Patent Publication Number: US-2022227452-A1

Title: Human powered reciprocal (linear) motion drive system, and applications thereof

Description:
FIELD OF THE INVENTION 
     The field of the invention generally relates to human powered drive systems and transmissions thereof, more particularly, to human powered reciprocal-linear motion drive systems, and applications thereof. 
     BACKGROUND OF THE INVENTION 
     The majority of human powered devices, for example, winches (i.e., hand powered load hoisting or/and hauling machines), bicycles and tricycles, as well as human powered cranes, human powered vehicles, and human powered devices on water-based (marine type) vehicles or vessels (such as boats, yachts, and ships), among other possible human powered devices, use rotary (circular) motion to provide power to, and effect motion of, the work-producing parts of the human powered device. Reference is made to  FIG. 1  that shows a comparison of effective power [in terms of work per unit time, or Output Force (F)×Angular Displacement (pedal position) per unit time] generated by rotary (circular) motion vs. reciprocal (linear) motion of a bicycle (as an exemplary human powered device). As shown therein, rotary (circular) motion power, represented by line  10  is inherently inefficient, as a result of producing uneven levels of force throughout the angular displacement (pedal rotation). When a rider pushes on a bicycle pedal, there is more force in mid cycle  16  when the leg of the rider is essentially pushing downwards. At the beginning  12  and ending  14  of the cycle, the output force (F), and therefore, the power, generated is substantially reduced. 
     By contrast, reciprocal-linear motion drive systems produce a uniform force throughout the motion cycle (or cycle), while requiring the same equivalent input power from the user as for rotary drive systems. As shown in  FIG. 1 , the reciprocal (linear) motion drive cycle (cycle) is represented by line  20 . The output force (F) is more closely related to the input power such that reciprocal (linear) motion is far more efficient. The output force (F) is constant throughout the reciprocal (linear) motion aside from a very small gap  22  in the power delivery where the timing of the gap  22  is dependent on the speed that the rider or user switches the side (pedal) of driving the reciprocal-linear motion. 
       FIG. 1  demonstrates that at least with respect to the effective power generated, reciprocal-linear drive motion systems (hereinafter, briefly referred to as “linear drive system”) are significantly advantageous compared to rotary-circular drive systems (hereinafter briefly referred to as “rotary drive system”). However, the adoption of linear drive systems has been limited primarily due to complexities associated with the transmission (gear) mechanisms, that transfers the generated power to the load, such as the wheels in the case of a bicycle. 
     The transmission or gear mechanisms that are used in rotary drive systems are not suitable for use in linear drive systems, as they make use of rotational (circular) force as part of their operation. Additionally, transmission or gear mechanisms known in the art rely on multiple gear wheels, and a chain that “jumps” between wheels, resulting in a jarring gear change and wear on the chain and gear mechanism during each gear change. Still further, users of prior art transmission or gear mechanisms must become familiar with specific gear numbers and cannot simply shift up or down, or skip multiple gears, when selecting a more acute (rapid or sharp) change in power supplied to a load. 
     In view of the above discussion, there is need for developing and practicing new and improved human powered linear drive systems, and applications thereof. There is also need for providing such drive systems that can be manufactured in a cost-effective manner, such that human powered devices made with such systems will have reasonable costs for consumers. 
     SUMMARY OF THE INVENTION 
     The system relates to a human powered reciprocal motion drive system, which comprises two independently driven first and second drive assemblies for interchangeably operating in driving and return strokes, each drive assembly comprising: (a) a spiral cone; (b) a driving cable, a first end of the driving cable being connected to a first winding group on the spiral cone, and a second end of the same driving cable being connected to a second winding group on the same spiral cone; (c) a pedal which is attached to said driving cable; and (d) a gear assembly for defining a ratio between the number of revolutions in said first winding group and the number of revolutions in said second winding group on the same cone, thereby to define an operative position along the thread of the spiral cone, and a respective torque that the cone applies; wherein the system further comprising a reciprocal motion mechanism which is separate from any of said two cones, a first end of the reciprocal motion mechanism being in communication with said pedal of the first drive assembly and a second end of said reciprocal motion mechanism being in communication with the pedal of the second drive assembly, said reciprocal motion mechanism, during each driving motion by one of said pedals, causes a return motion of the other of said pedals to bring it to an initial state, thereby to be ready for a next driving motion during a driving stroke of this specific drive assembly. 
     In an embodiment of the invention, the driving motions in the first drive assembly is simultaneous with a return motion in said second drive assembly, and vice versa. 
     In an embodiment of the invention, the any ratio definition by the gear assembly takes place during a return motion. 
     In an embodiment of the invention, the definition change of said ratio by the gear assembly involves an inner or outer shift of the operative position along the respective spiral cone. 
     In an embodiment of the invention, the spiral cone of the first drive assembly and the spiral cone of the second drive assembly are configured to alternately drive a load. 
     In an embodiment of the invention, the spiral cone of the first drive assembly and the spiral cone of the second drive assembly each comprises a one-way ratchet such that only rotation in one direction during the respective driving stroke of each spiral cone imparts movement to the load. 
     In an embodiment of the invention, the definitions by the two gear assemblies of the operative positions along each of the two spiral cones, respectively, are independent from one another. 
     In an embodiment of the invention, the gear assembly of the first drive assembly and the gear assembly of the second drive assembly, each comprising: (a) a forward/backward cable shift mechanism, for selectively moving the gear assembly either forward or backward along the driving cable; (b) a set-up mechanism for selectively defining either a forward motion or a backward motion along said driving cable; and (c) a brakes mechanism for locking the gear mechanism to the driving cable at a desired location. 
     In an embodiment of the invention, each gear assembly is attached to a pedal of one driving assembly. 
     In an embodiment of the invention, each gear assembly is attached to the respective pedal either directly or indirectly. 
     In an embodiment of the invention, each set-up mechanism is divided into an upper set-up unit and a lower set-up unit, to selectively define forward or backward displacement of the gear mechanism along the driving cable, respectively. 
     In an embodiment of the invention, each set-up mechanism includes a mechanism for defining an extent of displacement. 
     In an embodiment of the invention, the gear assembly of the first drive assembly and the gear assembly of the second drive assembly, each comprising: (a) a cable flip wheel; (b) a cable pulley wheel mounted on a gear axle cylinder wherein the driving cable passes around the cable pulley wheel and cable flip wheel in the gear assembly; and (c) a lower shift gear wheel and an upper shift gear wheel mounted on the gear axle cylinder such that rotation of either one of the lower shift gear wheel or the upper shift gear wheel causes rotation of the gear axle cylinder and of the cable pulley wheel to thereby shift gears by shifting the operative position of the driving cable on the respective spiral cone. 
     In an embodiment of the invention, each of the gear assemblies further comprising: (a) an upper gear changing mechanism comprising a plurality of push teeth for engaging with and rotating the upper shift gear wheel, wherein the number of the push teeth deployed from the upper gear changing mechanism is selected using a gear selector; and (b) a lower gear changing mechanism comprising a plurality of push teeth for engaging with and rotating the lower shift gear wheel, wherein the number of the push teeth deployed from the lower gear changing mechanism is selected using the gear selector. 
     In an embodiment of the invention, the number of the plurality of push teeth deployed for a gear change is between one push tooth and all of the plurality of push teeth. 
     In an embodiment of the invention, a gear change by the gear assembly is semi-automatic. 
     In an embodiment of the invention, each of the gear assemblies further comprising a reset mechanism for returning the upper gear changing mechanism or lower gear changing mechanism to a starting position following engagement with the upper shift gear wheel or lower shift gear wheel. 
     In an embodiment of the invention, the reset mechanism comprising: (a) a reset tooth configured to engage a blocking wedge mounted on an inner surface of a drive assembly enclosure to cause a gear change; (b) a reset spring; and (c) a bearing ramp mounted on an inner surface of a gear enclosure such that the reset bearing engages the ramp following a gear change to thereby retract the reset tooth such that the reset spring pulls the upper gear changing mechanism or lower gear changing mechanism to a starting position. 
     In an embodiment of the invention, each of the gear assemblies is mounted and travels within a respective drive assembly enclosure. 
     In an embodiment of the invention, each of the driving cables is looped around a respective drive roller tensioned by a respective throttle spring attached to the respective drive assembly enclosure, the tensioned drive roller being adapted for absorbing slack from the driving cable when it shifts in position around the respective spiral cone. 
     In an embodiment of the invention, the reciprocal motion mechanism is a reciprocal motion cable or a reciprocal motion chain. 
     In an embodiment of the invention, the reciprocal motion cable is looped over at least one reciprocal pulley wheel mounted onto a load frame, wherein the reciprocal motion cable is attached at each of its two ends to the respective gear assembly, which is in turn attached to a respective pedal. 
     In an embodiment of the invention, a gear selector is attached to a gear change cable and wherein the gear change cable is attached to a gear swivel, wherein the gear swivel is mounted on the same axle as a pedal bar such that the gear swivel swivels when the pedal bar moves as part of its reciprocal motion, wherein a gear swivel pin moves within the gear swivel such that movement of the gear swivel caused by the gear selector causes movement of the gear swivel pin, wherein the gear swivel pin is attached to a gear change cable extension which in turn is attached to the plurality of push teeth, such that movement of the gear swivel pin results in engagement of one or more of the plurality of push teeth with the upper shift gear wheel or the lower shift gear wheel for rotating the upper shift gear wheel or lower shift gear wheel for effecting a gear change. 
