Abstract:
A human-powered vehicle ( 100, 560 ) includes a structural frame ( 105 ) supported on multiple road wheels including driven wheels ( 110 ) each rotatable about an axle for propulsion, a seat ( 115 ) secured to the frame ( 105, 554 ) for supporting an operator, a hand crank ( 250 ) disposed above the driven wheel ( 110 ) and rotatable by hand by an operator seated in the seat ( 115 ), and a steerable rear wheel ( 120 ) operably linked to the seat ( 115 ) such that pivoting of the seat ( 115 ) about a seat pivot axis causes pivoting of the rear wheel ( 120 ) to steer the vehicle ( 100, 560 ).

Description:
TECHNICAL FIELD  
       [0001]     This invention relates to mobility assistance devices, and more particularly to a wheeled vehicle for handicapped or rehabilitating users, as well as able-bodied individuals.  
       BACKGROUND  
       [0002]     Wheelchair designs provide very limited mobility when one considers the types of terrain and the varied environments which they are incapable of navigating with any sense of ease.  
         [0003]     There are many variations and adaptations derived from the conventional design, including both three-wheeled and four-wheeled assisted mobility devices. Unfortunately, many of these designs also have significant limitations when applied to a wide range of environments and varied terrain and are limited by a combination of one or more of the following: a high risk of tipping over on uneven ground; difficulty in riding over small or moderately-sized obstacles such as ruts, stones or missing pieces of pavement; a high incidence of fatigue or strain involving the hand and wrist; an inability to be operated by a rider having limited use of one hand or arm; difficulty in mounting and dismounting the vehicle due to inherent design constrictions; awkward or inefficient steering and propulsion functions. A vehicle is desired which satisfies a number of these functional limitations.  
       SUMMARY  
       [0004]     According to one aspect, the invention features a human-powered vehicle having a structural frame, two front wheels mounted to fixed axles at a forward portion of the frame for rotation, a seat secured to the frame, the seat positioned between the front wheels and adapted to pivot about a seat pivot axis, and a steerable rear wheel mounted to the frame behind the seat and defining a rear wheel kingpin axis, the rear wheel operably linked to the seat such that pivoting of the seat about the seat pivot axis causes pivoting the rear wheel about the kingpin axis to steer the vehicle.  
         [0005]     According to another aspect, the invention features a human-powered vehicle comprising a structural frame, two front wheels mounted to a forward portion of the frame for rotation, a seat secured to the frame, the seat positioned between the front wheels and adapted to pivot about a seat pivot axis, a steerable rear wheel mounted to the frame behind the seat and defining a rear wheel kingpin axis, the rear wheel operably linked to the seat by a flexible chain assembly such that pivoting of the seat about the seat pivot axis causes pivoting of the rear wheel about the kingpin axis to steer the vehicle, and a neutral bias actuator connecting the seat and the structural frame and biasing the seat toward a neutral pivot position, wherein the seat pivot axis is declined toward the front of the vehicle to define a declination angle of between about 25 and 75 degrees, wherein at least one of the two front wheels is operably connected to a hand-operable crank for propulsion of the vehicle.  
         [0006]     According to another aspect, the invention features a human-powered vehicle comprising a structural frame, two front wheels mounted to a forward portion of the frame for rotation, a seat secured to the frame, the seat positioned between the front wheels and adapted to pivot about a seat pivot axis, a steerable rear wheel mounted to the frame behind the seat and defining a rear wheel kingpin axis, the rear wheel operably linked to the seat by a flexible chain assembly such that pivoting of the seat about the seat pivot axis causes pivoting of the rear wheel about the kingpin axis to steer the vehicle, and a neutral bias actuator connecting the seat and the structural frame and biasing the seat toward a neutral pivot position, wherein the seat pivot axis is substantially vertical, wherein at least one of the two front wheels is operably connected to a hand-operable crank for propulsion of the vehicle.  
         [0007]     In one embodiment, the seat pivot axis is substantially vertical. In another embodiment, the seat pivot axis is declined toward the front of the vehicle to define a declination angle between about 25 and 75 degrees, more preferably between about 35 and 50 degrees and most preferably about 45 degrees. The seat pivots at the declination angle about at least two pivot points.  
         [0008]     In one embodiment, at least one of the two front wheels of the vehicle is operably connected to a hand-operable crank for propulsion of the vehicle. The vehicle may include two independent hand-operable cranks, each crank operably connected to a corresponding one of the front wheels. In another embodiment, the hand-operable cranks of the vehicle are adapted to be rotatable about substantially horizontal axes disposed above the front wheels. The hand-operable cranks can include crank sprockets and the front wheels can include wheel sprockets, the crank sprockets being coupled to the wheel sprockets by means for positive engagement. The wheel sprockets can be coupled to the wheels by freewheel sprockets.  
         [0009]     In another embodiment, each of the independent hand-operable cranks is adapted to drive a miter gear and each of the two front wheels is adapted to be driven by a bevel gear. The crank miter gear is coupled to the wheel hub bevel gear by a driveshaft for positive engagement. The hub bevel gear is attached to the front wheel hub for positive rotation of the front wheel.  
         [0010]     In one embodiment, the seat is operably connected to the rear wheel by a flexible chain. The chain may be trained about a drive sprocket secured to the seat and a driven sprocket secured to the wheel, the chain being crossed between the drive and the driven sprockets. The seat is operably linked to the rear wheel to define a steering ratio of between about 3:1 and 6:1, and preferably about 4.5:1.  
         [0011]     In another embodiment, the seat is operably connected to the rear wheel by a flexible cable. The cable may be trained about a drive pulley secured to the seat and a driven pulley secured to the wheel, the cable being crossed between the drive and the driven pulleys.  
         [0012]     In another embodiment, the seat assembly is operably connected to the rear wheel assembly by one or more miter gears, bevel gears and a drive shaft. The seat assembly rotates upon a vertical axis and is adapted to rotate a bevel gear. The rear wheel assembly is adapted to be rotated by a miter gear. The seat assembly bevel gear is coupled to the rear wheel assembly miter gear by a drive shaft for positive engagement.  
         [0013]     In another embodiment, the seat assembly is operably connected to the rear wheel assembly by a drive sprocket, a chain, a driven sprocket, a drive shaft and two bevel gears. The seat assembly rotates upon a horizontal axis and is adapted to rotate a drive sprocket, a chain, and a driven sprocket. The rear wheel assembly is adapted to be rotated by a bevel gear. The seat assembly driven sprocket is coupled to the rear wheel assembly bevel gear by a drive shaft for positive engagement.  
         [0014]     In another embodiment, the seat assembly is operably connected to the rear wheel assembly by one or more bellcranks, hydraulic cylinders and hydraulic lines. The seat assembly rotates upon a vertical axis and is adapted to rotate a forward bellcrank. The rear wheel assembly is adapted to be rotated by a rear bellcrank. The seat assembly bellcrank is coupled to the rear wheel assembly bellcrank by hydraulic cylinders and hydraulic lines for positive engagement.  
         [0015]     In another embodiment, the seat assembly is operably connected to the rear wheel assembly by pinion gears and a gear rack. The seat assembly rotates upon a vertical axis and is adapted to rotate a forward pinion gear. The rear wheel assembly is adapted to be rotated by a rear pinion gear. The seat assembly pinion gear is coupled to the rear wheel assembly pinion gear by a gear rack for positive engagement.  
