Abstract:
Improvements to personal vehicles including self-propelled and balancing personal vehicles. Ready detachability of a seat, footrest, seat back, control unit, wheels and caster assembly is provided using quick disconnect mechanisms.

Description:
The present application is a divisional application of Ser. No. 09/978,711, filed Oct. 16, 2001 now U.S Pat. No. 6,715,845, itself a divisional application of Ser. No. 09/325,463, filed Jun. 3, 1999 now U.S. Pat. No. 6,405,816. Each of these applications is hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention pertains to mechanical improvements to personal vehicles including self-propelled personal vehicles. 
     BACKGROUND OF THE INVENTION 
     Personal vehicles, such as may be used by handicapped persons, may be self-propelled and user-guidable, and, further, may entail stabilization in one or more of the fore-aft or lateral planes, such as when no more than two wheels are in ground contact at a time. More particularly, such vehicles may include one or more clusters of wheels, with wheels in each cluster capable of being motor-driven independently of the cluster in its entirety. One example of such a vehicle is described in U.S. Pat. No. 5,701,965, which is incorporated herein by reference. Since personal vehicles operate under stringent constraints of weight and power, the features of such vehicles are typically limited to those essential to the propulsion of the vehicle, with safety left largely in the hands of the operator, and comfort largely foregone. Vehicles of this sort may be more efficiently and safely operated employing mechanical features supplementary to those described in the prior art. 
     SUMMARY OF THE INVENTION 
     In accordance with a preferred embodiment of the invention, there is provided a personal vehicle for carrying a payload including a user. The vehicle has a ground-contacting module that supports the payload and has at least one ground-contacting member. The vehicle also has a motorized drive arrangement, mounted to the ground-contacting module, that causes automatically balanced operation of the vehicle in an operating position that is unstable with respect to tipping when the motorized drive arrangement is not powered. The vehicle has a seat for supporting the user, the seat being coupled to the ground-contacting module in such a manner that the seat may be removed without the use of a tool, such as by means of a quick-disconnect assembly. 
     In accordance with another embodiment of the present invention, the personal vehicle has a footrest coupled to the ground-contacting module for supporting the foot of the user, where the footrest may also be decoupled from the ground-contacting module without the use of a tool. The footrest may be coupled to the ground-contacting module through the seat assembly such as by means of a mounting pin inserted in a J slot. 
     In accordance with another embodiment of the invention, there is provided a personal transportation vehicle having a seat back coupled to the seat assembly, the seat back being tiltable with respect to the seat assembly. The vehicle may also have a sensor arrangement that provides a signal corresponding to the tilt of the seat back. The seat back may be positionable at one of a plurality of positions provided with respect to the seat assembly, thereby positioning the CG of the user at a desired position with respect to the ground-contacting module. 
     In accordance with further embodiments of the invention, the personal vehicle may have at least one caster capable of being brought into engagement with the ground during operation of the vehicle. In one embodiment of the invention, motion of the caster in a direction having a vertical component is coordinated with motion of the seat assembly of the vehicle. 
     The caster assembly may be decoupled from the ground-contacting module without the use of a tool, and may include a suspension mechanism for dampening transmission of vibration to the vehicle. 
     In accordance with another embodiment of the invention, the personal vehicle may have a power module disposed substantially beneath the seat assembly and contained substantially within the areal projection in the horizontal plane of the seat assembly. The personal vehicle may have a user interface module for permitting a user to command the motorized drive arrangement and a differentially frangible coupling for attaching the user interface module to the support structure. 
     In accordance with yet another embodiment of the invention, the personal vehicle may have a belt tensioning mechanism for tensioning a belt that transmits torque from a motor to a rotary member having an axis of rotation. The belt tensioning mechanism has a motor having a roller for engaging the belt and a cam plate. The cam plate has a slot ridge for receiving the motor, a rotation ridge disposed eccentrically with respect to the slot ridge, and a plurality of circumferential sprocket teeth. Finally, the tensioning mechanism has a transmission plate fixed with respect to the axis of rotation of the rotary member, the motor having a rotational orientation defined with respect to the transmission plate, the transmission plate having a substantially elliptical cam plate rotation shelf for receiving the cam plate rotation ridge such that a lateral position of the motor with respect to the transmission plate may be changed by rotation of the cam plate while the rotational orientation of the motor remains substantially constant. 
