that are spaced around the longitudinal axis about which the sheave  26  and the drive shaft  24  rotate. The number of driving moons  34  may vary. For instance, in one embodiment, there are three driving moons  34 , each of which is angularly offset at one-hundred twenty degrees from the other driving moons  34 . In other embodiments, more or fewer driving moons  34  may be present, and the driving moons  34  may be spaced at equal or unequal intervals around the longitudinal axis of the drive shaft  24 . In embodiments in which the wrapping member  28  is a chain, the driving moons  34  may be sprockets or other gears that have teeth configured to mate with the chain and mesh therewith. For instance, the links of such a chain may have a specific pitch corresponding to a pitch of the sprockets, such that as the sprockets engage the chain, the sprocket teeth enter pockets of the chain and the sprockets transfer power to the chain. 
     The driving moons  34  may also be configured in this embodiment to have multiple rotational motions. For instance, in  FIG. 1 , each driving moon  34  is coupled, about its center, to a driving moon shaft  36 . The driving moon shafts  36  may rotate, and the driving moons  34  can be fixed to the driving moon shafts  36 . As a result, as the driving moon shafts  36  rotate, the driving moons  34  rotate about a longitudinal axis passing through the driving moon shaft  36  and the center of the driving moon  34 . The illustrated driving moon shafts  36  on which the driving moons  34  operate extend through the sheave halves  26   a ,  26   b ; however, this is merely exemplary as in other embodiments a shaft on which the driving moons  34  rotate may be located between the sheave halves  26   a ,  26   b  and need not extend through one or both of the sheave halves  26   a ,  26   b.    
     Furthermore, the driving moon shafts  36  can be coupled to the drive shaft  24 . According to at least one embodiment, the driving moon shafts  36  are rotationally coupled to the drive shaft  24 . In this embodiment, the driving moon shafts  36  are coupled to the synchronizer system  38  and a correction component  40 . The synchronizer system  38  and correction component  40  are optionally rotationally coupled to the drive shaft  24  and configured to rotate with the drive shaft  24 . By fixing the driving moon shafts  36  to the synchronizer system  38  and the correction component  40 , as the drive shaft  24  rotates, the driving moon shafts  36  and the driving moons  34  are can be caused to orbit around the drive shaft  24  at a speed corresponding to the speed of the drive shaft  24 . As the axis of rotation is external to the driving moons  34 , the driving moons  34  effectively orbit about the drive shaft  24  while also being enabled to rotate about their respective internal axes. The directions of the internal rotation and external orbital motion may be the same, or they may be in opposing directions. Embodiments of the synchronizer system  38  and the correction component  40  are described in greater detail hereafter. In this embodiment, such system and component are merely exemplary and may be directly or indirectly coupled to the driving moon shafts  36 . In some embodiments, for instance, the driving moon shafts  36  may attach to plates or disks. Such plates or disks could also optionally cause the driving moons to be rotationally coupled to the drive shaft  24 . Such plates or disks, or other components could provide other features such as radially moving the driving moons  34  and/or causing selective rotation of the driving moons  34 . 
     As the driving moons  34  orbit around the drive shaft  24 , the driving moons  34  can each enter into and out of engagement with the wrapping member  28 . More particularly, the drive shaft  24  can rotate. By virtue of the driving moons  34  being linked to the drive shaft in this embodiment, the driving moons  34  can rotate about the drive shaft  24  at the same or a different rotational speed. While undergoing such orbital motion, the driving moons  34  will alternately engage the wrapping member  28 . 
     For instance, in an exemplary embodiment, the driving moons  34  may be angularly spaced at approximately one-hundred twenty degree intervals. When one driving moon  34  orbits to a position that approximately coincides with a portion where the wrapping member  28  first engages the sheave  26 , the driving moon  34  may engage the wrapping member  28 . Such a driving moon  34  can then remain engaged with the wrapping member  28  through a portion of the orbital path of the driving moon  34 , as that orbital path may have a size corresponding to the curved path of the wrapping member  28  around the sheave  26 . The engaged driving moon  34  may then disengage from the wrapping member  28  at approximately a location where the wrapping member  28  disengages from the sheave  26 . It should be appreciated that the angular interval over which driving moons  34  remain engaged with the wrapping member  28  can vary based on the specific design of transmission  10 . For example, in one embodiment, each of driving moons  34  may remain engaged for an angular interval of approximately one-hundred eighty degrees, however other intervals are contemplated (e.g., intervals varying from about one-twenty degrees to about two-hundred forty degrees). Additionally, the wrapping member  28  can engage the driving moons  34  and the sheave halves  26   a ,  26   b , although in other embodiments the wrapping member  28  may engage only the driving moons  34 , or the driving moons  34  may be removed or retracted so that the wrapping member  28  engages only the sheave halves  26   a ,  26   b . Additionally, in one embodiment according to the present disclosure, the driving moons  34  carry substantially the full load and the sheave halves  26   a ,  26   b  can be eliminated. 
     By virtue of the orbital motion of the driving moons  34  around the drive shaft  24 , at least one driving moon  34  can remain in mesh with wrapping member  28  at all times at which the wrapping member  28  rolls around the sheave  26 . The same driving moon  34  need not, however, be engaged with the wrapping member  28  at all times, and the driving moons  34  can alternately engage the wrapping member  28 . Moreover, more than one of driving moons  34  may be engaged with the wrapping member  28  at the same time. For example, in the embodiment in  FIG. 1  the two illustrated driving moons  34  may both be engaged simultaneously with the wrapping member  28 . 
     Although it is not necessary that the driving moons  34  and the sheave halves  26   a ,  26   b  be utilized together in all embodiments, the use of the driving moons  34  with the sheave halves  26   a ,  26   b  to drive the wrapping member  28  provides various features that may be desirable in some applications. For example, existing transmission systems may employ a belt drive that operates around a sheave. Such systems rely on frictional engagement between the belt and sheave to operate. As with any friction-based system, the friction element is required to allow the sheave to engage and transfer power to the belt. More particularly, with insufficient friction, the belt can slip relative to the sheave, thereby reducing the efficiency of the power transfer. Indeed, in any such friction-based system, at least some amount of slip occurs. Slippage of the belt relative to the sheave leads to inefficiencies in the system. While the slippage can be reduced, the cost is typically an increase in friction which also leads to inefficiencies at least in the form of added heat generation. 
     In the present embodiment, however, the use of the driving moons  34  between the sheave halves  26   a ,  26   b  can eliminate or at least significantly reduce the slippage between the wrapping member  28  and the sheave  26 . This is particularly so in embodiments in which the wrapping member  28  is a chain and the driving moons  34  are sprockets or other gears. For instance, in such an embodiment, the transmission  10  can include an optional locking system  42 . The locking system  42  may act as a brake that locks such sprockets or other driving moons  34  when they are under load (e.g., at one or more locations of the driving moons  34  during which the driving moons  34  are in mesh with the wrapping member  28 ). The locking system  42  may specifically lock the driving moons  34  to avoid counter-rotation about their internal axes, and optionally locks the driving moons  34  against any rotation about their internal axes. By locking the driving moons  34 , the driving moons  34  may resist slippage of the wrapping member  28  relative to the sheave  26 . 
     Additionally, friction-reliant systems have heretofore been suitable for some applications, but largely impractical for other applications for one reason or another. For example, a belt-drive system that relies on friction between the belt and sheave or pulley has not been shown to be suitable for high torque applications. For instance, a belt may be made of a polymeric material that operates between two sheaves. The higher the torque, the higher the frictional forces and the heat generation. If a large amount of torque is applied, the frictional forces create heat that can burn through or otherwise degrade the polymeric belt, and may also cause a torque spike. Even if such polymeric materials are combined with composites, metals, and the like, the high heat creates wear on the belt and/or sheaves and significantly reduce their useful lifecycle. Furthermore, if the polymeric material were to be replaced with metal materials, there could be better properties for heat resistance and possibly for heat generation. However, the metal-to-metal contact would result in reduced frictional properties, thereby leading to increased slippage. 
     While the foregoing describes some limitations of existing belt-and-sheave systems, the transmission  10  described herein may be used in any of the scenarios or embodiments disclosed herein, including embodiments in which the driving moons  34  are eliminated, and the sheave operates as a largely friction-based system with polymeric, metal, composite, or other belt and sheave materials. However, when the driving moons  34  are included and used in combination with the sheave  26 , various desirable characteristics can be obtained. For example, even if the wrapping member  28  is made of a material that is prone to slippage, the driving moons  34  can engage the wrapping member  28  and the wrapping member  28  continues to rotate around the sheave  26 . Thus, the driving moons  34  can operate as an additional drive that may not only reduce slippage relative to the sheave  26 , but can also provide an additional input so that friction between wrapping member  28  and the sheave  26  is reduced. In some embodiments, the sheave  26  may thus be used largely for positioning of the wrapping member  28 , while the driving moons  34  are primarily used for power transfer to the wrapping member  28 . 
     As discussed previously, the wrapping member  28  may engage the sheave  26  and orbit therearound. However, the radius of such orbit about the sheave  26  may change as the sheave halves  26   a ,  26   b  move axially, thereby also causing the wrapping member  28  to move radially inward or outward. As will be appreciated in view of the disclosure herein, the driving moons  34  may thus engage the wrapping member  28  at one position of the sheave  26 . If, however, the sheave  26  changes its axial position, the driving moons  34  may either become disengaged from the wrapping member  28 , or obstruct movement of the wrapping member  28  to a correspond to a new position of the sheave  26 . 
     To account for such changes to the sheave  26  and the wrapping member  28 , the driving moons  34  may be configured to move radially relative to the drive shaft  24 , although in other embodiments it may not be necessary for the driving moons  34  to move radially. For instance, a wrapping member  28  may be connected to a sheave of the output system  20  and to the driving moons  34  of the input system. As the sheave in the output system  20  moves, thereby causing the wrapping member  28  to change position about the driven member  30 , the wrapping member  28  may remain engaged with the driving moons  34  of the input system  18 . The wrapping member  28  can thus remain positively engaged with the driving moons  34  and, particularly if a tensioner is used, can reduce or prevent slippage of the wrapping member  28 . 
     Alternatively, the driving moons  34  may themselves move radially inward and outward to correspond to axial movement by the sheave  26 , such that the driving moons  34  can remain engaged with the wrapping member  28  as the wrapping member  28  moves radially inward and/or outward relative to the drive shaft  24 . Any suitable mechanism may be used for synchronizing movement of the driving moons  34  and the sheave halves  26   a ,  26   b . In  FIG. 1 , for instance, the synchronizer system  38  is coupled to the driving moon shaft  36  and includes the sheave actuators  32 . The synchronizer system  38  may obtain information relating to the desired position of the sheave  26  and cause the sheave actuators  32  to move the sheave  26 , while also causing the driving moon shaft  36  to move a corresponding amount to maintain engagement between the driving moon  34  and the wrapping member  28 . The synchronizer system  38  may include or use an electro-mechanical or other device, such as a controller, that controls the sheave actuators  32  and/or components for moving the driving moons  34 . Additionally, or alternatively, a sensor or encoder that detects a corresponding position of the sheave halves  26   a ,  26   b  may be used to identify proper radial movement of the driving moons  34 . The synchronizer system  38  may also have logic stored therein. For instance, a logic component may be able to use information about an engine speed or gear ratio and move the sheave  26  and driving moons  34  to proper locations. A logic component may also be used in connection with a sensor or encoder and cause a mechanical, hydraulic, pneumatic, electrical, or some other mechanism, or a combination of the foregoing, to adjust the position of the driving moon shaft  36  based on sheave  26  positioning. In other embodiments, the synchronizer system  38  does not include a logic storage for moving the driving moons  34 . For instance, a mechanical system may relate movement of the sheave  26  to movement of the driving moon shaft  36  such that the synchronizer system  38  can move one or both of the sheave  26  and the driving moons  34  using a purely mechanical system. 
     Some embodiments of the present disclosure thus relate to a transmission in which driving members (e.g., sheave  26  and/or driving moons  34 ) move axially or radially to produce gear ratio changes. Accordingly, the sheave  26  is one example of a means for driving a wrapping member  28 . Further, the driving moons  34  are individually and collectively also one example of a means for driving a wrapping member  28 . Furthermore, movement of the wrapping member  28 , driving moons  34  and/or sheave  26  may occur while at least some of the driving members are under load. The sheave  26  and/or the driving moons  34  may also cause the wrapping member  28  to move. Thus, the sheave  26  is one example of a means for radially positioning a wrapping member  28 . Similarly, the driving moons  34  are individually and collectively, one example of a means for radially positioning a wrapping member. Particularly for embodiments in which the transmission  10  includes a chain as the wrapping member  28 , another aspect to consider is the radius of the sheave  26  and the corresponding radius of the wrapping member  28  around the sheave  26 . In particular, the radius of the wrapping member  28  may correspond to a non-integer position as described below. 
     In particular, the inventors hereof have identified various challenges that can occur when a positive engagement transmission attempts to slide between gear ratios in very small, and possibly infinitely small, increments. More particularly, a positively engaged transmission can make use of gear teeth and/or chain links to maintain tooth engagement that does not rely primarily on friction. For instance, meshing gear teeth can mate in tooth-to-tooth engagement according to the principles of involutometry, and frictional effects of the engagement can be considered negligible. Similarly, a sprocket or other gear can mate with a chain and similar tooth engagement with the chain can drive, or be driven by, the chain, with minimal friction considerations. 
     Positive engagement largely performs well because engagement of gear teeth and/or chain links can be considered relatively frictionless because a gear or chain has constant and fixed characteristics. For instance, mating gear teeth may be on gears of different sizes, but can still mesh properly where the teeth have the same pitch. Similar meshing occurs for a gear tooth on a sprocket that engages a link of the chain when the chain link and the gear tooth have the same pitch. In a conventional sprocket and chain system, the sprocket remains in a fixed radial position relative to its rotational center. The sprocket is also equally divisible into an integer number of teeth, and there are no partial teeth around the circumference of the sprocket. As a result, after each full rotation of the sprocket, the gear teeth are in the same position. 
     In the transmission of  FIG. 1 , the driving moons  34  can collectively act as a sprocket. However, unlike a conventional sprocket, the radial position of the gear teeth can change relative to the rotational center (i.e., the drive shaft  24 ). One challenge of sliding between gear ratios with fixed sizes of driving members has been termed by the inventors hereof the non-integer tooth problem. In short, the non-integer tooth problem is that as a set of gears moves radially, there are only certain, discrete radii at which the circumference of the path of the orbiting gears is wholly divisible by the pitch of the gear teeth and/or chain links. At other locations, the circumference of the drive mechanism is not equally divisible by the pitch of a chain link or sprocket. Consequently, after each full rotation of the set of driving moons  34 , the gear teeth do not necessarily end up in the same position in which they started. 
     To account for such variations, the illustrated embodiment of the transmission  10  includes a correction component  40 . In effect, the correction component  40  measures or otherwise determines an amount by which teeth of the driving moons  34  are offset with respect to a desired position for engagement with the wrapping member  28 , and then corrects such tooth position. Such a determination can be made using an encoder, sensor, mechanical system, or some other component, or a combination of the foregoing. In the illustrated embodiment, the correction component  40  is coupled to the driving moon shaft  36 . Based on such a determination, the correction component can determine the amount by which the rotation of the driving moon  34  is to be corrected about their own axes. Using a hydraulic, pneumatic, electrical, mechanical, or other actuator, or a combination of the foregoing, the correction component  40  can then adjust the position of the driving moons  34 . 
     In the illustrated embodiment, the correction component  40  is coupled to the driving moon shafts  36 . Accordingly the correction component  40  can implement the correction by rotating the driving moon shafts  36 , thereby also causing the driving moons  34  to rotate a corresponding amount. It will be appreciated in view of the disclosure herein that the correction that occurs may occur to each driving moon  34  at a different time. For instance, as noted previously, rotation of the driving moons  34  may be locked using the locking mechanism  42 . Such locking mechanism  42  may operate while the driving moons  34  are under load. The correction component  40  may adjust positioning of the driving moons  34 , including any gear teeth thereon, while the driving moons  34  are not under load. By way of illustration, the correction component  40  may correct a gear tooth location during the portion of the orbit of the driving moon  34  around the drive shaft  24  during which the driving moon  34  is disengaged from the wrapping member  28 . The driving moon  34  can then be brought into alignment with the wrapping member  28  at least just before the driving moon  34  reenters into engagement with the wrapping member  28 . 
     Without corrections for the non-integer tooth problem, a transmission operating with gear ratio changes that occur at very small increments, and even in infinitely small increments, may operate but encounter some difficulties in certain circumstances. For instance, teeth may mesh properly at one radial location of the driving moons  34  and/or wrapping member  28  (e.g., at a position which is equally divisible into an integer number of teeth or chain links), but may not properly mesh at a second location (e.g., at a position which is not equally divisible into an integer number of teeth). There may also be some raking between the teeth. In either case, the transmission, although functional, can operate at a lower efficiency and with less desirable wear characteristics. Thus, in the illustrated embodiment, the optional correction component  40  allows for efficient correction of the driving moons  34 . As a result, as the wrapping member  28  and driving moons  34  move to provide gear ratios in very small, or infinitely small, increments, teeth on the driving moon  34  can be corrected as necessary so as to maintain proper engagement at both integer and non-integer locations of the driving moons  34  and wrapping member  28 . 
     With continued reference to  FIG. 1 , the transmission  10  also includes an optional differential system  22 . The differential system  22  can act in any number of different manners and provide a number of different functions. For instance, the differential system  22  can allow the transmission  10  to maintain engagement between a power source and a load, even when the transmission output  14  has zero rotational speed. The differential system  22  can also split torque such that the input and output systems  18 ,  20  run under less load. In another embodiment, the differential system  22  can cause further gear ratio changes within the transmission  10 . 
     In  FIG. 1 , the differential system  22  is connected to both the transmission input  12  and the transmission output  14 . Furthermore, the differential system  22  can be connected to the driven member  30 . For instance, in one embodiment, the transmission input  12  and the driven member  30  provide two inputs to a differential component  46 . The two inputs can be provided directly or indirectly, and the differential system  22  can combine the two inputs and provide the resultant output, which may be zero, to the transmission output  14 . 
     To use inputs from both the transmission input  12  and the driven member  30 , the differential system  22  of  FIG. 1  includes an input relay member  48 . In this embodiment, the input relay member  48  may include a gear, pulley, sheave, belt, or other member. The input relay member  48  can be directly or indirectly coupled to the transmission input  12 . As a result, as a power input is received by the transmission  10 , the transmission input  12  may rotate and the input relay member  48  can experience a corresponding rotation. The input relay member  48  is, in this embodiment, coupled to a first transfer member  50 . The first transfer member  50  may be coupled to the input relay member  48  in a manner that transfers rotational power. For instance, the first transfer member  50  may be a gear that engages the input relay member  48 . As the input relay member  48  rotates, the first transfer member  50  also rotates. The first transfer member  50  may engage a second transfer member  52  and transfer a corresponding rotation thereto. 
     In the illustrated embodiment, the second transfer member  52  rotates about a central axis, and a differential input shaft  54  is coupled to the second transfer member  52 . As the second transfer member  52  rotates, the differential input shaft  54  also rotates. The differential input shaft  54  may extend into the differential component  46 . In one embodiment, the differential input shaft  54  passes through a second differential input member  56  that is also coupled to the differential component  46 . For instance, the second differential input member  56  may be a gear with an opening therein, and the differential input shaft  54  may pass through the opening and into the differential component  46 . In other embodiments, power from the transmission input  12  may be passed to a differential input shaft  54  in other manners. For instance, a pass-through shaft may extend through the drive shaft  24 , or be integral therewith, and directly or indirectly connect to a differential input shaft. 
     The driven member  30  may also provide an output as described herein. For instance, as the wrapping member  28  rotates, the driven member  30  may rotate about its own axis. In some embodiments the driven member  30  is coupled to an output member  58 . For instance, a shaft, belt, pulley, gear train, or other mechanism, or a combination thereof, may rotationally couple the driven member  30  to the output member  58 . As a result, as the driven member  30  rotates, the output member  58  may also rotate. In this embodiment, an output transfer member  60  may be coupled to the output member  58  and the second differential input member  56 . For instance, the output member  58  and the output transfer member  60  may be gears that are engaged with each other. The second differential input member  56  may also be a gear that engages the output transfer member  60 . Consequently, rotation of the output member  58  is transferrable to the output transfer member  60  and the second differential input member  56 . 