         [0016]     The vehicle may further include independent hand-operable front and rear brakes. In accordance with further embodiments of the invention, the vehicle includes an actuator connecting the seat and the structural frame and biasing the seat toward a neutral pivot position. In one embodiment, the actuator is an adjustable pressurized cylinder or spring, for example. In another embodiment, the front wheels are each mounted for rotation about a respective axle secured to the frame by a fork spanning the wheel. In another embodiment, the front wheels are each mounted for rotation about a respective cantilevered axle secured to the frame. In one embodiment, to improve stability, the front wheels are slanted toward each other to define a positive camber angle with respect to vertical. According to one embodiment, the seat is positioned such that the rear wheel carries between about 20 and 40 percent of the total combined weight of the operator and the vehicle in a static condition.  
         [0017]     In accordance with one embodiment, the vehicle includes a steering assembly alignment device located beneath the seat, which includes a shaft collar affixed to the steering drive sprocket. The shaft collar is mounted upon the vertical seat post shaft, and held in position by one or more setscrews. Loosening the setscrews located within the shaft collar allows the drive sprocket to be adjusted relative to the seat post shaft, thereby adjusting alignment of the seat position relative to the position of the rear wheel.  
         [0018]     In accordance with further embodiments of the invention, the vehicle may include a damper connecting the rear wheel fork and the structural frame, allowing for improved steering and handling by preventing excessive rotational motion of the rear wheel fork assembly. In another embodiment, the damper is a bi-directional torsion spring which is fitted to the vertical steering tube and vehicle frame and provides a dampening effect to any rotational forces.  
         [0019]     In accordance with further embodiments of the invention, the vehicle may include a dual position handle attached to each of the hand operable cranks. The handle may be positioned in either a horizontal position for circular cranking or in a vertical position for forward and back reciprocal lever cranking.  
         [0020]     In accordance with further embodiments of the invention, the vehicle may include one or more locking brakes and one or more retractable footrests. The locking brake positively engages a frame mounted retractable pin and a brake disc affixed to each front wheel. The retractable footrest is mounted to a forward position of the vehicle frame.  
         [0021]     The mobility assistance device described herein can provide a safe, efficient and improved approach to enhanced mobility under a wide range of settings and conditions. In addition, it can enable a number of rehabilitative functions, as well as providing recreational cross-training opportunities for able-bodied individuals. It is particularly useful in enhancing the mobility of users with a lower extremity disability and a moderate level of upper body strength. The modes of steering and propulsion of the vehicles can be adapted and configured to complement the unique physical capabilities of such users. In addition to enhancing the mobility of the user, the vehicles can provide therapeutic and rehabilitative benefits.  
         [0022]     One embodiment of the invention is especially well suited for providing mobility within confined indoor spaces while still providing excellent mobility for rough or uneven outdoor terrain. One embodiment utilizes shaft-drive propulsion and a compact frame design.  
         [0023]     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
     
    
     DESCRIPTION OF DRAWINGS  
       [0024]      FIG. 1  is a perspective view of the vehicle according to one embodiment of the invention.  
         [0025]      FIGS. 2A and 2B  depict top views of the vehicle of  FIG. 1  in neutral and turned positions, respectively.  
         [0026]      FIG. 2C  is a detailed side view of the vehicle of  FIG. 1 , depicting the steering assembly alignment device.  
         [0027]      FIG. 2D  is a detailed bottom view of the vehicle of  FIG. 1 .  
         [0028]      FIG. 3  is a side view of the vehicle of  FIG. 1 .  
         [0029]      FIG. 4  is a front view of the vehicle of  FIG. 1 .  
         [0030]      FIG. 5  is a detailed view of the rear wheel steering assembly of the vehicle of  FIG. 1 .  
         [0031]      FIG. 6  is a perspective view of the vehicle according to another embodiment of the invention.  
         [0032]      FIGS. 7A and 7B  are top views of the vehicle of  FIG. 6 , in neutral and turned positions respectively.  
         [0033]      FIG. 8  is a side view of the vehicle of  FIG. 6 .  
         [0034]      FIG. 9  is a front view of the vehicle of  FIG. 6 .  
         [0035]      FIG. 10  is a front view of an alternative embodiment of the vehicle of  FIG. 6  where the front drive wheels are cambered to enhance stability of the vehicle.  
         [0036]      FIGS. 11A and 11B  are side views of a reverse gear drive in an engaged and disengaged position, respectively.  
         [0037]      FIGS. 12A and 12B  show detailed views of the reverse gear of  FIGS. 11A and 11B .  
         [0038]      FIG. 13  shows a detailed view of components of the reverse gear drive of  FIGS. 11 and 12 .  
         [0039]      FIG. 14  is a perspective view of the vehicle according to another embodiment of the invention.  
         [0040]      FIG. 15  is a side view of the vehicle in  FIG. 14 .  
         [0041]      FIG. 16  is a front view of the vehicle in  FIG. 14 .  
         [0042]      FIG. 17  is a perspective view of the shaft-drive propulsion for the vehicle in  FIG. 14 .  
         [0043]      FIG. 18  is a front view of the (right side) shaft-drive propulsion for the vehicle in  FIG. 14 .  
         [0044]      FIG. 19A  is a side view of the vehicle according to another embodiment of the invention.  
         [0045]      FIGS. 19B through 19D  are various detail views of the vehicle of  FIG. 19A .  
         [0046]      FIG. 20  is a top view of the vehicle of  FIG. 19  in a turned position.  
         [0047]      FIGS. 21A and 21B  are front views of the vehicle of  FIG. 19  in neutral and turned positions, respectively.  
         [0048]      FIG. 22  is a side view of the vehicle according to another embodiment of the invention.  
         [0049]      FIG. 23A  is a side view of the vehicle according to another embodiment of the invention.  
         [0050]      FIGS. 23B and 23C  are various detail views of the vehicle of  FIG. 23A .  
         [0051]      FIG. 24  is a front view of the vehicle of  FIGS. 23A through 23C .  
         [0052]      FIGS. 25A and 25B  are top views of an alternative embodiment of the vehicle of  FIG. 1  where the steering is actuated by a hydraulic assembly in turned and neutral positions, respectively.  
         [0053]      FIGS. 26A and 26B  are top views of an alternative embodiment of the vehicle of  FIG. 1  where the steering is actuated by a rack and pinion gear assembly in turned and neutral positions respectively.  
         [0054]      FIG. 27  is a front view of the left side of an alternative embodiment of the crank arm assembly and an alternative embodiment of the brake assembly of the vehicle of  FIG. 14 .  
         [0055]      FIGS. 28A and 28B  are detail side views of the crank arm assembly of  FIG. 27 .  
         [0056]      FIG. 29A  is a rear view of a crank arm assembly and the (right side) locking brake assembly.  FIG. 29B  is a detail view of the locking brake assembly of  FIG. 29A .  
         [0057]      FIG. 30  is a detailed view of an alternative embodiment of a footrest assembly for the vehicles of  FIGS. 1, 6 ,  14 ,  19 A,  22  and  23 A. 
     
    
     DETAILED DESCRIPTION  
       [0058]     Throughout the discussion of the illustrative embodiments, it is to be understood that in the figures, like references generally refer to like elements throughout the different views.  
         [0059]     Referring to  FIGS. 1, 2A  and  2 B, a vehicle  100  has a structural frame  105 , two front drive wheel assemblies  110   a ,  110   b  (hereafter collectively referred to as  110 ), a seat  115 , and a steerable rear wheel assembly  120 . In one embodiment, frame  105  is of tubular construction and consists of a horizontal equilateral triangle with an extension  125  to support the rear wheel assembly  120 . The two front drive wheel assemblies  110  may include front forks  130   a ,  130   b  which are affixed to a forward portion of the frame  105  in front of the seat  115 .  