     The personal vehicle may have a self-pulling mechanism for a wheel having a tapered axle bore and a hub. The self-pulling mechanism has an axle having a taper corresponding the bore of the wheel and a threaded end, a retaining ring seated on an inside groove of the hub of the wheel, and a wheel nut having a threaded bore corresponding to the threaded end of the axle such that upon tightening the wheel is retained on the axle and upon loosening a force is applied to the retaining ring for removing the wheel from the axle. 
     In accordance with alternate embodiments of the invention, there is provided a vehicle for carrying a payload having a power module with left and right compartments capable of interchangeably receiving a power pack, where the respective compartments of the power module may be coupled to redundant power circuits. The personal vehicle of embodiments of the present invention may also have a handle having an adjustable extension for retention by an assistant in operating the vehicle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which: 
         FIG. 1A  is a side view of a personal vehicle employing embodiments of the present invention; 
         FIG. 1B  is a rear view of the power base of the personal vehicle of  FIG. 1A ; 
         FIG. 1C  shows the same view as  FIG. 1B , with the battery tray removed to show the position of the electronics box; 
         FIG. 2  shows a front cross-sectional view of a swing-arm caster wheel suspension assembly in accordance with an embodiment of the present invention; 
         FIG. 3  is an exploded view of the caster wheel suspension assembly of  FIG. 2 ; 
         FIG. 4  shows a front view in cross section of a mechanism for coupling the caster suspension assembly of  FIGS. 2 and 3  to a member of a personal vehicle in accordance with an embodiment of the present invention; 
         FIGS. 5A–5B  show side and top cross-sectional views of a seat supporting assembly for a personal vehicle showing a quick-disconnect coupling and latch assembly in accordance with an embodiment of the present invention; 
         FIGS. 6A–6D  show views of a transmission plate with drive motor mounting cam plate in accordance with an embodiment of the present invention; 
         FIG. 7A  shows a side view in cross-section of a retaining structure for a user command interface coupling for a personal vehicle showing a differentially frangible coupling between the user command interface and the support of the personal vehicle in accordance with an embodiment of the present invention; 
         FIGS. 7B and 7C  show embodiments of a latching tongue for the differentially frangible coupling mechanism of  FIG. 7A ; 
         FIG. 7D  is a perspective view of a user command interface for a personal vehicle showing a latching tongue for the differentially frangible coupling of  FIG. 7A ; 
         FIG. 7E  is an exploded view of the assembly of the differentially frangible quick disconnect mechanism of  FIG. 7A  to the armrest of a personal vehicle in accordance with an embodiment of the invention; 
         FIGS. 8A and 8B  show side views of a wheel assembly including a self-pulling wheel mechanism in accordance with an embodiment of the present invention; 
         FIG. 8C  shows a cross-sectional side view of the self-pulling wheel mechanism of  FIG. 8A ; 
         FIGS. 9A and 9B  show a battery retention assembly, including rails for rapid battery switchout, for use in a personal vehicle in accordance with an embodiment of the present invention; 
         FIGS. 10A–10C  show views of a removable footrest assembly for a wheelchair-type vehicle in accordance with an embodiment of the present invention; and 
         FIGS. 11A and 11B  show components of an extensible attendant handle and seat back orientation sensor mechanism for a wheelchair-type vehicle in accordance with an embodiment of the present invention; 
         FIG. 11C  shows a front view of a magnetic sensor disk component of an orientation sensor mechanism in accordance with an embodiment of the present invention; 
         FIGS. 12A and 12B  show diagrams illustrating mechanisms for adjusting the seat depth of the seat back of a personal vehicle, in accordance with embodiments of the present invention; 
         FIGS. 13A and 13B  show perspective views of an embodiment of a seat assembly for use with a personal vehicle in accordance with an embodiment of the present invention; 
         FIGS. 13C and 13D  show exploded and assembled views, respectively, of a rotatable armrest support for use with a personal vehicle in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to  FIG. 1A , a side view is shown of a personal vehicle, designated generally by numeral  10 . Vehicle  10  may be described in terms of two fundamental structural components: a support  12  for carrying a passenger  14  or other load, and a ground-contacting module  16  which provides for transportation of support  12  across the ground, or, equivalently, across any other surface. The passenger or other load may be referred to herein and in any appended claims as a “payload.” As used in this description and in any appended claims, the term “ground” will be understood to encompass any surface upon which the vehicle is supported. 
