Patent Publication Number: US-2021185873-A1

Title: Dual-direction tiller/cultivator

Description:
BACKGROUND 
     Fertile soil is the foundation to any lawn or garden project. Vegetable gardens, planting beds, and grasses need rich, loose, drainable soil to ensure root growth and abundant crops. Successful planting typically involves properly preparing the soil with a cultivator or tiller. Finding the right tiller depends on the soil type, the size of the subject garden, the garden layout, and whether a new garden is being created or whether the soil needs to be tilled in an existing garden. Rear-tine tillers (in which the tines are positioned toward the rear of the machine, for example, between the user and the motor or engine) are helpful for creating gardens in which the soil is tough, or a layer of sod covers the ground. 
     For a rear-tine tiller to perform well, the transmission should be narrow, the center of gravity of the tiller should be as low to the ground as possible while maintaining adequate ground clearance, the tiller should be balanced about the wheel axle front to back, and the tiller should be balanced about the centerline side to side. Existing rear-tine tillers are inadequately balanced and have undesirably high centers of gravity, in part due to their reliance on old transmission and driveline arrangements. 
     For breaking ground, it may be advantageous for the tines to rotate opposite to the rotational direction of the wheels, an arrangement commonly described as “Counter Rotating Tines” (“CRT”). For cultivating already tilled soil, it may be advantageous for the tines to rotate in the same direction as the rotational direction of the wheels (or other rotational propulsion, such as tracks), an arrangement commonly described as “Standard Rotating Tines” (“SRT”). A tiller having both a CRT mode and an SRT mode may be described as having “Dual Direction Tines” (“DDT”), such that a DDT tiller&#39;s tines rotate in either the same direction as, or the opposite direction to, the rotational direction of the wheels, depending on the selected mode. 
     For example, a DDT tiller can counter-rotate the tines (CRT mode) to break sod and to break untilled ground. After the sod is broken, or in previously tilled ground, some tillers may not be sufficiently heavy for the rotational propulsion (wheels) to gain traction sufficient to overcome the force of the counter-rotating tines in CRT mode. Accordingly, a DDT tiller can also rotate the tines in the same direction as the rotational direction of the wheels (SRT mode) to help propel the tiller across the workspace. 
     Conventional DDT tillers may have five general modes of operation, depending on the rotation of the wheels, the rotation of the tines, and whether the tines or the wheels are powered: (1) wheels forward/tines forward; (2) wheels forward/tines reverse; (3) wheels forward/tines neutral (tines not powered); (4) wheels neutral (wheels not powered)/tines neutral (tines not powered); (5) wheels reverse/tines neutral (tines not powered). In order to achieve these modes, conventional DDT tillers require transmissions with many parts, which contribute to conventional DDT tillers being top-heavy and side-heavy. 
     A conventional rear-tine tiller with DDT function positions the heavy and complicated transmission parts in the center of the machine above the tine and wheel-drive sprockets. In other words, the input shaft is at the top, the shifting gears, drive sprockets, and other gears are in the middle, and the driven sprockets and output shafts are on the bottom. This arrangement of power transmission (gearing and shafting) causes the machine to have a high center of gravity because the heavy gear sprockets and housing are on the top of the power transmission pyramid. 
     In an attempt to produce a compact package and minimize material costs of the machine, the engine in a conventional rear-tine tiller with DDT function may be positioned as close as possible to the transmission and wheels. However, placing the engine (more specifically, the engine flywheel) close to the machine&#39;s propulsion wheels may result in balance problems that often are resolved by adding extra weight to balance the machine properly (and weights may be added for other reasons). Additional weight is undesirable as it increases cost and decreases efficiency. 
     Existing rear-tine tillers with DDT function may have a high center of gravity because the transmission center of gravity is high and the engine center of gravity is high, so the tiller is susceptible to tipping. In addition, if a tiller&#39;s weight distribution is such that there is too much weight on the tines, as opposed to the wheels (or other propulsion devices), the tiller may perform poorly in CRT mode due to reduced traction. In SRT mode, the tines of such a tiller will have a tendency to propel the unit forward regardless of the speed of the wheels due to low traction on the wheels. Existing DDT tillers are not only top heavy but are also heavy to the side of the engine flywheel and transmission bulge. Accordingly, while in operation, existing units typically tip toward the flywheel/transmission bulge side. To compensate for this unequal weight distribution, existing DDT tillers include additional weight positioned toward the front of the machine and opposite the transmission bulge. But this additional weight increases cost and complexity. 
     What is needed is a rear-tine tiller with dual-direction tines (DDT function) that overcomes the foregoing issues presented by conventional rear-tine tillers. 
     SUMMARY 
     A driveline assembly for agricultural equipment, such as a tiller, may include a pair of counter-rotating bevel gears supported on a wheel shaft and rotatable relative to the wheel shaft. The driveline assembly includes a first slider gear movable between a first position in which the first slider gear is engaged with a first bevel gear of the pair of bevel gears, and a second position in which the first slider gear is engaged with a second bevel gear of the pair of bevel gears. When the first slider gear is engaged with the first bevel gear, the first bevel gear becomes operatively connected to a rotatable tine shaft to rotate tines in a first direction. When the first slider gear is engaged with the second bevel gear, the second bevel gear becomes operatively connected to the rotatable tine shaft to rotate the tines in a second direction opposite the first direction. 
     Representative embodiments of the present technology address several problems with conventional tillers. For example, representative embodiments of the present technology lower the center of gravity of the transmission, orient the engine and the transmission to balance the overall tiller from side to side, and position components (such as the high torque gears and flywheel) toward the front of the machine to balance the machine without including the additional weight relied on by conventional tillers. 
     Thus, in some embodiments of the present technology, the centers of gravity of the transmission, the tiller, and the engine are lowered, and the driveline is simplified by making the input shaft axis intersect the wheel shaft axis. 
     In some embodiments of the present technology, the driveline direction is parallel to the engine rather than parallel to the output shaft while also reducing the speed output from the engine. 
     In some embodiments of the present technology, two directions of rotation are gained by utilizing a single bevel pinion contacting two beveled plate gears. 