         [0060]     The seat  115  is rotatably mounted to the frame  105  between and aft of the two front drive wheels assemblies  110 . The seat  115  is operably connected to the rear wheel assembly  120  such that rotation of the seat  115  causes rotation of the rear wheel assembly  120  to effect steering of the vehicle  100 . Advantageously, the seat  115  includes a seat base  117  and a seat back  119 , the seat base  117  declined rearward to keep the rider well positioned in the seat  115 . In some embodiments, the vertical height of the seat base  117  is adjustable and the angle of inclination of the seat back  119  is adjustable. The seat may be constructed from fiberglass, metal or other substantially rigid material. Alternatively, the seat  115  is a simple platform with aluminum rails (not shown) having fabric mesh laced thereon for improved comfort on the seat base  117  and the seat back  119 . The seat  115  may include layers of foam or other resilient materials to increase rider comfort and reduce fatigue. In some embodiments, the vehicle includes a footrest  128 . The footrest  128  is attached to a forward lower portion of the frame  105  between the front drive wheel assemblies  110 . Appropriate configured rests (not shown) may be included along the footrest  128  for receiving and retaining the feet of the rider.  
         [0061]     The rear wheel assembly  120  may include a rear fork  132 , a rear hub and rim combination  133  for supporting a rear tire  134 . In one embodiment, the rear tire has a high profile for improved rider comfort and stability of the vehicle  100 . The front drive wheel assemblies  110  include front drive hubs  140   a ,  140   b , spokes  141  or other means of attaching the hub to the rim, rims  145   a ,  145   b  for supporting front tires  150   a ,  150   b . In one embodiment, the front drive hubs  140  are conventional bicycle-style hubs as shown in  FIG. 1 . In another embodiment, the front drive hubs  140  are a cantilever-style axle and hub combination supported by a single wheelchair-style mount  399  ( FIG. 14 ). In one embodiment, the front forks  130  are 24-inch bicycle forks and may include gussets (not shown) to add additional strength.  
         [0062]     Advantageously, the vehicle  100  is configured to enable a user to mount and dismount the seat  115  independently or with minimal assistance. In one embodiment, the user mounts and dismounts the seat  115  from the front of the vehicle  100  between the front drive wheel assemblies  110 . Mounting and dismounting the vehicle can vary according to the combined abilities and disabilities of the particular user. The overall size and configuration of the vehicle  100  may be modified to accommodate the size of the user and the intended application for the mobility device (e.g., indoor or outdoor use). In one embodiment, the seat  115  is located on the frame  105  aft of the front drive wheel assemblies  110  such that the rear tire  134  carries between about 20 and 40 percent of the total combined weight of the operator and the vehicle  100  in a static condition. The configuration of the frame  105  and the diameter of the rear wheel  134  ensures a relatively low center of gravity for enhanced stability of the vehicle  100 , particularly over uneven terrain. In some embodiments the front drive wheel assemblies  110  are slanted toward each other above the frame  105  to define a positive camber angle with respect to vertical (see  FIG. 10 ) to improve overall vehicle stability.  
         [0063]     The frame  105  may be constructed from a range of materials including for example, aluminum, steel, or steel alloy, depending on the intended application of the vehicle  100 . In one embodiment, the frame  105  is constructed of primarily 1¼-inch 4130 chrome moly tubing, which has been gas metal arc welded (MIG welded). The 4130 chrome moly tubing provides a high strength-to-weight ratio.  
         [0064]     Referring now collectively to  FIGS. 2A, 2B ,  3  and  4 , and in one embodiment, steering of the vehicle is accomplished by rotation of the seat  115  about a substantially vertical axis  160  ( FIG. 4 ). The seat  115  is mounted to a platform  165  that is affixed to the top end of a steering support shaft  170 . The seat steering support shaft  170  is rotatably affixed to the frame with a bearing assembly to permit free rotation of the seat  115 . A drive sprocket, pulley or chain ring  175  is affixed to the lower end of the seat support shaft  170 . The rear fork  132  includes a driven rear sprocket or pulley  180  attached to the fork steerer tube  198  and rotatably affixed to the frame  105 , with a headset or other bearing assembly. The driven rear sprocket or pulley  180  is attached to the fork steerer tube  198  below the bearing surface on the frame  105 .  
         [0065]     In one embodiment, a chain  185  is trained around the steering drive sprocket  175  and the rear driven sprocket  180  to operably connect the seat  115  and the rear wheel assembly  120 . The chain  185  may be, for example, a flexible chain, roller chain, cable or nylon belt. Advantageously, the chain  185  is disposed about the drive sprocket  175  and the rear driven sprocket  180 , crossed in a “figure-8” configuration as shown in  FIGS. 1, 2A  and  2 B. The chain  185  can include turnbuckles  190   a ,  190   b  to enable the adjustment of the tension of the chain  185  and prevent the chain  185  from derailing from the drive sprocket  175  and rear driven sprocket  180 . In some embodiments, the relative position of the drive sprocket  175  can be adjusted to properly establish the chain line between the drive sprocket  175  and the rear driven sprocket  180 .  
         [0066]     Referring to  FIG. 2C , one embodiment of the vehicle  100  includes a steering alignment assembly  191  located beneath the seat  115 , which includes a shaft collar  192  affixed to the steering drive sprocket  175 . The shaft collar  192  is disposed upon the seat steering support shaft  170  and held in position by set screws  194 .  
         [0067]     Loosening the set screws  194  located within the shaft collar  192  allows the drive sprocket  175  to be adjusted relative to the seat steering post shaft  170 , thereby adjusting alignment of the seat position relative to the position of the rear wheel assembly  120 .  
         [0068]     Referring to  FIGS. 2C and 2D , and in one embodiment, the seat steering assembly  114 , comprised of the seat  115 , seat platform  165 , seat steering support shaft  170 , actuator  195 , drive sprocket  175 , steering shaft collar  192  and steering shaft collar set screw  194 , includes at least one actuator  195  disposed between the platform  165  at a first end and the frame  105  at a second end. When the seat  115  is rotated for turning the vehicle  100 , the actuator  195  is biased toward returning the seat  115  and consequently the rear wheel assembly  120  toward a centered, straight-ahead position. The actuator  195  may be a pre-tensioned adjustable spring, an adjustable pressurized cylinder, or a similar biasing device. In one embodiment, the actuator  195  is adjusted to accommodate, for example, the weight of the rider and the intended use of the vehicle  100 .  
         [0069]     In operation, when the rider rotates the seat  115  in one direction, the crossed chain  185  rotates the rear wheel assembly  120  in an opposite direction, but the vehicle turns in a direction corresponding to the direction of rotation of the seat  115 . As shown in  FIG. 2B , rotating the seat  115  toward the right, results in a rotation of the rear wheel assembly  120  toward the left. This results in the vehicle  100  turning to the right, corresponding to the direction of rotation of the seat  115 .  
         [0070]     Referring to  FIG. 5 , in one embodiment, the vehicle may include a damper  197  connecting the rear wheel fork  132  and the structural frame  105 , allowing for improved steering and handling by preventing excessive rotational motion of the rear wheel assembly  120 . In one embodiment, the damper  197  is a bi-directional torsion spring which is fitted to the fork steerer tube  198  and the frame  105  and provides a dampening effect to any rotational forces.  
         [0071]     Referring now to  FIG. 6 , in a second embodiment, steering of the vehicle  100  is accomplished by rotation of the seat  115  about a seat pivot axis  200 , which is declined toward the front of the vehicle  100  to define a declination angle D. The declination angle D is preferably between about 25 degrees and 75 degrees, more preferably between about 35 degrees and 50 degrees and most preferably about 45 degrees. In one embodiment, the seat  115  is suspended on and rotates about an upper pivot attachment point  205  and a lower pivot attachment point  210  positioned along the seat pivot axis  200 .  
