Patent Publication Number: US-10307315-B2

Title: Drive assembly for manually powered wheelchair and methods of using the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of, and incorporates herein by reference in its entirety, U.S. Provisional Patent Application No. 62/571,585, which was filed on Oct. 12, 2017. 
    
    
     TECHNICAL FIELD 
     In various embodiments, the present invention relates to a drive assembly for driving a manually powered wheelchair and to methods of using the drive assembly. 
     BACKGROUND 
     Manually powered wheelchairs come in a variety of sizes for a variety of purposes. Two of the most common types of manually powered wheelchairs are the standard folding wheelchair and the non-folding, rigid frame wheelchair. Many individuals with a spinal cord injury from the five cervical vertebrate down to the lumbar vertebrates use a lightweight, rigid frame, manually powered wheelchair for everyday use. The wheelchair is typically powered by the wheelchair user gripping the rims of the rear push wheels and pushing clockwise or counterclockwise for a specified direction and speed. However, there are many situations where using a manually powered wheelchair can be difficult or even unrealistic, such as during lengthy outings, when propelling long distances, when traversing uneven or sloped terrain, and/or when the wheelchair user&#39;s deficits are of such a degree that manual propulsion becomes painful, exhausting, or relatively impossible given time or circumstances. 
     Although electrically powered wheelchairs exist and can be used for those situations, they are generally not prescribed unless the user lacks the ability to use a manually powered wheelchair. Insurance carriers, for example, generally will not pay for a user to have both types of wheelchairs. Moreover, electrically powered wheelchairs tend to be expensive, heavy, and cumbersome. 
     While power attachments for manually powered wheelchairs exist, they often are not easy to attach and detach from the conventional, manually powered wheelchair. Additionally, many power attachments require modification of the manually powered wheelchair and/or have to be pre-sized to fit a particular manually powered wheelchair&#39;s dimensions, such as its height, width, and frame layout, which can vary greatly from one wheelchair manufacturer, or model, or version to the next. Having to add attachment accessories to the manually powered wheelchair and/or having to pre-size the power attachment typically requires tools, time, and/or intervention on the part of the wheelchair user or others that severely limits the convenience of using the power attachment. Moreover, for a child that is confined to a wheelchair, having to replace a pre-sized power attachment each time that the child requires the use of a larger wheelchair as he or she grows can be extremely inconvenient and expensive for the child&#39;s parents and/or guardians. 
     Accordingly, a need exists for an improved power attachment for a manually powered wheelchair. 
     SUMMARY OF THE INVENTION 
     In various embodiments, the retrofitable drive assembly described herein attaches and detaches quickly, easily, and reversibly from a conventional, manually powered wheelchair and is employed to convert the manually powered wheelchair into an electrically powered wheelchair. The conversion occurs without the use of tools or wheelchair modification and the drive assembly need not be pre-sized to fit a particular manually powered wheelchair&#39;s dimensions. Rather, the size and/or configuration of the drive assembly itself are fully adjustable to accommodate any manually powered wheelchair, regardless of that wheelchair&#39;s size and/or configuration. For example, the drive assembly may be adjusted to accommodate different distances between the rear push wheels of different manually powered wheelchairs (e.g., different wheelchair widths), different diameters in the rear push wheels of different manually powered wheelchairs, or both. Accordingly, the retrofitable drive assembly described herein addresses many of the above-mentioned issues that are present in existing power attachments for manually powered wheelchairs and is an improvement over those existing power attachments. 
     In general, in one aspect, embodiments of the invention feature a drive assembly for driving a manually powered wheelchair. The drive assembly includes wheel troughs extending from a front end towards a rear end of the drive assembly, two drive wheels, and a single caster-wheel assembly. Each wheel trough is adjustably sizeable to receive therein a rear push wheel of a wheelchair. The two drive wheels are positioned towards the front end of the drive assembly and impart motion to the drive assembly, and thereby drive the wheelchair, when the rear push wheels of the wheelchair are positioned within the wheel troughs. The single caster-wheel assembly (which may, for example, include a single caster wheel or, alternatively, multiple caster wheels) is positioned towards the rear end of the drive assembly. Optionally, the drive assembly may also include accessory rollers positioned at the front end of the drive assembly. 