     In some embodiments of the present technology, the center of gravity of the driveline is lowered and the driveline is simplified by positioning the input shaft axis below the tine and wheel driver sprocket axis. 
     In some embodiments of the present technology, the center of gravity of the driveline is lowered and the driveline is simplified by using the wheel shaft as a plate gear idler shaft. 
     In some embodiments of the present technology, the tiller is balanced side to side by positioning the engine flywheel on the centerline of the machine and keeping the driveline symmetrical about the centerline of the tiller. 
     In some embodiments of the present technology, a bevel gear arrangement is provided wherein a pinion shaft drives one or more beveled plate gears and the shaft on which the beveled plate gears is located does not spin at the same speed as the plate gears, yet is a driven shaft in the same driveline. 
     In some embodiments of the present technology, a bevel gear arrangement is provided, wherein the plate gear rotates in a direction opposite to the direction of the shaft about which it rotates. 
     In some embodiments of the present technology, the rotational (angular) velocity of the shaft supporting the bevel gears is always less than the rotational (angular) velocity of the bevel gears, which idle on the shaft. 
     In some embodiments of the present technology, a shift drum has an enlarged radius relative to a diameter of the shaft that supports it (such as a pivot shaft). For example, the radius of the shift drum may be two or more times the radius of the shaft that supports it, or three or more times the radius of the shaft that supports it. 
     In some embodiments of the present technology, a shift drum is actuated by a lever that is mechanically fastened to the shift drum without relative movement between the lever and the shift drum. 
     Other features and advantages will appear hereinafter. The features described above and below can be used separately or together, or in various combinations of one or more of them. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present technology are better understood with reference to the following drawings. The components in the drawings are not necessarily to scale. Instead, emphasis is placed on clearly illustrating the principles of the present technology. 
       In the drawings, wherein the same reference number indicates the same element throughout the views: 
         FIG. 1  illustrates a schematic top view of a tiller configured in accordance with embodiments of the present technology. 
         FIG. 2  is a schematic side view of a lower portion of the tiller illustrated in  FIG. 1 , depicting a generally low center of gravity of the tiller. 
         FIG. 3  illustrates a schematic side view of a portion of the tiller illustrated in  FIG. 1 . 
         FIG. 4  illustrates a perspective view of the driveline assembly shown in  FIG. 3 . 
         FIG. 5  illustrates an exploded perspective view of the driveline assembly shown in  FIGS. 3 and 4 . 
         FIG. 6  is a schematic bottom view of the tiller illustrated in  FIG. 1 , showing components of the driveline. 
         FIG. 7  is a partially schematic, cross-sectional rear view of the tiller shown in  FIG. 1 . 
         FIG. 8  is a partially schematic view of a portion of the driveline shown in  FIGS. 3-7 , illustrating the drive-mode selector gear having been moved by the wheel selector fork such that the drive-mode selector gear is not engaged with the wheel drive gear. 
         FIG. 9  is a partially schematic perspective view of portions of the driveline shown in  FIGS. 3-7 , positioned in the tiller. 
         FIGS. 10A and 10B  illustrate perspective views of a shift drum configured in accordance with embodiments of the present technology. 
         FIG. 10C  illustrates a side schematic view of the shift drum shown in  FIGS. 10A and 10B . 
         FIG. 11  illustrates a lever attached to a shift drum in accordance with embodiments of the present technology. 
     
    
    
     DETAILED DESCRIPTION 
     The present technology is directed to dual-direction, rear-tine tillers/cultivators (such as rototillers), and associated systems and methods. Various embodiments of the technology will now be described. The following description provides specific details for a thorough understanding and enabling description of these embodiments. One skilled in the art will understand, however, that the invention may be practiced without many of these details. Additionally, some well-known structures or functions, such as structures or functions common to tillers, cultivators, engines, or transmissions, may not be shown or described in detail so as to avoid unnecessarily obscuring the relevant description of the various embodiments. Accordingly, embodiments of the present technology may include additional elements or exclude some of the elements described below with reference to  FIGS. 1-11 , which illustrate examples of the technology. 
     The terminology used in the description presented below is intended to be interpreted in its broadest reasonable manner, even though it is being used in conjunction with a detailed description of certain specific embodiments of the invention. Certain terms may even be emphasized below; however, any terminology intended to be interpreted in any restricted manner will be overtly and specifically defined as such in this detailed description section. 
     Where the context permits, singular or plural terms may also include the plural or singular term, respectively. Moreover, unless the word “or” is expressly limited to mean only a single item exclusive from the other items in a list of two or more items, then the use of “or” in such a list is to be interpreted as including (a) any single item in the list, (b) all of the items in the list, or (c) any combination of items in the list. Further, unless otherwise specified, terms such as “attached” or “connected” are intended to include integral connections, as well as connections between physically separate components. The term “operatively connected” includes direct or indirect connections that facilitate a functional relationship. 
     Specific details of several embodiments of the present technology are described herein with reference to tillers. For convenience, reference may be made to “tillers,” however, for the purposes of implementing embodiments of the present technology, it is understood that cultivators are included in the term “tillers” and are an example of “tillers.” Furthermore, the present technology may be used in other agricultural machines (including machines for gardening or yardwork). For example, the present technology may also be used with other machines that involve rotating implements (tines, reels, or other rotating implements) for stirring soil or other earthen material, or for cutting or grinding objects, such as harvesters, edgers, or other agricultural machines. 
     Turning now to the drawings,  FIG. 1  illustrates a schematic top view of a tiller  100  configured in accordance with embodiments of the present technology. The tiller  100  may have handles  103  for a user to manipulate the tiller, and the handles  103  may have suitable controls for operating various propulsive operations or tilling operations. The tiller  100  may include a number of tines, which may be under a protective shield  104  (to protect a user from the tines or from debris generated by the tines during operation). The tiller  100  includes a motor  105 , which may include a combustion engine or an electric motor, or a combination of combustion engine and electric motor. The motor  105  provides a rotational force to drive the tines and one or more rotational propulsive devices  110 , which may include wheels or tracks. 