         [0072]     The upper attachment point  205  is mounted high on the seat back  119  and the lower pivot attachment point is mounted in a frontward portion of the seat base  117 . As the angle of rotation of the seat  115  is not substantially parallel to the angle of rotation of the rear wheel assembly  120 , as previously described with reference to FIGS.  1  to  2 C, a modified steering linkage is utilized. A chain  215  is trained about the rear sprocket  180  of the rear wheel assembly  120 . Two steering cables  220   a ,  220   b  attached to each end of the chain  215  at turnbuckles  190   a ,  190   b  operably connect the rear sprocket  180  of the rear wheel assembly  120  to the seat  115  at cable attachment points  225   a ,  225   b . In one embodiment, the steering cables  220  are aircraft cables having swaged ends for attachment to the turnbuckles  190  and the seat  115 .  
         [0073]     Advantageously, the chain  215  is crossed about the rear sprocket  180  in a “figure-8” configuration as shown in  FIGS. 6, 7A  and  7 B. The turnbuckles  190  also provide adjustability of tension of the chain  215  about the rear sprocket  180 . With renewed reference to  FIG. 6 , the steering cables  220  are redirected from a substantially horizontal orientation to a substantially vertical orientation for attachment to the seat  115  at attachment points  225   a ,  225   b  through guides  230   a ,  230   b . The guides  230  are affixed to the frame  105 .  
         [0074]     Referring now collectively to FIGS.  6 ,  7 A- 7 B,  8  and  9 , in operation, when the rider leans to turn the seat  115  in one direction, the chain  215  rotates the rear wheel assembly  120  in an opposite direction, but the vehicle turns in a direction corresponding to the direction of rotation of the seat  115 . As shown in  FIG. 7B , rotating the seat back  119  toward the left results in a rotation of the rear wheel assembly  120  toward the right. This results in the vehicle  100  turning to the left. This left turn is initiated by the rider leaning to the left with the upper torso, which results in the seat base  117  rotating to the right. This steering configuration allows the rider to lean into turns and improves overall maneuverability and stability of the vehicle  100 . According to one embodiment, the ratio between the diameter of the rear sprocket  180  and the distance between attachment points S is selected such that, the seat  115  rotates in the direction of arrows  235  about 10 degrees to the left and right to achieve a full range of steering of the vehicle  100 .  
         [0075]     Referring now to  FIGS. 1 and 10 , in one embodiment, the vehicle  100  includes two independent hand-operable crank assemblies  250   a ,  250   b  each operably connected to a corresponding front drive wheel assembly  110  for propulsion of the vehicle  100 . The hand-operable crank assemblies  250  include crank sprockets  255   a ,  255   b , crank arms  260   a ,  260   b  and handles  265   a ,  265   b  rotatably mounted to the crank arms  260   a ,  260   b . In one embodiment, the crank sprockets  255   a ,  255   b  are conventional bicycle chain rings, the crank arms  260   a ,  260   b  are bicycle pedal cranks and the handles  265   a ,  265   b  are modified pedal spindle bolts surrounded with a padded sleeve for comfort and grip. The crank sprockets  255   a ,  255   b  are coupled to front wheel sprockets  270   a ,  270   b  by front drive chains  275   a ,  275   b . The chains  275   a ,  275   b  are roller chains, toothed nylon belts, or similar flexible connecting means. In one embodiment, the crank sprockets  255  are each a 28-tooth chain ring and the front wheel sprockets  270  are each a 32-tooth chain ring. The front wheel sprockets  270  are coupled to front wheel drive hubs  140 .  
         [0076]     In operation, rotating the handles  265  in a first direction, rotates the front drive wheel assembly  110  and the vehicle  100  in a forward direction. Advantageously, the front wheel sprockets  270  may be freewheel sprockets, which allow the rider to pedal the vehicle  100  forward and coast if not pedaling. Also, by employing freewheel sprockets, the handles  265  can be rotated in a second direction to position the handles  265  for maximum leverage when, for example, starting the vehicle  100  from a stationary position. Tension in the front drive chains  275  is maintained and adjusted by changing the height of the hand operable crank assemblies  250  which are attached to the upper ends of the external adjuster tubes  284  which are disposed over the front fork steerer tubes  280   a ,  280   b . The position of the external adjuster tubes  284  are held in place over the front fork steering tubes  280  by two pinch bolts, for example (not shown). Different lengths of the crank arms  260 , varying configuration of handles  265 , and crank sprockets  255  to front wheel sprockets  270  ratios are all contemplated by the invention to suit particular applications.  
         [0077]     In one embodiment, the vehicle  100  may include a reverse gear drive assembly  300  as depicted in  FIGS. 11A, 11B ,  12 A,  12 B and  13 . The reverse gear drive assembly  300  is attached to one or both adjustable crank assemblies  250  above the front drive wheel assemblies  110 . The circumferential surface of a reverse roller  305  is scored or knurled for direct positive engagement with the front tires  150 . The reverse direction is denoted by the arrow  307  and the direction of reverse rotation is denoted by the arrow  309 . The reverse cog  310  is positioned for engagement of the chain  275  against upper and lower jockey rollers  317 ,  319 . The reverse gear drive assembly  300  includes a reverse roller  305  ( FIG. 13 ) joined to a freewheeling reverse cog  310  which is rotatably attached to the bracket  315 . The bracket  315  is attached rotatably to a pivot  320 . A clamp handle  325  is rotatably attached to the bracket  315  via a first lever  335  and a second lever  340 . In one embodiment, the clamp handle  325  of the reverse gear drive assembly  300  is a Destaco-type clamp which simultaneously locks the reverse roller  305  into position for engagement with the front tires  150  and the reverse cog  310  into position for engagement with the front drive chain  275  until manually released. Other suitable clamp devices are contemplated.  
         [0078]     In operation, movement of the clamp handle  325  in the direction of the arrow  327  ( FIGS. 11B and 13 ) displaces the first and second levers  335 ,  340  thereby rotating bracket  315  about the pivot  320  and engaging the reverse roller  305  with the front tire  150  and engaging the reverse cog  310  with the chain  275   b . With the reverse gear drive assembly  300  engaged, rotation of the crank arm  260  in the direction of the arrow  345  rotates the reverse cog  310  and the reverse roller  305  for rotation of the front drive wheels  110  in the direction necessary for rearward propulsion of the vehicle  100 . The freewheeling reverse cog  310  allows for forward motion of the vehicle  100  while the reverse gear drive assembly  300  is engaged. Other types of reverse drive mechanisms are contemplated.  
         [0079]     With renewed reference to  FIG. 1 , and in one embodiment, the vehicle  100  includes individual braking controls. A first front brake lever  350  controls one or both of the front brakes  355  attached to the front forks  130  for braking the front drive wheel assemblies  110  and a second brake lever  360  may control either a front brake  355  or a rear brake  365  which is attached to the rear wheel assembly  120 . In one embodiment, front brakes  355  are linear side pull or center pull brakes positioned on the front forks  130  to come into contact with each front rim  145  when activated by a front brake lever  350 ,  360 . In another embodiment, the front brakes are hub brakes. In one embodiment, the rear brake  365  is a mechanical disc brake mounted to the hub of the rear wheel assembly  120 . The vehicle  100  includes a parking brake, which may be a lockable detent pin (not shown) within a front brake lever  350 ,  360  for locking one or more wheels. In such embodiments, the parking brake retains the vehicle  100  in a stationary position during transfers, mounting or dismounting.  
         [0080]     The activation mechanisms linking the first and second brake levers  350 ,  360  and the front brakes and rear brakes  355 ,  365 , can include, for example, stainless steel cables with or without a lined housing, or hydraulic lines. Other braking systems suited to accommodate a rider&#39;s abilities and the vehicle application, including the full range of hand-activated braking mechanisms designed for bicycles and motorcycles in various combinations with the activation mechanisms are contemplated.  