     A mechanism and process for automatically balanced operation of the vehicle in an operating position that is unstable with respect to tipping when the motorized drive arrangement is not powered is described in Kamen &#39;965 column 3, line 55 through column 5, line 44. 
     Referring further to  FIG. 1A , the modes of operation described herein apply to vehicles having one or more ground-contacting elements  18 , where each ground-contacting element is movable about an axis  20  and where the axis corresponding to a ground-contacting member can itself be moved. For example, ground-contacting element  18  may be a wheel, as shown, in which case axis  20  corresponds to an axle about which the wheel rotates. Active control of the position of the axis  20  about which ground-contacting element  18  rotates may be tantamount to active suspension of the vehicle in that the position may be controlled in response to specified conditions of the traversed surface or specified modes of operation of the vehicle. 
     Motion of axes  20  of respective ground-contacting elements is referred to in this description and in any appended claims as “cluster motion.” Wheels  18  may be movable in sets, with the moving assembly referred to as a cluster  36 . Cluster motion is defined with respect to a second axis  22 , otherwise referred to as a “cluster joint.” Additional driven degrees of freedom may be provided, such as motion of the second axis about one or more pivots which may, in turn, allow the height of seat  28  to be varied with respect to the ground. Alternatively, seat height may be varied by means of a telescoping post, or by means of any other mechanical artifice. An actuator may be associated with each driven degree of freedom and controlled using control strategies discussed in detail below. In preferred embodiments of the invention, the actuators include wheel servo-motors and cluster servo-motors, with current supplied to the respective motors by servo amplifiers. Additionally, non-driven wheels may be provided, such as casters or pilot wheels  30  coupled to footrest  32  or otherwise to support  12 . 
     An advantage to providing one or more caster wheels  30  coupled to footrest  32  is that such caster wheels may be engaged or disengaged with the ground  34  by controlling the height of seat (or support)  12  with respect to ground-contacting elements  18 . The engagement of caster wheel  30  for traversing curbs or other ground obstacles may comprise part of a control mode of the vehicle, as taught in copending U.S. provisional patent application, Ser. No. 60/124,403, filed Mar. 16, 1999, which is incorporated herein by reference. It is to be understood that one or more caster wheels  30  may also be provided aft of support  12 , and may be coupled to the support or, alternatively, may be controlled so as to be governed by the height of support  12  with respect to ground-contacting elements  18 . It is not required, within the scope of the invention, that a particular caster be in contact with the ground during all, or indeed any, of the duration of operation of the vehicle. 
     Referring to  FIG. 1B , seat  12  is coupled to power base  8  of the personal vehicle at seat connection flange  256 . Seat height is adjusted by seat height mechanism  6 . In order to allow traversal by personal vehicle  10  of terrain of varied surface structure or varied topologies such as stairs, personal vehicle  10 , it is advantageous to maximize clearance both beneath the vehicle and aft of the vehicle, the latter to permit maximal maneuverability on descending stairs. Under circumstances where a vehicle is not actively stabilized, it might be advantageous to optimize the distribution of components in order simply to lower the center of gravity in the interest of stability. In an actively stabilized vehicle, and in accordance with preferred embodiments of the invention, electronics module  4  and power pack shelf  462  are advantageously disposed above cluster axis  22 . Additionally, the rear contour of ground-contacting module is cut away in a convex contour in region  2 , to provide clearance for the vehicle upon descent of stairs. Electronics compartment  4  contains controller tray  2 , as shown in  FIG. 1C . 