     Various embodiments of this aspect of the invention include the following features. Each wheel trough may include a ramp (e.g., a spring-loaded ramp) at the front end of the drive assembly. Additionally or alternatively, each wheel trough may include a pin oriented substantially perpendicular to a longitudinal axis of the wheel trough. Optionally, each wheel trough may also include side plates, at least one of which may define a groove sized to permit slideable displacement therein of the pin towards and away from the front end of the drive assembly. In one embodiment, each wheel trough also includes a locking mechanism, disposed on at least one of the side plates, for locking the pin in place. The locking mechanism may include a set of teeth and a cam handle for releaseably engaging one of the teeth. The wheel troughs may thus be adapted to elevate and support (e.g., between the pin and the spring-loaded ramp of each wheel trough) the rear push wheels of the wheelchair above a ground surface. 
     In one embodiment, the drive assembly includes adjustable cross-tracks that extend between the wheel troughs. Each adjustable cross-track may include at least one T-bar and at least one corresponding sleeve for slideable displacement over the T-bar. The drive assembly may also include a handle to releaseably engage a T-bar and a corresponding sleeve of an adjustable cross-track. 
     In another embodiment, the drive assembly includes a joystick for controlling the motion of the drive assembly. The drive assembly may also include a joystick arm. The joystick arm may be releaseably mounted, at a first end, in proximity to a rear end of one of the wheel troughs, while the joystick may be coupled to a second, opposite end of the joystick arm. 
     The drive assembly may also include arms for securing the wheelchair when the rear push wheels of the wheelchair are positioned within the wheel troughs. Each arm may include a hook for engaging a portion of the wheelchair as well as, optionally, a strap for tightening a securement of the wheelchair to the drive assembly and/or a clamp for releaseably engaging the strap. 
     In general, in another aspect, embodiments of the invention feature a method for driving a manually powered wheelchair having two rear push wheels. In accordance with the method, each rear push wheel of the wheelchair is positioned within a corresponding, adjustably sizeable wheel trough of a drive assembly. Each wheel trough of the drive assembly extends from a front end towards a rear end of the drive assembly. The drive assembly also includes two drive wheels (positioned towards the front end of the drive assembly) and a single caster-wheel assembly (positioned towards the rear end of the drive assembly). The method also includes actuating the two drive wheels to impart motion to the drive assembly and to thereby drive the wheelchair. 
     Various embodiments of this aspect of the invention include the following features. Prior to positioning each rear push wheel of the wheelchair within the corresponding, adjustably sizeable wheel trough of the drive assembly, a length of each wheel trough may be adjusted to accommodate a diameter of the rear push wheel to be positioned therein and/or a first distance between each wheel trough may be adjusted to accommodate a second distance between the rear push wheels of the wheelchair. Positioning each rear push wheel of the wheelchair within the corresponding, adjustably sizeable wheel trough of the drive assembly may include reversing each rear push wheel of the wheelchair over a ramp of the corresponding wheel trough and/or elevating and supporting the rear push wheels of the wheelchair above a ground surface. The ramp may be positioned at the front end of the drive assembly. 
     After positioning each rear push wheel of the wheelchair within the corresponding, adjustably sizeable wheel trough of the drive assembly, but before actuating the two drive wheels to impart motion to the drive assembly, the wheelchair may be secured to the drive assembly. The method may also include controlling the motion of the drive assembly through use of a joystick, which may be coupled to a joystick arm of the drive assembly. In one embodiment, the method includes adjusting the joystick arm to accommodate a user of the wheelchair. 