     In an embodiment of the invention, the system is configured for humanly powering a human powered device selected from the group consisting of: winches, bicycles, tricycles, cranes, vehicles, and human powered devices on water-based, marine type, vehicles or vessels. 
     In an embodiment of the invention, the water-based, marine type, vehicles or vessels are selected from the group consisting of: boats, yachts, and ships. 
     In an embodiment of the invention, the driving cable is a driving chain. 
     In an embodiment of the invention, the system comprising a local reset for effecting a repetition of a gear change based on a defined set-up, and a global reset for zeroing any defined set-up. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  graphically illustrates a comparison of effective power [in terms of work per unit time, or Output Force (F)×Angular Displacement (pedal position) per unit time] generated by rotary (circular) motion vs. reciprocal (linear) motion of a bicycle (as an exemplary human powered device); 
         FIGS. 2A-2J  schematically illustrate exemplary embodiments of operation of an exemplary human powered linear drive system (of an exemplary human powered device being a bicycle), according to some embodiments of the invention; 
         FIGS. 3A-3V  schematically illustrate exemplary embodiments of the invention; 
         FIGS. 4A-4N  schematically illustrate exemplary embodiments of operation of an exemplary human powered linear drive system (of an exemplary human powered device being a bicycle), according to some embodiments of the invention; 
         FIG. 5  schematically illustrates an exemplary embodiment of an exemplary human powered vehicle (a tricycle) having an exemplary human powered linear drive system, according to some embodiments of the invention; and 
         FIGS. 6A-6B  schematically illustrate an exemplary embodiment of an exemplary water-based (marine type) vehicle or vessel (a boat) having several exemplary human powered devices employing exemplary human powered linear drive systems, according to some embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention, in some embodiments thereof, relates to a human powered linear drive system, and applications thereof. Some embodiments of the invention are in the form of human powered linear drive systems that are applicable to a wide variety of different types of human powered devices, for example, winches, bicycles, tricycles, cranes, vehicles, and human powered devices on water-based (marine type) vehicles or vessels (such as boats, yachts, and ships). 
     In exemplary embodiments of the invention, the transmission or gear mechanism is semi-automatic, requiring a user to only make an up-gear or down-gear selection, and a selection of the level (incremental or acute) of required gear change. Once the user has made the selection, the gear change continually takes place on every passive (return) cycle (until reset) allowing the user to feel when the correct gear ratio has been satisfactorily reached. Thus, a user does not have to select a specific gear, rather, only provide the selection of up-gear or down-gear, and level thereof, while continuing to pedal, until the pedaling effort required seems appropriate, resulting in a more user-friendly gear change process. The ability to select a level of change (incremental or acute) enables a user to make fast changes that skip several gear ratios per change. 
     Such a continual change of gears is enabled by use of a single spiral cone in each of the two sides of the linear drive system as a primary drive wheel, thereby enabling smooth gear shifting without the jarring typically associated with multi-gear rotary drive systems known in the art. Additionally, in exemplary embodiments of the invention, each gear change takes place during the return cycle, in which the tension on the gear assembly, on the cable (or chain) and on the spiral cone is substantially reduced. The automatic, return, and continuous gear change mechanism therefore reduces wear and tear on the parts involved in the overall linear drive system, resulting in a more reliable transmission and gear mechanism in the long term. 
     In exemplary embodiments of the invention, user activated levers (such as pedals, or similar types of leg or arm operated levers) are pushed or pulled by an operator to drive the spiral cones (one pedal for each cone), via matching gear assemblies, in order to drive the load of a human powered device. As disclosed herein, such a load may be of, or associated with, any form of a human powered device driven by reciprocal (linear) motion. Two cable (or chain) winding groups are provided along the thread of each of the cones, an “outer” winding group in proximity to the base of the cone, and an “inner” winding group in proximity to the tip of the cone. Hereinafter, for the sake of simplicity the term “cable” is used to encompass both of the cable and chain options. A single driving cable (or chain) connects between these two winding groups such that when a cable section is pulled from one of these groups, another section is collected by the other winding group, and vice versa. The position of the pedal along the driving cable in fact defines an active location along the cone&#39;s thread where the cable pulling and collection are made (namely whether the active location is on a more outer section of the thread or on an inner one), and this active location in fact defines the moment that the cone applies to the load. A gear selection is made using gear selectors that activate the transmission or gear mechanism to shift and define the position of the gear assembly along the drive cable. As the gear assembly is rigidly attached to the pedal, the shift of the gear assembly along the cable in fact defines the moment that the cone applies on the load. The use of a spiral cone thus enables a user to make gear changes by shifting the position of the active location along the spiral cone, resulting in effectively transferring power generated by reciprocal (linear) motion to a target load. 
     Implementation of exemplary embodiments of the present invention attempt to address, and overcome, at least some of the various limitations or problems associated with prior art human powered drive systems, particularly, drive systems that are based on rotary (circular) motion. In addition to the above aspects and advantages relative to prior art drive systems, exemplary embodiments of the herein disclosed human powered linear drive system can be manufactured in a cost-effective manner, such that human powered devices made with such systems will have reasonable costs for consumers. 
     Reference in the specification to ‘one embodiment’, ‘an embodiment’, ‘some embodiments’ or ‘other embodiments’ means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least one embodiment, but not necessarily all embodiments, of the present disclosure. It is understood that the phraseology and terminology employed herein are not to be construed as limiting and are for descriptive purpose only. 
     The terms ‘reciprocal motion’ and ‘linear motion’, as used herein, are interchangeable. ‘Reciprocal motion’, as used herein, in a non-limiting manner, refers to repetitive motion in a direction along a linear path, and which is generated on two opposing, and generally parallel, sides, alternately per each side, by at least two force appliers, such as, but not limited to, two arms or two legs of a user (i.e., one arm or one leg per side of the generated motion). 
     The term ‘reciprocal (linear) motion’, as used herein, includes two cycles, an active cycle and a return cycle. The active cycle is powered by the user acting (applying force) on a first side of a reciprocal (linear) motion mechanism. As illustratively described herein, simultaneously with the active cycle at the first side, a pulley mechanism causes the second side to undergo a return cycle-moving in the opposite direction to that of the active cycle. In such a manner, the pedal of the second side is returned to a position ready for a next active cycle. Active cycles may require (linearly) pushing or pulling by a user, depending on the application of the reciprocal (linear) motion mechanism and the position of the user relative to the reciprocal (linear) motion mechanism. 
     The terms ‘operator’, ‘rider’, and ‘user’, as used herein, are interchangeable, and refer to a human riding or using a linear drive system to power and effect motion of a load. The terms ‘transmission’ and ‘gear’, as used herein, are interchangeable. The term ‘pedal’, as used herein, refers to any attachment or pair of attachments (such as grips, handles, or levers) that are operatively connected to the herein disclosed exemplary embodiments of the linear drive system, and which may be pushed or pulled by force appliers (arms, legs) of an operator, rider, or user. Physical-orientational terms, such as, location, direction, ‘right side’, and ‘left side’ are used herein in a non-limiting manner. 
     For purposes of further understanding exemplary embodiments of the present invention, in the following illustrative description thereof, reference is made to the drawings. Throughout the following description and accompanying drawings, same reference numbers refer to same components, elements, or features. It is to be understood that the invention is not necessarily limited in its application to particular details of construction or/and arrangement of exemplary system or device components, or to any particular sequential ordering of exemplary method steps or procedures, set forth in the following illustrative description. The invention is capable of having other exemplary embodiments, or/and of being practiced or carried out in various alternative ways. 
     In exemplary embodiments, the herein disclosed invention is in the form of human powered linear drive systems that are applicable to a wide variety of different types of human powered devices, for example, winches, bicycles, tricycles, cranes, vehicles, and human powered devices on water-based (marine type) vehicles or vessels (such as boats, yachts, and ships). 
     These aspects of the present invention, in a non-limiting manner, are interrelated, in that illustrative description of characteristics and technical features of one aspect also relates to, and is fully applicable for, illustratively describing characteristics and technical features of other aspects of the present invention. For example, illustrative description of characteristics and technical features of the human powered linear drive system, or of a component (e.g., device, assembly) of the drive system, also relates to, and is fully applicable for, illustratively describing characteristics and technical features of one or more aspects about a method of humanly powering a human powered device. 
     Additionally, for example, in a non-limiting manner, embodiments of the human powered linear drive system, or of a component (e.g., device, assembly) of the drive system, are suitable for implementing embodiments of a method of humanly powering a human powered device. 
     Reference is now made to  FIGS. 2A-2J  that schematically illustrate exemplary embodiments of a human powered linear drive system, in this specific example, a bicycle. The bicycle of the invention has two independently-driven drive assemblies, a “first-side” drive assembly “A”, and a second side drive assembly “B”. As shown in  FIGS. 2A-2E , pedals  103 A and  103 B are pushed down by an operator to drive spiral cones  162 A and  162 B via gear assembly  120  to drive load  180 . Load  180  is here shown to be the rear wheel of a bicycle but as before, load  180  may be any suitable load. It should be noted that the term “independently driven”, as used throughout this application, refers only to the driving cycle during which a pushing force is applied to the pedal (or similar). This term does not intend to refer to the return cycle, nor to indicate that the return cycle by the two separate drive assemblies is performed independent from one another. 