     In at least one embodiment, the differential input shaft  54  and the second differential input member  56  both provide inputs to the differential component  46 , and the differential component  46  combines the two inputs into a single output. The single output may be provided to the transmission output  14 . For instance, the differential component  46  may be coupled to the second differential input member  56 . By way of illustration, a housing of the differential component  46  may be rotationally fixed relative to the second differential input member  46 , such that as the second differential input member  46  rotates, the housing of the differential component  46  also rotates about a central axis. The differential input shaft  54  may, however, be journaled with respect to the housing, or otherwise configured to rotate in a manner that does not necessarily cause the housing of the differential component  46  to rotate. Instead, the differential input shaft  54  may engage one or more gears, rollers, belts, pulleys, or other members within the differential component  46 . The rotational input of the differential input shaft  54  can combine with the rotation of the housing of the differential component  46  to produce an output that is conveyed to the transmission output  14 . 
     1. Two-Sheave Transmission Embodiment 
     Turning now to  FIG. 2 , an example embodiment of a transmission  100  is illustrated according to certain exemplary aspects of the present disclosure. The transmission  100  can operate in a manner similar to that described above relative to transmission  10  of  FIG. 1 . To avoid unnecessarily obscuring aspects of the illustrated embodiment, components, systems, and assemblies of the transmission  100  that operate in a manner consistent with that of transmission  10  will not be further discussed, or will be treated briefly. Accordingly, the following discussion of the transmission  100  will primarily relate to components that can supplement or replace, or otherwise vary from, components of the transmission  10  of  FIG. 1 . Unless otherwise stated, each component or feature of transmission  100  is considered to be interchangeable with those of other particular transmission embodiments disclosed herein, both individually and in combination with other components. 
     As shown in  FIG. 2 , the transmission  100  includes a transmission input  112 . The transmission input  112  may be adapted to receive a rotational power input from a power supply and to transmit the received input through a drive system  116  and to a transmission output  114 . The rotational speed of the transmission output  114  may also be related to the rotational speed of the transmission input  112  by a gear ratio that is defined at least in part by the drive system  116 . 
     In the illustrated embodiment, the drive system  116  includes an input system  118 , output system  120 , and a differential system  122 . The input system  118  receives power from the transmission input  112 . More particularly, in this embodiment, the transmission input  112  includes a rotating shaft  113  on which a transfer gear  115  is positioned. The transfer gear  115  can rotate at the same rotational speed as the rotating shaft  113 . The input system  118  can further include a drive shaft  124  having thereon a relay gear  125 . In this embodiment, the relay gear  125  mates with the transfer gear  115  on the rotating shaft  113 . Accordingly, as the transfer gear  115  rotates, the relay gear  125  also rotates and can cause the drive shaft  124  to rotate at a speed that is the same or different than the transmission input  112 . 
     The drive shaft  124  can rotate about a longitudinal axis passing through the center of the drive shaft  124 . Various components may also be connected to the drive shaft  124 . For instance, in this embodiment, a sheave  126  is secured to the drive shaft  124 , and the sheave  126  may be configured to rotate at the same speed as the drive shaft  124 . By way of example, the sheave  126  may be mechanically secured to the drive shaft  124  using a weld, spline connection, or other mechanism, or a combination of the foregoing. In some embodiments, the connection between the drive shaft  124  and the sheave  126  allows the sheave  126  to rotate at a different rotational speed than the drive shaft  124 . 
     Within the sheave  126  are a set of three driving moon gears  134  (see  FIG. 3 ). The three driving moon gears  134  can cooperate with the sheave  126  to drive a chain  128 . In particular, in this embodiment, a chain  128  is wrapped around a portion of the sheave  126  and extends between the sheave  126  and the output system  120 . 
     As discussed above with respect to transmission  10 , the transmission  100  may also be a variable transmission that can accommodate a large, possibly infinite, number of gear ratios. For instance, the sheave  126  and driving moon gears  134  may be radially moveable. Consequently, as the sheave  126  and driving moon gears  134  move inward or outward in respective axial and radial directions, the path of the chain  128  can be altered. By altering the path of the chain  128 , the gear ratio can change within the transmission  100 . In some embodiments, the sheave  126  and the driving moon gears  134  move in very small, and possibly infinitely small, increments, to provide a large, possibly, infinite, number of gear ratios. 
     In the illustrated embodiment, the output system  120  also includes a sheave  130 . The sheave  130  can act as a driven member as the sheave  130  is engaged by the chain  128 , and rotation of the sheave  130  can be caused by the chain  128 . In some embodiments, the sheave  130  has a set of driven moon gears (not shown) therein. The sheave  130  and driven moon gears of the output system  120  may, in such an embodiment, be substantially identical to the sheave  126  and driven moon gears  134  of the input system  118 , although the input and output systems  118 ,  120  can have different sheaves and driving or driven members. Accordingly, the sheave  130  and driven moon gears can move in respective axial and radial directions to further facilitate changes in gear ratio. 
     Sheave Actuators 
     As discussed with reference to  FIG. 1 , a transmission may have one or more sheaves and one or more driving moons that move radially inward and/or outward to adjust the gear ratio of the transmission. The transmission  100  illustrated in  FIG. 2  is similarly configured. For instance, in the illustrated embodiment, the input and output systems  118 ,  120  each include a set of sheave actuators  132 . On the input system, for instance, the sheave actuators  132  are aligned on the drive shaft  124 . The sheave actuators  132  can include a piston  133  that can be moved axially relative to the drive shaft  124 . For instance, the sheave actuators  132  may be hydraulically controlled. As hydraulic pressure is increased within the sheave actuators  132 , the pistons  133  may move axially along the drive shaft  124  in a direction extending towards the sheave  126 . The increased pressure can cause the pistons  133  to exert a retracting force on the sheave  126 . In particular, the pistons  133  may cause opposing halves of the sheave  126  to draw closer together. As a result, a beveled internal groove of the sheave can cause the chain  128  to move radially outward relative to the drive shaft  124 . 
     In contrast, if the pressure on the pistons  133  is backed-off, such that the pistons  133  move axially along the drive shaft  124  in a direction extending away from the sheave  126 , one or both halves of the sheave  126  may move axially outward relative to the other. The beveled internal surface of the sheave  126  may then allow the chain  128  to move radially inward relative to the drive shaft  124 . The sheave  126  may be spring loaded or otherwise biased to facilitate axial movement as the force exerted by the pistons  133  is backed-off. Such a biasing mechanism is, however, merely exemplary. In other embodiments, no biasing mechanism is used and the force of the chain  128  on the sheave  126  and/or the centrifugal forces on the sheave  126  as a result of the rotation of the sheave  126  around the drive shaft  124  may be sufficient to move the sheave in a radially outward direction. The sheave  130  of the output system  120  may be configured in a manner similar to that disclosed for the sheave  126  of the input system  128 . For instance, the sheave  130  may rotate on an output drive shaft  131 . Sheave actuators  132  may be positioned about the output drive shaft  131  and include pistons  133  that cause halves of the sheave  130  to move radially inward and outward relative to each other in a manner similar to that previously described. 
     While the foregoing description of the sheave actuators  132  describes the use of a hydraulic actuator and piston configuration, such an embodiment is merely exemplary. The sheave actuators  132  may be any suitable type of actuator that facilitates movement of one or both halves of a sheave  126 ,  130  along an axis. For instance, other examples of suitable sheave actuators  132  may include pneumatic actuators, worm gearing, electrical stepper or servo motors, or other actuators, or any combination of the foregoing. 
     As will be appreciated in view of the disclosure herein, as a sheave  126 ,  130  changes its axial position, the chain  128  may move radially inward or outward a corresponding distance, based on a bevel angle of an interior surface of the sheave  126 ,  130 , to effect a gear ratio change. In one exemplary embodiment, a sheave actuator  132  may be used in connection with a controller that provides a signal that causes the sheave  126  to move radially outward, thereby causing the chain  128  to rotate around a smaller radial section of the sheave  126 . If the sheave  130  remains the same size throughout such a change, slack may be introduced into the chain  128 . To maintain tension in the chain—which tension optionally remains about constant at multiple different gear ratios—a tensioning mechanism may be used. In one embodiment, the tensioning mechanism is at least partially integral with the synchronization system  138 . For instance, the chain  128  may be tensioned by making a corresponding adjustment to the size and/or position of the sheave  130 , to thereby maintain a desired tension in the chain  128 . Thus, the second sheave  130  can act as a tensioning device. In other embodiments, however, other tensioning devices may be used. For instance, one or more idlers or tensioning gears may be placed along an interior or exterior of the perimeter of the chain  128 , and may be movable to change the alignment of the chain  128  in a manner that produces a desired tension in the chain  128  while the transmission  100  is at a particular gear ratio and/or while the transmission  100  changes between gear ratios. 
     Synchronizing Sheaves and Moon Gears 
     As the sheaves  126 ,  130  move axially inward or outward (e.g., by having one or more halves of the sheaves  126 ,  130  that can move axially along a respective drive shaft  124 ,  131 ), the chain  128  can experience a corresponding positional change. More particularly, as the halves of the sheave  126  move in an inward axial direction, the chain  128  may move on the sheave  126  and in a radially outward direction relative to the drive shaft  124 . In contrast, as the halves of the sheave  126  move in an outward axial direction, the chain  128  may move on the sheave  126  in a radially inward direction relative to the drive shaft  124 . Similarly, as the halves of the sheave  130  move axially inward or outward, the chain  128  can move radially outward or inward, respectively, on the sheave  130  and relative to an output drive shaft  131 . 
     In embodiments in which the input and output systems  118 ,  120  include driving moon gears  134  ( FIG. 3 ) that act with the sheaves  126 ,  130  to engage the chain  128 , the driving moon gears  134  may also move in a radial direction relative to the drive shaft  124  and the output drive shaft  131 .  FIG. 3  illustrates a portion of an exemplary synchronization mechanism by which radial movement of the moon gears  134  can be synchronized with axial movement of the sheaves  126 ,  130 . 
     In particular,  FIG. 3  illustrates a partial view of the transmission  100  in which various components of the transmission  100  have been removed to more clearly illustrate an exemplary manner in which the synchronization system  138  operates. Inasmuch as the input and output systems  118 ,  120  of the transmission  100  can operate in similar manners, components of the synchronization system  138  in  FIG. 3  are shown as being located on either the input system  118  or the output system  120 . It should be appreciated, however, that such illustration is merely for simplicity and that each of the illustrated components of the synchronization systems  138  can be included and operate on both the input system  118  and the output system  120 . 
     In  FIG. 3 , two adjustment actuators  161  are illustrated. Each adjustment actuator  161  is shown as being coupled to a half of the sheave  130 , although corresponding adjustment actuators  161  can be connected to respective halves of the sheave  126 . As halves of the sheaves  126 ,  130  move axially inward or outward, the chain  128  can change its radial position and the adjustment actuators  161  can be activated. The actuators  161  have, in this embodiment, an arm  162  coupled to an adjustment ring  163 . The arm  162  may be selectively extended or retracted. As the length of the arm  162  changes, the arm  162  can cause the ring  163  to rotate. For example, the arms  162  can be fixed to the sheave  130  and by increasing the length of the arms  162 , the adjustment actuator  161  may cause the ring  163  to move in a clockwise direction in the illustration in  FIG. 3 , whereas retracting the aims  162  may cause the ring  163  to move in a counterclockwise direction. Such directions and motions, as well as the operation of adjustment actuators  161 , are merely for illustration. 
     In  FIG. 3 , three housings  164  are connected to the adjustment ring  163 . Each of the housings  162  is angularly offset from the other housings  164  at about a one-hundred twenty degree interval, and each housing  162  generally corresponds to a placement of a driving moon gear  134 . Within each housing  164  is an adjustment gear  165  that can meshes with gear teeth on the interior surface of the adjustment ring  163 . Each adjustment gear  165  is, in this embodiment, also coupled to a shaft  166  that extends inwardly, toward a respective driving moon gear  134 . On the distal end of shaft  166  is a pivoting arm  167  that connects to one of driving moon gears  134  via a stub shaft  137  about which the driving moon gears  134  can rotate. 
     The synchronization system  138  collectively, and each of the individual components illustrated in  FIG. 3 , are one example of a means for radially moving driving moon gears  134  relative to the drive shaft  124 . Moreover, when the synchronization system  138  coordinates such radial movement with axial movement of the sheaves  126 ,  130 , the driving moon gears  134  can remain engaged with the chain  128  at various radial positions of the chain  128 , and even during changes from one radial position of the chain  128  to another. As a result, the synchronization system  138  provides a mechanism for maintaining constant, positive engagement between the chain  128  and at least the driving moon gears  134  at not only discrete gear ratios, but throughout movement from one ratio to another, and while one or more of the driving moon gears  134  is under load. Thus, the chain  128  and the driving moon gears  134  can be positively engaged throughout very small, and possibly infinitely small, gear ratio changes, and thus through a corresponding infinite number of different ratios. In other words, the transmission  100  not only has the possibility, but not requirement, of maintaining substantially constant frictional engagement (e.g., between the chain  128  and the sheaves  126 ,  130 ), but can also maintain constant positive engagement (e.g., engagement between the chain  128  and the driving moon gears  134 ) over a range of very small, and possibly infinitely small, ratios. 
     The manner in which the various components of the particular embodiment provide such engagement can be appreciated from the illustration in  FIG. 3 . In particular, as the adjustment ring  163  rotates, the interior teeth of the adjustment ring  163  engage and rotate the adjustment gears  165 . The adjustment gears  165  may be coupled by a spline or other connection to the shafts  166 , and therefore may also rotate. The rotation of the shafts  166  may, in turn, cause the pivoting arms  167  to rotate. Inasmuch as the driving moon gears  134  can be connected to the pivoting arms  167 , the driving moon gears  134  may then also pivot around the center of the shafts  166 . The amount of rotation of the driving moon gears  134  around the shafts  166  can vary, and it is not necessary that the driving moon gears  134  be able to rotate fully around the shafts  166 . For instance, in one embodiment, the arms  167  and driving moon gears  134  rotate a maximum of between about fifteen and about ninety degrees around the shaft  166 . In other embodiments, a maximum rotation of the arms  167  and driving moon gears  134  relative to the shaft  166  is between about thirty and about sixty degrees. 
     As the pivoting arms  167  and the driving moon gears  134  rotate relative to the shafts  166 , the driving moon gears  134  can move radially inward or outward along a curved path that extends from an innermost position to an outermost position, and can move in very small, or possibly infinitely small, increments. In this manner, selective activation of the adjustment actuators  161 , can thereby cause the driving moon gears  134  to move radially inward or outward with the movement of the sheaves  126 ,  130 , and thus facilitates constant tooth engagement between the teeth of the driving moon gears  134  and pockets in the chain  128 . 
     Moon Gear Correction and Braking 
     Optionally, the transmission  100  includes a correction mechanism that allows for correction of the location of teeth of the driving moon gears  134 . Consequently, as the chain  128  and the driving moon gears  134  move so as to provide various different gear ratios, the teeth of the driving moon gears  134  can have a rotational position corrected as necessary so as to maintain proper alignment with the chain  128  at both integer and non-integer positions of the chain  128 . 
     More particularly,  FIG. 4  illustrates a partial view of the transmission  100  of  FIG. 2 . Similar to the illustration in  FIG. 3 , the transmission  100  in  FIG. 4  is illustrated with various components removed so as to more clearly illustrate interior components of the transmission  100 . For instance, the transmission  100  in  FIG. 4  may be generally identical to transmission  100  of  FIG. 2 , but is illustrated without differential system  122 , sheave actuators  132 , and half of the sheave  126 . Portions of the gear tooth correction mechanism are also removed on the input system  118  to more clearly illustrate various components thereof. 
     In one aspect, a correction system  140  is included in the transmission  100  and includes three correction actuators  168 . The three correction actuators  168  can be a part of the input system  118  or the output system  120 . In some embodiments, each of the input and output systems  118 ,  120  includes correction actuators  168 . Each of the correction actuators  168  can be selectively activated so as to correct a corresponding rotational position of a driving moon gear  134 , as necessary. 
     In particular, in this embodiment, the correction actuators  168  are each connected to a worm gear  169 , and each worm gear  169  is maintained in mesh with a worm wheel  170 . As the correction actuator  168  is selectively activated, the correction actuator  168  rotates the worm gear  169 , and the worm gear  169  causes the worm wheel  170  to rotate. The worm wheels  170  may be mounted on corresponding correction shafts  171  which, in this embodiment, extend through tube  172  that in turn connects to the pivoting arm  167 . Within the pivoting arm  167  of this embodiment is a correcting drive gear  173  that is mounted to the correction shaft  171 . The correcting drive gears  173  may be engaged with the driving moon gears  134 . 
     At least by virtue of the correction system  140 , a position of the driving moon gears  134  can be corrected so that the teeth of the driving moon gears  134  remain in alignment with the chain  128  both at integer and non-integer locations of the chain  128 . In particular, as noted previously, the worm gear  169  may cause the worm wheel  170  to rotate. Such rotation of the worm wheel  170  may cause the correction shaft  171  and the correcting drive gear  173  to rotate. As the correcting drive gear  173  is maintained in mesh with the driving moon gear  134 , the rotation of the correcting drive gear  173  can be used to cause the driving moon gear  134  to rotate. Moreover, the rotation of the driving moon gear  134  is controllable based upon the position of the sheaves  126 ,  130 . That is, as the sheaves  126 ,  130  move axially, the correction actuators  168  can be selectively engaged to rotate the driving moon gears  134  such that even at a non-integer positions of the chain  128 , sheaves  126 ,  130  and/or driving moon gears  134 , a tooth of the driving moon gear  134  can be aligned for proper meshing with the chain  128 . Such control over the corresponding motions of the sheaves  126 ,  130 , and the activation of the correction actuators  168 , as well as the activation of the adjustment actuators  161  may be mechanically, electrically, and/or computer controlled. The correction system  140 , collectively and its individual components, is thus one example of a means for correcting tooth positions of a driving moon gear  134 . 
     It should also be appreciated that it is not necessary that each of the driving moon gears  134  be corrected at the same time. For example, each driving moon gear  134  can be corrected separately and/or independently. Indeed, in one embodiment, the driving moon gears  134  have their rotational positions corrected only while they are not under load. More particularly, correction may occur during the time a driving moon gear  134  is not engaged with the chain  128 , and/or the transmission  100  may delay correcting a driving moon gear  134  until the driving moon gear  134  disengages from the chain  128 . 
     The worm gear  169  described in connection with the correction system  140  can thus facilitate coordinating actuation of the correction actuators  168  and movement of the driving moon gears  134 . The worm gear  169  may be replaced with another suitable type of gear; however, in some embodiments, the worm gear  169  may also be used to facilitate reduction of slip between the input system  118  and the chain  128 . For instance, even if the chain  128  has the tendency to resist movement by the driving moon gear  134  and to slip relative to the input system  118 , the transmission of torque through the driving moon gear  134  back through the correction actuator  168  can be substantially prevented or reduced. For instance, the worm gear  169  can act as a braking mechanism and resist such movement. Thus, the worm gear  169  may also act in some embodiments as a locking mechanism  142  that locks the driving moon gears  168  and prevents at least backward rotation of the driving moon gears  168 . Moreover, while the worm gears  169  are the only worm gears illustrated, other gears may be worm gears, helical gears, bevel gears, spur gears, or have any other suitable gear configuration. Additionally, the actuators  161 ,  168  can be any suitable actuator, including at least stepper or servo motors. The locking mechanism  142  and the worm gear  169  are thus examples of means for locking rotation of the driving moon gears  134 . 
     Differential System 
     Returning briefly to  FIG. 2 , the transmission  100  includes a transmission input  112  that is illustrated in the form of a shaft. As a torque is applied to the transmission input  112 , a rotational input is provided and transferred through the transmission  100  in the manner described herein (including in the discussion of transmission  10 ). As shown in  FIG. 2 , the transmission input  112  can include an input gear  152  that mates with the transfer gear  115  of the transmission input  112 . The input gear  152  can be integrally formed with, or attach to, a differential input shaft  154  that rotates as the input gear  152  is rotated by the transfer gear  115 . 