     The propulsive devices  110  (which will be referred to as wheels  110  herein for convenience) propel the tiller  100  across a working surface (or allow a user to push the tiller  100  if the wheels  110  are in an unpowered neutral mode) while the tines operate to cultivate, till, or perform other functions. A wheel shaft  115  may form the wheel axis to rotate the wheels  110 . The wheel shaft  115  may facilitate rotation of the wheels  110  at the same speed and in the same direction. In some embodiments, the wheel shaft  115  may include a continuous shaft (for example, a shaft formed from multiple pieces fixed together to form a continuous shaft, or a single integral shaft) extending from one wheel  110  to the other wheel  110 . For example, the continuous wheel shaft  115  may be formed in multiple pieces fixed together such that the pieces (and the wheels) rotate together (at the same speed) and do not rotate relative to each other, or the continuous wheel shaft  115  may be formed with a single integral shaft such that the wheels rotate together (at the same speed) and do not rotate relative to each other. 
     A tine shaft  120  may carry or support the tines to rotate the tines thereon. The motor  105  may have an output shaft  125  that is suitably connected to a driveline input shaft  130  to provide rotational force to the driveline input shaft  130 . The driveline input shaft  130  provides rotation to the various mechanical components (gears, shafts, etc.) that are operatively connected with one another to rotate the wheels  110  and the tines to propel the tiller  100  and to perform the tilling/cultivating functions. In some embodiments, as illustrated, the tiller  100  may be a rear-tine tiller, which generally means that the tines are positioned toward the user (rear) side  132  of the tiller  100 , for example, between the user and the wheels  110 . 
     According to embodiments of the present technology, the tiller  100  may be generally weight-balanced from side to side by positioning components along a centerline  135  or symmetrically relative to the centerline  135 . For example, the motor  105  may include a flywheel  140  positioned so that its rotational axis is parallel to the centerline  135  and positioned on, above, or below the centerline  135 . The tiller  100  may be generally weight-balanced between the rear side  132  and the front (forward) side  134  about the wheel shaft  115 . 
       FIG. 2  is a schematic side view of the tiller  100  illustrated in  FIG. 1 , depicting a generally low center of gravity  200  of the tiller  100 , resulting in part from positioning several of the driveline components in accordance with embodiments of the present technology. For example, in some embodiments, the rotational axis of the driveline input shaft  130  may intersect the rotational axis of the wheel shaft  115  (which extends in and out of the sheet on which  FIG. 2  is presented), thereby positioning the input shaft axis on the same horizontal plane as the wheel shaft. The center of gravity  200  may also be lowered and positioned closer to the axis of the wheel shaft  115  by positioning a substantial amount (such as most) of the weight of the driveline components on the wheel shaft  115  itself. Positioning most of the weight of the driveline components on the wheel shaft  115  enhances traction at the wheels  110 .  FIG. 2  also illustrates some of the tines  205  carried by the tine shaft  120 . 
     Weight-balancing and low positioning of the center of gravity may be accomplished by various embodiments of the present technology, as described in additional detail below. For example, embodiments of the present technology include a gear arrangement for positioning weight on the tiller wheel shaft  115 , a shift drum for selecting between various modes (e.g., SRT, CRT, etc.) of a DDT tiller, and a lever fixed to the shift drum for providing efficient operation of the shift drum when a user selects the various modes of a DDT tiller configured in accordance with embodiments of the present technology. 
     Gear Arrangement for Positioning Weight on Tiller Wheel Shaft 
       FIG. 3  illustrates a schematic side view of a portion of the tiller  100  illustrated in  FIG. 1 . The motor  105  (which is only partially shown) provides rotational force to the input shaft  130  via any suitable mechanism, such as a direct connection to the motor  105  output, or a geared connection between the motor  105  output and the input shaft  130 , or, as shown, a belt and pulley system  300 . The input shaft  130  may receive rotational force to rotate the input shaft  130  about its axis (see  FIG. 2 ) in a first direction and in a second direction that is opposite the first direction. In some embodiments, the belt and pulley system or other suitable connection between the motor  105  and the input shaft  130  facilitates selection between the first direction and the second direction. In other embodiments, the motor  105  itself may have reversible output. In some embodiments, the source of rotational force applied to the input shaft  130  may not be reversible and may only provide rotational force in one direction to the input shaft  130  (in such a case, the wheels  110  would be powered in only one direction when using the driveline assembly  305  described below). 
     The input shaft  130  is the input to a driveline assembly  305 , according to embodiments of the present technology. The driveline assembly  305  selectively transfers rotational forces from the input shaft  130  to the wheel shaft  115  and the tine shaft  120 . For example, the driveline assembly  305  includes gearing and a movable shift drum  310  that facilitates selection between multiple modes of operation of the tiller  100  (e.g., CRT mode and SRT mode), as explained in additional detail below. In some embodiments, the driveline assembly  305  may be connected to the tine shaft  120  via a chain  315 , a tine input sprocket  320 , and a tine output sprocket  325 . 
       FIG. 4  illustrates a perspective view of the driveline assembly  305  shown in  FIG. 3 .  FIG. 5  illustrates an exploded perspective view of the driveline assembly  305  shown in  FIGS. 3 and 4 . Several of the following paragraphs first describe how the driveline assembly  305  facilitates selection of a direction of rotation of the tines  205 , followed by a description of how the driveline assembly  305  facilitates selection of whether the wheels  110  are provided with rotational force for propulsion. The direction of rotation of the wheels  110  may be determined by selecting the direction of rotation of input to the input shaft  130 . Thus, embodiments of the present technology provide several modes of operation, including CRT mode, SRT mode, neutral tines (no tine rotation), forward propulsion, reverse propulsion, and neutral propulsion (no propulsion). 
     With reference to  FIGS. 4 and 5 , the input shaft  130  is positioned in an input assembly  502 . The input shaft  130  includes or is attached to a beveled input pinion  504 . The input shaft  130  rotates the input pinion  504 . A first bevel gear cluster  506  and a second bevel gear cluster  508  are connected to, and rotatable relative to, the input assembly  502 . Both bevel gear clusters  506 ,  508  idle on the wheel shaft  115 . For purposes of the present disclosure, a first component idling on a second component includes the first component being rotatable around—and rotatable relative to—the second component. According to embodiments of the present technology, the wheel shaft  115  may extend through both bevel gear clusters  506 ,  508  as a single wheel shaft such that both wheels  110  always rotate the same speed and direction, while the bevel gear clusters  506 ,  508  are rotatable relative to the wheel shaft  115 . In some embodiments, the input assembly  502  may include bearings to facilitate rotation of the wheel shaft  115  relative to the input assembly  502  (because the wheel shaft  115  passes through the input assembly  502  and the weight of the input assembly  502  may be at least partially supported on the wheel shaft  115 ). 