     The figures show a first (or left) side “A” and second (or right) side “B” of the same bicycle to illustrate relative positions of pedals  103  and associated gearboxes. Same parts of linear drive system  100  that are duplicated on each side share the same numbering with an “A” or “B” added to the reference numeral. As shown, the driving mechanisms of the first (or left) side and second (or right) side operate independently from each other (excluding the return mechanism which will be discussed separately herein below— FIGS. 2 h    and  2 I). 
     In  FIG. 2A , linear drive system  100  is shown in a starting position where pedal  103 B is at the top limit L T  of its range of travel, and pedal  103 A is at the bottom limit L B  of its range of travel. The range of travel of the pedals  103  is rigidly fixed (see for example arrows  117  in  FIG. 3B ). Pedals  103  are rigidly attached to a gear assembly enclosure  122 , which in turn houses gear assembly  120 . Therefore, gear assembly enclosure  122  and pedal  103  move together within the pedal range  117  (namely between points L T  and L B ), while the movement of the gear assembly enclosure is performed within drive assembly enclosure  101  (see  FIG. 3B ). Drive assembly enclosure  101  also houses the spiral cone assembly  160  (see  FIG. 3C ) which includes the two cones  162 . 
     In exemplary embodiments, each of the two cables  107  is wound through gear assembly  120  around drive roller wheel  105  and attached on both ends inside spiral cone  162 . More specifically, and as best shown in  FIG. 2F , a first end of each cable  107  is attached at an outer position  173  of cone  162 , and the other end of cable  162  is attached at an inner position  174  of a same cone  162 . In some embodiments, cable  107  is implemented as a chain and it should therefore be appreciated that either a cable or chain can be used, and the term cable as used herein covers both alternatives. As shown in  FIG. 2H , within gear assembly  120  cable  107  is wound around cable flip wheel  142  to flip its direction and then is wound around cable pulley wheel  138 . Cable pulley wheel  138  is adapted to be locked when no gear change takes place, such that cable  107  is locked at a fixed cable position into gear assembly  120 , whereby movement of gear assembly  120  results in movement of cable  107  and vice versa. Alternatively, when a chain  107  is used, the links of chain  107  are locked onto teeth (such as in the embodiment described below of  FIG. 4H ) provided on cable pulley wheel  138  and cable flip wheel  142 . 
     As shown in  FIGS. 2F and 2G , the two ends of each cable  107  are affixed at two inner and outer points,  173  and  174 , respectively of a same cone  162 . Each cone  162  contains two separate winding groups, an outer winding group  123 , and an inner winding group  124 . More specifically, a first end of cable  107  coming from gear assembly  120  is first wound around cone  162  at an outer location along the cone&#39;s thread to form the outer winding group  123 , and then attached at outer point  173 . The second end of cable  107  coming from the gear assembly  120  is first wound around the same cone  162  at an inner location along the cone&#39;s thread to form the inner winding group  124 , and then attached at inner point  174 . A very short thread gap  126  separates between the entry point E N  of the cable into the inner winding group  124  and between the entry point E W  into the outer winding group  123 . As will be discussed further below, while the respective locations of the entry points E N  and E W  along the thread dynamically change during the drive and return cycles, and even more during various gear changes, the thread gap  126  is always kept small, being a portion of a single thread. Each inner cable section  107 -I is wound inwards around spiral cone  162  and is fixedly attached at inner point  174  to spiral cone  162 . Outer cable section  107 -O is wound outwards around the same spiral cone  162  and is fixedly attached at its outer end  173  to spiral cone  162 . Cable  107  turns around a fixed drive roller  105  which is mounted at the bottom end of drive assembly enclosure  101  (see  FIG. 3B ). In  FIGS. 2A-2G , and in other figures herein, outer cable  107 -O is shown as engaging gear assembly  120 , and inner cable  107 -I is shown as passing by or through gear assembly  120  without engaging gear assembly  120 . It should be appreciated that this convention is purely for illustration, and in practice, inner cable  107 -I may engage gear assembly  120  when outer cable  107 -O passes through gear assembly  120 . Exemplary embodiments using chains, such as shown in  FIG. 4G , do not require the winding of inner and outer cables around spiral cones  162  (as in  FIGS. 2F and 2G ), as spokes over the outer surface of the spiral cone  462  hold the chain in place. 
     During a regular operation, and without affecting a gear change, the pedal, and in fact the entire gear assembly enclosure  122  is affixed to cable  107 . Therefore, and as shown in  FIG. 2F , during a drive cycle, the downward movement of pedal  103  causes the pulling of a specific cable section from the outer winding group  123  of spiral cone  162 , causing the cone  162  to turn counter clockwise (arrow  195 ), and the return of another cable section into the inner winding group  124  (due to same counter clockwise rotation of the spiral cone). During the return cycle, an opposite process in performed, where cable is pulled from the inner winding group  124 , and returned to the outer winding group  123  (however, in this case the cone operates in a non-load, namely in a free wheel manner of rotation). In  FIGS. 2A-2G  reference points A R  and A L  are shown respectively on cables  107 A and  107 B to illustrate movement and relative positions of cables  107  during pedal movement and during gear changes.  FIGS. 2A-2G  are provided for illustration of the principle of operation of the reciprocal (linear) motion drive (and mechanism) described herein and it should be appreciated that the illustrated rotations of spiral cones  162  and related movements of gear enclosures  122  and reference points A R  and A L  may or may not represent exact scale of movement of an actual constructed version of linear drive system  100 . 
     As shown in  FIG. 2B , pedal  103 B is pushed downward such as by a rider of a bicycle. Gear assembly enclosure  122 B, being attached to pedal  103 B, is thus also pushed downwards, and gear assembly  120 B, being attached to gear assembly enclosure  122 B, also moves downwards. Cable  107 B, being locked on one side into gear assembly  120 B, is pulled downward, and in turn pulls on spiral cone  162 B, causing rotation of spiral cone  162 B. In the exemplary embodiment shown in  FIG. 2B , spiral cone  162 B rotates in a counterclockwise direction, for illustration only, and linear drive system  100  may cause rotation or movement in any desired direction. Rotation of spiral cone  162 B results in rotation of load chain  108 , and thus rotation of load  180 , here shown as the wheel of a bicycle. As shown, reference points A R  and A L  remain at the same distance from gear assemblies  120 A and  120 B, respectively, as no gear change has taken place.  FIG. 2C  similarly shows a situation when pedal  103 A is pushed downwards, while pedal  103 B is pulled up. 
       FIGS. 2I and 2J  illustrate an embodiment of a reciprocal (linear) motion pulley mechanism for pulling up a pedal  103  on a first side (return cycle), when a pedal  103  on a second side is pushed down (active cycle), and vice versa. Gear assembly enclosures  122  are attached to reciprocal motion cable  193  using cable attachments  194 . Cable  193  is looped over reciprocal pulley wheels  191 . Pulley wheels  191  are mounted on reciprocal motion mount  192  which in turn is mounted onto load frame  190 . In the illustrated embodiment, load frame  190  is a bicycle frame. As shown, the reciprocal cable  193 , as well as the pullies  191 A and  191 B are entirely independent from the spiral cones  162 . As above, the active cycle may similarly be for a user to pull a pedal or handle  103  (rather than pushing) and in this case the return cycle will be the push cycle and the mechanism of  FIGS. 2I and 2J  will be adapted accordingly. 
     In use ( FIG. 2I ), when pedal  103 A is pushed down (for simplicity, only the bar of the pedal is shown), gear assembly enclosure  122 A is pulled down, pulling on reciprocal motion cable  193 . Cable  193  thus pulls gear assembly enclosure  122 B upwards along with pedal  103 B. Conversely, when pedal  103 B is pushed down ( FIG. 2J ), gear assembly enclosure  122 B is pulled down, pulling on reciprocal motion cable  193 . Cable  193  thus pulls gear assembly enclosure  122 A upwards along with pedal  103 B. 
     When pedal  103 B and gear assembly enclosure  122 B are pushed downwards, gear assembly enclosure  122 A and pedal  103 A move upwards and therefore gear assembly  120 A also moves upwards. Cable  107 A moves with gear assembly  120 A and causes spiral cone  162 A to rotate. For example,  FIG. 2B , shows that when pedal  103 A moves upwards during its return cycle, spiral cone  162 A rotates in a counterclockwise direction, however in a free-wheel manner that does not apply any force to the load  180 . More specifically, although spiral cone  162 A rotates, there is no movement caused in load chain  108  due to the use of a one-way ratchet mechanism in spiral cone assembly  160  (see  FIG. 3K ), as will be described further below. Thus, in the embodiment of  FIGS. 2A-2H , only a downward motion of pedals  103  causes movement of load  180 . 