     In  FIG. 2 , the input and output systems  118 ,  120  include sheaves  126 ,  130  that engage a chain  128 . Optionally, the input and output systems  118 ,  120  also include driving moon gears  134  that engage the chain  128 . As discussed herein, the sheaves  126 ,  130  and/or driving moon gears  134  can move with respect to the drive shafts  124 ,  131  to change a gear ratio of the transmission  100 . 
     The input system  118  thus receives a power input through the transmission input  112  and transfers such power to the sheave  130  of the output system  120 . The sheave  130  may be directly or indirectly coupled to the output drive shaft  131 , such that as the sheave  130  rotates, the output drive shaft  131  also rotates. For instance, a counterclockwise rotation of the chain  128  may cause the sheave  130  and the output drive shaft  131  to rotate in a counterclockwise direction. Moreover, the rotational speed of the output drive shaft  131  can be geared up or down relative to the power received at the transmission input  112  by virtue of the gear ratio defined by the relative positions of the input and output systems  118 ,  120 . 
     While the output drive shaft  131  may, in some cases, provide the final output of the transmission  100 , it need not do so in all embodiments. Indeed, in the illustrated embodiment, the output of the shaft  114  is further geared through the differential system  122 . The differential system  122 , in the illustrated embodiment, can provide a variety of features, one of which may be an engaged neutral by which the input  122 , while remaining positively connected to the load via the transmission output  114 , nonetheless provides zero output speed. 
     More particularly, power in the transmission  100  is optionally split along multiple paths. As described above one path may include power transmitted through the input and output systems  118 ,  120  to the output drive shaft  131 . Along a second path, as also described above, power can be transmitted from the transmission input  112  to the differential input shaft  154 . The power transmitted to the output drive shaft  131  may optionally be combined with the output transmitted through the differential input shaft  154 . For instance, the output drive shaft  131  may be attached to an output gear  158 . The output gear can mate with an output transfer gear  160  that, in turn, engages a differential input gear  156 . Such a transfer is merely exemplary, but illustrates one manner in which power can be conveyed from the output system  120  to a differential system  122 . 
     Now turning to  5 A and  5 B, a portion of the differential system  122  of  FIG. 2  is illustrated in greater detail. In particular,  FIGS. 5A and 5B  illustrate a differential system  122  in which a differential input shaft  154  and differential input gear  156  each provide separate inputs to be combined in providing power to the transmission output  114 . 
     In one embodiment, the differential input shaft  154  extends through the differential input gear  156  and into a differential housing  174 . Within the differential housing  174  is a differential drive gear  175 . The differential drive gear  175  may be coupled to the differential input shaft  154  by, for instance, being integrally formed with the differential input shaft  154 , or being secured thereto so as to rotate in the same direction and with the same rotational speed as the differential input shaft  154 . The differential drive gear  175  may also be coupled to the differential input shaft  154  in other suitable manners, including a spline connection, a weld, a linkage through one or more other gears, or in other manners, or in a combination of the foregoing. 
     As discussed previously with respect to  FIG. 2 , the differential system  122  can also include a differential input gear  156  that is linked to the output of a transmission output system. According to one embodiment, the differential housing  174  is directly or indirectly secured to the differential input gear  156  in a manner that causes the differential housing  174  to rotate with, or be rotated by, the differential input gear  156 . The rotation of the differential housing  174  may be configured in any suitable manner relative to the differential input gear  156  and/or the output drive shaft  131  ( FIG. 2 ). For example, the differential housing  174  may rotate at a rotational speed less than, equal to, or even greater than the rotational speed of the differential input gear  156  and/or the output drive shaft  131 . 
     As best illustrated in  FIG. 5B , the differential housing  174  may have multiple gears secured thereto, or therewithin. For instance, a first moon gear  176  may be connected to the differential housing  174  and can engage the differential drive gear  175 . In one embodiment, the differential drive gear  175  is approximately centered within the differential housing  174  and, as best illustrated in  FIG. 5B  (which has housing  174  illustrated in dashed lines to provide a better view within the differential housing  175 ), the first moon gear  176  need not be centered within the differential housing  174 . The positioning of the first moon gear  176  in the illustrated embodiment is such that as the differential housing  174  is rotated by the differential input gear  156 , the housing  174  causes the first moon gear  176  to orbit around the differential drive gear  175 . As the differential drive gear  175  mates with the first moon gear  176 , the orbital motion of the first moon gear  176  around the differential drive gear  175  can add to, or subtract from, the rotational motion of the differential drive gear  175 . The first moon gear  176  may also engage a second moon gear  177  that orbits with the differential housing  174 . As the first moon gear  176  thus orbits and rotates, it can thus also cause the second moon gear  176  to rotate in addition to its orbit provided through the differential housing  174 . 
     A differential output gear  178  is, in the illustrated embodiment, secured to the housing  174  and engages the second moon gear  174 . In this manner, as the second moon gear  174  rotates, the second moon gear  174  transfers power to the differential output gear  178 . The differential output gear  178  may, in turn, be connected to an output shaft which may be the transmission output  114 , or may be coupled to the transmission output  114 . 
     As will be appreciated by one skilled in the art in view of the disclosure herein, the differential system  122  can thus act as a type of differential. In a typical differential of an automotive system, a differential may be used in the final drive on an axle of the vehicle. In such a system, a single input may interconnect with two outputs—one going to either axle on a front drive. The illustrated differential system  122 , however, operates in a different manner and, in many regards, opposite the described typical differential. Specifically, the illustrated embodiment includes two inputs and provides a single output. Specifically, a first input to differential system  122  is provided from the transmission input  112  ( FIG. 2 ) and ultimately conveyed into the housing  174  through the differential input shaft  154  and the differential drive gear  175 . A second input to differential system  122  is provided from the output drive shaft  131  ( FIG. 2 ), and is applied to the housing  174  through the differential input gear  156 . 
     In the described manner, there may thus be two different inputs provided to the differential system  122 , and the two inputs may be combined into a single output. Additionally, based on the directions and magnitudes of such inputs, the inputs may be additive and/or subtractive within the differential system  122 . For example, it will be appreciated that through one or more gears, input from the differential input shaft  154  can be provided and transferred such that differential drive gear  175  rotates in a first direction (e.g., counterclockwise). Through appropriate gearing, the rotation of an output drive shaft  131  ( FIG. 2 ) may also be transferred to the housing  174  so that the housing  174  rotates in the same direction (e.g., counterclockwise), although the differential drive gear  175  and the housing  174  may, in other embodiments, provide inputs that are in opposite directions and/or opposite relative to the transmission input and output drive shaft. In the illustrated system, the variations to the respective magnitudes of the rotational inputs can ultimately provide a variety of different outputs at the transmission output  114 , including a reverse, neutral, drive, and overdrive for a transmission. Thus, two inputs can combine to provide a clockwise or counterclockwise rotation, or even to provide no output. 
     More particularly, as the transmission input gear  156  rotates, the housing  174  may also be rotating and causing the first and second moon gears  176 ,  177  to orbit around the differential drive gear  175  in the same direction as the rotation of the differential input gear  175 . At mating gears, the velocity of the gear teeth at the point of engagement must be equal as to direction and magnitude. Further, the velocity of gear teeth is related to the rotational and/orbital motion by the equation V=rω, where V is the linear velocity, r is the radius of rotation at the point of engagement, and ω is the angular velocity. 
       FIGS. 6A-6D  illustrate exemplary input and output conditions for a differential system  122 . For convenience, components from an input are illustrated in solid lines, whereas components of an output are illustrated in dashed lines.  FIG. 6A  illustrates an example differential drive gear  175  which provides an input by rotating counterclockwise about its own axis, as shown by Arrow A. A second input is provided (e.g., through rotation of the differential input gear  156 ) that causes the first moon gear  176  to orbit in a counterclockwise direction around the central axis of the differential drive gear  175 , as shown by Arrow B. In such an example, the radius of orbit at the point of engagement is equal for both rotations, as both are centered on the same axis, namely the axis of the differential drive gear  175 . Accordingly, if the angular velocity of the differential drive gear  175  is equal to the angular velocity of the first moon gear  176 , the linear velocities (V A  and V B ) are also equal at the point of engagement. Inasmuch as V A =V B , the introduction of any other velocity to one of the differential drive gear  175  or to the first moon gear  176  could cause an inequality at the point where the teeth on differential drive gear  175  mate with the teeth on the first moon gear  176 . For example, if the first moon gear  176  was to rotate about its axis, such rotation would also contribute to the total velocity of the first moon gear  176  at the point of contact (i.e., V B ). Such contribution would create an inequality between V A  and V B  unless some other motion is introduced into the differential drive gear  175 . The differential drive gear  175  may, however, be configured to provide an input that cannot be modified by the first moon gear  176 . Accordingly, to maintain an equality in the velocities of gear teeth at the point of contact, there can, in the illustrated embodiment, be no velocity contribution by the internal rotation of the first moon gear  176  about its own axis. The rotation of the first moon gear  176  about its own axis may be considered a sum of two inputs (e.g., rotational input from the differential drive gear  175  and the differential input gear  156 ); however, in this embodiment, there may be no output in the form of rotation of the first moon gear  176 . 
       FIG. 6B  illustrates an alternative example in which the orbital speed of the first moon gear  176  is greater than the rotational speed of the differential drive gear  175 . As a result, at the point of engagement between the first moon gear  176  and the differential drive gear  175 , the velocity component V A  of the differential drive gear  175  is, in the illustrated embodiment, less than the velocity component V B  of the orbital of the first moon gear  176 . Specifically, in the illustrated embodiment, the linear velocity component V B  provided by the orbital motion of the first moon gear  176  may be approximately twice the linear velocity V A  of the differential drive gear  175 , as represented by the magnitudes of the velocity arrows V A  and V B . In such a case, the velocities can be made equal, however, if a velocity component V c  is introduced by rotating the first moon gear  176  about its axis. Specifically, the inequalities of linear velocities V A  and V B  can cause the first moon gear  176  to rotate counterclockwise, in this embodiment, to provide a velocity component V c  that is an output and is equal to a difference between the linear velocity component V B  and the linear velocity component V A . In other words, by changing the gear ratio of a transmission such that the output of the transmission  100  ( FIG. 2 ) as conveyed as one input to a differential system  122  is greater than a second input to the differential system  122 , a rotation can be conveyed to the first moon gear  175 . 
     Notably, if the first moon gear  176  in the illustrated embodiment is rotating counterclockwise, the second moon gear  177  ( FIGS. 5A and 5B ) that engages the first moon gear  176  can have a clockwise rotation. The orbital and rotational motions of the second moon gear  177  can then be combined in a manner similar to that described with regard to the differential drive gear  175  and the first moon gear  176  to provide a rotation to the second moon gear  177  and/or the differential output gear  178 . Indeed, if the radii of gears  175 ,  176 ,  177  and  178  are equal and counterclockwise rotation is considered positive rotation, the output at the differential output gear  178  ( FIG. 5B ) can be related to the inputs at the differential drive gear  175  and the differential input gear  156  by the following equation: ω 178 =2ω 156 −ω 175 . 
     Thus, in the example in  FIG. 6A , an output rotational speed at the differential output gear  178 , and potentially at the transmission output  114  ( FIG. 5A ), may be equal to the input rotational speed at the differential drive gear  175  as well as of the differential input gear  156  and/or the differential housing  174  ( FIG. 5A ). For the example in  FIG. 6B , the output rotational speed at the differential output gear  178  may be three times the input rotational speed of the differential input gear  156 . 
       FIGS. 6C and 6D  illustrate still other examples of varying input and output conditions for the differential system  122 , and operate by the same principles described above for  FIGS. 6A and 6B . In  FIG. 6C , the input rotational speed A at the differential drive gear  175  is about twice the input rotational speed B of the differential input gear  156 . As a result, the velocity component V A  of the differential drive gear  175  is about twice the velocity component V B  of the first moon gear at the point of engagement. Consequently, the first moon gear  176  may also rotate to equalize the velocities at the point of engagement. To equalize the velocities, the first moon gear  175  can provide a velocity component V c  equal to the difference between the velocity component V A  and the velocity component V B , and such velocity can be provided by a clockwise rotation of the first moon gear  176  at a rotational speed about half the rotational speed of the differential drive gear  175 . Following the gear rotations through the differential system  122  and assuming all gears  175 - 178  ( FIG. 5B ) are the same size, the rotational speed of the output gear  178  is approximately zero. 
     In  FIG. 6D , the linear velocity V A  resulting from the rotational speed of the differential drive gear  175  is about three times the linear velocity V B  resulting from the rotational speed of the differential input gear  156 . As a result, the first moon gear  176  is caused to rotate about its internal axis to equalize the linear velocities at the point of engagement. More particularly, the first moon gear  176  may rotate about its own axis at a speed C that is approximately twice the orbital speed B of the first moon gear  176 . The rotation is, however, in an opposite and clockwise direction. As such motion is transferred through the differential system  122 , the output at the output gear  178  ( FIG. 5A ), assuming the same criteria described above, would end up being about equal in magnitude to the rotational speed of the differential input gear  156 , but opposite in direction (i.e., clockwise). 
     Returning to  FIGS. 5A and 5B , it should be appreciated that by varying the relationship between the rotational speed inputs at the differential input gear  156  and the differential drive gear  175  (e.g., by varying gear ratios between a transmission input and output system), a wide variety of final outputs can be received. Moreover the varied outputs can be obtained while the transmission maintains engagement between all drive and driven members, and can result in forward, reverse, and even neutral/stopped conditions with such engagement. Moreover, the transmission  100  may even operate at a constant input velocity. More specifically, a constant input velocity can be transmitted through the transmission and a variable output velocity can be obtained by varying the gear ratio in the transmission. 
     The differential system  122  provides one example of a means for combining two inputs to produce a single output, and one example of a means for providing an engaged neutral. It should be appreciated that the foregoing description of a differential system  122  is merely exemplary, and that other configurations can exist. For instance, in some embodiments and means, a second moon gear  177  may be eliminated entirely, or additional moon gears or other gears can be provided. Furthermore, gears within the differential housing  174  may be different sizes such that the relationship between the output and two input rotational velocities can change. In still other embodiments, the differential drive gear  175  may be disconnected and allowed to rotate freely, or held with zero internal rotation. In still other embodiments, the differential drive gear  175  and the housing  174  may receive inputs in opposite directions. Additionally, while only a single first moon gear  176  is illustrated, there may be additional first moon gears  176  that each engage the differential drive gear  175 , thereby dividing the torque among multiple gears. Naturally, there may also be additional second moon gears  177 , or other gears within the differential system  122 . Accordingly, the relative rotational motions, and the magnitudes thereof, of the transmission input gear  175  and the first moon gear  176  can thus act with or against each other, such that the rotational speed of first moon gear  176  (as opposed to the orbital motion of first moon gear) can be in a clockwise or counterclockwise direction. 
     One feature of the disclosed differential system  122  is the ability to start with engagement from a dead stop. For instance, a vehicle with a high torque engine (e.g., a semi-tractor trailer, tracked land vehicle, construction equipment) may be stopped in an engaged neutral on a road with a steep incline. With the above described differential system  122 , such a vehicle can maintain engagement while moving the load forward in infinitely small increments. In particular, infinitely small increments of change can be used to cause the vehicle to move, such that there is little to no rollback when starting the movement, and the infinitely small increments of change can also reduce a torque spike when engaging the engine. 
     In all regards, the embodiment described above with respect  FIGS. 5A-6D  is illustrative, and one skilled in the art will appreciate that various alternatives and/or additional components may be utilized. In some regards, for example, gears may be removed or added to provide additional gear ratio changes, and/or to link inputs or outputs to other components. In one embodiment, for instance, the differential housing  174  may be directly coupled to an output drive shaft and/or positioned in-line therewith. Additionally, it will be appreciated that the various gears and components described with regard to transmissions  10  and  100  may be positioned on bearing surfaces. For example, the first and second moon gears  176 ,  177  and/or the differential output gear  178 , may have bearing surfaces interfacing with the differential housing  174  to thereby allow rotation within the differential housing  174 . 
     Various embodiments may thus be provided to provide an engaged neutral, vary gear ratios, use a differential mechanism, and the like. For example,  FIGS. 7A and 7B  schematically illustrate various possible configurations. In  FIG. 7A , for example, differing angular velocities of power supplies can be engineered to provide a reverse, neutral, drive and overdrive gear. This basic illustration is true even when the first and second inputs (e.g., the primary and secondary supplies) are independent sources of power. For instance, the first and/or second inputs can be turbine engines, internal combustion engines, electric motors, or any other suitable input system. Additionally, the amount of load carried by each power supply can be determined by the ratio between the two inputs to the reverse differential. 
     Additionally, the secondary power supply may optionally be engineered to shut down, thereby allowing the primary power supply (which itself may be geared for overdrive) to run straight from the primary power supply to the load. Such a system may improve the efficiency to exceed that of even the standard transmission. 
     In  FIG. 7B , an alternative schematic is provided in which inputs are split from a single power source. In particular, the secondary power supply can be replaced by a transmission in order to vary speed and torque going into the reverse differential from the secondary power supply. This may be accomplished by tapping into the angular velocity of the primary power supply and splitting the torque between the two inputs to the reverse differential (e.g., via a transmission). The types of transmissions would include, but not be limited to: manual, automatic, belt-driven CVT, toroidal CVT, PECVT, hydraulic pump/motor transmissions, and any other type of transmission. 
     The configuration in  FIG. 7B  would provide for many variables between the velocity of the engine and the ratio of the transmission which combine at the reverse differential. The variables could be engineered, for example, to favor performance, fuel economy or the operating RPMs of a motor (e.g., an electric motor). The many options here noted would lend themselves to a wide range of applications. 
     The aspect of splitting the torque received at the input between multiple, different paths is itself an aspect that can also be desirable for various types of applications. For example, when the torque is split (e.g., using the transfer gear  115  in  FIG. 2 ), some of the torque can be passed through the variable portion of the transmission (e.g., throughout an input system, chain, and output system), while another portion is passable directly to a reverse differential. When splitting the torque in this or a similar manner, it should be noted that the torque can be reduced along both paths with respect to the initial torque input. As such, the torque carried by the variable portion of the transmission can be significantly lower, in some cases, than the amount of torque that would be supplied through the variable portion of the transmission were the splitter not present. By reducing the torque, the wear, heat, friction, and the like can be reduced thereby improving the life of the transmission and/or allowing smaller, lighter, and/or less expensive components to be utilized. 
     Chain 
     With reference now to  FIGS. 8A and 8B , the chain  128  is described in greater detail. It should be appreciated, however, that chain  128  is merely one example of a chain suitable for use with a transmission according to embodiments disclosed herein, and that other suitable chains may be used and are contemplated. In particular regard to the illustrated embodiments, it can be seen that the chain  128  is comprised of multiple links.  FIG. 8A , for example, illustrates a portion of the chain  128  that includes approximately three links. More links may be added so as to provide chain  128  a length suitable for use with a transmission as may be learned from the disclosure herein. 
     The portion of the chain  128  illustrated in  FIGS. 8A and 8B  includes a variety of interconnected components. For instance, the chain  128  includes three first side structure  179  and three opposing second side structures  180 . The first and second side structures  179 ,  180  ( FIG. 8B ) are essentially mirror copies of each other, and form the outer edge of the chain  128 . In the illustrated embodiment, outer chain links  181  and inner chain links  182  interpose the first and second side structures  179 ,  180 . In the particular embodiment illustrated in  FIG. 8A , for instance, the inner chain link  182  is positioned inside outer walls of the outer chain link  181 . Moreover, openings in the outer and inner chain links  181 ,  182  can be aligned so that a pin  183  can be positioned therein and secure an inner chain link  182  to an outer chain link  181 . The pins  183  can also secure the inner and outer chain links  181 , the  182  to the first and second side structures  179 ,  180 , and thus secure a first side structure  179  to a second side structure  180 . In some embodiments, the inner chain links  182  may be roller links, and the outer chain links  181  may be pin links. 
     In the illustrated embodiment, each of the first side structures  179  includes various portions. For example, the first side structures  179  can each include a body  184 . The body  184  is, in the illustrated embodiment, elongated and extends in a lateral direction that is generally parallel to the pin  183 . It should be noted, however, that the body  184  may be of any suitable shape and may, for example, be generally square or could be elongated and extend perpendicular to the pin  183 . 