     Under circumstances where one or more caster wheels  30  engage the ground during operation of the personal vehicle  10 , it is advantageous to reduce the transmission of vibration to the payload of the vehicle, for the safety and comfort of the passenger. Referring now to  FIGS. 2 and 3 , wherein identical numerals identify the same or similar features of the invention, a preferred embodiment of the invention is shown that provides an intermediate structure to dampen vibration and shock loads that would otherwise be transmitted from a caster to the vehicle and payload.  FIG. 2  shows a cross-sectional view is shown of suspension  200 , looking toward the vehicle from the front. Caster  30 , coupled to distal end  204  of caster arm  206 , engages the ground under circumstances discussed above. Caster arm  206  is pivotable about pivot  208  which may be a pin  208  as shown in  FIG. 3 . Proximal end  210  of caster arm  206  is engaged within caster housing  212 . Compression spring  214  is axially retained in compression about bolt  216  between caster housing  212  and preloading plate  220 . Compression spring  214  pushes upward on proximal end  210  of caster arm  206 , urging the caster arm against washer  218  and caster housing  212 . 
     Thus, in accordance with an embodiment of the invention shown in  FIGS. 2 and 3 , suspension  200  may be preloaded by virtue of compression spring  214  applying an upward force on the proximal end  210  of caster arm  206 . The upward force on proximal end  210  acts about pivot  208  to keep caster wheel  30  in contact with the ground. Caster wheel  30  may advantageously respond to bumps and dips in the ground surface because spring  214  takes up, as potential energy, that kinetic energy that would otherwise be transmitted to the payload.  FIG. 3  shows an exploded view of the components of the swing-arm caster wheel suspension assembly of  FIG. 2 . Caster arms  206  are shown pivotable about pivot pins  208  which traverse caster housing  212 . Springs  214  are also shown as are washer  218 , bolts  216 , and preloading plate  220 . 
     Another feature of caster suspension  200  is now described with reference to  FIG. 3  and with additional reference to  FIG. 4 . In accordance with a preferred embodiment of the invention, caster suspension is coupled to a caster mount  222  (shown in  FIG. 10A ) through which caster suspension  200  is, in turn, coupled to support  12  (shown in  FIG. 1 ), i.e., to the seat assembly. For purposes of storage or for ready transportation of the personal vehicle in an automobile, for example, it is advantageous that the vehicle be readily collapsible, and, in particular, it is advantageous that caster suspension  200  be readily detachable from its coupling to the support assembly. Caster housing  212  is clamped to caster mount  222  by means of a pair of quick-disconnect clamps  224  and  226 . Quick-disconnect clamps  224  and  226  each contain wedged slots  228  that apply lateral force to mating flanges of caster housing  212  and caster mount  222 , thereby retaining them with a small clamping force applied by cams  230  as latch levers  232  are rotated to urge quick-disconnect clamps  224  and  226  about caster housing  212  and caster mount  222 . A cross-sectional view of flange  240  of the seat assembly and flange  242  of the caster suspension as clamped by quick-connect wedge clamp  224  is shown in  FIG. 4 . Wedge clamps  224  and  226  and latch levers  232  are pivotably coupled to caster housing  212  and are retained with the caster suspension assembly  200  upon disassembly from the vehicle. 
     Referring now to  FIG. 5A , a side view is shown in cross-section of a quick seat disconnect assembly  250  for a personal vehicle  10 . Seat stem  252  terminates at flange  254  which is tapered in conjunction with a corresponding taper on flange  256  of vehicle base  258  in such a manner that Marmon or jaw clamps  260  may be applied to couple flanges  254  and  256 . Seat stem  252  is thus readily disconnected from vehicle base  258  without requiring the use of a tool. Springs  262  are mounted between flanges  254  and  256  so as to urge clamps  260  outward. Referring now to  FIG. 5B , a pair of bolts  264  connect clamps  260  and  266  and prevent the clamps from falling off flanges  254  and  256 . Bolts  264  are attached to handle housing  268 . Handle housing  268  contains a handle  270 , pivotally mounted about pivot  272  with respect to handle housing  268 . Handle  270  is shaped such that in one position end  274  of handle  270  applies a force against clamp  266  adjacent to handle housing  268 . When handle  270  is rotated, the force on clamp  266  is removed and clamps  260  and  266  can be removed and seat stem  252  disconnected from vehicle base  258 . 