     These and other features, along with advantages of the embodiments of the present invention herein disclosed, will become more apparent through reference to the following description, the accompanying drawings, and the claims. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, like reference characters generally refer to the same parts throughout the different views. But, for the purposes of clarity, not every component may be labeled in every drawing. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the present invention are described with reference to the following drawings, in which: 
         FIG. 1  schematically illustrates one example of a conventional, manually powered wheelchair; 
         FIG. 2  schematically illustrates a front, left, perspective view of a drive assembly in accordance with one embodiment of the invention; 
         FIG. 3  schematically illustrates a top view of the drive assembly depicted in  FIG. 2 ; 
         FIG. 4  schematically illustrates a left side view of the drive assembly depicted in  FIG. 2 ; 
         FIG. 5  schematically illustrates a front end view of the drive assembly depicted in  FIG. 2 ; 
         FIG. 6  schematically illustrates a wheel trough of the drive assembly depicted in  FIG. 2  in accordance with one embodiment of the invention; 
         FIG. 7  schematically illustrates an exploded component view of various components of the drive assembly depicted in  FIG. 2  in accordance with one embodiment of the invention; and 
         FIG. 8  schematically illustrates an arm of the drive assembly depicted in  FIG. 2  for securing a manually powered wheelchair to the drive assembly in accordance with one embodiment of the invention. 
     
    
    
     DESCRIPTION 
     In broad overview, embodiments of the present invention feature a drive assembly for driving a conventional, manually powered wheelchair.  FIG. 1  schematically depicts an example of one such conventional, manually powered wheelchair  100 . The depicted wheelchair  100  is a non-folding, rigid frame, manually powered wheelchair  100 . As shown, the wheelchair  100  includes a frame  104 , a seat  108 , a backrest  112 , two front caster wheels  116 , two rear push wheels  120  having push rims  124 , and a footrest  128 . 
       FIG. 2  schematically depicts a front, left, perspective view of a drive assembly  200  for driving a manually powered wheelchair, such as the wheelchair  100 , in accordance with one embodiment of the invention, while  FIG. 3  schematically depicts a top view of the same drive assembly  200 . As shown, the drive assembly  200  is generally symmetrical about a middle plane and includes a front end  204 , a rear end  208 , and a wheel trough  212  on each of its left and right sides for retaining and supporting the rear push wheels  120  of the manually powered wheelchair  100 . 
     In addition, the drive assembly  200  includes two drive wheels  216 , positioned towards the front end  204  of the drive assembly  200 . The drive wheels  216  may be actuated by one or more motor(s) (not shown) housed within a casing  220  of the drive assembly  200  to impart motion to the drive assembly  200  and thereby drive the manually powered wheelchair  100  when the rear push wheels  120  of the manually powered wheelchair  100  are positioned within the wheel troughs  212 . The casing  220  of the drive assembly  200  may, for example, house two drive motors—one for each drive wheel  216 . 
     As also shown in  FIGS. 2 and 3 , the drive assembly  200  may include one or more (e.g., two, as depicted) accessory rollers  224  positioned at the front end  204  of the drive assembly  200 . The accessory rollers  224  may, for example, facilitate transport of the drive assembly  200 , much like the wheels of a rolling suitcase facilitate the transport of the suitcase. In particular, one may grab and lift a handle  228  located at the rear end  208  of the drive assembly  200 , such that the drive assembly  200  is elevated at its rear end  208  and is supported on a ground surface at its front end  204  by the accessory wheels  224 . When positioned as such, the drive assembly  200  may be pulled across the ground surface to its intended destination. In addition, the accessory rollers  224  may function as an anti-tipping mechanism for the drive assembly  200 . In particular, when a load is placed on the front end  204  of the drive assembly  200  (e.g., when the rear push wheels  120  of the manually powered wheelchair  100  are rolled over ramps  248  (discussed further below) of the wheel troughs  212  as the manually powered wheelchair  100  exits the troughs  212 ), the accessory rollers  224  serve to prevent the drive mechanism  200  from tipping to far forward and over. 