     Extending from the body  184  is, in this embodiment, an exterior pin mount  185 , as well as an interior pin mount  186 . In the illustrated embodiment, the exterior pin mount  185  extends in a direction aligned generally with the length of the chain  128 . For instance, the exterior pin mount  185  may extend from approximately a center of the body  184 , and in a direction that is generally perpendicular to the pin  183 . The interior pin mount  186  can also extend generally in a direction aligned with the chain  128  and/or generally perpendicular to the pin  183 . In the illustrated embodiment, however, the pin mounts  185 ,  186  extend in opposite directions from the body  184 . Moreover, in this embodiment, the interior pin mount  186  is at a position on the body  184  that is inward relative to the exterior pin mount  185 . 
     The illustrated exterior and interior pin mounts  185 ,  186  each define openings therein, which openings are configured to receive the pins  183  therein. Additionally, when two first side structures  179  are positioned adjacent each other, an exterior pin mount  185  on one first side structure  179  can be positioned exterior to, and generally adjacent, an interior pin mount  186  on a second first side structure  179 . The pin  183  can then be inserted and can secure the two first side structures  179  together in a nested configuration. The pin  183  can also secure the first side structures  179  to one end of an outer chain link  181  as well as to an opposing end of an inner chain link  182 . As noted above, the second side structures  180  may have a similar structure, and may be mirror images of the first side structures  179 . 
     As discussed herein, a chain  128  can be positioned within sheaves and/or around sprockets. It can be seen from the illustrated figures that the interior and exterior chain links  181 ,  182  thus define pockets into which the gear teeth of a corresponding sprocket can be positioned to drive or otherwise engage the chain  128 . More specifically, each inner chain link  182  can include a sleeve or roller  187  centered around an opening into which the pins  183  are positioned. The distance between the sleeve or roller  187  may have a pitch corresponding to a pitch of the sprockets, such that a sprocket tooth can be positioned between two adjacent sleeves or rollers  187 . 
     With particular regard to  FIG. 8B , an exemplary manner in which the first and second side structures  179 ,  180  can facilitate use with sheaves is illustrated. More specifically, the side structures  179 ,  180  have exterior surfaces that can be offset at an incline, to define an angled outer edge rather than a square outer edge. In particular, rather than having a side surface that is generally perpendicular to top and/or bottom surfaces and/or a longitudinal axis of the pin  183 , the side structures  179 ,  180  have inclined outer edges  188 . The outer edges  188  may be offset at an angle generally corresponding to a beveled surface of one or more sheaves. Thus, as a sheave moves together or apart, the outer edges  188  of the chain  128  can correspondingly slide outwardly or inwardly relative to a rotation axis of the sheave. The outer edges  188  may maintain frictional contact with the interior surfaces of a sheave as the chain  128  moves. The chain  128  may also be suitably lubricated with respect to its operation with a sprocket and/or sheave so as to prolong the life of the chain  128  and the transmission components, and to possibly provide a substantially frictionless engagement between the chain  128  and a corresponding sheave. 
     It should also be appreciated in view of the disclosure herein that the angle of the outer edge surfaces  188  of the side structures  179 ,  180  can be varied in any desired manner, and can be modified based on the particular application, particular sheaves with which it is used, and the like. For instance, in one embodiment, the outer edge surfaces  188  of the chain  128  are beveled at an angle (φ) ranging between approximately five and fifty-five degrees, although the angle may be less than five or more than fifty-five degrees. In another embodiment, φ ranges between about ten and about thirty degrees. It should be appreciated in view of the disclosure herein that the chain  128  is one example of a means for conveying power, but is merely an exemplary embodiment of a suitable chain usable according to some aspects of the present disclosure. For instance, while the chain  128  may be a roller chain, in other embodiments the chain  128  may be an involute chain, a custom chain, or another type of chain, or a combination thereof. 
     2. Transmission Embodiment with Turbine Correction Mechanism 
     As discussed herein, various components of transmissions described herein are variable and/or interchangeable. Turning now to  FIGS. 9A-9C , another example embodiment of a transmission system  200  is described. In particular,  FIGS. 9A-9C  illustrate another transmission system  200  having at least synchronization and correction systems  238 ,  240  described in greater detail herein, and which are interchangeable with other transmissions described herein. Components of other transmissions described herein, or which may be learned by a review of the disclosure herein, may also be combined with the transmission system  200 . For instance, in the illustrated embodiment, a single sheave assembly  218  is illustrated. The illustrated sheave assembly  218  may act at least as a portion of an input and/or output. For instance, the illustrated sheave assembly  218 , or a portion thereof, may replace or supplement the input systems  18 ,  118  and/or output systems  20 ,  120  of  FIGS. 1 and 2 , as well as such systems described hereafter. 
     The sheave assembly  218  of  FIGS. 9A-9C  includes various components operating in a manner similar to other components described elsewhere herein. Accordingly, to avoid obscuring additional aspects of the sheave assembly  218 , such components will generally not be described, or only treated briefly, as a suitable discussion is found elsewhere herein. Rather, additional detail will be given to additional components in this particular embodiment. 
     In the illustrated sheave assembly  218 , and similar to other embodiments herein, a drive shaft  224  may pass through sheave assembly  218  and have attached thereto opposing halves of a sheave  226 . The halves of the sheave  226  are, in this example, attached to the drive shaft  224  using a spline connection on the shaft  224 , although other types of connections may also be used. The spline or other connection on the drive shaft  224  can allow the drive shaft  224  to rotate and further cause the sheave  226  to rotate; however, as the sheave assembly  218  may also operate in an output system, the sheave  226  may provide the input and cause the drive shaft  224  to rotate. 
     In some embodiments, and as described herein, halves of the sheave  226  may be axially movable along the drive shaft  224 . Such axial movement may, for example, allow a wrapping member such as a chain or belt to ride on the sheave  226  and to move radially inward and outward relative to the drive shaft  224 . Such movement can allow the transmission system  200  to effect changes in gear ratio. To facilitate movement of the sheave  226 , two sheave actuators  232  are provided and can compress the sheave  226 , or allow the sheave  226  to expand. The sheave actuators  232  can, as described herein, be or include hydraulic actuators that use fluid pressure that increases to compress the sheave  226  and decreases to expand the sheave  226 . The sheave actuators  232  may, however, include other actuators as described herein, and can reside on the drive shaft  224  as described herein, although such positioning is merely exemplary. 
     As also disclosed previously herein, one or more drive gears  234  can be positioned relative to the sheave  226  and be configured to engage with a chain (not shown) positioned around the sheave  226 . The drive gears  234  can engage the chain and act to prevent or reduce slippage of the chain on the sheave  226 . The number of drive gears  234  may be varied, although in one embodiment, three drive gears  234  are spaced around the drive shaft  224 . In other embodiments, more or fewer drive gears  234  may be used. For instance, four, five or six drive gears  234  may be used. 
     Inasmuch as the sheave  226  can be selectively positioned to cause a corresponding chain to move radially inward or outward relative to a longitudinal axis about which the sheave  226  rotates, the drive gears  234  may also be configured to move radially inward and/or outward relative to the longitudinal axis of the sheave  226 , which in this embodiment is centered in the drive shaft  224 . In the illustrated embodiment, a synchronization system  238  can be used to adjust the radial position of the drive gears. 
     Synchronizing System 
     In the illustrated embodiment, the synchronization system  238  may include a slot  262  and worm gear  263 . The drive gears  234  may rotate around a drive gear shaft  236  and the worm gear  263  may be directly or indirectly connected to an actuator (not shown). The actuator may include, for instance, a hydraulic or pneumatic actuator, an electrical actuator, a mechanical actuator, or some other type of actuator, or a combination of the foregoing. As such an actuator engages, the worm gear  263  may be caused to rotate. A carrier  267  may be coupled to the drive gear shaft  236  and can engage the worm gear  263 . As a result, as the worm gear  263  rotates, the carrier  267  and the drive gear shaft  236  can move radially inward or outward relative to the drive shaft  224 , depending on the direction of actuation of the worm gear  263 . The drive gear shaft  236  may extend through the slots  262  formed in one or both halves of the sheave  226  to allow for radial movement of the drive gear shafts  236  relative to the sheave  226 . As best illustrated in  FIG. 9A , the radial movement of the drive gears  234  may follow a generally linear path. In other embodiments, however, the drive gears  234  may follow an arcuate or other path. For instance, in the embodiment of the transmission  100  ( FIG. 2 ) described above, the driving moon gears  134  ( FIG. 3 ) can be rotated on a shaft to cause radial movement, thereby moving along an arcuate path. 
     According to one embodiment, the drive gears  234  generally move along the slot  262  when a corresponding drive gear  234  is not under load. As such, each drive gear  234  may be actuated or otherwise moved independently relative to each other drive gear  234 . In other embodiments, however, the worm gears  263  may be collectively coupled to an actuator or other mechanism that causes collective movement of the drive gears  234 . 
     In one embodiment, the synchronization system  238  may operate on two halves of the sheave  226 . For instance, to link movement of the drive gears  234  such that the drive gear shaft  236  is moved at or within both halves of the sheave  226 , the illustrated example embodiment includes a cross-over shaft  264 . The cross-over shaft  264  is, in this embodiment, coupled to a pair of linking gears  265  that may in turn drive the worm gears  263  directly or indirectly. In  FIG. 9B , for instance, the linking gears  264  drive a synchronizing ring gear  266  that couples to the worm gears  263 . The synchronizing ring gear  266  includes, in this embodiment, two tooth profiles. A first profile may mate with the linking gears  265 . The second tooth profile may include, for instance, a bevel gear set that mates with the worm gear  263 . 
     A single cross-over shaft  264  is illustrated; however, more may be included. For instance, the number of cross-over shafts  264  may correspond to a number of drive gears  234 . For example, multiple cross-over shafts  264  may be included to separately and independently move the drive gears  234 , although a single cross-over shaft  264  may be linked to collectively cause the drive gears  234  to move radially, or multiple cross-over shafts  264  may be used to cause collective radial translation of the drive gears  234  while reducing the load on each cross-over shaft  264  relative to a single shaft operating to coordinate radial movement of drive gears  234 . In some embodiments, the one or more cross-over shafts  264  are fixed, such that they do not orbit around the drive shaft  224 . As a result, as the sheaves  226 , drive gears  234 , and worm gears  263  rotate around the drive shaft  224 , an actuator interacting with the worm gears  263  can alternatively engage the cross-over shaft  264  (e.g., through the linking gears  265  or another mechanism) to coordinate the radial position of the drive gears  234 . In other embodiments, the one or more cross-over shafts  164  can co-rotate with the sheave  226  around the drive shaft  224 . 
     By translating the drive gears  234  as the sheaves  226  move axially inward or outward, the drive gears  234  may remain in constant contact with an associated chain, and optionally act as a non-slip mechanism. More particularly, in some embodiments, the drive gears  234  may carry the chain and transfer power to the chain. The sheave  226  may transfer some power, or may be used primarily to radially position the chain. The components of the synchronization system  238 , both collectively and individually, are thus examples of a means for radially positioning the drive gears  234  and/or a chain, and means for transferring power to the wrapping member. 
     The radial movement of drive gears  234  may be referred to herein as “synchronizing” as gears  234  are synchronized in radial movement to correspond to the radial position of the chain as determined by the sheave  226 . Another mechanism, referred to herein as “correcting” may relate to the rotational movement of the drive gears  234  to align teeth of the drive gears  234  with respect to pockets of a chain, and includes correction of tooth position by changing the rotational position of gear teeth when the radius of rotation of the chain on the sheave  226  corresponds to a non-integer ratios, as described herein. Thus, the term “synchronizing” when used in connection with drive gears or moon gears generally relates to the radial movement of the drive gears  234 , whereas “correcting” relates to the rotational movement of the drive gears  234 . 
     Correction System 
     With regard to correction of the drive gears  234  illustrated in  FIGS. 9A-9C , a correction system  240  may be used. For instance, the correction system  240  may be used to rotate the drive gears  234 , and to thereby advance and/or retreat teeth of drive gears  234  as desired for alignment with a chain. As described herein, tooth correction may be useful where, for instance, the drive gears  234  have teeth of a fixed pitch and changes in the radial position of the drive gears  234  and/or sheave  226  cause the chain to rotate around an effective or virtual circle having partial teeth. The particular embodiment described herein performs correction of the drive gears  234  while they are not under load (e.g., while not engaged with the chain), although in other embodiments it may be desired to correct motion while under load. In correcting the drive gears  234  while not under load, each drive gear  234  can be corrected independent of and/or at a different time than other drive gears  234 . 
     Particularly with regard to  FIG. 9B , the drive gears  234  may be corrected using a correction system  240  that includes a set of worm gears  269 . Specifically, the example embodiment in  FIGS. 9A-9C  includes one worm gear  269  for each of the three drive gears  269 , and the worm gear  269  is directly or indirectly coupled to a drive gear  234 . For instance, in the illustrated embodiment, the worm gear  269  is mounted to a housing  272  that is connected to the drive gear shaft  236 . According to at least one embodiment, the housing  272  is coupled to the worm gear  269  and the drive gear shaft  236  such that as the worm gear  269  rotates, a kinematic transfer of power causes the drive gear shaft  236  and a corresponding drive gear  234  to rotate. For instance, as shown in  FIG. 9B , the worm gears  269  may be coupled to a set of one or more driving gears  270 ,  271  that cause the worm gear  269  to rotate. As the worm gear  269  rotates, the housing  272  may rotate (e.g., by directly coupling to the worm gear  269  or through one or more relay gears), thereby rotating the drive gear shaft  236  and the drive gear  234 . According to one embodiment, the housing  272  includes a worm wheel mating with the worm gear  269 . The worm wheel may be co-axial with the drive gear shaft  236  such that as the worm gear  269  rotates the worm wheel, the drive gear shaft  236  rotates. 
     The particular manner of correcting drive gears  234 , as described and illustrated herein, is merely exemplary. Moreover, the manner of controlling such a correction mechanism may also be varied in any suitable manner. For example, an actuator may be included that mechanically, electrically, hydraulically, or otherwise controls indexing and/or correction of drive gears  234 . Moreover, a controller may be embedded within the actuator, or may be separate therefrom. In the illustrated embodiment, a hydraulic actuator is one exemplary mechanism for controlling correction of the drive gears  234 . 
     In the illustrated hydraulic actuator, a set of three turbine disks  243   a - c  is illustrated. Each turbine disk  243   a - c  of the illustrated embodiment may be a reversing turbine disk and can rotate around a longitudinal axis in both forward and reverse directions. Such rotation of the turbine disks  243   a - c , which can ultimately be transferred to the drive gears  234 , may be used to advance or retreat the teeth of the drive gears  234  and thereby correct tooth position in, by way of illustration, a partial-tooth position. For instance, as best shown in  FIGS. 9B and 9C , each of turbine disks  243   a - c  is linked to an interior main gear  244   a - c . Specifically, the first turbine disk  243   a  links to a first interior main gear  244   a , the second turbine disk  243   b  links to second interior main gear  4047   b , and the third turbine disk  243   c  links to a third interior main gear  244   c.    
     In  FIG. 9B , some components have been removed to provide a more clear view of the internal components of the transmission system  100 . For instance, the turbine disks  243   a - c  are optionally coupled to three gear sets, each of the three gear sets including the interior main gears  244   a - c . Each of the sets of interior main gears  244   a - c  may in turn also connect to a particular correction drive gear  245   a - c . For instance, the correction drive gear  245   b  in  FIG. 9B  may connect to the second interior main gear  244   b  of the illustrated drive gear set. In view of the disclosure herein, it should be appreciated that second drive gear sets may also couple to a correction drive gear although such correction drive gears are not illustrated in  FIG. 9B  so as to provide a more clear view of other features of the transmission  100 . 
     In the illustrated system, as the turbine disk  243   b  rotates, the interior main gear  244   b  is rotated, and the correction drive gear  245   a - c  may also rotate and transfer power to the driving gears  270 ,  271  (e.g., along a shaft). Such power transferred to the driving gears  270 ,  271  can ultimately correct the rotation of the drive gears  234 . For instance, in the illustrated example embodiment, each of the three turbine disks  243   a - c  can correct one of the drive gears  234 . Thus, any drive gear  234  can be corrected independent of any other drive gear  234  by using an appropriate turbine disk  243   a - c . Furthermore, while each correction drive gear set is illustrated as including three correction drive gears  245   a - c , this is merely exemplary. For instance, each correction drive gear set could include only one of the correction drive gears  245   a - c.    
     It should be appreciated in view of the disclosure herein, that any number of control and actuation mechanisms can accordingly be used to adjust a transmission according to the present disclosure. For example, one actuator may move the sheaves  226  axially, while a separate actuator may be used with the drive gears  234  to cause them to translate radially, while still another actuator can correct the drive gears  234  by causing them to rotate a desired amount that aligns a tooth with a chain. In some embodiments, some or all actuators may be combined together. For instance, radial translation of the drive gears  234  may be configured to also implement a correcting action. In some embodiments, the correcting action may be all or a part of the needed correction for a gear tooth. 
     Turning now to  FIG. 10 , an example of a portion of an exemplary turbine disk  243  is described in additional detail. It should be appreciated that the turbine disk  243  may be used in the sheave assembly  218  ( FIG. 9A ) described previously, but may also have additional applications. Moreover, the sheave assembly  218  may use other types of turbines or other correction or control mechanisms. For example, the sheave assembly  218  may use a turbine with a series of blades, rather than the disk as described herein, may use hydraulic, pneumatic, mechanical, electrical, or other actuators, or a combination of the foregoing, to correct a gear position. Moreover, while the turbine disk  243  is described in the context of a correction mechanism, it should be appreciated that a similar construction may be used as a synchronizing mechanism to, among other things, cause drive gears to move radially with respect to a drive shaft or sheave. 
     The turbine disk  243  as shown in  FIG. 10  is generally disk-shaped and includes a series of ports  246  configured to receive and reverse fluid (e.g., a liquid or gas) injected therein. In particular, a port  246  may include an opening  247  formed in the outer circumference of the turbine disk  243 . The opening  247  may have a generally circular or elliptical shape, although other shapes may also be used. In one embodiment, such an opening may be formed by drilling a series of radially inward directed holes towards a center of the turbine disk  243 , although any other suitable manufacturing method may also be used, including CNC machining, milling, laser etching, water jets, or other processes, or combinations thereof. 
     In practice, fluid in the form of a liquid or gas may be injected into the port  246 . Fluid may, for instance, be hydraulic fluid and injection of the fluid may be configured to cause the turbine disk  243  to rotate. As described herein, rotation of the turbine disk  243  may in turn cause other effects. For instance, in a transmission, the turbine disk  243  may correct or synchronize gears due to rotation. In other embodiments, the turbine disk  243  may rotate and be used to control sheave axial positions or perform a number of other functions. 
     To provide improved access to the ports  246 , one or more reliefs  248  may also be cut or otherwise formed on the turbine disk  243 . For instance, in the illustrated embodiment two reliefs  248  are formed on the outer perimeter of the turbine disk  243  and generally taper inward. As fluid is then injected towards the ports  246  (e.g., from a nozzle  250 ), the fluid may pass through the reliefs  248  and engage against an interior surface that defines at least a portion of the opening  247 . The shape of the interior surface and of the opening  247  may then optionally reverse the flow of the fluid. As fluid is injected through the turbine disk  243 , the flow can be reversed and pass through a corresponding relief  248  formed on an opposing edge of the disk  243 . The flow of fluid in this manner can cause the disk  243  to rotate, and the amount of rotation can be controlled hydraulically by at least pressure of the fluid and the duration of the flow. 
     As noted previously, the turbine disk  243  may be a reversing disk. In one aspect, a reversing disk may have reversible motion and the turbine disk  243  may be able to rotate in opposing directions. In particular, as shown in  FIG. 10 , the relief  248  may be an upper, or first relief, and there may be a lower, or second relief  249 . In particular, along all or a portion of the length of the port  246 , a lower relief  249  may be formed. Further, the lower relief  249  may be in an opposite direction relative to the upper relief  248 . As a result, another nozzle  250  may be aligned and positioned to inject fluid into the ports  246  along the lower relief  249 . As will be appreciated in view of the disclosure herein, a nozzle  250  aligned with the lower relief  249  may inject fluid in an opposite direction as compared to a nozzle  250  aligned with an upper relief  248 . As a result, based on which nozzle  250  is used to inject fluid, the direction of rotation of the turbine disk  243  can be controlled. Further, in some cases, it may be possible to inject fluid through nozzles  250  to the ports  246  in two directions. In such a case, the fluid injected in one direction may rotate the turbine disk  243 , while fluid injected in a second direction may act as a braking mechanism to stop rotation of the turbine disk  243 , or relative differences in the fluid flows may otherwise cause a controlled rotation of the disk  243 . 