     A spacer  510  and a lock nut  511  may help maintain a coaxial relationship between the gear clusters  506 ,  508 , the input assembly  502 , and the wheel shaft  115 . In operation, when the input shaft  130  is rotated (for example, by force from the motor  105 ), the input shaft  130  causes the input pinion  504  to rotate, which, by toothed engagement with the first bevel gear cluster  506 , causes the first bevel gear cluster  506  to rotate. Toothed engagement between the input pinion  504  and the second bevel gear cluster  508  causes the second bevel gear cluster  508  to rotate in a direction opposite the rotational direction of the first bevel gear cluster  506 . Thus, when the input shaft  130  is rotating, the bevel gear clusters  506 ,  508  are rotating in opposite directions (i.e., they are counter-rotating). For convenience in understanding their functions, the first bevel gear cluster  506  may be referenced as the SRT bevel gear cluster  506 , and the second bevel gear cluster  508  may be referenced as the CRT bevel cluster  508 . 
     When the motor  105  is applying rotational force to the input shaft  130 , both bevel gear clusters  506  and  508  rotate (they counter-rotate, in opposite directions relative to each other) via their toothed engagement with the pinion  504 . Whether the SRT bevel gear cluster  506  or the CRT bevel gear cluster  508  is selected to provide rotational force that ultimately rotates the tines is determined by a position of a first slider gear  513  (which may be a spur gear and may be called the tine-mode selector gear  513 ). The tine-mode selector gear  513  is moved along a first splined shaft  515  (which may be called the tine-mode shaft  515 ) by a tine shift fork  517 , which pushes or pulls the tine-mode selector gear  513  along the tine-mode shaft  515  depending on movement of the shift drum  310 , which is described in additional detail below. The tine-mode selector gear  513  is either in a neutral position in which it engages neither bevel gear cluster  506 ,  508 , or in a position in which it engages one of the bevel gear clusters  506 ,  508  via spur gear teeth on the gears  506 ,  508 ,  513 . 
     When the tine-mode selector gear  513  is positioned to engage the SRT bevel gear cluster  506 , the SRT bevel gear cluster  506  rotates the tine-mode selector gear  513 , which rotates the tine-mode shaft  515  (via a splined connection between the tine-mode shaft  515  and the tine-mode selector gear  513 ). A tine-mode intermediate spur gear  519  is fixed to the tine-mode shaft  515  and rotates the same direction as the tine-mode shaft  515 . The tine-mode intermediate spur gear  519  engages a tine input shaft  521  (for example, via a tine input gear  523 ) to rotate the tine input shaft  521 . 
     The tine output sprocket  325  is mounted to the tine input shaft  521 . Thus, the tine output sprocket  325  rotates, and with additional reference to  FIG. 3 , the tine output sprocket  325  drives the chain  315  and the corresponding tine input sprocket  320  to cause the tines  205  to operate. Accordingly, when the tine-mode selector gear  513  is engaged with the SRT bevel gear cluster  506 , the motor  105  is operatively connected to the tines  205 , which operate in SRT mode. The relative sizes and numbers of teeth for the gears in the driveline assembly  305  may be selected such that the tines rotate slowly relative to the motor  105 . Although SRT bevel gear cluster  506  and CRT bevel gear cluster  508  are referred to as such, in some embodiments, aspects of the driveline may be reversed or they may provide functions other than SRT or CRT. 
     In some embodiments, the wheels  110  may rotate at approximately 15 to 25 revolutions per minute (RPM), which may provide a suitable (such as optimal) walking speed for the overall tiller  100 , dependent upon the diameter of the wheels  110 . In other embodiments, the wheels  110  may rotate at higher or lower RPM values. Suitable wheels  110  may have diameters between approximately 12 inches and 16 inches, or other sizes. In some embodiments, a suitable (such as optimal) tine speed is between approximately 150 RPM and 300 RPM, although other speeds may be used, and the optimal speed may depend on the type of tines (for example, thicker and larger tines require more power to move than thinner and smaller tines). In some embodiments, a ratio of the tine speed to the wheel speed may be between 20:1 and 6:1. 
     The tine-mode selector gear  513  may be positioned (via operation of the shift drum  310  and the tine shift fork  517 ) to be disengaged from both bevel gear clusters  506 ,  508 . In such a configuration, the tine-mode intermediate spur gear  519  is not provided with rotational force, so the tines  205  are also not provided with rotational force from the motor  105 , which may be deemed a neutral mode of the tines. 
     When the tine-mode selector gear  513  is positioned to engage the CRT bevel gear cluster  508 , the tine-mode selector gear  513  receives a rotational force opposite the rotational force it receives when in SRT mode (because the CRT bevel gear cluster  508  rotates opposite the SRT bevel gear cluster  506 ). Likewise, the tine-mode shaft  515 , the tine-mode intermediate spur gear  519 , the tine input gear  523 , the tine input shaft  521 , and the tine output sprocket  325  rotate opposite their corresponding rotational directions, thereby causing the chain  315  and the tine input sprocket  320  to rotate opposite from SRT mode. Accordingly, the tine-mode selector gear  513  may be positioned to cause the tines  205  to operate in one direction or another, such as CRT mode or SRT mode, or the tine-mode selector gear  513  may be positioned to disengage from the bevel gear clusters  506 ,  508  such that the tines  205  are not driven (tine-neutral mode). The position of the tine-mode selector gear  513  may be determined by the shift drum  310 , which is described in additional detail below. 
     Several of the foregoing paragraphs describe the manner in which the driveline assembly  305  facilitates selection of the rotational direction of the tines  205 . The driveline assembly  305  also facilitates selection of whether the wheels  110  are driven or undriven (neutral). 