       FIG. 4  schematically depicts a left side view of the same drive assembly  200  that is depicted in  FIGS. 2 and 3 , while  FIG. 5  schematically depicts a front end view of that same drive assembly  200 . As best shown in  FIG. 4  (and as also visible in  FIG. 5 ), the drive assembly  200  may also include a single caster-wheel assembly  232 , which, in one embodiment, is positioned towards the rear end  208  of the drive assembly  200  and facilitates turning of the drive assembly  200  in, for example, a restricted space. The single caster-wheel assembly  232  may include a single caster wheel or, alternatively, multiple caster wheels, as will be understood by one of ordinary skill in the art. 
     Referring again to  FIG. 2 , in one embodiment, the drive assembly  200  also includes a joystick arm  236  having, at one end  336  thereof, a mounting ball  240  that couples to a joystick (not shown) that is in turn employed to control the motion of the drive assembly  200 . And, with reference to  FIGS. 2-5 , the drive assembly  200  may also include one or more (e.g., two, as depicted) arms  244  for securing the manually powered wheelchair  100  to the drive assembly  200  when the rear push wheels  120  of the manually powered wheelchair  100  are positioned within the wheel troughs  212  of the drive assembly  200 . Both the joystick arm  236  and the securement arms  244  are further described below. 
       FIG. 6  schematically depicts, in greater detail, one embodiment of the wheel trough  212  for the right side of the drive assembly  200 . In one embodiment, the wheel trough  212  for the left side of the drive assembly  200  is a mirror image of the wheel trough  212  for the right side of the drive assembly  200 . With reference to  FIGS. 2, 3, and 6 , in one embodiment, each wheel trough  212  extends from the front end  204  towards the rear end  208  of the drive assembly  200  and includes a ramp  248  (e.g., a spring-loaded ramp  248 ) at the front end  204  of the drive assembly  200 . In addition, each wheel trough  212  includes a pin  252  that is oriented substantially perpendicular to a longitudinal axis  256  of the wheel trough  212 , as well as inner and outer side plates  260 ,  264 . 
     In one embodiment, each wheel trough  212  is adjustably sizeable to receive therein, elevate, and support above a ground surface a rear push wheel  120  of the manually powered wheelchair  100 , regardless of the diameter of the rear push wheel  120 . For example, in one embodiment, at least one of the side plates  260 ,  264  defines a groove  268  that is sized to permit slideable displacement therein of the pin  252  towards and away from the front end  204  of the drive assembly  200 . As illustrated in  FIGS. 2 and 6 , in one embodiment it is the inner plate  260  that defines the groove  268  although, in alternative embodiments, it may be the outer plate  264  that defines the groove  268 , or both the inner plate  260  and the outer plate  264  that define grooves  268 . In any event, moving the pin  252  along the groove  268  towards the front end  204  of the drive assembly  200  decreases a distance between the pin  252  and the ramp  248 , thereby adjusting the wheel trough  212  to accommodate a smaller diameter wheel  120 . Conversely, moving the pin  252  along the groove  268  away from the front end  204  of the drive assembly  200  and towards the rear end  208  of the drive assembly  200  increases a distance between the pin  252  and the ramp  248 , thereby adjusting the wheel trough  212  to accommodate a larger diameter wheel  120 . In one embodiment, the wheel trough  212  is adjustable to accommodate rear push wheels  120  of any size, for example rear push wheels  120  of 10 inches in diameter to 26 inches in diameter. Together, in use, the ramp  248  and pin  252  of each wheel trough  212  elevate and support a rear push wheel  120  of the manually powered wheelchair  100  above a ground surface when the rear push wheel  120  is placed within the wheel trough  212 . 