     Referring now to  FIGS. 6A–6D , views are shown of a transmission belt tensioning mechanism  300  advantageously employed in the wheel drive of personal vehicle  10  in accordance with a preferred embodiment of the invention. Referring first to the outside view of  FIG. 6A , belt tensioning mechanism  300  may advantageously conserve the angular orientation of wheel motor  302  so that power and control cables (not shown) need not be disturbed as the position of wheel motor  302  is translated with respect to wheel transmission plate  304  in order to tension a belt or chain or other endless loop driven by the shaft of wheel motor  302 . The view of  FIG. 6A  is referred to herein as an ‘anterior’ view of the transmission plate.  FIG. 6B  shows the posterior side of transmission plate  304  and, more particularly, shows shaft  306  of wheel motor  302  extending through wheel transmission plate  304 . Belt roller  307  is rigidly coupled to motor shaft  306  for transmission of torque to a belt (not shown). Similarly, a sprocket may also be provided for driving a chain in an analogous manner. From this view, it is clear that motor shaft  306  extends through eccentric shaft opening slot  308 , the function of which will now be described. 
       FIG. 6C  shows an exploded anterior view of transmission plate  304  from which the wheel motor has been removed to clearly show shaft opening slot  308 . Motor  302  is seated within slot ridge  310  of tensioning cam plate  312 . The sprockets  314  of cam plate  312  are disposed eccentrically with respect to the slot ridge and the rotation ridge  316 , shown in  FIG. 6D . Rotation ridge  316  is seated, in turn, in cam plate rotation shelf  318  such that rotation of cam plate  312 , in the manner of a Scotch yoke, results in lateral translation of the shaft of the motor while the orientation of the motor with respect to the transmission plate may be kept constant. Once the motor has been translated to the point where a specified belt tension is attained, bolts are tightened to secure the motor housing to the transmission plate through the sprockets of the cam plate, thereby securing the motor against both rotation and translation. 
     Referring now to  FIGS. 7A–7C , a side view is shown in cross-section of a frangible coupling, advantageously employed for retaining a user command interface (not shown) in conjunction with a personal vehicle  10  so that the user command interface may either be attached to an armrest of the vehicle, for example, or detached for remote operation via a cable, such as retractable cable, or via wireless communication with the personal vehicle. In a preferred embodiment of the invention, a user command interface  376  (shown in  FIG. 7D ) is readily disconnected from armrest  378  (shown in  FIG. 7D ) of support  12  (shown in  FIG. 1 ) by means of an asymmetrical quick disconnect mechanism  350 , shown in a cross-sectional side view in  FIG. 7A .  FIG. 7B  shows a side view in cross-section of an asymmetrical latching tongue for retention by quick disconnect mechanism  350 . When latching tongue  352  is engaged in quick disconnect mechanism  350 , an upper roller  354  engages upper notch  356  while a lower roller  358  engages lower notch  360 . Upper roller  354  is urged downward by compression spring  362  acting against rocker arm  364  which pivots about pivot  366 . Since lower face  368  of latching tongue  352  is beveled, the latching tongue, and the user command interface to which it is attached, are relatively easily removed from the quick-disconnect mechanism  350  by pulling the user command interface in an upward direction. By way of contrast, upper face  370  of the latching tongue  352  runs horizontally substantially to the tip  372  of tongue  352 . Thus, the user command interface may not be as readily removed from the quick-disconnect mechanism  350  by pressing the user command interface in an downward direction. Typically, a force in excess of  25  pounds is required to remove latching tongue  352  by pushing downward on it with respect to quick disconnect mechanism  350 , whereas detachment can be achieved by pulling up on latching tongue with a force not exceeding 2 pounds. This differential frangibility is advantageous in preventing accidental detachment and breakage of the user command interface. Since notches  356  and  360  are substantially parallel grooves over the width of the latching tongue  352 , there is substantially no free play in the captured tongue, and side breakaway forces are substantially greater than either upward or downward breakaway forces. Of course, within the scope of the invention, the grooves may be oriented otherwise so as to provide differential frangibility favoring extraction of the tongue toward any specified direction, as will be readily evident to a person skilled in the art.  FIG. 7C  shows a cross-sectional view from the side of latching tongue  352 , wherein, in accordance with an alternate embodiment of the present invention, an auxiliary groove  372  is provided between upper groove  356  and tip  372 . If the user command interface is accidentally detached by force applied in a downward direction and upper roller  354  no longer engages upper groove  356 , upper roller  354  will still engage auxiliary groove  374  and the unit will not detach freely, as a safety feature and to prevent breakage. 