     As described above, the input shaft  130  rotates the first bevel gear cluster  506  (which may be referred to as the SRT bevel gear cluster  506 ). In addition to bevel teeth for engaging the pinion  504  and spur gear teeth  507  for engaging the tine-mode intermediate spur gear  519  to drive the tines in SRT mode, the first bevel gear cluster  506  further includes spur gear teeth  525  for engaging a drive-mode intermediate spur gear  527 . The spur gear teeth  525  may be carried on a separate gear attached to the first bevel gear cluster  506  or they may be integral to the first bevel gear cluster  506 . 
     The drive-mode intermediate spur gear  527  is fixed to a drive-mode shaft  529  and rotates with the drive-mode shaft  529  (for example, via a splined connection or another suitable fixed connection). The drive-mode shaft  529  carries a second slider gear  531  (which may include a spur gear and may be called the drive-mode selector gear  531 ), which also rotates with the drive-mode shaft  529  but may slide along the drive-mode shaft  529 . Accordingly, when the input shaft  130  is rotating, the drive-mode selector gear  531  is also rotating. 
     Whether the wheels  110  are driven or undriven depends, therefore, on the position of the drive-mode selector gear  531  along the drive-mode shaft  529 . The drive-mode selector gear  531  may be positioned to engage a wheel drive gear  533  (which may be in the form of a spur gear) mounted to the wheel shaft  115 , or it may be positioned to disengage from the wheel drive gear  533 . When the drive-mode selector gear  531  engages the wheel drive gear  533 , and the input shaft  130  is receiving input force from the motor, the input force is transferred to the wheel shaft  115  to rotate the wheels to propel the tiller  100 . When the drive-mode selector gear  531  is in a position to be disengaged from the wheel drive gear  533 , the wheels are free to rotate and are not driven (i.e., wheel neutral mode). 
     According to embodiments of the present technology, disengaging the wheel drive gear  533  disengages the wheels  110  from the remainder of the driveline assembly  305 , which results in a tiller  100  that is maneuverable due to minimal rolling resistance and due to the remainder of the driveline assembly  305  not being backdriven when the tiller  100  is moved in the wheel neutral mode. This is in contrast to existing technologies that include a wheel shaft driven by a chain and sprocket—in such existing technologies there is added friction during wheel neutral mode from the chain and sprocket that is avoided by embodiments of the present technology. 
     Whether one or more teeth of the drive-mode selector gear  531  are engaged with one or more teeth of the wheel drive gear  533  depends on the position of the drive-mode selector gear  531 , which is controlled by a wheel selector fork  535  and the shift drum  310  in a manner similar to control of the tine-mode selector gear  513  (described above). Specifically, movement of the shift drum  310  causes the wheel selector fork  535  to slide along a rod  537  (similarly, movement of the shift drum  310  causes the tine shift fork  517  to slide along the rod  537 ). As the wheel selector fork  535  moves, it pushes or pulls the drive-mode selector gear  531  along the drive-mode shaft  529  between a first position in which the motor is operatively connected to the wheels (via the drive-mode selector gear  531  engaging the wheel drive gear  533 ) and a second position in which the motor is disconnected from the wheels. 
     In some embodiments, components of the driveline assembly  305  may be supported by support elements, such that the driveline assembly  305  forms a discrete subassembly that is removable and replaceable within the tiller  100  or installed as a component during manufacture. In other embodiments, components of the driveline assembly  305  may be supported directly by structure of the tiller  100 . 
       FIGS. 4 and 5  illustrate a driveline assembly  305  supported by support elements in the form of bearing blocks  539 ,  541 , although in other embodiments, the bearing blocks  539 ,  541  may be integrated into other components of a tiller  100 , such as a frame or housing. The bearing blocks  539 ,  541  provide bearing surfaces (with or without ball bearing assemblies) for the rotation of several of the rotational components of the driveline assembly  305 , including the tine input shaft  521 , the shift drum  310 , the drive-mode shaft  529 , the tine-mode shaft  515 , and the wheel shaft  115 . The bearing blocks  539 ,  541  may also support components that do not rotate, such as the rod  537 , which may function as a tie rod holding the bearing blocks  539 ,  541  together. For example, threaded nuts  543  may engage threaded ends of the rod  537 . 
       FIG. 6  is a schematic bottom view of the tiller  100  illustrated in  FIG. 1 , showing components of the driveline assembly  305 . With continued reference to  FIGS. 1-6 , the driveline assembly  305  provides a configuration that positions the center of gravity  200  (see  FIG. 2 ) of the tiller  100  above the wheel shaft  115  and closer to the forward (motor) side  134  of the tiller  100 , while using the wheel shaft  115  as a fulcrum point, all of which contributes to generally balanced forward to rearward weight distribution relative to the wheel shaft  115  and improved maneuverability relative to existing technologies. 
     The driveline assembly  305  may also provide reduced weight overall relative to existing configurations (at least in part because the driveline assembly  305  facilitates omission of weights used in existing machines to attempt to balance them), which may reduce manufacturing and shipping costs. According to embodiments of the present technology, most or all of the heaviest parts of the tiller  100  are stacked (i.e., coaxial) on the wheel shaft  115  or are positioned forward in the engine (i.e., the engine&#39;s flywheel  140 ), which enhances the user experience by putting more weight on the traction elements (the propulsion system, such as wheels  110 ) and reducing the weight experienced by the user. 
     Driveline assemblies  305  configured in accordance with embodiments of the present technology may use a single beveled input pinion  504  to drive the bevel gear clusters  506 ,  508 . The dual-gear rotation provided by the bevel gear clusters  506 ,  508  facilitates selection between CRT mode and SRT mode. A unique aspect of driveline assemblies configured in accordance with embodiments of the present technology is that the bevel gear clusters  506 ,  508  idle on the wheel shaft  115  while counter-rotating relative to each other. Arrangements according to the present technology may not include a reversing lay shaft because a reversing lay shaft is unnecessary. 