     As shown in  FIG. 2C , pedal  103 A is pushed downward such as by a rider of a bicycle. Gear assembly enclosure  122 A being attached to pedal  103 A is thus also pushed downwards and gear assembly  120 A, being attached to gear assembly enclosure  122 A also moves downwards. Cable  107 A being locked on one side into gear assembly  120 A is pulled downward and in turn pulls on spiral cone  162 A causing rotation of spiral cone  162 A. In the illustration of  FIG. 2C , spiral cone  162 A rotates in a clockwise direction but it should be appreciated that this is for illustration only and system  100  may cause rotation or movement in any desired direction. The rotation of spiral cone  162 A results in the rotation of load chain  108  and thus rotation of load  180 , here shown as the wheel of a bicycle. 
     When pedal  103 A and gear assembly enclosure  122 A are pushed downwards, gear assembly enclosure  122 B and pedal  103 B move upwards (as described above with reference to  FIGS. 2I and 2J ). Cable  107 B moves with gear assembly  120 B and causes spiral cone  162 B to rotate. Spiral cone  162 B is here shown as rotating in a clockwise direction but it should be appreciated that this is for illustration only and system  100  may cause rotation or movement in any desired direction. Although spiral cone  162 B rotates, there is no movement caused in load chain  108  due to the use in spiral cone assembly  160  (see  FIG. 3K ) of a one-way ratchet mechanism as will be described further below. Thus, in the embodiment of  FIGS. 2A-2H  only downward motion of pedals  103  causes movement of load  180 . As before, points A R  and A L  remain at the same distance from gear assemblies  120 A and  120 B respectively as no gear change has taken place. 
       FIGS. 2D-2G  illustrate how the gear assembly  120  is used to alter the ratio of movement of pedals  103  to movement of load  180 . When required by the user of system  100  such as but not limited to a rider of a bicycle, gear selectors  146  (also shown in  FIG. 3A ) are used to change the gear ratio provided by gear assemblies  120 . In some embodiments, a selector  146  is provided for each side of linear drive system  100 , to enable different gearing per side. In some embodiments, selectors  146  are mounted on the handlebars of a bicycle as with gear selectors known in the art. 
       FIGS. 2D-2E  illustrate changing to a higher gear such that less pedal  103  movement is required for movement of load  180 , for example but not limited to when riding a bicycle down an incline.  FIGS. 2F and 2G  show the movement of cable  107 B but it should be appreciated that movement of cable  107 A is the same but reversed. In  FIG. 2D , pedal  103 B is shown at its bottom range of movement, while an arbitrary point A L  is marked at the left side of cable  107 B.  FIG. 2E  shows the situation when the pedal  103 B arrives the top of its range of movement, following its return (upwards direction) cycle, while a change of gear is performed during this return cycle. It can clearly be seen that in  FIG. 2E  the distance between point A L  and the gear assembly  122 B is significantly shorter than in  FIG. 2D . That means that a cable section was “taken” from the outer winding group  123  (see  FIG. 2F ) of the spiral cone  162 B and was given to the inner winding group  124 . Therefore, in the next drive cycle of pedal  103 B the cable  107 B will be pulled from a cone thread having a larger radius compared to the case of  FIG. 2D  (which shows the position of point A L  relative to assembly  122 B before the gear change. Therefore, in the situation of  FIG. 2E  a larger torque will be applied to the cone  162 B compared to the case of  FIG. 2D . As noted, according to preferred embodiments of the invention, a gear change is performed during the return cycle, when there is a very low tension on the cable  107 , on the respective spiral cone  162 , and on the gear mechanism  120  compared to the tension that these components sustain during the drive cycle. More specifically, any gear change occurs when the respective pedal  103  is pulled upwards in its return cycle, while the opposite pedal is in its drive (active) cycle. 
     As shown, the gear assembly  120  operates by either “taking” a cable portion from the outer winding group  123  and “giving” this portion to the inner winding group  124  (therefore causing future operation on a wider-radius of the cone&#39;s thread), or vice versa, namely, “taking” a cable portion from the inner winding group  124  and “giving” this portion to the outer winding group  123  (therefore causing future operation on a narrower-radius of the cone&#39;s thread). The radius from the center of spiral cone  162  to the entry point of cable  107 -O into spiral cone  162  is herein labelled R O  and the radius from the center of spiral cone  162  to the entry point of cable  107 -I into spiral cone  162  is herein labelled R I . The combination of R O  and R I  (R O +R I ) is herein referred to as “D”. An increased distance “D” results in a higher gear ratio. Movement of pedals  103  thus results in greater rotations of spiral cones  162  and thus greater rotations of load  180 . A similar gear change may be performed in the first side “A” during its return cycle, independent and even different from the change of the second side “D”. The mechanism used by gear assembly  120  to shift cable  107  is further described below with reference to  FIGS. 3D-3H . 
       FIG. 2G  illustrates a change to a lower gear such that greater pedal  103  movement is required for movement of load  180 , for example but not limited to when riding a bicycle up an incline. Gear assembly  120  moves cable  107  such that a cable portion is “taken” from the inner winding group  124 , and “given” to the outer winding group  123 . The shift of a cable portion from the inner cable  107 -I to the outer cable  107 -O (and therefore to the outer winding group  123 ) results in a decreased distance “D” between where outer cable  107 -O and inner cable  107 -I engage spiral cone  162 . The of decreased distance “D” results in a lower gear ratio. Movement of pedals  103  thus results in smaller rotations of spiral cones  162  and thus smaller rotations of load  180 . Changes to a lower gear also takes place on the return cycle as for the changes to a higher gear described above. 
     Reference is now made to  FIGS. 3A-3T  that schematically illustrate exemplary embodiments of operation of an exemplary human powered linear drive system (of an exemplary human powered device being a bicycle).  FIG. 3A  shows a bicycle  300  adapted to use the linear drive system  100  of the present disclosure. In use, pedals  103  are pushed alternately vertically downwards to drive load  180  which in this embodiment is the rear wheel of the bicycle  300 . Linear drive system functions as described above with reference to  FIGS. 2A-2J . In some embodiments, gear selectors  146 A and  146 B are positioned on the handlebars  302  of bicycle  300 . In some embodiments, drive assembly enclosures  101  are not parallel with one another such as shown in  FIG. 3A . The relative angle of drive assembly enclosures  101 A and  101 B is adjusted by removing locking pin  166  ( FIG. 3B ), swiveling the drive enclosure  101 , and then replacing locking pin  166  into the chosen locking slot  167 . 
     Linear drive system  100  is mounted onto bicycle  300  or another platform by attachment plate  106  ( FIG. 3B ). Spiral cone mounts  157  ( FIG. 3M ) mount spiral cone assembly  160  onto the inside of drive assembly enclosure  101 .  FIG. 3K  (described further below) shows only one of spiral cone mounts  157 A in order to simplify  FIG. 3M .  FIG. 3B  shows drive assembly enclosures  101  positioned parallel to one another. Pedal bars  103  are fixedly attached to gear assembly enclosures  122  ( FIG. 3C ) which are positioned inside drive assembly enclosures  101  so as to move when pushed by pedals  103 . Pedal slots  118  ( FIG. 3B ) formed in the sides of drive assembly enclosures  101  guide the movement of pedal  103  within the scope of movement as indicated by arrows  117 . Pedal locking pins  104  lock the bar of the pedal onto gear assembly enclosures  122 . 
     Reference is made to  FIG. 3C  which shows a semi-cutaway drawing of system  100 . Gear assembly  120 B is shown within gear assembly enclosure  122 B positioned upon the bottom inner surface of drive assembly enclosure  101 B. For a sake of brevity, gear assembly  120 A is shown without gear assembly enclosure  122 A and without drive assembly enclosure  101 A. Gear assembly enclosure  122  is mounted and moves within drive assembly enclosure  101 . Gear assembly enclosure  122  includes a plurality of roller wheels  119  mounted on the outer surface of gear assembly enclosure  122  to reduce friction of movement while the gear assembly enclosure  122  moves back and forth along drive assembly enclosure  101 B. 
     Drive cable  107  is attached at its ends to spiral cone  162  as shown in  FIGS. 2F and 2G . Cable  107  extends from a first winding group of spiral cone  162  and passes over gear assembly  120  before winding around drive roller  105 . Cable  107  then passes through gear assembly  120  (see  FIG. 2H ) for shifting of position (and changing gear), when necessary, as described with reference to  FIGS. 2A-2G , and then extends back to the other winding of the same spiral cone  162 . During normal operation, at times when no gear change takes place, cable pulley wheel  138  is adapted to lock into cable  107 , and in fact to lock into gear assembly  120  such that movement of the gear assembly  120 , such as by pushing on pedal  103 , results in pulling of a first side of cable  107  and unwinding cable from one of the winding groups of spiral cone  162 , rotation of the spiral cone, and winding on the other winding group of the spiral cone  162 . 
     Drive rollers  105  are mounted on drive roller axle  111  which is mounted in drive assembly enclosures  101  through drive roller mounting slot  112  ( FIG. 3B ). It should be appreciated that changes to R I  and R O  due to gear changes result in changes to the amount of cable  107  that runs through gear assembly  120  potentially resulting in slack on cable  107 . More specifically, there may be a slight difference between the length of the cable portion which is “taken” from one of the winding groups, and between the respective portion which is “given” to the other winding group of a same spiral cone. As shown in  FIG. 3B , drive roller mounting slot  112  is oblong in shape enabling slight movement of drive roller axle  111  to absorb slack of cable  107  caused by gear changes. Throttle spring  109  ( FIG. 3C ) tensions drive cable  107  for removing slack by pulling on drive roller axle  111  to which it is attached. Throttle spring  109  is mounted on one end to drive assembly enclosure  101  and on an opposite end to drive roller axle  111 . 