     While  FIG. 10  illustrates two nozzles  250  and upper and lower portions to the ports  246 , it should be appreciated that this is merely exemplary. In other embodiments, a single nozzle may, for instance, inject fluid in either of two directions and/or a port  246  may have a single portion that receives fluid directed in either of two or more directions. 
     A turbine disk  243  according to the present disclosure can therefore be used to allow selective control over a rotation used to control synchronization, correction, or other aspects of a transmission. Further, as noted previously, the turbine disks described herein are merely exemplary and other types of turbines, actuators, controllers, or other structures may be used. In one embodiment, a turbine disk  243  provides an advantage over traditional turbines with blades, inasmuch as the turbine disk  243  can provide two-directional rotation with a minimum number of parts and relative ease of manufacture. Indeed, the turbine disk  243  optionally has an integral construction such that only a single component need be formed. In contrast, other turbines may use a series of blades that increase the number of parts and/or the cost of manufacture and assembly. Nevertheless, other turbines may be used as they potentially increase the efficiency of the system and/or reduce wear, fluid losses, or for any other number of reasons. In some embodiments, the turbine disk  243  may operate at low power, such that efficiency losses may be negligible or the cost-savings associated with such disks may warrant use over more expensive, higher efficiency turbines. 
     As will be appreciated by one skilled in the art in view of the disclosure herein, while  FIG. 10  illustrates two nozzles, each of which direct fluid in a single direction, other configurations are possible. For instance, multiple nozzles may be aligned around the circumference of the turbine disk  243 , such that multiple nozzles can act to rotate the turbine disk  243 . In other embodiments, multiple turbine disks  243  may be used in a single system, and each turbine disk  243  may have its own set of one or more nozzles, or nozzles may be shared between turbine disks  243 . 
     Another aspect of the turbine disks  243  is that the series of ports  246  can, but are not necessarily, formed on the exterior surface of the disk  243 . As a result, the turbine disk  243  may have an exterior surface or edge that is interrupted by each port  246 . By positioning a sensor on such an interrupted surface or edge, or in a position where the sensor can obtain information from the interrupted surface or edge, the sensor may also be used as an encoder. For example, a magnetic reluctance or other sensor may be used to detect interruptions in the edge surface, thereby also providing positioning information that can be used to determine the precise rotation and/or position of the turbine disk  243 . By knowing the position and rotation of the turbine disk  243 , a corresponding position of, for example, a drive gear may also then be known. Accordingly, the turbine disk  243  may be used to advance, retreat, and track the position of a drive gear. 
     With reference now to  FIG. 11 , an example hydraulic system  290  is schematically illustrated. The hydraulic system  290  is one example of a control and/or actuation system usable to control a transmission as described herein, including a transmission that includes the sheave assembly  218  in  FIGS. 9A-9C . In the illustrated system, a hydraulic pump  291  is provided and is connected to an accumulator  292 . As fluid travels from the pump  291 , the accumulator  292  acts as a pressurized storage reservoir. From the accumulator  292 , fluid travels to a valve set. The valve set may include any number of valves  293 . For instance, one or all of the valves may be independently selectable to selectively be activated and opened to allow hydraulic fluid to pass from the pump  291  and/or accumulator  292 . Each valve  293  may, for example, correspond to a different nozzle, actuator, or other component with in a system. Such components are collectively illustrated as the actuators  294 , but may include any type of actuator, controller, and the like. 
     For instance, in the sheave assembly  218  in  FIGS. 9A-9C , a number of different components may be hydraulically driven. For instance, there are two sheave actuators  232  that may utilize hydraulics, and which are optionally separately driven. In addition, three turbine disks  243   a - c  may each have forward and reverse capabilities facilitated by a pair of nozzles  250 . Thus, six total nozzles  250  may be used to facilitate forward and reverse functionality for the set of turbine disks  243   a - c . Optionally, the cross-over shaft  264  may also have an associated hydraulic actuator to drive the linking gears  265  and thereby cause indexing of the drive gears  234  to a desired radial position. Thus, in total, two hydraulic actuators may be used to control axial movement of the sheave  226 , one hydraulic actuator may be used to control indexing and radial translation of the drive gears  234 , and six hydraulic actuators may be used to control correction of the drive gears  234  via as set of nozzles that control gear teeth advancement in forward and reverse directions. Of course, more or fewer actuators may also be used, or the manner of using actuators may be altered. For example, a single actuator may be used to control axial movement of the sheave  226 , multiple actuators (e.g., two) may be used for the indexing of the drive gears  234 , and more or fewer components may be combined or added to the transmission system  200 . 
     In view of the nine actuators discussed,  FIG. 11  illustrates nine valves  293  within a valve set. Each valve  293  can include a line leading to its own actuator  294 , which may be any of the actuators discussed, but also generally represent any other type of actuator as well. Each of the actuators  294  may then tie into one or more return lines that lead to a reservoir  295  that supplies hydraulic fluid to the pump  291 . 
     The components described herein can take any desirable form. For instance, in one embodiment, the pump  291  may be electrically driven, shaft driven, mechanically driven, or have another suitable configuration. As a result, the pump  291  may also have a pressure relief regulating valve that returns to the reservoir. Such a pump  291  may then run continuously and, when not needed, the pressure relief may bleed back the fluid into the reservoir  295 . An electrical pump may, for example, be used intermittently, and the accumulator  292  may instead be used to build up pressure for maximum usage conditions. Thus, an intermittently used pump—whether electrical, mechanical or otherwise driven—can optionally minimize pump usage time and power consumption and then peak its usage with an accumulator  292 , although the accumulator  292  is also not necessary. A pump  291  may be sized for the maximum usage condition and therefore bypass the need for the accumulator  292 , or a reduced power pump  291  may be used in connection with the accumulator  292 . An accumulator  292  may also compensate for changes in system volume due to expansion and contraction of hydraulic fluid. The illustrated hydraulic system  290  is therefore merely exemplary of a suitable hydraulic system, but numerous alternative hydraulic systems may also be used. Furthermore, while some actuators in a system may be hydraulically controlled, other actuators may be mechanical, pneumatic, electrical, or otherwise controlled, such that a hydraulic system may control actuation of only some components of the transmission system  200 . 
     With respect to the embodiments illustrated in  FIGS. 9A-10 , it should be appreciated that the individual and collective components of the correction system  240  and the hydraulic system  290  can thus act as examples of means for correcting a position of teeth of a driving gear  234 . The correction system  240  for a transmission may also act as a vibration control system. For example, in a belt drive system, a friction belt may stretch as it unwraps off a sheave, and due to the existing tension in the belt. According to similar principles, a chain drive system also may appear to stretch as the chain wears. More particularly, as a chain wears, the pitch of the chain changes. As a result, when the chain becomes disengaged from a gear and tension is applied, the wear can allow some amount of stretch to be observed. The chain may stretch link-by-link, as each link becomes disconnected from each tooth. The full stretching may not be instantaneous and some stretching may occur as the chain wraps around the sheaves; however, a large portion of the apparent stretching may still occur at disconnection between a chain link and a carrying sprocket/sheave. 
     As a result of the cycling of the chain and the link-by-link apparent stretching of the chain, a vibration may be produced. For example, if there are three sprockets or drive gears carrying the chain, the chain may stretch back to each other sprocket, such that vibration may occur as the angular relationship in the chain changes three times per revolution. The embodiments herein can, however, provide control to correct or minimize such vibration. For example, as noted herein, a transmission may include a correction system  240  to rotate the drive gears  234 . By correcting the drive gears  234  and rotating the drive gears  234  about their respective axes, the transmission can be adjusted to control at least the period of the vibration and reduce or minimize the effect of such vibration. 
     In some cases, the correction of the drive gears  234  to control the vibration may be produced with a small amount of slip occurring between the chain relative to the sheave. Such slip, while not necessarily desirable in itself, may nonetheless be desired on a system perspective as the slip can be managed and may help control unwanted vibration. Further, the amount of slip can be defined relative to the apparent stretch of the chain to limit the effect of the slip. Thus, advancing and/or retreating the drive gears  234  may be of significant use in controlling vibration of the transmission system  200 , and the forward/backward control of the rotation of the drive gears  234  permits the drive gear  234  to become loaded during rotation. 
     Chain 
     Turning now to  FIGS. 12A and 12B , an example chain link  229  that may be used in connection with the transmission system  200  ( FIGS. 9A-9C ) is illustrated. It should be appreciated, that multiple chain links  229  may be combined to form a chain that may then be coupled to the sheave assembly  218  of  FIGS. 9A-9C . It should be appreciated that the chain links  229  are merely exemplary embodiments of suitable chains and links that may be used in connection with the disclosed embodiment, and other chains and links are contemplated, including, but not limited to, chains and links described elsewhere herein. 
     More particularly,  FIG. 12A  provides an isometric view of a single chain link  229  that may be combined with other links  229  to form a chain. In particular,  FIG. 12A  illustrates a link  229  that has a generally elongated body  281 . In this embodiment, the body  281  includes a plurality of interlocking features  279 ,  280 . For example, on a first elongate side of the body  281 , the example embodiment of the chain link  229  includes six interlocks  279 . Specifically, the interlocks  279  are, in this embodiment, generally spaced apart at equal intervals, with the intervals between the interlocks  279  having a length generally corresponding to the length of the interlocks  279 . Similarly, a second side of the body  281  includes, in this embodiment, five interlocks  280 . As with the first interlocks  279 , the second interlocks  280  are also, in this example embodiment, spaced apart at generally equal intervals, and the intervals between the second interlocks  280  optionally have a length that corresponds generally to the axial length of the interlocks  280  and the axial length of the interlocks  279 . 
     According to one embodiment, the first and second interlocks  279 ,  280  have an offset configuration. For instance, the first interlocks  279  may be offset from the second interlocks  280 . In this particular example, the first interlocks  279  are generally positioned to be aligned with the intervals between the second interlocks  280 . In a similar fashion, the second interlocks  280  are aligned with the intervals between the first interlocks  279  on the opposing side of the chain link  229 . According to an example embodiment, such an arrangement allows chain links  229  to be connected in a side-by-side fashion, by positioning adjacent links such that the first interlocks  279  of an intermediate chain link  229  are placed within the intervals between the second interlocks  280  of an adjacent link  229 , and such that the second interlocks  280  of the intermediate chain link  229  are positioned between the intervals between the first interlocks  279  of a different chain link  229 . 
     When adjacent links  229  are positioned in the manner described above, the links  229  may then be connected together to form a chain. For instance,  FIG. 12B  illustrates a frontal view of the exemplary chain link  229  of  FIG. 12A . As shown in this embodiment, the first and second interlocks  279 ,  280  may have openings  282  therein. Such openings  282  may be configured to receive a pin  283 . A single pin  283  may pass through a set of first interlocks  279  on one chain link  229 , and through a set of second interlocks  280  on a second chain link, and thereby secure adjacent chain links  229  together. In other embodiments, however, two pins  283  may each pass through a single set of openings  282  defined by interlocked, adjacent chain links  229 . 
     While the pins  283  may be sized and shaped to correspond to a shape of the openings  282  in the first and second interlocks  279 ,  280  of a chain link  229 , this is not necessary. For instance, as shown in  FIG. 12B , the pins  283  may not be shaped or sized to fully fill openings  282 , or to have a shape corresponding to that of the openings  282 . In the illustrated embodiment, for instance, the openings  282  are generally circular while the pins  283  have an elliptical shape with a minor diameter that is about half the diameter of the openings  282 . As a result, when adjacent links  229  are positioned together, two pins  283  may each be positioned within a same opening  282  and used to secure adjacent links  229  together. As shown in  FIG. 12B , the openings  282  and/or pins  283  may also include corresponding tabs  284  that are used to position pins  283  within a corresponding structure of the openings  282 . Such feature is exemplary only, and in other embodiments, detents, lock fits, interference fits, or other structures, or a combination thereof, may be used to secure the pins  283  to the chain links  229 .  FIG. 12B  further illustrates, in dashed lines, that optional second pins may be included within the openings  282 . 
     As shown in  FIG. 12A , the chain link  229  can include first and second side faces  285 ,  286  that are configured to engage a sheave or other member. The first side face  285  and second side face  286  are further optionally angled. In this embodiment, for instance, the side faces  285 ,  286  angle inward from an outer surface towards an interior surface. The angle itself is optional, but may be desired particularly in embodiments in which the chain link  229  is used in connection with an angled sheave. For instance, the angle on side faces  285 ,  286  may match or otherwise generally correspond the angle on an adjoining sheave. Thus, as the sheave moves axially, a chain composed of the chain links  229  may move radially outward or inward relative to a central axis of the sheave, and along the face of the sheave. 
     Moreover, in some embodiments, the chain links  229  may be configured to engage a sprocket or other gear. For instance, as described herein, one or more gears may be configured to engage the chain links  229  to prevent or reduce slip between a chain and an adjoining sheave. In the illustrated embodiment, the chain link  229  has a curved configuration that facilitates engagement between the chain links  229  and a gear. For instance, relative to the orientation in  FIG. 12B , if a line L 1  is drawn between the centers of interlocks  279  and interlocks  280 , and follows the contour of the body  281 , a center point C 1  is positioned within body  281 , but is vertically offset from the centers of the openings  282 . Such an offset, and the curved shape of the body  281  is even more evident if a straight, horizontal line L 2  is drawn between the centers of the interlocks  279 ,  280  and/or the openings  282 . A center point C 2  of line L 2  remains in plane with the centers of the openings  282 , but is positioned vertically below the center point C 1  of the line L 1 . 
     Such a curved body  281  may also provide a gap in the body  281 . For example, along the horizontal line L 2 , the body  281  is shown as defining a channel  287 . The channel  287  may be a gap that is sized and otherwise configured to mate with a corresponding gear, such that as the gear engages the chain link  229 , the gear teeth may engage the interior surfaces of the interlocks  279 ,  280 . Moreover, as described previously, body  281  may also be elongated. As a result, an engaging gear optionally has a width that generally matches the elongated length of the chain link  229 . In other embodiments, the engaging gear may have a width substantially less than the elongated length of the chain link  229 . In still other embodiments, multiple engaging gears may engage the same chain link  229 . Moreover, as noted above, the chain link  229  is merely exemplary and in other embodiments a chain link may have fewer interlocks  279 ,  280 , may not be elongated to the extent illustrated particularly in  FIG. 12A . 
     One skilled in the art will appreciate in view of the disclosure herein that a lubricant is optionally used in connection with engagement between the chain links  229  and a sheave and/or drive gears. According to one embodiment, chain oil or another lubricant may be used in connection with a chain composed of the chain links  229 , and the lubricant may facilitate operation of the chain with a corresponding set of gears, sprockets, sheaves, or other components. 
     As discussed herein, a chain or other wrapping member may orbit around elements of an input and output system. As the chain rotates within the system, the rotational speed may have an effect on a lubricant or other materials on the chain. For example, based on the rotational speed of the sheave and/or a chain, the inertia of the lubricant may pressurize itself and a force may be exerted that is in a radial direction. More specifically, a force may tend to press the lubricant in a direction that extends radially outward relative to a center of the sheave. 
     According to some embodiments, while a lubricant may thus generally tend to move away from a chain and sheave, some embodiments of the chain may be configured to at least partially restrict or prevent such lubricant from freely flying away from the center of the sheave, and away from the chain. For instance, as best shown in  FIG. 12B , which offers a profile of a chain link  229  and illustrates engagement of the chain link  928  with a gear tooth, and as discussed above, a chain link  229  may have a curved configuration in which a channel  287  is formed. The channel  287  may be approximately centered within the body  281  of the chain link  229 , and can act as a trap for a lubricant. More particularly, the lubricant  288  may be trapped in the channel  287  such that as the inertial force is applied, the lubricant  288  becomes pressurized. Continued orbital motion of the chain link  229  can cause the lubricant  288  to remain trapped on the interior surface of the chain link  229  that defines the channel  287 . Furthermore, as the side faces of the chain link  229  may be positioned generally adjacent corresponding faces of a sheave, the lubricant may be radially and axially trapped within the channel  287 . In being trapped within the channel  287 , the lubricant  288  is collected and can not only lubricate the engagement between the chain link  229  and a gear tooth, but can also be delivered through the channel  287  to the lubricate the sheave contact area on the side faces of the chain link  229 . 
     When multiple links  229  are connected together (e.g., by using pins  283 ), a chain  228  may be formed.  FIG. 13 , for example, illustrates a chain  228  that is composed of a series of chain links  229 . Each of the chain links  229  may be connected to one or more adjacent links  229 . The illustrated chain  228  is only a partial chain, however, it will be appreciated that end links of the chain  228  may be attached so as to define a continuous chain  228 . Furthermore, in the illustrated embodiment, the side faces  285  of the chain links  229  may be contact surfaces where the chain  228  rides on a corresponding sheave. 
     In  FIG. 13 , the chain  228  is shown as being coupled to a sprocket  235 . Optionally, the chain  228  is also engaged with, or otherwise configured to operate in connection with, a sheave  227 . In one embodiment, the chain  228  and sprocket  235  can move radially with respect to the sheave  227 . In the illustrated embodiment, it can be seen that adjacent, connected links  229  of the chain  228  may be pivotally connected, such that each link  229  may at least partially rotate relative to adjacent links  229 . During such relative rotation, there may be a point of contact between the adjacent links  229 . In  FIG. 13 , for instance, each link  229  may be connected to an adjacent link  229  through the use of two pins  283  passing through a single opening  282  in a chain link  229 . In this embodiment, the pins  283  have generally elliptical shapes with minor diameters about half the diameter of the opening  282  such that a pin contact point  289  is formed approximately in the center of the openings  282 , and is defined by a point of contact between the two pins  283  within the opening  282 . 
     The sprocket  235  does not need to engage the chain  228  at the pin contact points. For instance, in the illustrated embodiment, sprocket contact faces  278  are formed on the interior faces of the link body  281 . The interior faces of the body  281  may, for example, be faces that at least partially define the channel  287 . 
     As will be appreciated in view of the disclosure herein, the shape and configuration of the links  229  and pins  283  may be such that the sprocket contact faces  278  are concentric with pin contact points  289 . Furthermore, in contrast to a typical “silent chain” configuration, which has chain link spacing dependent on the diameter of an engaging sprocket, the spacing of the chain links  229  can be independent of the diameter of the sprocket  235  around which chain  228  is wrapped. In other embodiments, a silent chain may be utilized. Regardless of the specific form of the chain  228 , the chain  228  may be used to convey power. Accordingly, the chain  228  and links  229  are each examples of means for transferring power. In embodiments in which the chain  228  retains fluid, the chain  228  and links  229  are further each examples of means for retaining lubricants and means for pressurizing lubricants. 
     Accordingly, it will be appreciated that a chain  228  according to embodiments of the present disclosure can provide numerous features. Included among such features is the ability to trap oil or another lubricant for use in a self-pressurizing lubrication system that delivers lubricant to a sheave contact area. Furthermore, a single link may be made to connect with adjacent links without necessarily requiring different links (e.g., “A” links and “B” links). 
     3. Transmission with Ring Gear 
     As noted herein, there are various alternative embodiments that may be used for any of the components, systems, sub-systems, or assemblies illustrated and/or described herein, and which are suitable to replace or supplement the specific embodiments disclosed herein.  FIGS. 14A-14C , for example, illustrate an embodiment of a sheave-and-belt transmission  300  according to another embodiment of the present disclosure. In the illustrated embodiment, only a portion of the transmission  300  is illustrated in order to more clearly view various components of the system (e.g., the illustrated portion may generally represent a power input and/or power output system). The transmission  300  may, however, operate on the input and/or output sides of a transmission. 
     In some regards, the transmission  300  can be operated in a manner similar to other transmissions described herein (e.g., transmissions  10 ,  100 , and  200 ). For example, the transmission  300  may include a sheave  326  that is optionally formed from one or more movable halves. The halves may be mirror images or may differ relative to each other. A wrapping member such as a belt or chain (not shown) may be used in connection with the sheave  326 , and can be used to drive another element, or can be used to drive the illustrated sheave  326 . For instance, as the transmission  300  may be an input system, the transmission  300  may drive the wrapping member as it connects to a sprocket, sheave, gear, or other component on an output system. The wrapping member may also connect to a driven sprocket and/or a chain tensioner to account for changes to the wrapping member by virtue of movement of the sheave  226 . 