     To facilitate the movement and placement of the pin  252 , the wheel trough  212  may include, as best illustrated in  FIGS. 2 and 6 , a locking mechanism  272  for locking the pin  252  in place. In one embodiment, the locking mechanism  272  is disposed on at least one of the side plates  260 ,  264 . For example, like the groove  268 , the locking mechanism  272  may be disposed on the inner plate  260 , on the outer plate  264 , or on both the inner plate  260  and the outer plate  264 . In the exemplary embodiment illustrated in  FIGS. 2 and 6 , the locking mechanism  272  is disposed on the inner plate  260 . In one embodiment, as illustrated, the locking mechanism  272  includes a set of teeth  276  and a cam handle  280  for releaseably engaging one of the teeth  276 . By lifting the cam handle  280 , the cam handle  280  is unlocked and disengaged from the teeth  276  of the locking mechanism  272 , which permits the pin  252  to be advanced or retracted (i.e., forward or backward) along the groove  268 . Once the pin  252  is positioned so that the rear push wheel  120  of the manually powered wheelchair  100  properly fits between and is elevated and supported by the ramp  248  and the pin  252  (i.e., so the rear push wheel  120  will not contact the ground surface when loaded), the cam handle  280  may be lowered to once again engage and lock the teeth  276  of the locking mechanism  272 . 
     While, as just described, the drive assembly  200  may be adjustable to accommodate different diameters in the rear push wheels  120  of different manually powered wheelchairs  100 , the drive assembly  200  can also, in certain embodiments, be adjustable to accommodate different wheelchair  100  widths—e.g., different distances between the rear push wheels  120 .  FIG. 7 , for example, schematically depicts an exploded component view of various components of the drive assembly  200  described above. As shown, the drive assembly  200  may include one or more adjustable cross-tracks (e.g., front and rear adjustable cross-tracks  284 ,  288 , as illustrated) that extend between the wheel troughs  212  and that couple components from the left side  292  of the drive assembly  200  to components from the right side  296  of the drive assembly  200 . In one embodiment, each adjustable cross-track  284 ,  288  includes at least one T-bar  300  and at least one corresponding sleeve  304  for slideable displacement over the T-bar  300 . With reference to  FIGS. 2-5 , the drive assembly  200  may also include one or more handles (e.g., pull-pins)  308 . For example, the drive assembly  200  may include two handles  308  for the adjustable cross-track  288  that is positioned most closely towards the rear end  208  of the drive assembly  200  (see,  FIG. 7 ). In one embodiment, each handle  308  releaseably engages (e.g., locks and unlocks) a T-bar  300  and a corresponding sleeve  304  of the rear adjustable cross-track  288 . In one implementation, as depicted, handles are not employed in connection with the front cross-track  284 . As such, the T-bars  300  and corresponding sleeves  304  of the front cross-track  284  are continuously unlocked from one another. 
     In operation, the illustrated handles  308  may be turned and lifted to disengage the handles  308  from the T-bars  300  and sleeves  304  of the rear cross-track  288 . In this unlocked state, the sleeves  304  of both the front cross-track  284  and the rear cross-track  288  may be slideably displaced over their respective T-bars  300  in order to adjust the distance between the left  292  and right  296  sides of the drive assembly  200  (i.e., the distance or width between the two illustrated wheel troughs  212 ). In particular, the distance or width between the two illustrated wheel troughs  212  may be either increased or decreased to accommodate a manually powered wheelchair  100  having either a larger or smaller distance or width between its two rear push wheels  120 . Once the distance between the two illustrated wheel troughs  212  is adjusted to match the distance between the rear push wheels  120  of the manually powered wheelchair  100 , the handles  308  may be lowered and turned in the opposite direction to re-engage the rear cross-track  288  joining the left  292  and right  296  sides of the drive assembly  200 . In this locked state, the sleeves  304  of both the front cross-track  284  and the rear cross-track  288  are prevented from being slideably displaced over their respective T-bars  300 . In one embodiment, the distance or width between the two wheel troughs  212  is adjustable between 16 inches and 26 inches to accommodate manually powered wheelchairs  100  of different sizes. 
     In one embodiment, once the wheel troughs  212  have been adjusted to fit both the diameter of and the width between the rear push wheels  120  of the manually powered wheelchair  100  to be placed therein (using the locking mechanisms  272  and adjustable cross-tracks  284 ,  288 , respectively), the wheelchair  100  is reversed over the spring-loaded ramps  248  of the wheel troughs  212 , until the wheelchair&#39;s rear push wheels  120  fall into the wheel troughs  212  between the side plates  260 ,  264  and abut the pins  252 . While, with the rear push wheels  120  so positioned, the wheel troughs  212  elevate and support the rear push wheels  120  above a ground surface, the securement arms  244  of the drive assembly  200  (see,  FIGS. 2-5 ) may nevertheless be employed, in one embodiment, to secure the manually powered wheelchair  100  to the drive assembly  200 . 