     The gear assembly  120  of the invention operates in four operational states, as follows:
         a. Normal State: The normal state is the state of operation during which the gear operates most of the time. During the normal state cable  107  is locked to the gear assembly  120 , while there is no rotation of the gear pullies  138  and  142 , nor shift of cable along these pullies. The normal state in fact spans both the times when the gear assembly slides back and forth along the drive assembly enclosure  101 , or when the apparatus is stationary.   b. Gear set-up state: The gear set-up state may take place substantially any time during the normal operation of the apparatus. The gear setting is initiated by the user, who adjusts a gear selector  146 , to define a level of gear change request.   c. Gear changing state: The gear changing state preferably takes place anytime during the return cycle when the driving cable  107  is relatively loose (i.e., without tension). A mechanism is provided at a specific location along the route of the gear assembly in order to initiate the gear change. Typically, the process of the gear change lasts up to 1 second. During the gear changing state the location of the gear assembly  120  along cable  107  changes, either towards the outer winding group  123 , or towards the inner winding group  124 . As will be elaborated hereinafter, the gear change state involves rotation of pully  138  either clockwise or counterclockwise to advance cable  107  either forward or backward, during the gear change. Typically, the setting of a gear change remains as long as the user does not initiate a reset, so a gear change cycle may repeat for a same setting several consecutive return cycles.   d. Reset: When the user finds that a satisfactory gear rate has been reached, he may reset the setting of the gear assembly, such that no further gear changes will occur (until the user will initiate a next gear set-up state. The reset is performed within a fraction of a second. The reset state is the operational state which follows a global mode of the forward/backward cable shift mechanism  161  (see next paragraph).       

     It should be noted, and will be elaborated hereinafter, that each of the upper and lower set-up mechanisms  227  includes at least the gear change cable  230 , gear cable conduit  232 , guide plate  212 , push teeth  220 , push teeth pins  222 , local reset pin  241 , and local reset tooth  240 . 
       FIG. 3U  illustrates in a block diagram form the structure of the gear assembly  120  (only the “A” side of the gear mechanism is shown, the “B” side is identical). “A” drive cable in ( 107 -I), coming from the inner winding group  124  passes through a forward/backward cable shift mechanism  161 , and leaves the gear assembly  120 A at “A” drive cable out ( 107 A-O). In addition, a cable shift rate (i.e., amount of gear change), either forward or backward, is defined by the user at selector  146 A, and conveyed to the gear assembly selectively by either the upper shift cable  230 U or by the lower shift cable  230 L, respectively. The forward/backward cable shift mechanism  161  operates in one of four modes: (a) “lock mode”: during the normal state of the gear assembly (as discussed above), a brakes mechanism  140 A locks cable  107  to the gear assembly  120  ( FIG. 3D ); (b) “shift mode”: during a gear changing state, the brake mechanism  140 A releases the lock, allowing the forward/backward cable shift mechanism  161  to shift cable  107  passing through it, therefore to change the relative position of the gear assembly  120  along cable  107 ; the shift is performed by mechanism  161  either forward (to a rate as conveyed by the “upper” set-up mechanism  227 U), or backward (to a rate as conveyed by the “lower” set-up mechanism  227 L), and then the forward/backward cable shift mechanism  161  returns to a “lock mode” at the shifted position. As noted, the shift rate definition is made by use of selector  146 A, and the selection is performed during the normal state of operation of the gear assembly  120 A; and (c) “global reset mode”: During the global reset mode, the “lower” set-up mechanism  227 L or the “upper” set-up mechanism  227 U, whichever is relevant, returns to its initial state of zero-shift, so no gear change will be performed in a future return cycle (unless another future change is defined by the user at selector  146 A) Preferably, as long as no reset is performed by the user (i.e., release of the tension in either the upper shift cable U 230  or the lower shift cable  230 L), the “lower” or “upper” set-up mechanism  227  remains in its previous gear-change definition, therefore, in that case a gear change state is initiated each consecutive return cycle of drive cable  107 , continuing to advance the cable at a rate, as defined. Only upon a global reset, the previously defined “lower” or “upper” set-up mechanism  227  resets, thereby terminating any further shift (backward or forward) of cable  107 ; and (d) “local reset mode”: As noted, when a specific set-up is defined, a definition is made with respect to the intensity of gear change during each return cycle. Therefore, after each gear change which is performed during a single return cycle, a local reset is performed to return the mechanism (still with a same set-up definition) to its previous status, such that it will be ready to perform the next gear change (with a same set-up) during the next return cycle. 
     Reference is now made to  FIGS. 3D-3H  showing the structure of gear assembly  120 . Gear assembly  120  is mounted inside gear assembly enclosure  122 , which in turn alternately moves back and forth to the drive direction D and the return direction R, as indicated by arrows  169  ( FIG. 3D ). As described above, two gear assemblies are provided as part of system  100 , one for each pedal  103 . Each gear assembly  120  includes two primary wheels and a dual gear changing mechanism as described further below. The two primary wheels are cable flip wheel  142  and cable pulley wheel  138 . Cable flip wheel  142  is mounted on flip wheel axle  143  which is attached to gear assembly enclosure  122 . Cable flip wheel  142  is grooved around its perimeter to accommodate cable  107  wound around it. Cable pulley wheel  138  is fixedly mounted on gear axle cylinder  132 . Gear axle cylinder  132  fits over and freely rotates around main gear axle  130 . Cable pulley wheel  138  is also grooved around its perimeter to accommodate cable  107  wound around it. 
     Gear assembly  120  is adapted to rotate pulley wheel  138  in either direction so as to shift the cable  107 -O on the pully either towards the outer winding  123  or away from it, therefore to either increase the amount of windings of cable  107  within the outer winding group, or to decrease it, thereby to change the gear ratio. 
     As also shown in  FIG. 3D , three additional wheels are fixedly mounted onto gear axle cylinder  132 : lower shift gear wheel  137 , upper shift gear wheel  135  and brake wheel  133 . Lower shift gear wheel  137  and upper shift gear wheel  135  interact respectively with the dual gear changing mechanism  125 L and  125 U to rotate lower shift gear wheel  137  and upper shift gear wheel  135  to thereby rotate pulley wheel  138  in either direction (depending on whether upper  125 U or lower  125 L gear changing mechanisms are used), to thereby either shift cable  107  from the outer winding group  123  to the inner winding group  124 , or vice versa, i.e., from the inner winding group  124  to the outer winding group  123 . 
     With a particular reference to  FIGS. 3D, 3T, and 3V , static sloping surface  139  is positioned between lower shift gear wheel  137  and sliding sloping surface  134 . The sliding sloping surface in fact slides slightly together with axle  130  such that surface  134   a  moves relative to surface  139   a  (towards its narrower profile) in order to transfer from a lock mode to a shift mode. Static sloping surface  139  is sloped on the side adjacent to sliding sloping surface  134  which has a slope at a complementary angle. Upper and lower protrusions  134   c  and  134   d  maintain the relative position between the two surfaces, and ensure a proper sliding. Static sloping surface  139  is rigidly mounted to gear assembly enclosure  122 . The pully wheel  138  is divided (“cut”) into two separate portions  138   a  and  138   b , while the “cutting” direction is perpendicular to axle  130 . Moreover, the half portion  138   b  of pully wheel  138  which is remote from the static sloping surface  139  is fixedly attached to gear axle cylinder  132 , while the opposite portion  138   a  of pully  138  (namely, the portion which is closer to static sloping surface  139 ) is loose on gear axle cylinder  132 . During the lock mode of the cable shift mechanism  161 , the sliding sloping surface  134 , facing at a wider profile of surface  139 , presses against the “loose” portion  138   a  of pulley wheel  138  (as shown in  FIG. 3T ), to keep cable  107  firmly held in pulley wheel  138 , namely the cable is firmly pressed in between the two internal surfaces  201   a  and  201   b  of pully portions  138   a  and  138   b , respectively. In such a manner, the lock assures that the cable  107  will not slide over the surface of the groove of wheel  138 , particularly when a relatively large force is applied on it during a drive cycle. During a shift from a lock mode to a shift mode of the cable shift mechanism  161 , main gear axle  130  moves in direction F ( FIG. 3T ) within elongated slot  189  (shown in  FIG. 3V ), and sliding sloping surface  134  also moves in direction F (as it is installed loose about axle  130 ), thus reducing (note entirely) the pressure which surface  134  applies on pulley wheel portion  138   a  such that pully  138  becomes free to rotate (if and when a force is applied on it via axle  130 ). Moreover, cable  107  is free to follow the shift of pully  138  during a gear change. Optionally, any other mechanism can be used for locking or unlocking cable  107  in gear assembly  120  and the use of sloping surfaces  134  and  139  should not be considered limiting. The wheels ( 135 ,  137 ,  138 ) mounted on gear axle cylinder  132  are prevented from rotating when gear brake  140  engages with brake wheel  133  (such as shown in  FIGS. 3E, 3F, and 3N-3P ). 