     In the illustrated embodiment, the transmission  300  includes a set of sprockets  334  that can act as drive gears. For instance, the sprockets  334  may be disposed within the sheave  226 . As with other transmission embodiments described herein, the sprockets  334  may engage the wrapping member and may also move radially inward and outward relative to the sheave  226 . Such radial movement of the sprockets  334  may generally correspond to axial adjustments made by the sheave  326 . 
     Synchronization System 
     The transmission  300  may include a synchronization system  338  that is used to adjust the position of the teeth of the sprockets  334 , so as to ensure the sprocket teeth are aligned with a wrapping member. In some embodiments, the synchronization system  338  may act to correct sprocket teeth when the wrapping member is running at a gear ratio corresponding to a non-integer position. 
     With particular regard to  FIG. 14B , a synchronization system  338  is illustrated. For clarity, only a single sprocket  334  is illustrated, although it will be appreciated that more sprockets  334  may also be used. For instance, the transmission  300  can include four sprockets  334  spaced at ninety degree intervals. More or fewer than four sprockets  334  may also be used. 
     In  FIG. 14B , a ring gear  366  is illustrated. The ring gear  366  is connected to a linking gear  365  in the illustrated embodiment, although there may be one linking gear  365  for each sprocket  334 . When the sheave  326  is moved axially, it may be desirable to also move the sprockets  334 . As a result, to coincide with the movement of the sheave  326 , the ring gear  366  can be rotated. Rotation of the ring gear  366  may cause the linking gears  365  to rotate as well. According to one embodiment, the ring gear  366  rotates independently relative to the sheave  326 . In another embodiment, the ring gear  366  rotates about a longitudinal axis of a drive shaft of the sheave  326 , and relative rotation of the ring gear  366  is used to drive the sprockets  334 . 
     According to the illustrated embodiment, the linking gears  365  are attached to an arm  367  which in turn attaches to a shaft  364  ( FIG. 14A ). Rotation of the linking gears  365  causes the arm  367  to rotate. The arm is positioned within an arcuate channel  362  in the sheave  326 . As the arm  367  rotates, the shaft  364  is moved along the arcuate path defined by the channel  362 . The sprocket  334  is attached to the shaft  364  in this embodiment, such that as the shaft  364  moves along the channel  362 , and changes a radial position relative to the sheave  326 , the sprocket  334  is also moved radially. The components of the synchronization system  338 , thus collectively and individually, are examples of means for radially moving the sprockets  334  and/or a chain that engages the sprockets  334 . 
     In other embodiments, the ring gear  366  of the synchronization system  228  may be eliminated. For example, in some embodiments, the sheave  326  may have channels formed therein along which the shafts  364  move. Optionally, the shafts  326  can be fitted within the channels  362 , and can float therein in a manner such that movement of the sheave  326  automatically causes the shafts  364  to move to a corresponding radial position. 
     Correction System 
       FIGS. 14A and 14C  further illustrate exemplary components of a correction system  340  that can be used to selectively rotate sprockets  334 . For instance, such system may selectively rotate the sprockets  334  to provide tooth correction in chain positions corresponding to partial tooth effective circles. 
     More particularly, the illustrated correction system  340  includes a correction actuator  368  that can cause an outer gear  369  to rotate. The outer gear  369  engages a correction ring gear  370  that rotates. An interior gear  371  may be positioned within the ring gear  370 , and potentially multiple interior gears  371  (e.g., one corresponding to each sprocket  334 ) may engage the ring gear  370 . Notably, in this embodiment, and as best shown in  FIG. 14C , the correction ring gear  370  may be positioned off-center relative to a drive shaft  324  on which the sheave  326  is positioned. As a result, as the sheave  326  and drive shaft  324  rotate, the various interior gears  371  may alternately engage the ring gear  370 . In other words, some but not all of the interior gears  371  may engage the ring gear  370  at any particular point of time. The interior gears  371  may also engage a worm driving gear  372 . The worm driving gear  372  may be coupled to a worm gear  373  that rotates as the worm driving gear rotates  372 . For instance, the worm driving gear  372  may rotate a shaft on which the worm gear  373  is positioned. A worm wheel  374  may be co-axial with the sprocket axles  336 , or an axle on which a gear that engages the sprockets  334  rotates. The worm wheel  374  may engage the worm gear  373 , such that as the worm gear  373  rotates, the worm wheel  374  and the sprocket axles  336  are selectively rotated. In some embodiments, the worm gear  373  may cause the sprockets  334  to rotate while not under load. For instance, the alternate engagement of the interior gears  371  with the ring gear  370  may occur only while the corresponding sprocket  334  is not engaged with a chain. 
     One aspect of the embodiment in  FIGS. 14A-14C , and which can be applied equally to all embodiments disclosed herein, is that the transmission  300  provides mechanical intelligence for correcting the sprockets  334 . For example, in the illustrated system, the off-center position of the correction ring gear  370  relative to the drive shaft  324  facilitates a mechanical intelligence whereby each of the sprockets  334  is automatically adjusted, so that the mechanism corrects itself. The correction system  340 , as well as the illustrated and described components thereof, thus are examples of means for correcting a tooth position of a sprocket  334 , and examples of means for providing mechanical intelligence to correct a tooth position of a sprocket  334 . 
     Moreover, the use an eccentric or off-center gear is not the only manner in which mechanical intelligence may be utilized in this regard. For example, in another example, there may be multiple chains running on multiple sheaves. For example, four chains may be positioned on four sheaves. During operation, only one sheave may be carrying the load. 
     Additionally, in another embodiment a differential is used as a mechanical intelligence device. For instance, with a differential, there may be two inputs that are related to each other by the differential and used to produce an output. As the inputs change relative to each other (e.g., by changing the distance between sheave halves so that the chain moves radially), a corresponding change will be obtained as an output of the differential. More specifically, as rotational size changes, there may be a proportional change in the rotational output of the differential. In knowing that the drive shaft  324  will turn a certain amount with each rotation, and by knowing the proportion of change in the rotational motion of the drive shaft  324 , the proportions can tied back into the sprockets  334  to automatically adjust the sprockets  334  for engagement with a chain at non-integer locations. Thus, sensors, encoders, motors, actuators, and the like may not be necessary for correcting the sprockets  334 . 
     Additionally, while the above examples illustrate correction of the sprockets, in other embodiments the chain itself may be corrected. For example, a roller may be placed outside the chain, and can then adjust the chain position to engage even at non-integer locations. 
     Chain 
     The transmission  300  of  FIGS. 14A-14C  may use any suitable chain or other wrapping member that can carry a load between an input and an output system.  FIG. 15  illustrates an example embodiment of a chain link  329  that can be utilized in connection with the system herein. As shown in  FIG. 15 , a chain link  329  includes a set of rollers  387 . The rollers  387  may be inclined and configured to rotate about respective internal axis. As such, when the rollers  387  of the chain link  329  roll against a sheave, or on a layer of fluid on a sheave, the rollers  387  can roll, instead of drag, thereby reducing dynamic friction in the system. The chain link  329  can also include corresponding connection structures  330 ,  331  for connecting the chain link  329  to adjacent links. For instance, in  FIG. 15 , the chain link  329  includes a first structure  330 , which may include a pin. The chain link  329  may also include a second structure  331  that optionally includes a receptor, which may be a channel, opening, or other receptor. The pin of one link  329  may be received within the receptor of an adjacent link  329  to form a chain. 
       FIGS. 16A and 16B , schematically illustrate another example embodiment of a chain link  429  according to one embodiment. As noted herein, a chain may operate with one or more sheaves in a reduced friction manner, and may possibly have no significant dynamic friction during engagement. One manner in which reduced friction can be accomplished is by using a chain link  429  that includes a fluid retention system  380 . 
     The fluid retention system  480  is, in this embodiment, configured to substantially prevent a lubricant (e.g., gear oil) from weeping out from between link  479  and a corresponding sheave  426 . An embodiment in which the chain link  429  is contrasted against a link without a retention system  480  is shown in  FIGS. 16A and 16B , and it can be seen that with the fluid retention system  480 , a thicker film of lubricant  488  may be positioned between the sheave  426  and the chain link  429 . The increased fluid film layer can improve the wear characteristics by preventing or reducing metal-to-metal contact. Further, the preservation of the lubricant between the sheave  426  and the link  429  can allow regular gear oil to be used as a lubricant, thereby eliminating the need for traction fluids that are not only expensive but which can also have only a short shelf life. Further, such traction fluids are typically more viscous that a gear oil, and thereby absorb torque from the system. In short, the fluid retention system  480  can relax the requirements for fluid properties in a lubricant between the chain link  429  and the sheave  426 . 
     In this embodiment, the fluid retention system  480  includes a set of O-rings  482  positioned around the exterior of the chain link  429 . The O-rings  482  are optionally compressible. For instance, the O-rings  482  can be made of a polymeric material, such as silicone, that can be compressed. The O-rings  482  may, however, be made of other materials. For instance, the O-rings  482  can be made from other polymers, metals, organic materials, alloys, composites, other materials, or combinations of the foregoing. 
     The O-rings  482  can engage against the sheave  426 , or against fluid on the sheave  426  as shown in  FIGS. 16A and 16B . Moreover, the O-rings  482  may form a seal around fluid trapped therebetween, thereby preventing or at least reducing the amount of fluid weeping out from between the sheave  426  and the link  429 . In some embodiments, the O-rings  482  may maintain the fluid seal for only a short period of time (e.g., 25 ms, 1/60 second), although based on the speed and other requirements of the transmission, such time may be increased or decreased. Inasmuch as the chain links  429  can be on a chain that constantly has the links  429  moving in and out of engagement with input and output systems, the time for fluid retention can be reduced and, further, the film of lubricant  488  can constantly renew itself as the transmission operates. 
     Accordingly, while the sheave  426  and chain link  429  may be described herein as being in frictional engagement, in some embodiments it is not necessary that significant dynamic friction be present, or even that the chain link  429  directly engage the sheave  426 . For example, in the above embodiment in which an O-ring traps lubricant for a time while placed under compression due to an interface between the sheave  426  and the chain link  429 , the chain link  429  effectively floats on a bed of lubricant  488 , and near frictionless engagement can occur. Accordingly, in at least some embodiments, the chain link  329  and the chain link  429  are examples of means for transferring power. In some embodiments, the chain link  429  is further one example means for retaining lubrication fluid. 
     4. Transmission with Pivoting Tension Mechanism 
     Turning now to  FIGS. 17A and 17B , another exemplary aspect of a transmission  500  is described in additional detail. The transmission  500  may include various and components aspects as described above. Accordingly, the following discussion related to  FIGS. 17A and 17B  is intended to provide additional detail with respect to various components, assemblies, and features, but is not intended as a complete discussion of transmission  500 , particularly inasmuch as the components and operation of other embodiments of transmissions described herein, can be equally applied to the transmission  500 . Accordingly, other aspects of exemplary transmissions as described herein are also incorporated into, and usable in connection with, the transmission  500  of  FIGS. 17A and 17B . 
     As reflected in  FIGS. 17A and 17B , the transmission  500  may include variety of different components and assemblies. In one exemplary embodiment, the transmission  500  includes an input assembly  518  and an output assembly  520 . The input assembly  518  of the illustrated embodiment may also be considered a sheave assembly, although in other embodiments, the output assembly  520  is additionally, or alternatively, a sheave assembly. In this embodiment the output assembly  520  is optionally connected to the input assembly  518  by using a wrapping member (not shown) that wraps at least partially around elements of the input assembly  518  and the output assembly  520 . The wrapping member may include a chain or belt, although in other embodiments, other components such as gears, may connect the output assembly  520  to the input assembly  518 . In the illustrated embodiment, the wrapping member is not illustrated so as to avoid obscuring various components of the input and output assemblies  518 ,  520 . Nevertheless, it will be appreciated in view of the disclosure herein that any suitable chain or other wrapping member, including those disclosed elsewhere herein, may be utilized. 
     In  FIGS. 17A and 17B , the output assembly  520  is illustrated as including a driven gear  530 , rather than sheaves. In view of the disclosure herein, it will also be appreciated that the output assembly  520  may also have a sheave or be otherwise configured. In still other embodiments, the input assembly  518  may have a drive gear and lack a sheave. Accordingly, while the illustrated embodiment shows illustrates an embodiment in which a wrapping member may engage a driven gear  530  of the output assembly  520 , with the driven gear  530  acting as a sprocket, it will be noted that such single sheave embodiment is exemplary only. In other embodiments, a wrapping member may engage a set of sheaves, a sheave cluster, internal moon gears, other types of output gears or members, or a combination of the foregoing. 
     Tensioning System 
     In the illustrated embodiment, the output assembly  520  is connected to a tensioning system  544 . The tensioning system  544 , as well as the individual components illustrated and described with respect thereto, are examples of means for controlling tension in a wrapping member. 
     As discussed herein, the input assembly  518  may be configured such that it can move a wrapping member radially relative to the axis of the input assembly  518 . As the wrapping member moves, tension or slack may occur within the wrapping member. In some embodiments, the tensioning system  544  may be used to adjust the tension in the wrapping member so as to increase or decrease the tension therein. For instance, when the wrapping member moves on the input assembly  518  in a manner that increases tension (e.g., increasing the radius around which the wrapping member extends), the tensioning system  544  may be used to relieve some of the tension in the wrapping member. Alternatively, when the wrapping member moves on the input assembly  518  and slackens, the tensioning system  544  may be used to increase the tension to take up some or all of the slack. Accordingly, although not necessary, the tensioning system  544  can be used to dynamically adjust the tension in a wrapping member. In some embodiments, the tensioning system  544  may be used to maintain the wrapping member at a generally constant tension despite changes in gear ratios and/or positioning of the wrapping member. In other embodiments, the tension may vary based on the gear ratio or other considerations. 
     To facilitate increasing or decreasing the tension in the wrapping member, the tensioning system  544  may be configured in any suitable manner. According to one embodiment, such as that illustrated in  FIGS. 17A and 17B , the tensioning system  544  may include a tensioner arm  570  and a tensioner  572 . In the illustrated example, the tensioner arm  570  is arranged such that it engages with, and optionally holds thereon, the driven gear  530 . As a result, by moving the tensioner arm  570 , the position of the driven gear  530  may be altered, thereby changing the path of the wrapping member and affecting the tension in the wrapping member. More particularly, the illustrated embodiment of the tensioner arm  570  is configured to be fixed at a pivot  573 , and connected to the tensioner  572  at a location displaced from the pivot  573 . Thus, as the tensioner  572  applies a force to the tensioner arm  570 , the direction of the force can cause the tensioner arm  570  to rotate around the pivot  573  in either of two directions. Optionally, the pivot  573  is placed along a longitudinal axis that extends in a direction that is about parallel to the longitudinal axis about which the driven gear  530  rotates. 
     The tensioner arm  570  may further be connected to the tensioner  572 . In some embodiments, the tensioner  572  may act as an actuator, or be connected to an actuator. Thus, upon determining that a change in the tension of wrapping member is desired, the tensioner  572  can be actuated to move the tensioner arm  570 . As shown in  FIGS. 17A and 17B , the tensioner  572  may have a piston/cylinder arrangement to facilitate movement of the tensioner arm  570 . Such an arrangement may be actuated in any suitable way, including mechanically, electrically, pneumatically, hydraulically, or in another manner, or in a combination thereof. 
     In the illustrated embodiment, one end of the tensioner  572  is illustrated as being coupled to the tensioner arm  570 , while an opposing end of the tensioner  572  is illustrated as being free. Such a free end may be connected to a transmission housing (not shown) to ground against such housing in providing the actuating force to move the tensioner arm  570 . While a piston/cylinder actuator is illustrated, still other types of actuators may be used. Indeed, any suitable actuator that may be used to adjust the position of the input assembly  518  or output assembly  520 , or to adjust the wrapping member to modify the tension therein. 
     In view of the disclosure herein, it will thus be appreciated that some example embodiments may operate in a manner that does not require opposing sheaves to act in opposing directions to maintain tension in a wrapping member. For instance, the tension in a wrapping member may be adjusted by moving the driven gear  530  as shown in  FIGS. 17A and 17B . While the illustrated movement of the driven gear  530  is rotational, the driven gear  530  could alternatively be moved in a linear motion. In still other embodiments, the tension in a chain or other wrapping member may be adjusted by using a tensioner gear that operates on one or both of an input assembly. For instance, one or more tensioner gears may be placed along the inside and/or outside of the wrapping member. One or more of the tensioner gears may then be moved to adjust the position of the wrapping member, thereby also adjusting the tension in the wrapping member. 
     Reverse Differential 
     With continued reference to  FIGS. 17A and 17B , another optional aspect of the transmission  500  is described in additional detail. More particularly, the transmission  500  may include a differential system  546 . The differential system  546  collectively, and with respect to its individual components, are examples of means for combining two inputs into a single output and well as means for providing an engaged neutral. 
     In some embodiments, the differential system  546  may have two inputs that are combined to produce a single output. For instance, in the illustrated embodiment, the differential system  546  may have a first differential input provided by a differential input shaft  547 , as well as a second differential input provided by a carrier driver  548 . Within the differential system  546 , these two inputs may be combined in a manner that produces a single output, such as may be output by an output shaft  514 . 
     To provide the two described, exemplary inputs to the differential system  546 , a pass-through shaft  549  may be positioned within at least a portion of the input assembly  518 . In one embodiment, the pass-through shaft  549  may pass through all, or substantially all, of the input assembly  518 . For instance, the pass-through shaft  549  may be positioned within the drive shaft  524 , or may be integral with the drive shaft  524 . Further, the rotational speed of the pass-through shaft  549  may be directly related to the transmission input  512  input, or may otherwise be related to a partial gear-ratio that may not be influenced by, for example, the output assembly  520 . 
     The pass-through shaft  549  may, in this example, also be connected to a first input transfer gear  550 . A second input transfer gear  551  that is optionally aligned with the differential input shaft  547  may engage the first input transfer gear  550 . In such a manner, the rotational speed of the pass-through shaft  549  may be passed to the differential input shaft  547 , although one or more transfer or other gears may be used to produce a gear ratio between the rotational speed of the pass-through shaft  549  and the rotational speed of the differential input shaft  547 . 
     In this exemplary embodiment, the second input to the differential system  546  is optionally received from an output of the output assembly  520 . More particularly, the output assembly  520  includes, in this embodiment, a driven gear  530  that is driven by a wrapping member. The driven gear  530  may be connected to, engage, or otherwise be related to one or more other gears of an output gear chain  552 . The output gear chain  552  may be configured to receive a rotational or other input from the driven gear  530  and translate the input to a carrier driver  548 . The carrier driver  548  is, in this embodiment, a gear configured to mate with an external gear profile on a housing of the differential system  546 . By virtue of such relationship, the output of the driven gear  530  may be transmitted to the carrier driver  548 , which in turn may cause the housing of the differential system  546  to rotate. Internal components of the differential system  546  may be fixed to the housing, such that the internal components may rotate relative to a central axis of the housing in the differential system  546 . 
       FIG. 18  schematically illustrates an example manner in which the differential system  546  can operate. As shown in such figures, a carrier  556  may be configured to rotate around a sun axis  574 , and the carrier driver  548  may rotate around a carrier driver axis  575 . A first input may be received through a differential input shaft  547  that is connected to an input sun gear  553  that is, in this embodiment, positioned within the carrier  556 . The second input may be received from the carrier driver  548  which rotates around the carrier driver axis  575  and engages gear profile on the carrier  556 . 
     As each of the two inputs is received, a compound gear ratio may be defined. For instance, interior to the carrier  556 , the input sun gear  553  may engage a first planet gear  554 . The first planet gear  554  may in turn engage one or more other gears. For instance, in this schematic illustration, the first planet gear  554  engages a second planet gear  555 , and the second planet gear  555  in turn engages an output sun gear  557 . The output sun gear  557  is, in this embodiment, connected to an output shaft  514  that rotates around the sun axis  574 . In other embodiments, the first planet gear  554  may directly engage the output sun gear  557 , more than two planet gears may be used, the output shaft  514  may not be aligned with the sun axis  574 , or other configurations may be used. 