         [0081]     Referring now to  FIGS. 14 through 18 , in one embodiment, the vehicle  100  includes two independent hand-operable crank assemblies  250   a  and  250   b , each operably connected to corresponding front drive wheel assemblies  110  for propulsion of the vehicle  100  in a forward and reverse direction.  
         [0082]     With specific reference to  FIG. 18 , and in one embodiment, the crank handle  265  is rotatably attached to the crank arm  260  which is mounted to the crank arm housing  385 . A roller clutch  386  is pressed into the crank arm housing  385 . The crank arm housing  385  is attached to the crank drive shaft  387  for rotation. The crank drive shaft  387  is attached to the crank drive shaft housing  388  for rotation. The crank drive shaft  387  is supported by two bearings, an inboard bearing  420  and an outboard bearing  389  which are attached to the crank drive shaft housing  388 .  
         [0083]     The crank drive shaft housing  388  is attached to the upper end of the main drive shaft housing  390 . Affixed to the crank drive shaft  387 , in one embodiment, is a miter gear  391 . This miter gear  391  engages a second miter gear  392  which is attached to the upper end of the main drive shaft  393 . The main drive shaft  393  is housed within the main drive shaft housing  390 . The main drive shaft  393  is held in place, for rotation, by an upper bearing  394  and a lower bearing  395 , which are attached to the main drive shaft housing  390 . The main drive shaft housing  390  is attached to the frame  105  by one or more mounting brackets  400 .  
         [0084]     Attached to the lower end of the main drive shaft  393  is a bevel gear  396 . This bevel gear  396  is positioned in such a way as to engage a hub bevel gear  397  which is attached to the hub  398  of the front drive wheel assembly  110 . The hub  398  is attached to a cantilevered axle  399  which is attached to the frame of the vehicle  105 .  
         [0085]     In one embodiment, there is a hand-retractable spring plunger  401  mounted on the crank arm housing  385 . The hand-retractable spring plunger  401  can be positioned in either an engaged or a disengaged position. The hand-retractable spring plunger  401 , when placed in the engaged position, slides into a detent hole  402  which is located on the crank drive shaft  387 . The crank drive shaft  387  may have one or more detent holes  402 . When placed in the disengaged position, the hand-retractable spring plunger  401  is fully retracted into the body of the crank arm housing  385 , and no longer engages the detent hole  402  in the crank drive shaft  387 . Referring further to  FIG. 18 , the arrow  403  indicates the direction for disengaging the hand-retractable spring plunger  401 . The arrow  404  indicates the direction for engaging the hand-retractable spring plunger  401 . The hand-retractable spring plunger  401  is held in place in the disengaged position by the rider rotating the hand-retractable spring plunger  401  90 degrees into a locked position.  
         [0086]     In operation, the rider rotates the hand crank assembly  250  in a forward direction to propel the vehicle forward. This can be either a circular motion or a forward-and-back motion, both resulting in forward motion of the vehicle  100 . This is accomplished when the hand-retractable spring plunger  401  is in the disengaged position. This position is referred to as “freewheeling” in bicycling terminology. In this position, in the case of traveling down a hill, the front drive wheel assemblies  110  rotate while the hand crank assemblies  250  remain stationary.  
         [0087]     With the hand-retractable spring plunger  401  in the engaged position, the crank drive assembly  250  becomes a fixed drive. In this case, when the rider rotates the hand crank assembly  250  in a forward direction, the front wheel  110  rotates forward. When the rider rotates the hand crank assembly  250  in a reverse direction, the front drive wheel  110  rotates in a reverse direction. When the rider holds the hand cranks  250  stationary, the front wheels  110  will also remain stationary.  
         [0088]     In operation, the hand crank arm  260  turns the crank drive shaft  387 , which rotates the crankshaft miter gear  391  which rotates the upper drive shaft miter gear  392 , which rotates the main drive shaft  393 , which rotates the lower bevel gear  396  which rotates the hub bevel gear  397 . This accomplishes the rotation of the front drive wheel assembly  110  in a forward or reverse direction.  
         [0089]     Specifically, with the hand-retractable spring plunger  401  in the disengaged position, the forward motion of the hand crank arm  260  causes the roller clutch  386  to engage the crank drive shaft  387 . When the hand crank arm  260  is rotated in a reverse direction or remains stationary while the vehicle  100  is in a forward motion, the roller clutch  386  will disengage the hand crank arm  260  from the crank drive shaft  387 .  
         [0090]     With the hand-retractable spring plunger  401  in the engaged position, the hand crank arm  260  is positively engaged with the crank drive shaft  387 . In this instance, either forward or reverse rotation of the hand crank assembly  250  will result in a corresponding forward or reverse rotation of the front wheel assembly  110 .  
         [0091]     In another embodiment, the bevel gear  396  at the lower end of the main drive shaft  393  engages a modified coaster brake hub (not shown), such as the Sram internal gear hub with coaster brake which is a standard component within the bicycling industry.  
         [0092]     In operation, the modified Sram hub allows the rider to pedal forward for forward motion, freewheel in forward motion, and pedal in reverse for reverse motion. In the case of this embodiment, the roller clutch  386  and the spring loaded plunger  401  are excluded.  
         [0093]     In another embodiment, the inventors contemplate an adaptive feature which allows the rider to propel the vehicle using a lever-drive motion instead of a circular hand-crank motion. This would be accomplished by removing one or more of the crank handles  265  and replacing it with a specially fitted lever (not shown). This lever adaptation kit would include 2 adjustable stops which would determine the range of the lever&#39;s extension and retraction according to what is ideal for each individual (not shown).  
         [0094]     Referring now to  FIGS. 19A through 19D , and in one embodiment, a seat steering assembly  500  is suspended on and rotates about a forward pivot attachment point  502  and a rear pivot attachment point  504  positioned about a horizontal pivot axis  506 .  
         [0095]     The seat steering assembly  500  includes a seat back  508 , a seat base  510 , a seat frame  512 , and a steering shaft assembly  518 . The seat steering assembly  500  can also include left and right neutral bias actuators  540 . The steering shaft assembly  518  operably connects the seat frame  512  to a rear wheel assembly  552 . The forward portion of the seat frame  512  is rotatably attached to the forward pivot attachment point  502  with a bolt and a bearing assembly  514  ( FIG. 19B ). The rear portion of the seat frame  512  is affixed to the upper steering shaft  516 . The rear portion of the upper steering shaft  516  is rotatably affixed to an upper flange bearing  520  at the rear pivot attachment point  504 . The left and right neutral bias actuators  540  are disposed between the seat frame  512  on the first end and the vehicle frame  544  at a second end. When the seat assembly  500  is rotated for turning the vehicle  560 , the actuator  540  is biased toward returning the seat assembly  500  and consequently the rear wheel assembly  552  toward a centered, straight-ahead position. The actuator  540  may be a pre-tensioned adjustable spring, an adjustable pressurized cylinder or other biasing device.  
         [0096]     The steering shaft assembly  518  includes an upper steering shaft  516 , an upper flange bearing  520  ( FIG. 19C ), an upper drive sprocket  522 , a lower flange bearing  524 , a lower driven sprocket  526 , a roller chain  528 , a lower steering shaft  530 , a rear shaft support bearing  532  ( FIG. 19D ), a lower steering shaft bevel gear  534 , a vertical steering shaft bevel gear  536  and a vertical steering shaft  538 . In this embodiment, the steering shaft assembly  518  between the seat steering assembly  500  and rear wheel assembly  552  can permit more compact configurations of the vehicle  560 . In one example, the shafts  516 ,  530  and gears  534 ,  536  are completely or substantially enclosed by housing components, thereby reducing the rider&#39;s exposure to moving parts and reducing maintenance requirements.  