     With a particular reference to  FIG. 3G , each of the two (upper and lower) gear changing mechanisms  125  within each gear assembly  120  includes a guide plate  212  attached to a guide rail  214 , multiple push teeth  220  for engaging with gear wheels  135  and  137 , respectively, and a local reset mechanism which includes a local reset tooth  240  and local reset bearing  242 . Guide rail  214  includes a single channel  215 , while guide plate  212  includes three channels, as will be further elaborated below. Each gear changing mechanism  125  is manipulated by its own gear selector  146  (which is positioned, for example, on the handlebars of the bicycle) that selectively activates one of gear change cables  230  (either a cable of the upper gear changing mechanism  125 U mechanism to higher the gear, or a cable of the lower gear changing mechanism  125 L to lower the gear). Each gear change cable  230  is threaded through gear cable conduit  232  and attached to gear cable mount  234  at a protrusion from guide plate  212 . Cable conduit  232  is rigidly attached to push teeth enclosure  221 . Spring  239  is connected between gear cable mount  234  (at guide plate  212 ) and protrusion  247  at push teeth enclosure  221 . Guide rail  214  ( FIG. 3G ) is rigidly attached to gear enclosure  122  (best shown in  FIG. 3C ), such that there is no relative movement between the guide rail and enclosure  122 . As will be further discussed below, push teeth enclosure  221 , together with the guide plate  212  which is attached to it, is moveable (in a first direction during a shift mode, and in a direction opposite to the first direction during local reset mode) as guided by channel (groove)  215  of the guide rail  214 . Guide plate  212  is further movable with respect to push teeth enclosure  221  (specifically during the gear set-up state), in a manner which will be further described below. 
     As best shown in  FIG. 3H , guide plate  212  includes three channels: push teeth channel  217 , guide plate channel  218 , and local reset pin channel  219 . Guide reset spring  216  (best shown in  FIG. 3I ) is attached on one end to guide rail  214  and on its other end to push teeth enclosure  221  (which, as said, is movable relative to guide rail  214  during the shift mode and during the local reset mode, respectively). The movement of push teeth enclosure  221  relative to guide rail  214  therefore changes the tension on guide reset spring  216 . 
     Multiple push teeth  220  ( FIG. 3J ) are positioned inside push teeth enclosure  221  and, depending on the relative position between push teeth enclosure  221  and guide plate  212 , they can be shifted to stick out of push teeth enclosure  221  as shown in  FIG. 3H . Push teeth pins  222  protrude from push teeth enclosure  221  and engage push teeth channel  217 . In the illustrated embodiment, seven push teeth  220  are shown but it should be appreciated that more or less push teeth may be used depending on the range of gear change options to be provided to a user. 
     Local reset enclosure  245 , which is rigidly attached to push teeth enclosure  221  (or a part thereof), holds local reset tooth  240  which protrudes from the local reset enclosure  245 . Local reset bearing  242  is slidably mounted on local reset enclosure  245 . Local reset pin  241  is also mounted on local reset enclosure  245  and engages reset pin channel  219 . Enclosure channel pins  224  hold push teeth enclosure  221  and local reset enclosure  245  level while moving, by engaging enclosure channel  218 . 
     The structure of each of the teeth  220  and  340  is shown in  FIG. 3J . Each tooth  220  and  340  consists of a base portion  270 , which is held in in its place by either pin  269  (in the case of tooth  240 ) or pin  222  (in the case of tooth  220 ). The tooth is non-symmetric along its longitudinal axis y. The tooth has a ramp surface  271 , and a vertical surface  272 , in order to provide a different reaction to a horizontal force (the term “horizontal” refers specifically relative to the view of  FIG. 3J ) which is applied onto said two surfaces. More specifically, a horizontal force on the vertical surface  272  of the tooth does not change its position, while a horizontal force on the ramp surface  271  will cause upward retraction of the tooth. 
     The amount of a desired gear change (i.e., the intensity of the shift of the location of the gear assembly  120  along cable  107 ) which is performed during each gear changing state is defined during the gear set-up state. Any time when the user wishes to change gear either up or down in one of the left or right units (“A” or “B”), he uses a respective selector unit  146  “A” (for example, at the left of the handlebars) or gear selector unit  146  “B” (for example, at the right of the handlebars) to define the direction and the intensity of the change. Each of the two gear selectors  146  includes three adjusting levers, an up-gear lever, a low-gear lever, and a reset lever. The up-gear lever and the low-gear lever are each configured to pull either the upper shift cable  230 U or the lower shift cable  230 L (see  FIGS. 3G and 3U ). The amount of cable pulling, which is performed during a gear set-up state, defines the intensity of shift which will be performed on the cable drive  107  during each of the following gear change states. The reset lever releases the tension on the respective shift cable, thereby to cause a global reset, as defined above. 
     Reference is now made to  FIGS. 3G and 3H . During the set-up state, when an upper or lower shift cable  230  is pulled against the tension of spring  239 , guide plate  212  is also pulled (in the direction of arrow  250 ) since gear change cable  230  is attached to gear cable mount  234 .  FIG. 3G  shows the status of the gear change mechanism  125  following a global reset, when all of the teeth are at their withdrawn state, i.e., they are all located up within the push teeth enclosure  221 .  FIG. 3H , shows a case when a user has elected to make a relatively average gear change of three teeth  220  by pulling of cable  230 . Starting from the case of  FIG. 3G , as guide channel plate  212  moves in direction  250 , three push teeth pins  222  are guided down by push teeth channel  217 , forcing three respective teeth  220  to descend and protrude from push teeth enclosure  221  (as shown in  FIG. 3H ). Additionally, local reset pin  241  is guided up by local reset pin channel  217 , forcing local reset tooth  240  to protrude out of local reset enclosure  245 . Spring  239  is also tensioned (see  FIG. 3I ) as plate  212  is pulled relative to push teeth enclosure  221 . This completes the set-up state by fixing a relative position between the guide state and the teeth enclosure  221 , and the assembly is now ready for a gear shift which will occur during a next return cycle (the intensity of the shift has been defined by the number of teeth  220  that protrude from push teeth enclosure  221 ). 
     During the gear shift mode, the position of the gear assembly  120  along cable  107  is modified Two separate types protrusions are used to initiate and terminate, respectively, the gear shift mode. More specifically, each of the upper and lower gear change mechanisms  125  is provided with both an initiating protrusion  243  at the internal surface of the stationary drive enclosure  101 , and a terminating protrusion ramp  244  at the internal surface of the moving gear assembly enclosure  122  (see, for example,  FIGS. 3N-3S ). As will be discussed further below, the local reset tooth  240  of the gear change mechanism  125  engages with the initiating protrusion  243  to begin the shift mode, and local reset bearing  242  of the gear change mechanism  125  engages with the terminating ramp  244  to terminate the shift mode. 
     As noted above, in order to change the gear ratio, the location of the gear assembly  120  along cable  107  is shifted, and this shift changes the ratio between the windings in the outer winding group  123  and the windings in the inner winding group  124 . The shifting of the location of the gear assembly  120  along cable  107  is performed during the return cycle, when cable  107  is relatively loose. The shift is performed by first transferring the gear assembly from its lock mode to its shift mode. Then, during the shift mode, the shift of location is carried out by rotating either the upper shift gear wheel  135  or the lower shift gear wheel  137 , each of which in turn rotates cable pulley wheel  138  respectively, either forward or backwards. 
     Gear change mechanism  125  force the rotation of upper shift gear wheel  135  or lower shift gear wheel  137  by causing engagement of push teeth  220  with the teeth on upper shift gear wheel  135  or lower shift gear wheel  137 , as defined during the set-up state. 
     As noted, the gear assembly enclosure  122 , with all the components included therein moves back and forth along a route as defined by drive assembly enclosure  101 , during the drive (denoted DR) and return (denoted R) cycles, respectively. As noted, if a gear shift request has been defined during a set-up state, a local reset tooth  240  protrudes out of the local reset enclosure  245 , and in fact it also protrudes out of the gear assembly enclosure  122  (see, for example,  FIGS. 3C and 3F ). In fact, in order to carry out a gear shift, only one of the two local reset teeth  240 , namely either the upper or the lower, protrudes, as respectively defined. If none of the gear teeth  240  protrudes, no gear shift will be performed. 
     During a return cycle, gear assembly enclosure moves in direction R (see  FIGS. 3F and 3N ). If, for example, the set-up state has defined a protrusion of three push teeth  220 , the first three push teeth  220  protrude out of push teeth enclosure  221 . In addition, one of the two local reset tooth  240  (either  240 U or  240 L) protrudes out of both the local reset enclosure  245 , and the gear assembly enclosure  122  (see  FIG. 3C  and  FIG. 3O ). 