     According to one aspect, the two planet gears  554 ,  555  may be fixed to the carrier  556  and can be configured to have both orbital and rotational motions. The planet gears  554 ,  555  may, for instance, each rotate about respective internal, central axes (e.g., the first and second plane axes  576 ,  577 ). The planet gears  554 ,  555  may also be coupled to the carrier  556  in a manner that allows or causes the planet gears  554 ,  555  to orbit around the sun axis  574 . Optionally, the planet gears  554 ,  555  are connected to the carrier  556  using a bearing or other similar device so as to facilitate rotation of the plane gears  554 ,  555  about their own axes within the carrier  556 . Accordingly, the planet gears  554 ,  555  may not only rotate about internal axes, but may also orbit around the input and output sun gears  553 ,  557  that may be aligned with the sun axis  574 . 
     Accordingly, as will be appreciated in view of the disclosure herein, the input sun gear  553  may rotate and at least partially cause the planet gears  554 ,  555  to rotate and transmit a rotation to the output sun gear  557 . In a circumstance where the carrier  556  is fixed such that the carrier  556  and the planet gears  554 ,  555  do not orbit around the sun axis  574 , a simple gear ratio may be identified. However, where the carrier  556  is not fixed and can rotate, the rotational speed of the carrier  556  may be added to, or subtracted from, the overall gear train value, thereby producing compound addition to determine the resulting output at the output shaft  514 . The overall gear ratio may thus determined by the relative speed of the rotation of the carrier  556  to the rotation of the input sun gear  553 , and is dependent on the sizes and profiles of the gears within the carrier  556 . In effect, such a configuration provides a two-stage planetary gear system that does not require the use of ring gears. 
     As one skilled in the art will appreciate in view of the disclosure herein, by using different sizes of gears and/or numbers of teeth, the overall speed ratio and overall transmission ratio may be changed. For example, the illustrated differential system  546  may be set-up to have a train value of 1, ½, 3/2, 2, or any other suitable value. In effect, by changing the number of teeth and/or other gear parameters, the dynamic range of the transmission  500  and/or the differential  546  may also be changed. By allowing different sizes of gears within the differential system  546 , there may not only be compound addition, but a multiplication factor allowing for a significant variation in gear ratios. Accordingly, for any application, the differential system  546  may itself be designed with particular gear ratios that allow an overall transmission, and/or the differential system itself, to operate at a reduced size and/or with reduced parts. As also discussed elsewhere herein, a differential system  546  similar to that described herein may act as a reverse differential that accepts two energy streams (e.g., first and second inputs) using a differential-style planetary that may also drive the output speed to zero, and thus provide a neutral speed while continuing to maintain a connection between a power source and a load. 
     A more particular discussion of the schematic differential system of  FIG. 18  is provided in  FIGS. 19A and 19B . In  FIG. 19A , for example, a partial view of the differential system  546  of  FIGS. 17A and 17B  is shown. In  19 A, the carrier  556  for the differential system  546  has been removed. Additional components such as bearings, journals, rollers, duplicate planet gears  554 ,  555 , and the like have also been removed to enable a clear view of particular aspects of the differential system  546 . 
     In  FIG. 19A , a differential input shaft  547  may receive an input. For instance, the input shaft  547  may be directly or indirectly connected to a pass-through or other shaft from an input system, or to an output shaft of an output system. The input shaft  547  may be connected to an input sun gear  553 . The input sun gear  553  may, for example, be fixed in relation to the input shaft  547  such that they have the same rotational speed. In other embodiments, however, the input sun gear  553  may rotate at a speed different than that of the input shaft  547 . 
     The input sun gear  553  is illustrated as engaging a first planet gear  554 , although as shown in  FIG. 19B , the input sun gear  553  can engage a set of first planet gears rather than a single planet gear  554 . In this example, the input sun gear  553  and the first planet gear  554  each include helical gear teeth that mate together. As a result, when the input sun gear  553  rotates, the input sun gear  553  engages the first planet gears  554  and may cause the first planet gears  554  to rotate about their own axes. If the rotation of the input sun gear  553  defines a linear velocity at a point of engagement that is about equal to the linear velocity from the orbital motion of the first planet gear  554  as described herein, the first planet gear  554  may orbit around the input sun gear  553  without rotating on its own longitudinal axis. 
     The first planet gears  554  may actually include two profiles along a shaft. A first of the gear profiles may mate with the input sun gear  553 , while the second profile may mate with a second planet gear  555 . The two gear profiles may be the same or different, as desired. In some embodiments, the first planet gears  554  have two gear profiles that each have opposing helix angles (e.g., one right hand and one left hand). Such arrangement may act to reduce thrust loads on bearings operating in concert with the first planet gears  554 . Further, the use of opposing helix angles may be eliminated in other cases, or may be used regardless of whether the two gear profiles have differing numbers or characteristics of gear teeth. 
     The second planet gears  555  are optionally similar to the first planet gears  554 . Accordingly, the second planet gears  555  may include one or more gear profiles. For instance, if two gear profiles are included, the two gear profiles may have the same or a different number of teeth, be the same or different sizes, and may have the same or different helix angles. The second gear profile of the second planet gears  555  in  FIG. 19A  may in turn engage the output sun gear  557  which itself may be used to drive an output shaft  514 . 
     While only a single first planet gears  554  and a single second planet gear  555  are illustrated in  FIG. 19A , this is merely illustrative. For example, a partial frontal view of the differential system is illustrated in  FIG. 19B , and illustrates that multiple sets of planet gears may be used. For example, in  FIG. 19B , three first planet gears  554  are angularly spaced around the longitudinal axis of the differential input shaft  547 . Each first planet gear  554  may also correspond to a separate one of three second planet gears  555 . Each of second planet gears  555  may then engage and drive the same output sun gear  557  ( FIG. 19A ). 
     While not illustrated in  FIGS. 19A and 19B , it will be appreciated that the differential system  546  optionally includes a housing that can receive a second input. In some cases, the housing may operate as a carrier in which all or portions of the components illustrated in  FIGS. 19A and 19B  are contained. For example, the first and second planet gears  554 ,  555  may be fixed within the housing such that as the housing rotates, the first and second planet gears  554 ,  555  also orbit around the input sun gear  553  and/or the output sun gear  557  as described herein. The housing may be used in producing a compound gear ratio in which the rotation of the first and second planet gears  554 ,  555 , for example, are dependent upon the rotation of the input sun gear  553 , as well as an input received in the form of a rotation to the housing. 
     5. Transmission with Brake Mechanism 
     Turning now to  FIG. 20 , an exemplary transmission  600  according to still another embodiment is disclosed. It will be appreciated that the illustrated transmission  600  may operate in a manner generally consistent with various embodiments disclosed herein. For instance, the transmission  600  may include or act as an input system  618  that includes a sheave  626  and a set of moon drive gears  634 . The sheave  626  and the moon drive gears  634  may engage a wrapping member such as a chain (not shown) that is also connected to an output system. While the illustrated embodiment is described in the context of an input system, it should be appreciated that the disclosure with respect to this embodiment is equally applicable to an output system. In particular, rather than drive a wrapping member, the moon gears  634  and sheave  626  can be driven by a wrapping member. 
     As with some of the exemplary embodiments herein, the exemplary transmission  600  may provide gear ratios that change in very small, and possibly infinitely small increments. For instance, the sheave  626  may move axially while the moon drive gears  634  move radially. Accordingly, a wrapping member can also move radially with respect to the sheave  626  to vary a gear ratio in the transmission. 
     According to one embodiment, the transmission  600  may include various components, systems, and assemblies. For instance, as described in greater detail hereafter, the transmission may include a synchronization system  638 , a locking system  642 , and a correction system  640 . The synchronization system  638  may be used to adjust the radial position of the moon drive gears  634 . The locking system  642  optionally locks one or more moon drive gears  634  to prevent rotation of the moon drive gears  634  along at least a portion of the orbit of the drive gears  634  around an axis of the sheave  626 , and the correction system  640  can be used to selectively rotate the moon drive gears  634  to align gear teeth for a tooth engagement with the wrapping member, and can further effect such correction even at non-integer gear ratios in which the effective circle of the sheave produces a partial tooth relative to a pitch of the wrapping member and/or the drive gears  634 . 
     Synchronization System 
     With reference to the synchronization system  638 , it will be noted that the described and illustrated components of the synchronization system  638  are individually and collectively examples of means for synchronizing movement of a sheave  626  with movement of moon drive gears  634 , as well as means for radially moving the moon drive gears  634  and/or a wrapping member. However, the synchronization system  638  is merely exemplary, and can be replaced with any other suitable synchronization system, including those describe herein. Similarly, the synchronization system  638  of  FIG. 20  can be implemented in other transmissions and can replace other synchronization systems described herein, or which may be learned by a review of the disclosure herein. 
       FIG. 21A  illustrates a side perspective view of the synchronization system  638  of  FIG. 20 . To simplify the discussion herein, only a single moon drive gear  634  is illustrated in  FIG. 21A , although it will be appreciated that the discussion herein applies equally to each of multiple moon drive gears  634  that operate within the synchronization system  638 . 
     The synchronization system  638  in  FIG. 21A  is configured to adjust the radial position of the moon drive gears  634  in a controlled, predictable, and selectable manner. Moreover, according to one embodiment, the synchronization system  638  may rotate at least partially independent of the input system  618  ( FIG. 20 ) of the transmission. For instance, the synchronization system  638  may be non-co-axial with the sheaves of the transmission, or may be co-axial, but may be on a bearing or other surface such that at least a portion of the synchronization system  638  does not rotate with the sheaves and/or drive shaft. 
     In the illustrated embodiment, the synchronization system includes two shifting arms  650 . The shifting arms  650  are, in this embodiment, axially offset along a longitudinal axis of the synchronization system  238 , and are coupled to each other. For instance, in  FIG. 21A , the shifting arms  650  are connected using a mechanical fastener  651 , such that the shifting arms  650  collectively move. For instance, a bolt, rivet, cotter pin, or other mechanical fastener may be used. In still other embodiments, a weld, adhesive, solder, or other mechanism may be used to join the shifting arms  650 , or a single shifting arm  650  may be used. 
     As shown in  FIG. 21A , the shifting aims  650  are seated upon the drive shaft  624  or are co-axial relative to the drive shaft  624 . More particularly, in the illustrated embodiment, the shifting arms  650  are seated upon a collar  655 , although such an embodiment is merely exemplary. Additionally, as noted herein, it is not necessary that the shifting arms  650  rotate with the drive shaft  624 . For instance, in one embodiment, the shifting arms  650  may ride on bearings that allow an internal shaft to rotate without causing a corresponding rotation in the shifting aims  650 . In other embodiments, the shifting arms  650  may co-rotate with the drive shaft  624  and/or the collar  655 . 
     As further illustrated in  FIG. 21A , three intermediate gears  652 - 654  are positioned between the shifting arms  650 , and generally co-axial with the drive shaft  624  and the collar  655 . Each of the intermediate gears  652 - 654  of the illustrated embodiment may be separately formed relative to each other. For instance, the first intermediate gear  652  is, in accordance with one embodiment, integrally formed with a cam plate  656 . The cam plate  656  and the first intermediate gear  652  may be seated on the collar  655 . In one embodiment, the collar  655  is coupled to the drive shaft  624 . For instance, a spline connection, gear or belt drive, or other connection, or a combination thereof, may be used to cause the collar  655  to rotate as the drive shaft  624  rotates. As the cam plate  656  is seated on the collar  655 , the cam plate  656  may also rotate; however, in other embodiments, the cam plate  656  is seated on a bearing so that the collar  655  can rotate without directly causing the cam plate  656  to rotate. 
     The second intermediate gear  653  is, in this embodiment, positioned adjacent the first intermediate gear  652 . The second intermediate gear  653  may be formed in any suitable manner. According to one example embodiment, the second intermediate gear  653  is integrally connected to the collar  655 , or is otherwise secured thereto. Accordingly, in at least one embodiment, the second intermediate gear  653  rotates as the drive shaft  624  rotates. The third intermediate gear  654  is positioned adjacent the second intermediate gear  653  and opposing the first intermediate gear  652 . The third intermediate gear  654  may be formed separately from the first and second intermediate gears  652 ,  653 . For instance, in one embodiment, the third intermediate gear  654  is a single gear that is seated on the collar  655 . The third intermediate gear  654  may also be coupled to the collar  655  to co-rotate therewith, or may be on a bearing or other similar surface that allows the collar  655  and the second intermediate gear  653  to rotate without causing the third intermediate gear to rotate. 
     In  FIG. 21A , the mechanical fastener  651  may have a longitudinal axis about which two cam drive gears  657 ,  658  are seated. The cam drive gears  657  may be separate, integrally formed, or permanently connected. In the illustrated embodiment, for instance, the cam drive gears  657 ,  658  may be integrally connected. The cam drive gears  657 ,  658  also engage the second and third intermediate gears  653 ,  654 . 
     As noted previously, the second intermediate gear  653  may rotate with the drive shaft  624 . Accordingly, as the second intermediate gear  653  engages the cam drive gear  657 , the cam drive gear  657  may rotate. In the illustrated embodiment, in which the cam drive gears  657 ,  658  are integrally formed, the second cam drive gear  658  may in turn engage and cause the third intermediate gear  654  to rotate. Optionally, the cam drive gears  657 ,  658  are on a bearing to facilitate rotation thereof. 
     A second set of cam drive gears  659 ,  660  are also connected to the intermediate gears  652 ,  654 . As shown in  FIG. 21A , a first cam drive gear  659  may engage the third intermediate gear  654  and be rotated thereby. A second cam drive gear  660 , which is illustrated as being co-axial with the first cam drive gear  659 , can engage the first intermediate gear  652 . Thus, as the third intermediate gear  654  rotates, the cam drive gears  659 ,  660  optionally cause the first intermediate gear  652  and the cam plate  656  to rotate. 
     In accordance with at least one embodiment, the cam plate  656  rotates at a speed that corresponds generally to the speed of the drive shaft  624 . As a result, the moon drive gears  634  and the cam plate  656  may be rotating around the drive shaft  624  at the same speed. In contrast, the shifting arms  650  may not rotate with the drive shaft  624 , but may have an independent rotation mechanism. For instance, the shifting arms  650  may be manually rotated, or coupled to an actuator that causes them to rotate at least partially around the collar  655 . As the shifting arms  650  rotate, the shifting arms  650  cause the first set of cam drive gears  657 ,  658  to also orbit around the intermediate gears  653 ,  654 . Such movement can introduce an additional rotational component that adds to, or subtracts from, the rotation of the drive shaft  624 . The added rotation from the shifting arms  650  may also cause the cam drive gears  657 ,  658  to rotate, thereby changing the rotations of the intermediate gears  653 ,  654  and the second set of cam drive gears  659 ,  660 . Ultimately, the rotation or change in rotation speed is transferred from the cam drive gear  660  to the cam plate  656 , which also rotates. More particularly, while the shifting arms  650  are moving, the introduction of additional rotation from the shifting arms  650  can cause the cam plate  656  to rotate at a speed that is different relative to a rotational speed of the drive shaft  624 . 
     A reverse perspective view of the cam plate  656  is illustrated in  FIG. 21B . As shown in the illustrated embodiment, the cam plate  656  may include a set of cam tracks  661  formed therein. In the illustrated embodiment, the cam tracks  661  are linear, but the cam tracks  661  may take other shapes or forms. As the cam plate  656  rotates (or rotates at a different speed relative to the drive shaft  624 ), a cam follower  662  within the cam tracks  661  can change position. In particular, the cam follower  662  may be coupled to the moon drive gear  634  and orbit around the drive shaft  624  at the same rotational speed as the drive shaft  624 . Thus, as a difference in relative rotational speed between the cam follower  662  and the cam plate  656  occurs, the cam follower  662  can move within the cam track  661 . The cam follower  662  may further be coupled to a shaft  663 . The shaft  663  can, in turn, be coupled to an arm  664  in which the moon drive gear  634  is positioned. 
     As noted previously, when the cam plate  656  rotates at a different rotational speed relative to the drive shaft  624  and/or the moon drive gears  634 , the cam follower  662  can shift its position within the track  661 . The cam plate  656  has, in at least some embodiments, a generally triangular shape, with the cam tracks  661  aligned along respective sides of the triangle. When the cam plate  656  rotates, the cam follower  662  moves in the track  661 , and due to the change in position the cam follower  662  rotates relative to a central axis of the shaft  663 . Consequently, the shaft  663  and arm  664  rotate around a center of the shaft  663 . Inasmuch as the moon drive gear  634  is coupled to the arm  664 , the moon drive gear  634  also rotates relative to the axis of the shaft  663  and can follow an arcuate path which varies the radial position of the moon drive gear  634  relative to the drive shaft  624 . Moreover, inasmuch as the cam follower  662  may slide within the cam track  661 , the radial position of the moon drive gears  634  can be varied continuously in very small, and possibly infinitely small, increments. 
     Accordingly, it should be appreciated in view of the disclosure herein, that the exemplary embodiment of a synchronization system  638  is merely one example embodiment for adjusting a radial position of the moon drive gear  634 , and that alternative or additional methods and systems may be employed. Furthermore, while the cam track  661  has defined ends, this is also not necessary. The defined ends may, for instance, limit the degree to which the shifting arms  650  can rotate. In other embodiments, the track  661  may be continuous. In still other embodiments, the cam plate  656  may have other configurations. For instance, the cam plate  656  may be circular, square, diamond-shaped, or have any other construction, size, or shape. 
     Locking System 
     Briefly returning to  FIG. 20 , an exemplary embodiment of a transmission  600  according to at least some embodiments includes a locking system  642 . The components of the locking system  642 , as well as the collective locking system  642 , are examples of means for locking rotation of the moon drive gears  634  in at least one direction. The locking system  642  may include various components and provide a number of different functions. In at least one embodiment, the locking system  642  stops or slows rotation of the moon drive gears  634  about their central axes. Such a mechanism may be used to, for instance, reduce or eliminate slip of a wrapping member relative to a sheave  626 . To simplify the discussion of the locking system  642 , only a single moon drive gear  634  is illustrated, although more or fewer moon drive gears  634  may also be included. 
     With reference now to  FIGS. 22A and 22B , the locking system  642  of  FIG. 20  is illustrated in greater detail. In the illustrated embodiment, the locking system  642  includes a cam ring  665 , a rotating carrier  667 , and a set of rollers  668 . For instance, in one embodiment, the cam ring  665  may be fixed to the housing, or otherwise configured to have a static position relative to the drive shaft  624  ( FIG. 20 ). As the drive shaft  624  rotates, the moon drive gears  634  may also orbit around the drive shaft  624 . As best illustrated in  FIG. 22B , the moon drive gears  634  may be coupled to a drive moon shaft  636 . 
     The drive moon shafts  636  may each be coupled to the carrier  667 . Within the illustrated carrier  667  are a set of pivoting arms  669 , each of which couple to a respective roller  668 . The rollers  668  and arms  669  each rotate with the carrier  667 , and the rollers  668  engage an inner profile of the cam ring  665 . As particularly visible in  FIG. 22A , the cam ring  665  may have a variable profile. For instance, in the illustrated embodiment, the cam ring  665  has a first thickness over about two-hundred forty degrees and a second thickness over about one-hundred twenty degrees. As the rollers  668  pass along the cam ring  665 , the arms  669  can pivot to maintain engagement with the variable cam profile. 
     Pivoting of the arms  669  may, in some embodiments, cause the moon drive gears  634  to be locked toward internal rotation. For instance,  FIG. 22B  illustrates a cross-sectional view of portions of the locking system  642  and illustrates the arm  669  which extends around the drive moon shaft  636 . The arm  669  may cooperate with an adjacent plate  670  to cause rotational motion of the arm  669  to be translated into an axial motion. For instance a ball bearing in the arm  669  may be positioned within a ramped pocket in the plate  670 . As the arm  669  rotates, the ball may exit the pocket, or may move along the ramp, and exert a force moving the plate  670  in an axial direction away from the arm  669 . The plate  670  may also be positioned adjacent a spring  671 . Movement of the plate  670  in an axial direction away from the arm  669  and towards the spring  671  may compress the spring  671 , which in turn may press on a set of clutch disks  672 . As the clutch disks  672  are compressed, they may grip the moon drive shaft  636 , thereby preventing or impeding rotation thereof. Accordingly, the clutch disks  672  can effectively apply a break or lock that stops or limits the rotational motion of the moon drive gears  634  by locking rotation of a moon drive shaft  636  which rotates as the moon drive gears  634  rotate. 