     Because the bevel gear clusters  506 ,  508  idle on the wheel shaft  115 , the wheel shaft  115  has a variable rotational velocity relative to both bevel gear clusters  506 ,  508 , which may rotate at different speeds or in different directions relative to the wheel shaft  115 . The wheel shaft  115  may rotate at a different (such as slower) rate than either bevel gear cluster  506 ,  508  (for example, due to the gear ratios between the SRT bevel gear cluster  506 , the drive-mode intermediate spur gear  527 , and the drive-mode selector gear  531 ), which contributes to providing a comfortable walking speed for a user while also providing sufficient tilling speed (via the gear ratios in the gear train from the bevel gear clusters  506 ,  508 , depending on which is selected, to the tine output sprocket  325 , via the intermediate connections including the tine-mode selector gear  513 , the tine-mode intermediate spur gear  519 , and the tine input gear  523 ). 
       FIG. 7  is a partially schematic, cross-sectional rear view of the tiller  100  shown in  FIG. 1 . The wheel drive gear  533  may be fastened to the wheel shaft  115  in any manner suitable for facilitating transfer of rotation from the wheel drive gear  533  to the wheel shaft  115 , such as via welding, fasteners, a splined connection, or other suitable manners of attachment. In some embodiments, the bevel gear clusters  506 ,  508  may include optional roller bearings  509  for facilitating idling of the bevel gear clusters  506 ,  508  on the wheel shaft  115  (i.e., rotation of the bevel gear clusters  506 ,  508  relative to the wheel shaft  115 ). 
       FIG. 8  is a partially schematic view of a portion of the driveline assembly  305  shown in  FIGS. 3-7 , illustrating the drive-mode selector gear  531  having been moved by the wheel selector fork  535  such that the drive-mode selector gear  531  is not engaged with the wheel drive gear  533 . In such a configuration, the wheels are in neutral, non-driven mode, and may be free to roll (unpowered). Movement of the tine-mode selector gear  513  relative to the bevel gear clusters  506 ,  508  (to engage or disengage one or the other bevel gear cluster) may be similar to the movement of the drive-mode selector gear  531 . For example, each of the selector gears  531 ,  513  may include circumferential slots or grooves to receive their corresponding forks  535 ,  517 . 
     Shift Drum 
       FIG. 9  is a partially schematic perspective view of portions of the tiller&#39;s driveline assembly  305  shown in  FIGS. 3-7 . In particular,  FIG. 9  shows a representative location of a shift drum  310  within the tiller according to embodiments of the present technology. 
     For context, the sequential shift pattern in existing DDT rear-tine tiller/cultivators uses one shift fork to move one shifting gear into the five different modes of operation described in the background section above. In contrast, in some embodiments of the present technology, two shift forks may be used (one for each slider gear  513 ,  531 ) to facilitate selection of the various operating modes. In addition, positioning a majority of the gears on or near the wheel shaft (which provides several advantages, as described above, such as improving weight and balance of the machine) may result in a need for two shift forks (for example, if a user desires propulsion control in addition to tine control with the same shift handle or other shifting interface). Using two shift forks may necessitate two shift grooves to control the shift forks. 
     Due to packaging constraints outside of the driveline assembly  305 , a user-operable shift lever for controlling modes of a DDT tiller/cultivator may only have space to be movable a small distance from one mode to another (see  FIG. 11 ). Specifically, in some embodiments, there may be only a small area to actuate the shift lever connected to the shift drum  310  to actuate the shift forks  517 ,  535 . A shift drum  310  configured in accordance with embodiments of the present technology facilitates movement among several modes of operation (for example, four modes) while operating the shift lever through a range of approximately 90 degrees or less (i.e., the shifter need only move within a range of a maximum of 90 degrees in some embodiments, or less in other embodiments, to access all modes). In some embodiments, the shift lever may be configured to move through a range of approximately 180 degrees or less. As explained in additional detail above, in some embodiments, the present technology provides reverse wheel movement via reversing the input to the input shaft  130 . 
       FIGS. 10A and 10B  illustrate perspective views of a shift drum  310  configured in accordance with embodiments of the present technology. In contrast with conventional shift drums, which are generally cylindrical and often formed from a solid piece of bar stock or cast or billet material, the shift drum  310  may include a curved sheet portion  1000  (which may be formed with sheet metal) attached to a rod portion  1005  (attached with welding or fasteners, or one or more other suitable attachments). In some embodiments, sheet metal may be bent into a fan shape (for example, not a full cylinder) to form a rounded surface illustrated in  FIGS. 10A and 10B  before or after cutting shift grooves  1010 ,  1012  into the sheet portion  1000 , and the formed sheet portion  1000  may then be attached to the rod portion  1005 . Accordingly, construction of the shift drum  310  may be less complicated and less costly than shift drums in other transmissions, and the shift drum  310  may weigh less than other shift drums. With reference to  FIG. 5 , the rod portion  1005  may be positioned in the bearing blocks  539 ,  541  so the drum  310  pivots about the axis x of the rod portion  1005 . 
     The shift grooves  1010 ,  1012  on the rounded surface of the shift drum  310  engage projections  1015 ,  1020  on the shift forks  535 ,  517  (see  FIG. 5 , for example) by receiving the projections  1015 ,  1020  in the grooves  1010 ,  1012 . For example, the projection  1015  of the wheel selector fork  535  slides within the wheel selector groove  1010 , and the projection  1020  of the tine shift fork  517  slides in the tine selector groove  1012 . As the shift drum  310  rotates about the axis x, the grooves  1010 ,  1012  push the projections  1015 ,  1020 , which cause the forks  535 ,  517  to slide on the rod  537  (see  FIG. 5 , for example), which in turn push the respective gears  531 ,  513  into or out of engagement with their corresponding respective gears  533 ,  508 , and/or  506  (as described above with regard to  FIG. 5 , for example). In some embodiments, the rod portion  1005  of the shift drum  310  may include a flattened surface  1006  or other surface (such as a splined surface) for providing an area or surface for an operating handle to engage with the rod portion  1005  in order to deliver torque to the shift drum  310  to cause it to rotate to change the tiller between modes (in other embodiments, a handle may be attached with welding, adhesive, fasteners, or other suitable means of attachment). 