       FIG. 3N  shows the gear assembly just before the set-up. It can be seen that the guide plate  212 U is at its extreme location to the left relative to push teeth enclosure  221 , none of push teeth  220  protrudes from teeth enclosure  221 , nor the reset tooth protrudes from the reset enclosure  245 .  FIG. 3O  shows the gear mechanism just after the set-up. It can be seen that the guide plate  212 U is somewhat pulled to the right relative to the state of  FIG. 3N  (by cable  230 U—not shown), therefore three teeth  220  protrude from teeth enclosure  221 , and the local reset tooth  240  protrudes from the reset enclosure  245  and out of the gear assembly enclosure  122  (through an opening in the enclosure). At this stage the forward/backward cable shift mechanism  161  is still in the lock mode, where the brake  140  engages the brake wheel  133 , and the sliding sloping surface  134  also presses portion  138   a  of pully  138  to lock cable  107  ( FIG. 3V ). The set-up may occur either during a movement of the gear assembly to the DR direction or to the R direction. As long as the set-up occurs during a movement to the DR direction, nothing happens, until reversing the direction towards the R direction. 
     As shown in  FIG. 3P , the gear assembly enclosure  122  is pulled to the R direction by reciprocal motion cable  193  along drive assembly enclosure  101  until local reset tooth  240  intercepts with the initiating protrusion  243  on drive assembly enclosure  101 . This interception transfers the gear changing mechanism  125  from the gear set-up state to the gear changing state. It can be seen the frontal protruding tooth  220  just begins to engage the teeth of the upper shift gear  135 . Up to this stage the push teeth enclosure  221  remains at a same stationary location relative to the gear assembly enclosure  122  (i.e., same as in  FIG. 3O ). Until the time when the frontal protruding push teeth  220  engages with upper shift gear wheel  135 , upper shift gear wheel is prevented from rotating by gear brake  140 . Upon engagement, first of push teeth  220  pushes on upper shift gear wheel  135  forcing main gear axle  130 , gear axle cylinder  132  and the wheels ( 135 ,  137 ,  138 ,  133 ) mounted on gear axle cylinder  132  to move in a direction “B”, pushing the brake wheel  133  away from gear brake  140 . Moreover, the movement to of axle  130  to direction B releases the pressure which surface  134  applies on pulley wheel portion  138   a  such that pully  138  becomes free to rotate (see that the position of axle  130  has been displaced to direction relative to its previous location in  FIG. 3O ). Cable  107  is now free to follow the rotation of pully  138  during a gear change. Gear axle cylinder  132  is now also free to rotate. 
     As shown in  FIG. 3Q , gear assembly enclosure  122  continues to be pulled along drive assembly enclosure  101  by reciprocal motion cable  193  to direction R. The three push teeth  220  that protrude outside of push teeth enclosure  221  now engage with upper shift gear wheel  135 . As can also be seen, the front  212   a  of the guide plate  212  is closer to the edge  122   a  of the gear assembly enclosure  122  relative to its previous location in  FIG. 3P . Teeth  220  now force upper shift gear wheel  135  to rotate in a direction “C”, resulting in rotation of cable pulley wheel  138  and a shift of cable  107 , and advancement of the location of the gear assembly  12   o  along cable  107 , as desired. 
     As shown in  FIG. 3R , upon continuation of the relative displacement of guide plate  212 , push teeth enclosure  221 , and the local reset enclosure  245  relative to gear assembly enclosure  122 , teeth  220  have now completed their engagement with the shift wheel  135  and therefore, the rotation of the wheel terminates. Guide reset spring  216  extends at this stage to its full length, and the front  212   a  of the guide plate  212  is out of the edge  122   a  of the gear assembly enclosure  122 . At this stage, the rate of rotation that shift wheel  135  has made is proportional to the number of protruding teeth  220 , as was defined during the set-up. Teeth  220  continue to remain protruding. When the reset bearing  242  engages the termination ramp  244  (as shown), the ramp pushes down the bearing, and therefore the reset tooth  240  against its own spring  223  (see  FIG. 3J ), thereby releasing the reset  240  tooth from its engagement with the initiating protrusion  243 . This release results in a transfer of the gear assembly to a local reset mode. As shown in  FIG. 3S , the spring  216  has reset the gear assembly  120  by returning the push teeth enclosure  221 , the guide plate  212 , and the local reset enclosure  245  to their original location within the gear assembly enclosure  122  (same relative location as in  FIG. 3O ). The relative position between the guide plate  212  and the push teeth enclosure  221  still remain unchanged, namely, as previously defined in the set-up mode. It should be noted that during this local reset, the ramp surface  271  (see  FIG. 3J ) of each protruding teeth  220  engages with the teeth of the shift gear wheel  135  in a “reverse” direction, where the force which is applied on each protruding tooth causes a temporary withdrawal of the protruding tooth return to of it to its previously protruding state. Therefore, this local reset does not involve any rotation of the shift gear wheel  135 . 
     As a result of the change of location of the gear assembly along cable  107 , a gear change has been performed. The gear change intensity has been defined in the set-up mode. Following the gear change and the local reset, those protruding teeth  220  remain in their protruding state. Therefore, a gear change of a same intensity, as defined (either up or down), will follow each return cycle, until a global reset by the user by reset by means of gear selector  146 . The global reset is performed when the user feels that a sufficient cable  107  has passed from one winding group of spiral cone  162  to the other winding group (outer to inner or vice versa). 
     It should therefore be appreciated that the transmission mechanism as disclosed herein is semi-automatic, requiring a user only an up-gear or down-gear selection and choice of the level of change (effected by the number of push teeth  220  selected) using gear selectors  146 . Once the user has made the choice, the gear change continually takes place on every return cycle until global reset allowing the user to feel when the correct gear ratio has been reached. Thus, a user does not have to select a specific gear, only provide the selection of change required and continue pedaling until the effort required seems appropriate. Moreover, the user can define a different gear rate for the two “A” and “B” units. 
     As shown in  FIGS. 3K-3M , spiral cone assembly  160  includes two spiral cones  162 A and  162 B fixedly attached to, respectively, a counterclockwise ratchet  152  and a clockwise ratchet  151 , where ratchets  151  and  152  are mounted on cone axle  164 . Counterclockwise ratchet  152  enables clockwise motion but eliminates counterclockwise motion by providing a free wheel structure. Clockwise ratchet  151  enables counterclockwise motion but eliminates clockwise motion by providing a free wheel structure. In some embodiments, spiral cones  162  have between 9 and 15 spiral layers. 
     As described above with reference to  FIGS. 2A-2G , spiral cones  162  alternately drive primary load wheel  150  ( FIG. 3L ) which is attached to load chain  108  to drive load chain  108  which in turn drives load  180 . The direction of rotation of load  180  can be altered by means of rotation switch  153  by moving rotation switch handle  154 . Rotation switch  153  moves rotation switch cable  155  that alters the engagement of rotation switch gears  156  with primary load wheel  150  to thereby cause primary load wheel  150  to be driven in a clockwise or counterclockwise direction as required to therefore change the direction of rotation of load  180 . 
     Reference is now made to  FIGS. 4A-4N  that schematically illustrate exemplary embodiments of the operation of an exemplary human powered linear drive system (of an exemplary human powered device being a bicycle).  FIGS. 4A and 4B  show alternative embodiments of bicycles humanly powered by linear drive system  400 . Bicycle  490  (of  FIG. 4A ) uses a chain drive alternative and bicycle  494  ( FIG. 4B ) uses a cable drive alternative. The reference number  407  is used herein to refer to both a drive cable and drive chain and the term cable  407  should be understood to also describe chain  407  and cable  407 . Throughout this application the terms “cable” and “chain” may be used interchangeably, with some required modifications. In some embodiments, gear selectors  446  are positioned on the handlebars  492  of bicycles  490  and  494 . 
     In use, pedals  403 A and  403 D are pushed alternately vertically downwards to move chain  407  ( FIG. 4C ) to rotate spiral cones  462  to drive load  180  which in this embodiment is the rear wheel of bicycles  490  and  494 . Pedals  403  are mounted on pedal bars  402 . Pedal bars  402  are fixedly attached to gear assembly enclosures  422 . Pedal bars  402  pivot around rear pedal pivot  470 . 
     Linear drive system  400  functions as shown in  FIGS. 4C-4E .  FIGS. 4C-4E  show only one side of the drive mechanism of system  400  and it should be appreciated that a second side functions in a symmetrical manner. In  FIG. 4C , pedal bar  402  is shown in a starting position. Cable  407  is attached to spiral cone  462  in the same way that cable  107  is attached to spiral cone  162  (see  FIGS. 2F-2G ). Alternatively, chain  407  is wound through gear assembly  420  and spiral cone  462  as shown in  FIGS. 4F-4G . As shown in  FIGS. 4C and 4D , chain  407  is routed from spiral cone  462  over upper drive roller  405 U, through gear assembly  420 , around lower drive roller  405 L, and then back to spiral cone  462 . Within gear assembly  420 , chain  407  is routed around cable flip wheel  442  and then over cable pulley wheel  438 . As before, the gear mechanism is adapted to shift the position of chain  407  around spiral cone  462  to thereby alter the drive ratio (herein referred to as a “gear change”). 