         [0097]     The upper steering shaft  516  is rotatably attached to the upper flange bearing  520 . The upper flange bearing  520  is affixed to the vertical frame plate  542  of the frame  544 . The upper drive sprocket  522  is affixed to the upper steering shaft  516  between the upper flange bearing  520  and the seat frame  512 . The lower driven sprocket  526  is affixed to the forward portion of the lower steering shaft  530 . The forward portion of the lower steering shaft  530  is rotatably attached to the lower flange bearing  524  which is affixed to the vertical frame plate  542 . The rear portion of the lower steering shaft  530  is supported by the rear shaft support bearing  532  which is affixed to the frame extension tube  546 . The lower steering shaft bevel gear  534  is affixed to the rear portion of the lower steering shaft  530 . The vertical steering shaft bevel gear  536  is affixed to the vertical steering shaft  538  and positioned within the rear steering housing  548  to be actuated by the lower steering shaft bevel gear  534 . Referring to  FIG. 19C , the upper drive sprocket  522  and the lower driven sprocket  526  are connected by a continuous loop of roller chain  528 . The upper flange bearing  520  incorporates a chain tension adjuster (not shown) which allows for tension adjustment of the roller chain  528 .  
         [0098]     Referring now to  FIGS. 19A and 19D , the vertical steering shaft  538  is affixed to the rear wheel assembly  552 , such that the rotation of the vertical steering shaft  538  causes a corresponding rotation of the rear wheel assembly  552 .  
         [0099]     With continued reference to  FIG. 19A , the seat base  510  and the seat back  508  can be adjusted in both the vertical and horizontal planes in order to accommodate various riding conditions, and the varied needs and abilities of the rider. Specifically, the seat base  510  can be located on, above or below the horizontal pivot axis  506 . To accomplish this, the seat base  510  is mounted upon an adjustable seat post  554  that is affixed to the seat frame  512  by a shaft collar clamp  556 .  
         [0100]     In one embodiment, the ratio between the degree of seat assembly rotation and the degree of rear wheel assembly rotation can be adjusted by varying the sizes of the upper drive sprocket  522  and the lower driven sprocket  526 .  
         [0101]     Referring now to  FIGS. 20, 21A  and  21 B, in operation, the rider leans to rotate the seat assembly  500  in one direction, which causes the upper drive sprocket  522  to rotate in the same direction, which causes the roller chain  528  to rotate the lower driven sprocket  526  in the same direction, which causes the lower steering shaft  530  to rotate the lower steering shaft bevel gear  534  in the same direction, which causes the vertical steering shaft bevel gear  536  to rotate the rear wheel assembly  552  in the opposite direction, thereby turning the vehicle  560  in a direction corresponding to the direction of rotation of the seat back  508 . The left and right neutral bias actuators  540  bias the seat assembly  500  toward a centered, straight-ahead position.  
         [0102]     Referring specifically to  FIG. 20 , rotating the seat back  508  toward the right results in a rotation of the rear wheel assembly  552  toward the left. This results in the vehicle  560  turning to the right when moving in a forward direction, corresponding to the direction of rotation of the seat back  508 .  
         [0103]     Referring now to  FIG. 22 , in another embodiment, the seat assembly  500  is positioned in such a manner that there is a single steering shaft  558  operably connecting the seat frame  512  to the rear wheel assembly  552 . The forward end of the steering shaft  558  is affixed to the rearward portion of the seat frame  512 . The steering shaft bevel gear  534  is affixed to the rear portion of the steering shaft  558 .  
         [0104]     Referring now to  FIGS. 23A, 23B ,  23 C and  24 , and in one embodiment, steering of the vehicle  570  is accomplished by rotation of the seat  572  about a substantially vertical axis  574 . The seat  572  is mounted to a platform  576  which is affixed to the upper end of the vertical steering shaft  578 . The vertical steering shaft  578  is rotatably affixed to the frame  580  with a bearing assembly  582  to permit free rotation of the seat  572 . One or more neutral bias actuators  581  are disposed between the seat platform  576  at the first end and the vehicle frame  580  at the second end. When the seat  572  is rotated for turning the vehicle  570 , the actuator  581  is biased toward returning the seat  572  and consequently the rear wheel assembly  608  toward a centered, straight-ahead position. The actuator  581  may be a pre-tensioned adjustable spring, an adjustable pressurized cylinder or a similar biasing device.  
         [0105]     In this embodiment, the steering shaft assembly  584  is comprised of the vertical steering shaft  578 , vertical shaft bearings  582 , a forward steering shaft housing  586 , an upper bevel gear  588 , a forward bevel gear  590 , a horizontal steering shaft  592 , horizontal shaft support bearings  594 , a rear steering housing  598 , a rear upper miter gear  600 , a rear lower miter gear  602 , a fork steerer shaft  604  and fork steerer shaft bearings  606 .  
         [0106]     In this embodiment, the upper bevel gear  588  is affixed to the lower end of the vertical steering shaft  578 . The upper bevel gear  588  engages the forward bevel gear  590  which is affixed to a forward portion of the horizontal steering shaft  592 . The horizontal steering shaft  592  is rotatably attached to the forward steering shaft housing  586  and the rear steering shaft housing  598  by the horizontal shaft support bearings  594  affixed to the forward housing  586  and the rear housing  598 . The lower rear miter gear  602  is affixed to the rearward end of the horizontal steering shaft  592 . The upper rear miter gear  600  is attached to the fork steerer shaft  604  and engages the rear lower miter gear  602 . The fork steerer shaft  604  is rotatably attached to the rear housing  598  by bearing assemblies  606  affixed to the upper and lower portions of the rear housing  598 .  
         [0107]     In operation, the rotation of the seat  572  causes a corresponding rotation of the vertical steering shaft  578 , which rotates the upper bevel gear  588 , and leads to a corresponding rotation of the forward bevel gear  590  and the horizontal steering shaft  592 . The rotation of the steering shaft  592  causes a corresponding rotation of the rear lower miter gear  602 , which leads to a corresponding rotation of the rear upper miter gear  600  and the fork steerer shaft  604 , which causes a corresponding rotation of the rear wheel assembly  608 .  
         [0108]     In this example, rotating the seat  572  in one direction causes the rear wheel assembly  608  to rotate in an opposite direction, resulting in the vehicle  570  turning in the direction of the seat rotation. If the seat  572  is rotated to the left, the rear wheel assembly  608  rotates to the right, thereby steering the vehicle  570  to the left in a forward direction.  
         [0109]     Referring now to  FIGS. 25A and 25B , and intone embodiment, steering of the vehicle  630  is accomplished by rotation of the seat  632  about a substantially vertical axis  634 . The seat  632  is mounted to a platform  636  which is affixed to the upper end of the vertical steering shaft  644 . The vertical steering shaft  644  is rotatably attached to the frame  638  with a bearing assembly  640  to permit free rotation of the seat  632 . One or more neutral bias actuators  639  are disposed between the seat platform  636  at the first end and the vehicle frame  638  at the second end. When the seat  632  is rotated for turning the vehicle  630 , the actuator  639  is biased toward returning the seat  632  and consequently the rear wheel assembly  662  toward a centered, straight-ahead position. The actuator  639  may be a pre-tensioned adjustable spring, an adjustable pressurized cylinder or a similar biasing device.  
         [0110]     In this embodiment, the hydraulic steering assembly  642  consists of the vertical steering shaft  644 , a forward bellcrank  646 , a left master cylinder  648 , a right master cylinder  650 , a left slave cylinder  652 , a right slave cylinder  654 , a rear bellcrank  656 , a hydraulic line  658  connecting the left master cylinder  648  to the right slave cylinder  654 , a hydraulic line  658  connecting the right master cylinder  650  to the left slave cylinder  652  and four tie rod ends  660 , one of which is connected to each of the four hydraulic cylinders.  