       FIG. 8  schematically depicts one embodiment of a securement arm  244  of the drive assembly  200 . As shown, the securement arm  244  extends between a proximal end  312 , at which the arm  244  is coupled to the drive assembly  200  (e.g., using one or more fastening mechanisms, such as nuts and bolts), and a distal end  316 , at which the arm  244  includes components for engaging a portion of the manually powered wheelchair  100 . In particular, in the illustrated embodiment, the securement arm  244  includes a hook  320  towards its distal end  316 . The hook  320  may, for example, be hooked to a rear portion of the frame  104  of the manually powered wheelchair  100  (see,  FIG. 1 ). In addition, the securement arm  244  may include strap  324  and/or a clamp  328  proximate its distal end  316 . In one embodiment, once the hook  320  is hooked to the rear portion of the frame  104  of the manually powered wheelchair  100 , the strap  324  and/or clamp  328  (which releaseably engages the strap  324 ) are employed to tighten a securement of the manually powered wheelchair  100  to the drive assembly  200 . In particular, with the handle of the clamp  328  elevated to disengage the clamp  328  from the strap  324 , an individual assisting a user of the manually powered wheelchair  100  may pull on the strap  324  to tighten the securement of the manually powered wheelchair  100  to the drive assembly  200  (i.e., to remove slack in the strap  324 ). Then, once the slack in the strap  324  is removed to a satisfactory amount, the handle of the clamp  328  may be lowered so that the clamp  328  re-engages and locks the strap  324  in place, thereby securing the manually powered wheelchair  100  to the drive assembly  200 . 
     With reference back to  FIG. 2 , in one embodiment, as previously mentioned, the drive assembly  200  also includes a joystick arm  236  having a first end  332  and a second, opposite end  336 . In one embodiment, the joystick arm  236  includes a mount  340 , a mounting tube  344 , and a main arm  348 . As shown in  FIGS. 6 and 7 , through holes  352  may be defined through the inner side plate  260  of each wheel trough  212  at a rear end  356  of the side plate  260 . Accordingly, as best shown in  FIG. 3 , the mount  340  may be removeably fastened, for example using nuts and bolts or other removeable fastening mechanisms that extend through the through holes  352 , to the rear end  356  of either one of the slide plates  260 . 
     Referring again to  FIG. 2 , the mounting tube  344  may be inserted into the mount  340  and be removeably fastened thereto, for example again using nuts and bolts or other fastening mechanisms. For its part, the main arm  348  is slideable over the mounting tube  344 . The mounting tube  344  may, for example, include on its exterior surface a push pin that is biased to project outwards from the exterior surface, but that may be pushed in to be flush with the exterior surface in order to slide the main arm  348  thereover. Though holes  360 , corresponding in size to the push pin of the mounting tube  344 , may be present along a hollow length of the main arm  348 . Accordingly, in one embodiment, the push pin of the mounting tube  344  is pushed in in order to permit slideable movement of the main arm  348  over the mounting tube  344 , and remains pushed in until a desired one of the through holes  360  is aligned with the push pin. The push pin, in accordance with its bias, then returns to the state in which it projects outwards from the exterior surface of the mounting tube  344  (i.e., through a through hole  360 ), thereby locking the mounting tube  344  and main arm  348  together. In this way, because the main arm  348  includes multiple through holes  360  along its length, the height of the joystick arm  236  may be adjusted to accommodate a user of the drive assembly  200 . 
     In addition, the main arm  348  of the joystick arm  236  may include a release button  362 . When the release button  362  is pressed inwards, the portion of the main arm  348  extending between the release button  362  and the end  336  may have its pitch adjusted to accommodate a user of the drive assembly  200 . For example, with the release button  362  pressed inwards, that portion of the main arm  348  may be rotated counterclockwise (e.g., so that it is flipped straight up) or clockwise (e.g., so that it is flipped straight down). 