     Referring now to  FIG. 7D , a perspective view is shown of a user command interface  376  for a personal vehicle showing latching tongue  352  of the differentially frangible coupling mechanism that has been described. An exploded view is shown in  FIG. 7E  of the assembly of the differentially frangible quick disconnect mechanism  350  of  FIG. 7A  to armrest  378  of a personal vehicle by means of fasteners such as screws  380 . In accordance with an embodiment of the invention, one of a series of icons may be displayed to the user on visual display monitor  377  (shown in  FIG. 7D ), with each distinct icon characterizing a corresponding mode of operation of the personal vehicle. 
     Referring now to  FIGS. 8A–8C , a self-pulling wheel assembly  400  is shown for removal of a wheel  402 .  FIGS. 8A and 8B  show side views of the components of the assembly, while  FIG. 8C  shows a cross-sectional view. Axle bore  404  of wheel  402  has a tapered inside surface  406  corresponding to the taper of axle  408  so that torque may be transferred from axle  408  to the wheel. Wheel  402  is mounted by pressing axle bore  404  onto axle  408  by driving wheel nut  410  onto threaded spindle  412  of axle  408 . Wheel nut retention clip  420  retains the wheel nut against rotation with respect to the wheel hub. Hub  414  of wheel  402  has a retaining snap ring  416  that is snapped into an annular groove  418  behind wheel nut  410 . Thus, wheel nut  410  is captured between the wheel and the retaining ring. Retaining ring  416 , in a preferred embodiment, is a snap ring. By unscrewing nut  410  in an outward direction, an outward force is exerted on hub  414  through ring  416 , thereby pulling the wheel  402  off axle  408 . Thus the wheel may advantageously be pulled without application of a separate puller tool. 
     Referring now to  FIG. 9A , a perspective view is shown of a battery pack, designated generally by numeral  450 , that may be used to supply electrical power to a personal vehicle. Any source of electrical power internal to battery pack, such as chemical cells of any sort known in the art, is within the scope of the present invention. Battery pack  450  is configured, as will be described, for convenient insertion and extraction of the battery pack to provide for ready switchout when it becomes necessary to renew or recharge the energy source, or for disassembly and shipping of the personal vehicle. In accordance with a preferred embodiment of the invention, up to two power packs  450  are borne by the power base  6  (shown in  FIG. 1 ) of personal vehicle  10  beneath seat pan  28  and proximate to the seat. Electrical power is supplied by battery pack  450  to power base  6  via electrical connector  452  that engages a mating connector (not shown) when battery pack  450  is fully inserted into a battery tray in the power base. Battery pack  450  is guided into position in the battery tray by guides  460  extending above shelf  462  of the battery tray, as shown in  FIG. 9B . Guides  460  ride within battery tray slots  454  as the battery pack is removed or inserted, thus ensuring straight insertion and proper coupling of connector  452  with its counterpart in the power base. After insertion of one of the battery packs  450 , retaining latch  464  (shown in  FIG. 9B ) is closed behind the inserted battery pack, urging the pack into its fully inserted position and into electrical contact with the power base. When retaining lever  464  is opened, battery pack  450  is urged out of its inserted position, and out of electrical contact with the power base, by operation of a compressed spring (not shown) against spring ledge  456 . Thus, power is not delivered by the battery pack unless it is affirmatively retained by the battery retaining latch  464 . Battery pack  450  and the battery tray of the power base have complementary symmetries, such that battery pack  450  may be inserted into either the left-hand or right-hand battery slot by rotating the battery pack about its long axis. In a preferred embodiment, each battery pack powers a separate power base control circuit, thus providing full redundancy. Additionally, the interchangeability of the battery packs  450  may advantageously prolong the lifetime of the battery packs if the power drain on the respective sides of the battery tray is uneven. 
       FIG. 9B  shows shelf  462  of the battery tray with the right battery retaining latch  464  shown in a closed position, and the left battery retaining latch  466  shown in an open position. Lever locking sleeve  468  slides over both left and right retaining latches, thus locking both battery packs in place for safety of operation. 