     It should be appreciated in view of the disclosure herein that the illustrated locking system  642  is merely one example of a locking mechanism that may be used. For instance, while the illustrated spring  671  may in some embodiments be a Bellville spring, any other suitable biasing mechanism may be used. Furthermore, the locking mechanism  642  could operate in reverse to the manner described. By way of illustration, a ball may be located on the plate  670  and a ramped pocket in the arm  669 . In another embodiment, compressing the clutch disks  672  may cause a lock to be released rather than engaged. In still other embodiments, other types of mechanisms may be used. For instance the plate  670  and/or the arm  669  may have angled adjoining surfaces, or have one or more wedges along the surfaces. As the arm  669  rotates relative to the plate  670 , the wedges or angled surfaces can cause the distance between the centers of the plate  670  and the arm  669  to increase. One skilled in the art will appreciate that any number of different mechanisms may be used to convert the rotational motion of the arm  669  to an axial displacement, or convert the rotation of the roller  668  along a cam path to an axial movement or other movement that applies a lock or brake, may be used. 
     Furthermore, while the illustrated locking system  642  is described and illustrated with regard to a cam ring  665  having a one-hundred twenty degree interval over which the moon drive gear  634  remains in a locked position, such embodiment is merely exemplary. In particular, the duration during which a lock is applied can vary. According to one embodiment, there may be three moon drive gears  634 . By applying a lock over one-hundred twenty degree intervals, one of the three evenly spaced moon gears  634  can be in a locked position at any given time. Nevertheless, more or fewer moon drive gears  634  may be used, and/or more than one gear may be locked at any particular instant. 
     Correction System 
     The transmission  600  of  FIG. 20  may further include, in at least some embodiments, a correction system  640 . Elements of the correction system  640 , and the correction system  640 , are examples of means for selectively correcting a tooth position of a moon drive gear  634 . The correction system  640 , both collectively and with regard to the illustrated and described components thereof, are further example means for selectively rotating a moon drive gear  634 . 
     According to one aspect, the correction system  640  may be used to selectively rotate a moon drive gear  634  such that teeth of the moon drive gear  634  are positioned at a location corresponding to a receiving portion of a chain. In at least some embodiments, the correction system  640  corrects driving moon gears  634  when the driving moon gears  634  orbit along an orbital path that is a non-integer path. The effective size of such a non-integer path, if divided by the pitch of the gear teeth on the driving moon gears and/or pitch of the chain, corresponds to a size having a partial tooth. The correction system  640  may thus be used to correct gear teeth positions at partial tooth positions of the wrapping member. 
     With reference to  FIG. 23 , a schematic illustration of an exemplary transmission system  700  is illustrated. In the illustrated embodiment, the transmission system  700  includes an input system  718  and an output system  720 . By way of illustration, the input system  718  and/or the output system  720  may include a sheave, sprocket, gear, wheel, or other mechanism that may be used to transfer power to, or receive power transferred from, a wrapping member  728 . For instance, the wrapping member  728  may be a belt or chain. 
     In  FIG. 23 , in addition to such components of the drive and driven system, a set of one or more additional structures may also engage a chain, belt, or other wrapping member that extends between the drive and driven systems  718 ,  720 . For instance, in this embodiment, three structures  721 ,  723 ,  725  may be used. According to one embodiment, two of the structures (e.g., structures  721 ,  723 ) may have a fixed position. A third structure (e.g., structure  725 ) may be moveable. In such an embodiment, the third structure  725  may act in some embodiments as a tensioner that can be used to adjust the tension in the wrapping member  728 . For instance, the third structure  725  may be moved to adjust the position of the wrapping member  728  and take up, or release, portions of the wrapping member  728  to maintain a desired tension in the wrapping member  728 . In one embodiment, tension may be adjusted to remain constant while changes in gear ratios occur, or the tension may vary as desired. Further, while only a single tensioner  725  is illustrated, multiple tensioners may be used, or may even be eliminated according to some embodiments as discussed herein. 
     The other two structures  721 ,  723  may be used in any suitable manner. According to one embodiment one or both of the structures  721 ,  723  operate as reference components. For instance, as discussed herein, one aspect of an infinitely variable transmission is that such a transmission may operate at non-integer ratios. In a transmission using gears that move radially, the size of a sheave and/or the position of the gear teeth may correspond to a circle that is not wholly divisible by the pitch of the gear teeth and/or the pitch of a chain, so as to result in an integer number of teeth were the full circle covered in teeth or chain links. As a result, some correction in gear teeth may be performed. As discussed, such correction may be performed by, for instance, using one or both of the structures  721 ,  723  that are static relative to the wrapping member  728 . By way of illustration, the structure  721  can act as a set reference for a chain inasmuch as regardless of the chain&#39;s position on a set of sheaves, sprockets, or the like, the position of the structure  721  when engaged by the wrapping member is known or can be determined. In one embodiment, the structure  721  may be a gear that remains in constant contact with the wrapping member  728 , such that a tooth position of the gear can be determined and used to correct gears of the input and/or output system  718 ,  720  to correspond with an expected position of the chain at a point of engagement. 
     In one embodiment, a sensor, angular encoder, or other device determines a position of the sheave, chain, sprocket, and/or other components, and adjusts the position of a sprocket to correspond to a proper pocket location in a chain. According to another embodiment, a sensor, angular encoder, or other device determines a position of the structure  721 , including one or more gear teeth thereon, if any, to identify a desired position of a chain tooth at a point of engagement between the wrapping member  728  and the input system  718  or output system  720 . In still another embodiment, a mechanical, electrical, or other system, or a combination of the foregoing may be used to monitor the structures  721 ,  723 . For instance, a mechanical intelligence system may provided automated intelligence identifying the angular position of the chain and/or the structures  721 ,  723 . In some embodiments, monitoring the structures  721 ,  723  may be desirable to avoid accumulating errors. For instance, components of the system, including the wrapping member  728  and the sheave may wear over time. If an angular position of a sheave is measured, the wear of the sheave may influence the sensor output, while wear of the wrapping member  728  may cause additional deviations. However, by monitoring one or both of the structures  721 ,  723  directly, the errors that accumulate with the sheave can be reduced or eliminated as the output is a direct correlation to the position of the wrapping member. Thus, by monitoring or otherwise knowing the position of such a fixed structure  721 ,  723 , the location and position of a wrapping member can be determined, as well as the required position of a sprocket, gear, or other engaging member. 
     Returning briefly to  FIG. 20 , the exemplary transmission  600  generally corresponds to a portion of the schematically illustrated transmission system  700  of  FIG. 23 . In the transmission system  600  of  FIG. 20 , a single side of a transmission  600  is illustrated (e.g., an input system), although it will be appreciated that other exemplary embodiments may include the illustrated system as an output, or in both drive and driven systems. 
     According to the embodiment in  FIG. 20 , a sheave  626  cooperates with one or more moon drive gears  634  to engage a chain, belt, cable, or other wrapping member. A follower gear  621  may also be included. The follower gear  621  may correspond, for example, to the static structure  721  illustrated in  FIG. 23 . 
     In the illustrated embodiment, the position of the wrapping member on the follower gear  621 , and the deviation from an expected position for a whole integer reference circle, are at least partially measured and quantified using a gear train  673  that is coupled to the follower gear  621 . In effect, the gear train  673  acts as a separate transmission that relates position information from the follower gear  621  to the input system  618 . The gear train  673  may take any suitable form. In the illustrated embodiment, for instance, the follower gear  621  rotates on a same shaft as a first coupling gear  674 . The first coupling gear engages a second coupling gear  675  at a desired ratio. A sheave  676  may rotate on the same shaft as the second coupling gear  675 , and can be connected to a second sheave  677  via a belt, chain, cable, or other wrapping member. The second sheave  677  is, in this embodiment, co-axial with a third coupling gear  678  which engages a drive ring  679 . Thus, through the gear train  673 , the rotation of the follower gear  621  can be transferred to the drive ring  679 . Optionally, the drive ring  679  is seated such that the drive ring is centered on the drive shaft  624 . 
     It should be appreciated in view of the disclosure herein that the gear train  673  is merely exemplary and that other types of gear trains or mechanisms may be used. For instance, as discussed herein, an angular encoder may be used to detect the position of the follower gear  621 , such that the gear train  673  can be removed. In other embodiments, different numbers and sizes of gears, belts, sheaves, and the like may be used to produce the gear train  673 . According to one embodiment, the gear train can provide usable information relative position of the follower gear  621  regardless of the ratio increase or reduction between the follower gear  621  and the drive ring  679 . 
     Turning now to  FIG. 24 , a partial view of the transmission  600  is illustrated to specifically illustrate aspects of the correction system  640 . As shown in  FIG. 24 , the rotation of the drive ring  679  can be tied to rotation of the moon drive gears  634 . For instance, in this particular embodiment, a sun gear  680  is coupled to the drive ring  679 . For instance, the sun gear  680  and the drive ring  679  may be integrally formed, coupled together, or coupled to a same shaft. As a result, the sun gear  680  and the drive ring  679  can have the same rotational speed. The sun gear  680  engages three correction gears  681  in the embodiment in  FIG. 24 . The sun gear  680  may, for instance, be on a shaft (not shown) on which a spring  682  and reference wheel  683  are seated. 
     In one embodiment, the reference wheel  683  is positioned to correspond with a mating correction wheel  684 . For instance, as shown in  FIG. 24 , the reference wheel  683  and correction wheel  684  may include a plurality of pockets formed in the mating surfaces thereof. The pockets defined by the reference and correction wheels  683 ,  684  may, for instance, be generally semicircular so that a set of balls  685  may be placed therein. The balls  685  can be packed together and reside within the pockets in each of the reference and correction wheels  683 ,  684 . 
     The size of the pockets in the reference and correction wheels  683 ,  684  may be varied as desired for a particular application. According to one exemplary embodiment, the pockets are sized to correspond to the pitch of the teeth in the moon drive gears  634  and the pitch of chain links in a corresponding wrapping member. In some cases, the reference and correction wheels  683 ,  684  are spring loaded. In one embodiment, for instance, as the correction gears  681  rotate, the shafts (not shown) attached to the correction gears  681  may rotate, thereby causing the reference wheels  683  to rotate, and as the reference wheels  683  rotate, the springs  682  are compressed. 
     The shaft of the correction gear  681  may, in some embodiments, not couple directly to the moon drive shaft  636 . In such an embodiment, rotation of the reference wheel  683  may cause the pockets of the reference and correction wheels  683 ,  684  to become misaligned. Because the balls  685  may be configured to fit within the pockets, shifting the position of the pockets may cause the correction wheel  684  to rotate and try to correct alignment of the pockets with respect to the balls  685 . Such alignment may, for instance, correspond to a correction amount for the moon drive gears  634 . In at least some embodiments, if the reference wheel  683  rotates a full pitch relative to the correction wheel  684 , the pockets may realign. In such a case, the reference and correction wheels  683 ,  684  may snap back to an aligned position and the load in the spring  682  is optionally released. 
     It should be appreciated in view of the disclosure herein that the illustrated embodiment, and the description related thereto, are merely exemplary of the types of correction systems that may be implemented in accordance with aspects of the present disclosure. In other embodiments, alternative or additional correction systems, assemblies, and/or components may be used. For instance, in one embodiment, the spring  683  may include a Bellville spring, although other types of springs may be used. In another embodiment, the correction wheel  684  may be spring loaded in addition to, or as an alternative to, the spring loading of the reference wheel  683 . In another embodiment, the sun gear  680  may be removed. For instance, the drive ring  679  may have an interior tooth profile such that the correction gears  681  directly engage the drive ring  679 . In still other embodiments, other types of correction systems described herein or as may be learned by a review of the present disclosure may be used. 
     6. Transmission with Wedge Locking System 
     Turning now to  FIGS. 25A-25C , another example embodiment of a transmission  800  is contemplated within the scope of the present disclosure. As will be appreciated, the transmission  800  includes various components, assemblies and systems that may operate in a manner similar to components, assemblies, and systems described elsewhere herein. Accordingly, to simplify the discussion relating to the transmission  800 , a discussion of the operation of the similar components will not be repeated. Thus, the transmission  800  is intended to incorporate the discussion herein related to other systems, including at least disclosed input, output differential, synchronization, and correction systems. 
     With regard to the transmission  800  a particular reference is made to transmission  600  of  FIG. 20 . More particularly, the transmission  800  of the present embodiment is similar in various regards to the transmission  600 . One notable departure is, however, with respect to the locking system  842  of the transmission  800 . 
     The locking system  842  is best illustrated in  FIGS. 25B and 25C . In particular,  FIG. 25B  illustrates a rear view of the transmission  800  and of the locking system  842 .  FIG. 25C  illustrates a cross-sectional view of components of the locking system  842  of  FIGS. 25A and 25B . In this particular embodiment, the locking system  842  is configured to operate in connection with the drive gears  834 , each of which may be used to drive or be driven by a chain or other wrapping member. More particularly, in the illustrated embodiment, the locking system  842  couples to the drive gear shafts  836  to selectively stop or limit rotation of the drive gear shafts  826 . On the drive gear shafts  826  are one or more linking gears  833  that engage the drive gears  834  and, when rotated, cause the drive gears  834  to rotate. 
     More specifically, a ring  869  may be attached to the transmission  800 . In one embodiment, the ring  869  is fixed relative to the transmission  800 . For instance, the ring  869  may be fixed to, or incorporated within, the transmission housing. In other embodiments, however, the ring  869  may be selectively or otherwise movable. The ring  869  is illustrated as including a cam profile. Specifically, the illustrated ring  869  has at least two different sections, and the widths of such sections vary. A first section  870  extends around approximately two-hundred forty degrees of the ring  869 , while the second section  871  extends over about one-hundred twenty degrees. Such degrees are, however, merely exemplary and may vary. For instance, in one embodiment, a portion may extend around about ninety degrees of the ring  869 , while another portion may extend less than ninety degrees or even more than two-hundred forty degrees. According to at least one embodiment, the first section  870 , or a section over which the ring  869  is configured to lock the drive gears  834  is defined by a Vernier factor. In effect, the Vernier factor locks drive gears  834  over an interval defined by the equation V F =360/N±10%, wherein V F  is the Vernier factor and N is the number of drive gears  834 . Accordingly, for the transmission  800  that includes three drive gears  834 , the Vernier factor defines a locking interval ranging between about one-hundred eight degrees and about one-hundred thirty-two degrees. 
     The locking system  842  further includes, in this embodiment, a set of cam followers  872 . The cam followers  872  can include, for instance, a roller or other structure adapted to follow along the cam profile of the ring  869 . In accordance with one aspect of the present disclosure, the cam followers  872  can be used to, for instance, lock a drive gear shaft  836  and cause the drive gear shaft  836  and/or drive gears  834  to lock at a fixed position, or lock the drive gears to reduce a chance or extent of backward motion. Accordingly, the locking system  842  can facilitate avoiding or reducing rotation that may cause slippage between a chain and sheave. 
     As best illustrated in  FIG. 25C , the cam follower  872  may be used in connection with a wedge  873  and/or a yoke  874 . More particularly, the cam profile of the ring  869  includes changes as to the width of the ring  869 . As the width changes, the can follower  872  may move radially. For instance, as the cam follower  872  enters a thinner portion  871 , the cam follower  872  may extend radially outward. In contrast, as the cam follower  872  enters a thicker portion  870 , the cam follower  872  may move radially inward. As the cam profile changes, a linkage  875  may move the wedge  873  radially inward or outward. As the wedge  873  moves radially inward, for instance, the wedge  873  may cause greater separation between two halves of the yoke  874 . In contrast, as the wedge  873  moves radially outward, the wedge  873  may cause lesser separation between the two halves of the yoke  874 . 
     Changes in positioning of the yoke  874  can enable locking of the drive gear shaft  836 . For instance, in  FIG. 25C , the drive shaft  836  may include one or more structures  876  therein. For instance, exemplary structures include cut-outs, tabs, detents, other structures, or combinations thereof. The yoke  874  may include, or be attached to, a lock element  877 . The lock element  877  can be moved into engagement with the structures of the drive gear shaft  836 . By way of illustration, the lock element  877  may include an angle, plate, clutching mechanism, other structure, or a combination thereof that will lock against the structures  876  of the drive gear shaft  836  to prevent or restrict rotation of the drive gear shaft  836 . Such action may lock the drive gear shaft  836  in place to prevent or limit back rotation of the linking gear  833 , which in turn locks or restricts rotation of the drive gear  834  that may engage a chain. 
     7. Additional Embodiments 
     It should be appreciated in view of the disclosure herein that a number of different transmissions and transmission components, systems, and assemblies are contemplated within the scope of the present disclosure. For simplicity, various different features have been disclosed particularly in combination with other features. Such disclosure has been merely for convenience, however, and in no way is intended to limit the scope of the present disclosure. Indeed, as noted herein, the various components, systems, and assembles are largely considered interchangeable and workable in combination with any number of other features or components, in addition to those combinations specifically illustrated. 
     Accordingly, according to one aspect of the present disclosure,  FIG. 26  illustrates an exemplary method  900  of designing a transmission is disclosed. The acts of the method  900  need not be performed in the order shown in  FIG. 26 , but may be performed in any other suitable order. In one embodiment, various elements of a transmission may be selected and interchangeably combined. In accordance with at least some embodiments, a sheave construction is selected (act  901 ). For instance, a single sheave may be selected for an input or output s system, or dual sheaves may be selected. In still other embodiments, more than two sheaves may be used (e.g., for multiple wrapping members). Sheaves may also be selected based at least in part on sheave actuation mechanisms. For instance, a sheave may be selected based on a hydraulic, pneumatic, mechanical, electrical, or other actuator used to move the sheave in an axial direction. 
     In addition, the exemplary method  900  may include selection of a chain construction (act  902 ). As disclosed herein numerous types of chains may be used, including roller chain, involute chain, single piece links, and chains with integral lubrication channels. An O-ring may be used on a chain. Angled rollers or beveled sides carrying chain link portions may also be used. In some embodiments, multiple chain types may be combined. For instance, an O-ring may be combined with a single piece link. 
     The method  900  may further include selecting a correction mechanism (act  903 ). Multiple types of correction mechanisms may be used in accordance with the present disclosure, each of which is interchangeable with other listed features. For instance, correction mechanisms making use of actuators, worm gears, turbine disks, encoders, sensors, off-center drivers, ball and pocket wheels, mechanical intelligence, and other correction mechanisms may be used. In some embodiments, multiple correction mechanisms may be combined. 
     According to another embodiment, the illustrated method  900  may further include selecting a synchronization mechanism (act  904 ). For instance, synchronization mechanisms that are independently selectable include linear sprocket paths, arcuate sprocket paths, slots in sheaves, worm gear driven mechanisms, outer ring mechanisms, cross-over shafts, independent rotation arms, and other suitable mechanisms. For instance, a spring loaded or floating mechanism may be used in accordance with some embodiments herein. 
     A locking mechanism may also be selected (act  905 ) in accordance with still another embodiment of the present disclosure. Exemplary locking mechanisms may employ any number of suitable features, including worm gears, cam rings, clutch disks, hydraulic turbines, or wedge and yoke constructions. Multiple features may also be combined together, such as a cam ring with a wedge and yoke and/or clutch disk. In still other embodiments, a single gear may be locked at any time, or multiple gears may be selected. 
     In still another aspect, the method  900  may include selecting a differential to include in the transmission (act  906 ). For instance, a differential may be a reverse differential and/or provide an engaged neutral. In still another embodiment, an input may be split and directed to two inputs of the differential. A second input may come from a secondary power source and/or inputs may be directed to an input shaft and a housing. 
     Additionally, a tensioning mechanism is configurable. For instance, in one embodiment, the method  900  includes selecting a tensioning mechanism (act  907 ). Exemplary tensioning members that may be selected include, but are not limited to, use of multiple sheaves, or a moving tensioning gear such as an idler gear. An output or input system may also pivot to tension a chain or other wrapping member. 
     The method  900  may be implemented in any number of manners. For instance, upon selecting one or more components, the transmission may be built into a physical model conforming with the selected features. In another embodiment, a computing device is encoded with instructions related to criteria, qualifications, features, and the like for various components and options. A computing system may make use of an expert system to, for instance, automate selection of the criteria for the transmission in accordance with the method  900 . 
     Embodiments of the present disclosure may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of this disclosure is, therefore, indicated by the appended and later added or amended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.