     As illustrated in  FIG. 2 , the joystick arm  236  may be releaseably mounted, at its first end  332 , in proximity to a rear end  364  of one of the wheel troughs  212 . For a right-handed user of the manually powered wheelchair  100 , the joystick arm  236  may be mounted, as shown, on the left side  292  of the drive assembly  200 . Alternatively, the removeable fastening mechanism securing the mount  340  to the rear end  356  of the side plate  260  located on the left side  292  of the drive assembly  200  may be removed and the mount  340  attached to the rear end  356  of the slide plate  260  located on the right side  296  of the drive assembly  200 , so that the joystick (not shown) of the joystick arm  236  may be employed by a left-handed user of the manually powered wheelchair  100 . 
     As shown in  FIG. 2 , in one embodiment, a mounting ball  240  is present at the second end  336  of the joystick arm  236 . In one such embodiment, a joystick (not shown) is coupled to the mounting ball  240  and movement of the joystick controls movement of the drive assembly  200 . Data representing the movement of the joystick may, for example, be communicated wirelessly to electronics housed within the casing  220  of the drive assembly  200 , which may then control the one or more motor(s) that actuate the drive wheels  216 . Alternatively, a hard wire connection may run through the joystick arm  236 , so that it may couple to a port in the casing  220  that is in communication with the electronics controlling the one or more motor(s). 
     In one embodiment, a knob  368  present on the main arm  348  of the joystick arm  236  controls how far from or close to the front end  204  of the drive assembly  200  the joystick is located. In particular, the knob  368  may be loosened and slid through a groove  372  of the main arm  348  to permit displacement of the joystick towards or away from the front end  204  of the drive assembly  200 . When the joystick reaches its desired position, the knob  368  may be tightened to lock the joystick in place. Accordingly, in this way as well, the joystick arm  236  may be adjusted to accommodate a user of the manually powered wheelchair  100 . 
     In one embodiment, the drive assembly  200  described herein weighs less than 35 pounds, but is able to support use by an individual user who weighs up to 250 pounds. The drive assembly  200  may have, in the absence of the joystick arm  236 , a height of less than 6.5 inches. 
     Exemplary Method of Use 
     In operation, when the drive assembly  200  is to be used in connection with a particular manually powered wheelchair  100  of given size and dimensions, the length of each wheel trough  212  may be adjusted (as described above) to accommodate the diameter of the rear push wheel  120  to be positioned therein and the distance (e.g., width) between each wheel trough  212  may be adjusted (as described above) to accommodate a distance (e.g., width) between the rear push wheels  120  of the manually powered wheelchair  100 . Then, each rear push wheel  120  of the manually powered wheelchair  100  may be reversed over the ramp  248  of a wheel trough  212  to position each rear push wheel  120  within its respective wheel trough  212 . As described above, in this state, the ramp  248  and pin  252  of each wheel trough  212  together act to elevate and support the rear push wheel  120  positioned therein above the ground surface. In addition, as also described above, with the manually powered wheelchair  100  positioned in this state, the wheelchair  100  may be secured to the drive assembly  200 , for example by using the hooks  320 , straps  324 , and/or clamps  328  of the securement arms  244 . A user of the wheelchair  100  may then use the joystick (optionally, after the joystick arm  236  has been positioned to accommodate the user of the wheelchair  100 ) to control the motion of the drive assembly  200 . In particular, as described above, movement of the joystick actuates the two drive wheels  216  of the drive assembly  200  to impart motion to the drive assembly  200 , thereby driving the otherwise manually powered wheelchair  100 . 
     Having described certain embodiments of the invention, it will be apparent to those of ordinary skill in the art that other embodiments incorporating the concepts disclosed herein may be used without departing from the spirit and scope of the invention. Accordingly, the described embodiments are to be considered in all respects as only illustrative and not restrictive.