     As shown in  FIGS. 4D and 4E , pedal bar  402  is pushed downward such as by a rider of a bicycle pushing on pedal  403 . Gear assembly enclosure  422  being attached to pedal bar  402  is thus also pushed downwards and gear assembly  420 , being included within gear assembly enclosure  422  ( FIG. 4N ) also moves downwards. Chain  407  being locked into gear assembly  420  is pulled downward and in turn pulls on spiral cone  462  causing rotation of spiral cone  462 . In the illustration of  FIGS. 4D and 4E , spiral cone  462  rotates in a clockwise direction but it should be appreciated that this is for illustration only and system  400  may cause rotation or movement in any desired direction. The rotation of spiral cone  462  results in the direct rotation of load  480  here shown as the wheel of a bicycle that is mounted on the same axle  464  as spiral cone  462 . 
     The mechanism for gear change is described with reference to  FIGS. 4H-4L . As shown the gear mechanism rotates upper shift gear wheel  435  or lower shift gear wheel  437  to thereby rotate pulley wheel  438  and shift the position of chain  107  on pulley wheel  438  and thus also on spiral cone  462 . Other means of shifting chain  107  are contemplated and the description herein should not be considered limiting. A gear selector  446  is provided for each side of bicycles  490  or  494  each connected to two gear change cables  530  (one cable for changing up and one for changing down). Optionally a single selector  446  changes gears for both sides of bicycles  490  or  494 . 
     Gear change cables  530  are connected to gear swivels  550  such that pulling on gear change cable  530  results in movement of gear swivel  550  such as shown in  FIG. 4L . Gear swivel pin  552  moves backwards and forwards within swivel slot  553  as pedal bar  402  moves up and down. Gear swivel pin is attached to gear change cable extension  531  which in turn is attached to push teeth  520 . Push teeth  520  are mounted in push teeth enclosure  521 . Upper push teeth  520 U rotate upper shift gear wheel  435  and lower push teeth  520 L rotate lower shift gear wheel  435  to cause a gear shift up or down. 
     When gear swivel  550  is pulled forward by gear change cable  530  such as shown in  FIG. 4L , gear swivel pin is pulled forward as pedal bar  402  moves up and down. Gear swivel pin thus pulls on gear change cable extension  531  thereby pulling push teeth  420  which push one of upper gear wheel  435  or lower gear wheel  437  to thereby rotate pulley wheel  438  ( FIGS. 4H and 41 ) and shift the position of chain  407  on spiral cone  462 . Use of the gear swivel  550  mechanism enables gear changes powered by the movement of pedal bars  402 . The amount of cable extension  531  that is pulled will determine the number of teeth  420  that engage upper gear wheel  435  or lower gear wheel  437  and thereby the level of gear change (incremental or acute depending on the number of teeth  420  engaged). Gear changes will continue on every cycle of pedal bar  402  as long as gear swivel  550  is pulled forward by gear change cable  530 , thus until the gear selection is cancelled by the user or by a gear cancel mechanism (not shown). Thus, the mechanism for gear change as described with reference to  FIGS. 4H-4L  is semi-automatic (a user selects gear change direction and level but gear change happens while pedaling) and continuous (takes place on every pedal cycle). 
       FIGS. 4M and 4N  illustrate an embodiment of a reciprocal (linear) motion pulley mechanism for pulling up a pedal  403 A on a first side when a pedal  403 B on a second side is pushed down and vice versa.  FIG. 4N  shows only those parts that are part of the mechanism. Gear assembly enclosures  422 A and  422 B are attached to reciprocal motion cable  483  using cable attachments  484 . Cable  483  is looped over reciprocal motion pulley wheels  481 . Reciprocal motion pulley wheels  481  are mounted on reciprocal motion mount  482  which in turn is mounted onto load frame  490  (or  494 ). In the illustrated embodiments load frames  490 / 494  are bicycle frames. 
     In use, when pedal  403 A is pushed down, gear assembly enclosure  422 A is pulled down, pulling on reciprocal motion cable  483 . Reciprocal motion cable  483  thus pulls gear assembly enclosure  422 B upwards along with pedal  403 B. Conversely, when pedal  403 B is pushed down, gear assembly enclosure  422 B is pulled down, pulling on reciprocal motion cable  483 . Reciprocal motion cable  483  thus pulls gear assembly enclosure  422 A upwards along with pedal  403 B. When pedal  403 A is pushed downwards, pedal  403 B moves upwards. As with system  100 , a ratchet mechanism within spiral cones  462  prevents the rotation of spiral cone  462 B from causing rotation of load  480 . Thus, in the embodiment of  FIGS. 4A-4N  only downward motion of pedals  403  causes movement of load  480 . 
     Reference is now made to  FIG. 5  that schematically illustrates an exemplary embodiment of an exemplary human powered vehicle (a tricycle) having an exemplary human powered linear drive system. As shown therein, tricycle  500  includes, and is humanly powered using, exemplary linear drive system  100  ( FIGS. 2A-2E ) as described hereinabove, which, in turn, is operated via reciprocal (linear) arm movements of a rider  501  of tricycle  500 . Movement of handles  503  (outwardly extending from drive assembly enclosure  505 ) causes rotation of drive chain  508  that drives tricycle wheel  510 . In exemplary embodiments of operating tricycle  500 , the (linear) pull cycle is active and the reverse (linear) push cycle is passive. 
     Reference is now made to  FIGS. 6A-6B  that schematically illustrate an exemplary embodiment of an exemplary water-based (marine type) vehicle or vessel (a boat) having several exemplary human powered devices employing exemplary human powered linear drive systems. As shown therein, yacht or boat  600  includes, and is humanly powered using, several of the exemplary linear drive system  100  ( FIGS. 2A-2E ) as described hereinabove, via translating reciprocal (linear) movement into power for effecting movements of, and performing work by, various parts of yacht or boat  690 . In exemplary embodiments, linear drive system  100 - 1  is humanly operated and used to rotate propeller  602  for propulsion of yacht or boat  690 . In exemplary embodiments, linear drive system  100 - 2  is humanly operated and used to convert reciprocal (linear) motion into power for raising and lowering of main sail  604 . In exemplary embodiments, linear drive system  100 - 3  is humanly operated and used to convert reciprocal (linear) motion into power for raising and lowering of a load  606  held by crane  608 . 
     Each of the following terms written in singular grammatical form: ‘a’, ‘an’, and ‘the’, as used herein, means ‘at least one’, or ‘one or more’. Use of the phrase ‘one or more’ herein does not alter this intended meaning of ‘a’, ‘an’, or ‘the’. Accordingly, the terms ‘a’, ‘an’, and ‘the’, as used herein, may also refer to, and encompass, a plurality of the stated entity or object, unless otherwise specifically defined or stated herein, or, unless the context clearly dictates otherwise. For example, the phrases: ‘a unit’, ‘a device’, ‘an assembly’, ‘a mechanism’, ‘a component’, ‘an element’, and ‘a step or procedure’, as used herein, may also refer to, and encompass, a plurality of units, a plurality of devices, a plurality of assemblies, a plurality of mechanisms, a plurality of components, a plurality of elements, and, a plurality of steps or procedures, respectively. 
     Each of the following terms: ‘includes’, ‘including’, ‘has’, ‘having’, ‘comprises’, and ‘comprising’, and, their linguistic/grammatical variants, derivatives, or/and conjugates, as used herein, means ‘including, but not limited to’, and is to be taken as specifying the stated component(s), feature(s), characteristic(s), parameter(s), integer(s), or step(s), and does not preclude addition of one or more additional component(s), feature(s), characteristic(s), parameter(s), integer(s), step(s), or groups thereof. Each of these terms is considered equivalent in meaning to the phrase ‘consisting essentially of’. 
     The term ‘method’, as used herein, refers to a single step, procedure, manner, means, or/and technique, or a sequence, set, or group of two or more steps, procedures, manners, means, or/and techniques, for accomplishing or achieving a given task or action. Any such herein disclosed method, in a non-limiting manner, may include one or more steps, procedures, manners, means, or/and techniques, that are known or readily developed from one or more steps, procedures, manners, means, or/and techniques, previously taught about by practitioners in the relevant field(s) and art(s) of the herein disclosed invention. In any such herein disclosed method, in a non-limiting manner, the stated or presented sequential order of one or more steps, procedures, manners, means, or/and techniques, is not limited to that specifically stated or presented sequential order, for accomplishing or achieving a given task or action, unless otherwise specifically defined or stated herein, or, unless the context clearly dictates otherwise. Accordingly, in any such herein disclosed method, in a non-limiting manner, there may exist one or more alternative sequential orders of the same steps, procedures, manners, means, or/and techniques, for accomplishing or achieving a same given task or action, while maintaining same or similar meaning and scope of the herein disclosed invention. 
     It is appreciated that certain aspects, characteristics, and features, of the present invention, which are, for clarity, illustratively described in the context of separate embodiments, may also be illustratively described in combination in the context of a single embodiment. Conversely, various aspects, characteristics, and features, of the present invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. 
     Although the present invention has been illustratively described in conjunction with specific exemplary embodiments, and examples thereof, it is evident that many alternatives, modifications, and variations, thereof, will be apparent to those skilled in the art. Accordingly, it is intended that all such alternatives, modifications or/and variations are encompassed by the scope of the appended claims. 
     All publications, patents, or/and patent applications, cited or referred to in this disclosure are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent, or/and patent application, was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed or understood as an admission that such reference represents or corresponds to prior art of the present invention.