       FIG. 10A  is a perspective view of a footrest assembly, designated generally by numeral  700 , attached to seat pan assembly  702 . The rear portion of the seat pan assembly has been cut away for easier viewing. A footrest  704  is attached to a pair of lower footrest legs (not shown) which telescope inside the upper footrest legs  706  thereby providing a footrest length adjustment. The lower legs are locked in place by a pair of extension locks  708 . A tilt adjustment assembly  710  spans the two upper footrest legs  706  and can slide along the upper footrest legs. Tilt assembly  710  includes a front piece  712  and a rear  714  piece that are attached to each other by screws  716 . The ends of the front and rear pieces capture the upper legs. When screws  716  are loosened, tilt assembly  710  can slide along the upper legs  706  but when screws  716  are tightened, the tilt assembly  710  is locked into place. Rear tilt assembly piece  714  extends perpendicular to the plane defined by the two upper legs and rests against the caster mount face  698  of caster mount  222 . Moving the tilt assembly  710  upward on the upper legs  706  increases the tilt angle  718  of the footrest assembly  700 . The terminal end  720  of each of the upper legs  706  is cut away to engage the footrest assembly  700  onto the seat pan assembly  702 . The terminal end of each of the upper legs has a footrest mounting pin  722  that engages the footrest assembly mount  724  and forms a pivot for the tilt assembly. 
       FIG. 10B  is a side view of the seat pan assembly  702 . Footrest assembly mount  724  has a truncated elliptical profile with a J slot  726  to accommodate the footrest mounting pin  722  (shown in  FIG. 10A).FIG .  10 C shows a detailed side view of the terminal ends  720  of the footrest assembly engaging the footrest assembly mount  724 . Terminal ends  720  of the footrest assembly are initially positioned perpendicular to the caster mount face  698  and are slid into the footrest assembly mount  724  until the mounting pin  722  slides into the J slot  726  of the assembly mount. The truncated elliptical profile is preferred so that the terminal ends of the footrest assembly can slide over the truncated portion of the assembly mount. The terminal ends have a front cut-away and a rear cut-away. The depth of the front cut-away is dimensioned such that when the mounting pin is at the end of the J slot, the terminal end can be rotated into the downward configuration without interference between the front cut-away and the curved portion of the assembly mount while at the same time preventing upward motion of the footrest assembly relative to the assembly mount. The rear cut-away depth is dimensioned to allow the terminal ends to slide over the assembly mount during mounting or dismounting of the footrest assembly from the seat pan assembly. In accordance with the embodiments described, the footrest assembly may advantageously be disassembled from the personal vehicle without operation of any screws or other fasteners and without the use of tools. 
       FIG. 11A  shows a seat back assembly  730  for a personal vehicle, with the seat back cover removed. In accordance with a preferred embodiment of the invention, a handle  732  is provided to permit an assistant to exert forces on the vehicle. Operation of a balancing personal vehicle in an assisted mode of operation is described in copending provisional application 60/124,403. The height of handle  732  may be adjusted, typically over a range of 18–20 inches above seat back  734 , using any method of locking telescoping members known in the mechanical arts, such, for example, as wedge clamps secured by tightening of handle adjustment locks  736 . 
     Referring to  FIG. 11B , seat back  734  may be tilted and locked in various tilted positions by engaging locking pins  750 , urged by locking pin springs  752 , into one of several locking pin holes  754  as seat back  734  pivots about tilt pivot  748 . Tilt plates  756  disposed on either the right or left sides of the seat pan, or both, allow adjustment of the seat back with respect to seat pan mount  760  to fit the user. Locking pins  750  are activated by a cable actuating a locking pin cam  758  or otherwise as known to persons skilled in the mechanical arts. 
     In order to provide information to controller  2  as to the current position of seat back  734 , a sensor mechanism  762  is provided. Sensor mechanism  762  includes a magnetized orientation plate  764  with respect to which the seat back moves as it is being tilted, and magnetic sensors fixed with respect to the seat back. In a preferred embodiment, two magnetic sensors, such as Hall effect sensors, for example, are mounted in sensor mounting holes  766  so as to sense the pattern of magnetization of orientation plate  764  as it passes by the sensors. The magnetization pattern of magnetized orientation plate  764 , in accordance with a preferred embodiment, is shown in  FIG. 11C , where the hatched areas are south magnetic pole and the unhatched areas are north pole. The asymmetry of the magnetization pattern allows the resolution, with redundancy, of three positions using only two sensors. The use of differing magnetization patterns and numbers of sensors are also within the scope of the invention. 