         [0111]     In this embodiment, the forward bell crank  646  is affixed to the lower end of the vertical steering shaft  644 . The left master cylinder  648  is connected to the left arm of the forward bellcrank  646  by a tie rod end  660 . The right master cylinder  650  is connected to the right arm of the forward bellcrank  646  by a tie rod end  660 . The left and right master cylinders  648 ,  650  are affixed to the frame  638 . The left master cylinder  648  is connected to the right slave cylinder  654  by a hydraulic line  658 . The right master cylinder  650  is connected to the left slave cylinder  652  by a hydraulic line  658 . The left slave cylinder  652  is connected to the left arm of the rear bellcrank  656  by a tie rod end  660 . The right slave cylinder  654  is connected to the right arm of the rear bellcrank  656  by a tie rod end  660 . The slave cylinders  652 ,  654  are rotatably affixed to the frame  638 . The rear bellcrank  656  is affixed to the rear wheel assembly  662 .  
         [0112]     In operation, the rotation of the seat  632  causes a corresponding rotation of the vertical steering shaft  644 , which causes a corresponding rotation of the forward bellcrank  646 , which causes a corresponding retraction of the piston  664  in one master cylinder  650 , which causes the connected slave cylinder rod  666  to extend, which causes a corresponding rotation of the rear bellcrank  656 , which causes a corresponding rotation of the rear wheel assembly  662 . Each slave cylinder  652 ,  654  is rotatably affixed to the frame  638 , allowing the slave cylinder  652 ,  654  to rotate for proper alignment relative to the position of the rear bellcrank  656  through its degrees of rotation.  
         [0113]     In this example, rotating the seat  632  in one direction causes the rear wheel assembly  662  to rotate in an opposite direction, resulting in the vehicle  630  turning in the direction of the seat rotation. If the seat  632  is rotated to the right, the rear wheel assembly  662  rotates to the left, thereby steering the vehicle  630  to the right in a forward direction.  
         [0114]     Referring now to  FIGS. 26A and 26B , and in one embodiment, steering of the vehicle  680  is accomplished by rotation of the seat  682  about a substantially vertical axis  684 . The seat  682  is mounted to a platform  686  which is affixed to the upper end of the vertical steering shaft  694 . The vertical steering shaft  694  is rotatably affixed to the frame  688  with a bearing assembly  690  to permit free rotation of the seat  682 . One or more neutral bias actuators  689  are disposed between the seat platform  686  at the first end and the vehicle frame  688  at the second end. When the seat  682  is rotated for turning the vehicle  680 , the actuator  689  is biased toward returning the seat  682  and consequently the rear wheel assembly  706  toward a centered, straight-ahead position. The actuator  689  may be a pre-tensioned adjustable spring, an adjustable pressurized cylinder or a similar biasing device.  
         [0115]     In this embodiment, the rack and pinion steering assembly  692  consists of a vertical steering shaft  694 , a forward pinion gear  696 , a gear rack  698 , a rear pinion gear  700  and multiple guide bushings  702 .  
         [0116]     In this embodiment, the forward pinion gear  696  is affixed to the lower end of the vertical steering shaft  694 . The forward end of the gear rack  698  engages the forward pinion gear  696 . The rear end of the gear rack  698  engages the rear pinion gear  700 . The rear pinion gear  700  is affixed to the rear wheel assembly  706 . The multiple guide bushings  702  are rotatably affixed to the frame  688  and positioned near the forward, middle and rearward portions of the gear rack  698 .  
         [0117]     In one embodiment, the forward portion of the gear rack  698  has teeth  708  located on the right side of the gear rack  698  for positive engagement of the forward pinion gear  696 . The rear portion of the gear rack  698  has teeth  710  located on the left side of the gear rack  698  for positive engagement of the rear pinion gear  700 . The guide bushings  702  are rotatably mounted to the frame  688  and positioned in contact with the gear rack  698  to effectively support and align the gear rack  698  in relation to the forward and rear pinion gears  696 ,  700  for positive engagement. The guide bushings  702  provide horizontal and vertical alignment and support of the gear rack  698 .  
         [0118]     In operation, the rotation of the seat  682  causes a corresponding rotation of the vertical steering shaft  694 , which causes a corresponding rotation of the forward pinion gear  696 , which causes a corresponding linear movement of the gear rack  698 , which causes a corresponding rotation of the rear pinion gear  700 , which causes a corresponding rotation of the rear wheel assembly  706 .  
         [0119]     Referring now to  FIG. 26A , rotating the seat  682  in one direction causes the rear wheel assembly  706  to rotate in an opposite direction, resulting in the vehicle  680  tuning in the direction of the seat rotation. If the seat  682  is rotated to the right, the rear wheel assembly  706  rotates to the left, thereby steering the vehicle  680  to the right in a forward direction.  
         [0120]     Referring now to  FIGS. 27, 28A  and  28 B in one embodiment, the dual drive crank arm assembly  730  is comprised of a revolving folding handle  732 , a crank arm  734 , a crank arm housing  752 , a crank drive shaft  756 , a crank drive shaft detent hole  762 , a roller clutch  764 , a retractable spring plunger  746 , a lever  748  and a flexible cable  750 .  
         [0121]     The revolving folding handle  732  is affixed to the crank arm  734  which is affixed to the crank arm housing  752 . The roller clutch  764  is affixed to the crank arm housing  752  in a forward engaged position. The roller clutch  764  is rotatably affixed about the crank drive shaft  756 . The crank drive shaft  756  is rotatably affixed to the crank drive shaft housing  766 . The crank shaft detent hole  762  is located outboard of the roller clutch  764  and in alignment with the retractable spring plunger  746 . The retractable spring plunger  746  is positioned within the crank arm housing  752  to permit engagement of the plunger  746  with the crank drive shaft detent hole  762 . The lever  748  is rotatably affixed to the crank arm  734  and connected to the retractable spring plunger  746  by a flexible cable  750 .  
         [0122]     The default position of the handle  738  is a horizontal position for a rotational operation of the crank arm assembly  730 . The alternate position of the handle  740  is a vertical position for a reciprocating lever operation of the crank arm assembly  730 . This is accomplished by the rider pulling outward and upward on the handle  732 , which disengages it from the locked horizontal position and re-engages it in a locked vertical position.  
         [0123]     In operation, there are three modes of propulsion. In the first mode, with the handle  732  in the horizontal position  738  and the spring plunger  746  in the retracted position  744 , forward rotation of the crank arm  734  will result in forward propulsion of the vehicle. In this mode, there is a freewheel function which permits the crank arm  734  to remain stationary while the vehicle is moving forward. In the second mode, with the handle  732  in the horizontal position  738  and the spring plunger  746  in the engaged position  754 , forward rotation of the crank handle  732  will result in forward propulsion of the vehicle. Reverse rotation of the crank handle  732  will result in reverse propulsion of the vehicle. This is referred to as a fixed drive mode.  
         [0124]     In the third mode, with the handle  732  in the vertical position  740  and the spring plunger  746  in the retracted position  744 , a forward motion of the handle  732  will result in forward propulsion. A rearward motion of the handle  732  will disengage the roller clutch  764  from the crank drive shaft  756 , allowing the rider to reposition the handle  732  for the next forward propulsion stroke. This is referred to as reciprocating lever drive propulsion.  
         [0125]     In this example, the vehicle may be operated in a narrow hallway or doorway by reducing the overall width of the vehicle. There is also the increased mechanical advantage provided by the extended length of the crank arm and vertical handle combination.  
         [0126]     The retractable spring plunger  746  is actuated by a rotating lever arm  748  connected to the spring plunger  746  by a flexible cable  750 . The spring plunger  746  is disengaged from the crank drive shaft  756  by rotating the lever  748  in a direction which retracts the cable  750  and consequently, the spring plunger  746 . To re-engage the spring plunger  746 , the lever  748  is moved in the opposite direction.  