     In some embodiments, the wheel selector groove  1010  has two functional positions  1025 ,  1030 . For the sake of convenience, transitional positions  1011  between the two functional positions are not explained in detail (the transitional positions  1011  are positions of the projection  1015  between functions, in which the projection  1015  is partially engaged between one or both of the two functional positions or not engaged with either functional position). When the projection  1015  is in a first position  1025 , the drive-mode selector gear  531  is disengaged from the wheel drive gear  533  (see  FIGS. 4, 5 ), and the tiller is in a neutral mode, such that the wheels (via wheel shaft  115 ) do not receive rotational force. When the shift drum  310  is rotated to position the projection  1015  in the longer slot generally indicated by position  1030 , the drive-mode selector gear  531  engages the wheel drive gear  533  to apply rotational force to the wheels. Thus, the wheel selector groove  1010  provides two modes: powered wheels or unpowered (neutral) wheels. 
     In some embodiments, the tine selector groove  1012  has four functional positions  1040 ,  1045 ,  1050 ,  1055 . For the sake of convenience, transitional positions  1035  between each two adjacent main positions are not explained in detail (the transitional positions  1035  are positions of the projection  1020  between functions, in which the projection  1020  is partially engaged between one or both of two adjacent main functional positions or not engaged with any functional position). When the projection  1020  of the tine shift fork  517  is in a first position  1040 , the tine-mode selector gear  513  is disengaged from both bevel gear clusters  506 ,  508 , and the tines are unpowered (a neutral mode). When the drum  310  rotates to slide the projection  1020  into a second position  1045 , the tine-mode selector gear  513  engages the CRT bevel cluster  508  to cause the tines to rotate opposite the direction of the rotation of the wheels (which are powered in this position of the shift drum  310  due to the projection  1015  being in position  1030 ). When the drum  310  rotates to slide the projection  1020  into a third position  1050 , the tine-mode selector gear  513  disengages the CRT bevel cluster  508  and is not engaged with the SRT bevel cluster  506 , such that the tines do not receive rotational force and only the wheels  110  are powered (wheels moving, tines neutral). When the drum  310  rotates to slide the projection  1020  into a fourth position  1055 , the tine-mode selector gear  513  engages the SRT bevel cluster  506  and is not engaged with the CRT bevel cluster  508 , such that the tines rotate the same direction as the wheels (which are powered in this position of the shift drum  310  due to the projection  1015  being in position  1030 ). 
     Accordingly, the shift drum  310  provides four modes as the shift drum  310  rotates and moves the shift forks  535 ,  517 : (1) wheels neutral, tines neutral; (2) wheels powered, tines rotating opposite wheels; (3) wheels powered, tines neutral; (4) wheels powered, tines rotating same direction as wheels. Each mode may be reversed if the input to the input shaft  130  is reversed, as explained above. Thus, the driveline provides DDT functionality for a tiller. 
     Although two grooves are illustrated and have functions and positions described herein, such functions and positions are only representative functions and positions. Shift drums configured in accordance with embodiments of the present technology may include more or fewer grooves with more or fewer positions to manipulate shift forks and gears in other drivelines or transmissions. For example, positions may be reversed to reverse the order of CRT mode or SRT mode, or shift drums may be implemented in machines other than tillers. 
     One consideration for shift drums is the angle between the groove and the axis of rotation. If a groove traverses a surface of a shift drum circumferentially or otherwise perpendicular to the axis of rotation, relatively very little force is required to move the shift drum because the resistance (such as friction) between the groove and the shift fork projection is minimized. Conversely, if a groove is nearly parallel to the axis of rotation of the shift drum, significantly more force is required to rotate the shift drum (making rotation impossible if the groove is aligned with the axis of rotation). Accordingly, grooves that cause the projections to move in directions that are as close as reasonably possible to perpendicular to the axis of rotation are desirable, while still causing movement of the shift forks. 
     One challenge for shift drums is that a relatively high-torque motor often calls for larger gear faces (relative to motors with less torque output), which further calls for larger shift throws between gears. But when shift drums have small circumferences, and the shift forks must move a lot (for example, to traverse a large gear face or several shift positions), the shift grooves must be closer to parallel (“steeper”) with the rotational axis in order to move the shift forks the relatively longer distances. In such circumstances, shifting may require a lot of force to overcome resistance due to the steep shift grooves. Conversely, a large shift drum may be required to reduce the resistance. Large shift drums may be weight and/or space-inefficient. 
     Shift drums configured in accordance with embodiments of the present technology have relatively shallow shift angles, providing less resistance to rotation of the shift drum while moving the shift forks as required. At the same time, shift drums configured in accordance with embodiments of the present technology do not require rotation through large rotation angles (as explained above). 
     Shift drums configured in accordance with embodiments of the present technology accomplish the features of small rotation angles with sufficient movement of shift forks and reduced friction due to their large surface areas, for example. 
       FIG. 10C  illustrates a side schematic view of the shift drum  310 , configured in accordance with embodiments of the present technology. In some embodiments, the shift drum  310  includes an enlarged shift drum radius R relative to the diameter D of the pivot shaft rod portion  1005 . In general, in some embodiments, the circumference of the pivot shaft rod portion  1005  is less than the shift drum  310  radius R. With additional reference to  FIGS. 10A and 10B , such a configuration facilitates large motion of the surface  1060  of the shift drum  310  with relatively little rotation of the pivot shaft rod portion  1005 , which allows a lever (see  FIG. 11 ) to move only a small amount (such as within a range of less than 180 degrees, or less than 90 degrees, as described above in additional detail) while still facilitating movement of the shift forks, because the large motion of the surface  1060  allows for shallower angles of the grooves  1010 ,  1012  (see  FIGS. 10A, 10B ). 
     In a particular example, a shift drum radius R may be 51 mm, while a corresponding pivot shaft  1005  diameter D may be 13 mm, resulting in a circumference of the pivot shaft  1005  of approximately 40.82 mm, which is less than the shift drum radius R of 51.00 mm. Different dimensions may be used, and embodiments of the present technology may implement various relative relationships between the shift drum radius R and the diameter D of the pivot shaft rod portion  1005 . For example, in some embodiments, the shift drum radius R may be equal to or greater than the circumference of the shaft rod portion  1005 . The shift drum radius R may be two or more times (such as three or more times) the radius (D/2) of the shaft rod portion  1005 . For example, with additional reference to  FIG. 10A , the rounded surface of the sheet portion  1000  (i.e., the surface with grooves  1010 ,  1012 ) may extend a radial distance from a pivot axis x of the shift drum  310  that is three or more times a radius of the rod portion  1005 . 