     The location of the center of gravity (CG) of the user is important on a dynamically stabilized personal vehicle because it determines the desired pitch angle which the power base tries to maintain whether operated in a balancing mode, on fewer than three wheels, or in an enhanced stability mode wherein the vehicle may otherwise be statically stable. The CG plays a role in determining the stability even of a vehicle operated in a mode that is not actively stabilized. Therefore, it is desirable to provide for controlling the location of the user&#39;s CG via seat adjustments. 
       FIG. 12A  shows a schematic diagram of one seat adjustment scheme, in accordance with an embodiment of the invention, where back frame  800  of seat  802  is fixed in location with respect to power base  804 . Seat  802 , which is attached to power base  804  via seat quick-disconnect  806  discussed above in reference to  FIG. 5 , is positioned for the smallest likely user  808  so that the user&#39;s legs  810  can clear the power base  804 , and then the seat pan  812  is lengthened to accommodate larger users  814 . Although mechanically simple, this seat adjustment scheme results in the CG  816  of the large user being far forward of the desired position, which is directly over the cluster axis  818 , along a line designated  820 . The problem is further exacerbated by the fact that the largest user is also the heaviest, making the gravitational torque placed on the system by the user (about the point of contact  822  of the forward wheel, for example) dramatically larger. 
       FIG. 12B  shows a further seat adjustment scheme, in accordance with a preferred embodiment of the invention, where the front edge  824  of the seat pan  812  is fixed with respect to the power base  804 , and the seat size is adjusted by moving the seat back in the aft direction. This results in the CG of the large user  814  and the CG of the small user  808  remaining relatively close to the desired location. To further optimize the seat adjustment, the entire seat location may be made adjustable in the fore-aft direction, allowing optimal placement of the CG for all users. 
     Referring now to  FIG. 13A , a perspective view is shown of an embodiment of a seat assembly  850  for use with a personal vehicle. Caster assembly  200  is shown, as described above with reference to  FIGS. 2–4 . Also shown are footrest assembly  700  (described with reference to  FIGS. 5A–5B ), seat pan  812 , armrest  378 , rotatable armrest support  848 , extensible attendant handle  732 , and seat back  734 . The seat pan assembly, designated generally by numeral  852 , is shown in greater detail in the perspective view from below of  FIG. 13B . Seat pan  812  is drilled with armrest assembly mounting holes  702  for attachment of an armrest assembly as described below. The multiplicity of armrest assembly mounting holes, along with the provision for changing the size of the seat pan allow flexibility in tailoring the seating arrangement to the dimensions of the occupant of the seat. To provide additional flexibility, and to optimize placement of the CG of the user as discussed above with reference to  FIGS. 12A and 12B , multiple seat back assembly mounting holes  854  are provided in seat runner weldment  856 . Flange  254  of seat stem  252  is shown as used in conjunction with the seat quick-disconnect mechanism described above in reference to  FIGS. 5A and 5B .  FIG. 13C  shows an exploded view of rotatable armrest support  848 , and  FIG. 13D  shows an assembled view of the same rotatable armrest support. The height of armrest  378  (shown in  FIG. 13A ) may be adjusted to suit the user, in accordance with an embodiment of the invention, by raising or lowering upper riser weldment  860  which slides inside armrest bracket weldment  862 . Upper riser weldment  860  is locked into place by tightening torque collar screw  864  on shaft collar  866 . Pivot weldment  868  is notched to accept armrest tilt locking pin  870  on armrest bracket weldment  862  so as to lock the armrest riser in the upright position. The armrest may be rotated by pulling the armrest riser outward, thereby compressing spring  872  and disengaging pin  870  from notch  874 . Slots  876  allow for adjustment of the position of the armrests as weldment  868  is secured to the seat pan. 
     The described embodiments of the invention are intended to be merely exemplary and numerous variations and modifications will be apparent to those skilled in the art. All such variations and modifications are intended to be within the scope of the present invention as defined in the appended claims.