         [0127]     In a further embodiment, the roller clutch  764  is replaced by a bi-directional ratchet drive (not shown) affixed to the crank arm housing  752 . In this example, the operator may propel the vehicle in a fourth mode, in addition to the three modes noted above. The fourth mode is reverse reciprocal lever drive.  
         [0128]     Referring now to  FIG. 27 , and in one embodiment, the front brakes  780  are linear side pull brakes which are positioned on a forward portion of the frame  782  to come into contact with the brake disc  784  which is affixed to the front wheel assembly  786 .  
         [0129]     Referring now to  FIGS. 29A and 29B  in one embodiment, there is a locking brake assembly  788  which consists of a brake disc  784  having a series of countersunk holes  790  which are located on the circumferential edge of the disc  792 , a brake engagement rod  794 , an engagement rod housing  796 , a registration collar  798 , a compression spring  800 , a spring stop  802  and an engagement rod handle  804 .  
         [0130]     In one embodiment the brake disc  784  is affixed to the front wheel assembly  786 , the engagement rod housing  796  is affixed to the vehicle frame  782 , the registration collar  798  is affixed to the engagement rod housing  796 , the engagement rod  794  is rotatably positioned within the engagement rod housing  796 , the compression spring  800  is located between the lower portion of the engagement rod housing  796  and the spring stop  802 , the spring stop  802  is located on the lower portion of the engagement rod  794 . The handle  804  is located at the upper end of the engagement rod  794 . The registration collar  798  has two vertical slots. The engagement slot  806  is approximately ⅜ inch deeper than the disengagement slot  808 . The holes  790  located on the circumferential edge of the brake disc  792  are countersunk and spaced equidistant from one another.  
         [0131]     In operation, the engagement rod handle  804  is positioned in the disengagement slot  808  for operating the vehicle with the locking brake assembly  788  in the disengaged position  810 . In this example, the handle  804  is lifted and rotated which results in a corresponding lift and rotation of the engagement rod  794  which causes the lower end of the engagement rod  794  to become disengaged from the brake disc  784 . The handle  804  is then released into the disengagement slot  808  which causes the engagement rod  794  to remain fixed in the disengaged position  810 . The compression spring  800  provides a constant tension which secures the engagement rod  794  in the disengagement slot  808 .  
         [0132]     In a second example, the engagement rod handle  804  is positioned in the engagement slot  806  for engaging the locking brake assembly  788 . In this example, the handle  804  is lifted and rotated which results in a corresponding lift and rotation of the engagement rod  794 . The handle  804  is then released into the engagement slot  806  which causes the lower end of the engagement rod  794  to positively engage the brake disc  784  by descending into one of the holes  790  located on the circumferential edge of the brake disc  792 . This results in the brake disc  784  and the wheel assembly  786  being in a locked position. The compression spring  800  provides a constant tension which secures the engagement rod  794  in the registration collar engagement slot  806 . The countersunk holes  790  facilitate a positive engagement of the brake disc  784  and the engagement rod  794 .  
         [0133]     In one embodiment each of the two front drive wheels is equipped with a locking brake assembly  788 .  
         [0134]     Referring now to  FIGS. 23A, 24  and  30 , and in one embodiment, there is at least one footrest assembly  830  which is affixed to a forward portion of the frame  832  for support of the rider&#39;s lower limbs. The footrest assembly  830  consists of a mounting bracket  834 , a quick-release clamp  864 , an actuating handle  836 , an external tube  838 , an upper registration collar  840 , an upper registration pin  844 , a lower registration collar  866 , a lower registration pin  868 , a lower registration pin hole  870 , an internal tube  842 , a compression spring  846 , a lower spring stop  848  and a footrest  850 .  
         [0135]     The mounting bracket  834  consists of two clamps, the first of which is affixed to a forward portion of the frame  832 . The second clamp secures and positions the external tube  838 . The upper registration collar  840  is affixed to the upper portion of the external tube  838 . The internal tube  842  is located within the external tube  838 , extending in length beyond the upper and lower end of the external tube  838 . The actuating handle  836  is affixed to the upper end of the internal tube  842 . The upper registration pin  844  is affixed to the side of the internal tube  842 . The compression spring  846  is located about the lower end of the internal tube  842 , between the lower portion of the external tube  838  and the lower spring stop  848 . The lower spring stop  848  is affixed to the lower portion of the internal tube  842 . The footrest  850  is affixed to the lower end of the internal tube  842 .  
         [0136]     The mounting bracket  834  allows the footrest assembly  830  to be adjusted according to the individual needs of the operator. The footrest assembly  830  can be rotated for vertical height adjustment  852  of the footrest  850  ( FIG. 23A ). The external tube  838  can be rotated within the mounting bracket  834  in order to position the footrest  850  either above, below or on a horizontal plane  860  ( FIG. 24 ). The external tube  838  can be extended or retracted within the mounting bracket  834  to adjust the forward position of the footrest  850  ( FIG. 23A ).  
         [0137]     The upper registration collar  840  includes two vertical slots ( FIG. 30 ). The upper registration pin  844  is positioned in the engaged registration slot  856  to locate the internal tube  842  and therefore the footrest  850  in a position for supporting the foot of the operator. The upper registration pin  844  is positioned in the disengaged registration slot  858  to locate the internal tube  842  and therefore the footrest  850  in a retracted position  862  for mounting and dismounting the vehicle  570 . In one embodiment, the registration slots are positioned on the upper registration collar  840  to allow for a 110 degree rotation of the footrest  850 .  
         [0138]     In operation, the actuating handle  836  is pulled rearward and rotated to engage the upper registration pin  844  in a slot on the upper registration collar  840 . The handle rotation causes the internal tube  842  to rotate in a corresponding direction, which causes the footrest  850  to rotate in the same direction.  
         [0139]     The compression spring  846  provides a constant tension on the internal tube  842  to secure the upper registration pin  844  in a slot on the upper registration collar  840 .  
         [0140]     In one embodiment, the mounting bracket  834  of the footrest assembly  830  includes a cam-actuated quick-release clamp  864  which enables the external tube  838  to be quickly retracted or extended ( FIG. 30 ). In this example, a lower registration collar  866  is mounted to the external tube  838 . In the default position the lower registration pin  868  of the lower registration collar  866  is inserted into the lower registration pin hole  870  in the mounting bracket  834 .  
         [0141]     In operation, the lever of the quick release clamp  864  is rotated to release the clamping action on the external tube  838 , which causes the external tube  838  to move freely. This enables the external tube  838  to be extended or retracted. When the lower registration collar pin  868  is inserted into the lower registration pin hole  870  on the mounting bracket  834 , the external tube  838  is returned to a preset position.  
         [0142]     In one embodiment, there is a right and left footrest assembly, each of which is affixed to a forward portion of the frame for support of the rider&#39;s lower limbs. Each footrest assembly is independently adjustable and independently removable.  
         [0143]     A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims. For example, for rehabilitative applications, the vehicle can include a foot pedal assembly (not shown) configured as in a conventional bicycle foot crank mechanism to which the rider&#39;s feet can be positioned. In one embodiment, at least one of the hand crank sprockets  255  and the foot pedal assembly are operably connected by a direct drive arrangement. In this configuration, the drive chain  275  attached to the crank sprockets  255  provides propulsion of the vehicle  100  and simultaneously rotates the foot pedals, allowing improved circulation to and neuro-stimulation of the lower limbs.  
         [0144]     The foregoing embodiments are therefore to be considered in all respects illustrative rather than limiting of the invention described herein. The scope of the invention is thus indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced herein.