     In general, shift drums configured in accordance with embodiments of the present technology have a large peripheral radius compared to the shaft that supports it, to create a large surface area  1060  with reduced weight and with reduced angular rotation to accomplish shifts of the driveline. Shift drums configured in accordance with embodiments of the present technology provide circumferential travel of the surface  1060  of the shift drum  310  that is sufficient to accomplish four shift modes (via positioning and engagement between the shift drum grooves, such as grooves  1010 ,  1012  and corresponding shift forks, such as forks  535 ,  517 ), while the shift grooves maintain reasonable shift angles to facilitate reasonable shift force. In some embodiments of the present technology, all four shift modes may be accomplished within 90 degrees of rotation of the shift drum, which is operated by an engagement lever connected to the pivot shaft (such as the rod portion  1005 ). In other embodiments, all four shift modes may be accomplished within 180 degrees of rotation of the shift drum. 
     Shift drums configured in accordance with embodiments of the present technology are different from existing shift drums for a variety of reasons. For example, existing shift drums generally need to fit in small spaces, such that they are generally not larger than a few inches in diameter (such as a one-inch radius). If an existing shift drum (such as a motorcycle shift drum) were modified to meet the relative size arrangement of the present technology, the shift drum diameter could potentially be larger than the engine flywheel diameter. The flywheel is typically the largest circular element in an engine, so the engine would be increased in size and weight. Accordingly, embodiments of the present technology help reduce size and weight in the engine and transmission to achieve a balanced tiller/cultivator. Further, a motorcycle shifter incorporates a cylindrical shift drum that rotates nearly 360 degrees (for example, in 60 degree increments for a five-speed motorcycle with neutral), which requires an elaborate mechanism. In contrast, shift drums configured in accordance with embodiments of the present technology may not have a circular cross-section. As explained in additional detail below, embodiments of the present technology simplify a sequential transmission by simplifying the mechanism and reducing the required angle of travel of the engagement lever that manipulates the shift drum  310 . 
     Lever Fixed to a Shift Drum 
       FIG. 11  illustrates a lever  1100  attached to the shift drum  310  in accordance with embodiments of the present technology. The lever  1100  is connected to the shift drum  310  in a manner that omits movable linkages between the shift drum  310  and the lever  1100  (such as a direct attachment between the lever  1100  and the shift drum  310 ). Accordingly, a user may move the lever  1100 , which moves the shift drum  310  without relative movement between the lever  1100  and the shift drum  310 . The lever  1100  is shown bolted to the rod portion  1005  (near or on the flattened surface  1006 , see  FIGS. 10A-10C ) but, in other embodiments, the lever  1100  may be clamped, welded, glued, integral with the rod portion  1005 , or attached in another manner that facilitates a connection between the lever  1100  and the shift drum  310  that does not permit relative movement between the lever  1100  and the shift drum  310 . 
     In contrast with embodiments according to the present disclosure, existing shift drums for sequential transmissions may be moved with a user-operated actuator or lever that facilitates relative movement between the user-operated actuator or lever and the shift drum. For example, some existing sequential shift drums include an actuator or lever that momentarily applies a torque to the conventional shift drum in order to gain the next mode of operation, before releasing the torque, even if pressure is maintained on the lever. A motorcycle operator, for example, depresses the shift lever and actuates the shift drum to rotate a portion of 360 degrees (for example, 60 degrees in a 5-speed motorcycle with neutral). Then the operator lets the lever return to an inactive position at which time the lever can be depressed again or pulled to return to the previous mode. This type of depressing and pulling toggles between various modes (gears) and adds unnecessary complication to sequential transmissions for equipment such as tillers. Accordingly, in contrast, embodiments of the present technology include an actuator or lever that is mechanically attached to the pivot shaft  1005  (rod portion  1005 ), in a fixed manner, and is not toggled. 
     CONCLUSION 
     Embodiments of the present technology balance a tiller or cultivator about its centerline and place the center of gravity close to the wheels, which ultimately improves traction and performance without adding auxiliary weights. While balancing the unit side to side, the gearing is also positioned lower to the ground and closer the drive wheels. By positioning the gearing in this manner, the use of auxiliary weight is not required. The position of the weight affects the wheel traction of a rear-tine tiller/cultivator. Gear arrangements and mechanism arrangements according to embodiments of the present technology improve balance without adding weight and cost in the form of auxiliary weights. Accordingly, embodiments of the present technology may reduce cost relative to existing devices, including existing dual-direction rear-tine machines. A further advantage is that embodiments of the present technology may facilitate positioning of the engine flywheel  140  along the centerline  135  of a tiller  100 , opposite the tines, which dampens vibration from the tines that would otherwise be transferred to a user through the handles (see  FIG. 1 ). 
     From the foregoing, it will be appreciated that specific embodiments of the presently disclosed technology have been described herein for purposes of illustration, but that various modifications may be made without deviating from the scope of the technology. For example, although wheels are referenced for propulsion, in some embodiments, other propulsion systems may be used, such as tracks or rollers. Certain aspects of the technology may be used in electric or gas-powered tiller machines. Although dual-direction, rear-tine tillers/cultivators are described herein, aspects or embodiments of the present technology may be implemented in other tillers/cultivators, such as tillers/cultivators that are not rear-tine or dual-direction. 
     Although some intermediate gears are described, some may be optional, and more or fewer gears, or larger or smaller gears, may be used. When the term “gears” is used, it is understood that “gears” may include suitable teeth or engagement surfaces to facilitate operative connections between the interconnected parts described herein. In some embodiments, belts or other mechanisms suitable for transferring rotation may be used to transfer rotation between mutually engaged or operatively connected components. Certain aspects of the technology described in the context of particular embodiments may be combined or eliminated in other embodiments. 
     Further, while advantages associated with certain embodiments of the presently disclosed technology have been described in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages to fall within the scope of the technology. Accordingly, the disclosure and associated technology can encompass other embodiments not expressly shown or described herein.