Patent Publication Number: US-2015075880-A1

Title: Electric cart for facilitating the harvesting of berries and other crops

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to the field of electric vehicles, and more specifically, to an electric cart that is designed to facilitate the harvesting of berries and other crops. 
     2. Description of the Related Art 
     Current harvest machines tend to be large and powered by a combustion engine. These machines need to operate in close proximity to the operator (for convenience reasons) and often within a greenhouse structure. The exhaust and noise are a constant irritation to the operators. Furthermore, the combustion engines require support fluids, such as engine oil, fuel, and usually hydraulic oil. All of these fluids can ruin product viability if they come into contact with the crops. Combustion engines also require refueling and handling of flammable liquids often near ignition sources; as such, they require a constant vigilance in fire hazard safety. In the case of transient labor, there is often little time or opportunity for such training. Serviceability is rarely considered with conventional harvest machines, and maintenance is increased due to the use of combustion engines. All of these factors negatively impact productivity. 
     In order to be economically viable, conventional (combustion engine) harvest machines are often scaled so that they can be used by several picker/operators at a time. This requires greater skill levels (in terms of safety, maintenance, etc.) across an entire operating crew. Furthermore, the large size of most harvest machines leads to complications in handling or transporting the equipment, and it also increases the risk that the machine may cause serious injuries. In addition, the larger scale of the machine often causes a more significant impact on the soil structure, reducing crop health. Small component failure can often disable an entire machine until replacements are fitted. Breakdowns or adjustments usually stop large crews from working, which in turn reduces overall productivity. For the reasons explained below, all of these limitations are overcome by the present invention. 
     There are no existing inventions that embody the advantages of the present invention. For example, U.S. Patent Application Pub. No. 2012/0186213 (Orlando et al.) discloses an electrically powered agricultural funicular traction system consisting of two automatically driven, electrically powered machines connected by a cable. U.S. Patent Application Pub. Nos. 2013/0022430 and 2013/0019580 (Anderson et al.) provides a bidirectional harvesting vehicle comprised of a base unit and a material gathering device that is attached to either a first end or a second end of the vehicle, depending upon the direction in which the vehicle is traveling. Neither of these inventions possesses is structurally or functionally similar to the present invention. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is an electric cart for facilitating the harvesting of berries and other crops comprising: a steering side wheel assembly comprising a front wheel and a rear wheel connected by a first connecting member, wherein the front wheel is a steering wheel, and the rear wheel is a drive wheel connected to a first battery-powered motor; a caster side wheel assembly comprising a front wheel and a rear wheel connected by a second connecting member, wherein the front wheel is a caster wheel, and the rear wheel is a drive wheel connected to a second battery-powered motor; and a main cross-bar connecting the caster side wheel assembly to the steering side wheel assembly so that there is a certain distance between the first and second connecting members, wherein the certain distance between the first and second connecting members is adjustable. In a preferred embodiment, the invention further comprises a plurality of solar panels that charge at least one battery that supplies power to the first and second battery-powered motors. 
     In a preferred embodiment, a first pair of tubular extensions extends laterally from the first connecting member, and a second pair of tubular extensions extends laterally from the second connecting member; the main cross-bar comprises a first end and a second end, and the first end of the main cross-bar is inserted into the first pair of tubular extensions, and the second end of the main cross-bar is inserted into the second pair of tubular extension; and the main cross-bar rotates within the first and second pairs of tubular extensions to allow the electric cart to accommodate variations in the terrain. Preferably, the electric cart is fully collapsible for transport or storage. Each of the drive wheels preferably comprises a disengageable drive hub. 
     In one embodiment, the invention further comprises a first set of racks for storing empty trays and a second set of racks for storing full trays; the first set of racks is positioned on top of the steering side wheel assembly; and the second set of racks is positioned directly underneath the first set of racks. In another embodiment, the invention further comprising a first set of racks for storing empty trays and a second set of racks for storing full trays; the first set of racks is positioned on top of the caster side wheel assembly: and the second set of racks is positioned directly underneath the first set of racks. 
     In a preferred embodiment, the electric cart has a manual mode and an auto mode; and the electric cart travels at a pre-determined speed for a given time interval when the auto mode is activated. Preferably, the given time interval is adjustable by the operator. The electric cart preferably automatically reverts to manual mode after the given time interval expires. 
     In a preferred embodiment, the invention further comprises a guide handle that is pivotally attached to a bracket in proximity to an outer end of an axle of the steering wheel, and the guide handle is configured to be held in a first position when the electric cart is in manual mode and a second position when the electric cart is in auto mode. Preferably, the invention further comprises at least one emergency stop that terminates all power to the electric cart when activated. The invention preferably further comprises a forward/reverse switch that controls a direction of travel of the electric cart. 
     In a preferred embodiment, the invention further comprises a steering sensor; the steering side wheel assembly further comprises a steering fork assembly; and the steering sensor senses the position of the steering fork assembly and varies power to the first battery-powered motor to facilitate a turn. Preferably, the invention further comprises a steering sensor; the steering side wheel assembly further comprises a steering fork assembly; and the steering sensor senses the position of the steering fork assembly and varies power to the second battery-powered motor to facilitate a turn. The steering side wheel assembly preferably further comprises a steering fork assembly; the steering fork assembly comprises a steering fork; and the electric cart further comprises one or more stops that prevent over-rotation of the steering fork. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the present invention shown fully assembled. 
         FIG. 2  is a perspective view of the present invention showing how the empty and full trays are stored on the machine. 
         FIG. 3  is a detail perspective view of the storage racks for the empty trays. 
         FIG. 4A  is a perspective view of the empty tray storage assembly of the present invention shown with the storage racks in a first position. 
         FIG. 4B  is a perspective view of the empty tray storage assembly of the present invention shown with the storage racks in a second position. 
         FIG. 5A  is a perspective view of the present invention shown without any empty or full trays and with the solar panels tilted for transport. 
         FIG. 5B  is a detail view of the solar panel tilt mechanism. 
         FIG. 6  is a detail perspective view of the emergency stop. 
         FIG. 7  is a partial exploded view of the caster side of the present invention. 
         FIG. 8  is a detail perspective view of the rear control box. 
         FIG. 9A  is a detail perspective view of the guide handle shown in an up position. 
         FIG. 9B  is a detail perspective view of the guide handle shown in a down position. 
         FIG. 9C  is a detail side view of the release handle. 
         FIG. 10  is a rear view of the caster side wheel assembly and the steering side wheel assembly shown in a first relative position on the width adjustment tube. 
         FIG. 11  is a rear view of the caster side wheel assembly and the steering side wheel assembly shown in a second relative position on the width adjustment tube. 
         FIG. 12  is a rear view of the caster side wheel assembly and the steering side wheel assembly shown in a third relative position on the width adjustment tube. 
         FIG. 13  is an exploded view of the caster side wheel assembly, the steering side wheel assembly, and the width adjustment tube. 
         FIG. 14A  is an exploded view of the battery compartment. 
         FIG. 14B  is an exploded view of the battery compartment. 
         FIG. 15  is a detail perspective view of the main control box. 
         FIG. 16  is a partial exploded view of the main control box and batteries showing the internal harness. 
         FIG. 17  is a detail perspective view of the locking hub assembly shown with the hubs engaged. 
         FIG. 18  is a detail perspective view of the locking hub assembly shown with the hubs disengaged. 
         FIG. 19  is an exploded view of the locking hub assembly. 
         FIG. 20  is a front perspective view of the drive hub key. 
         FIG. 21  is a rear perspective view of the drive hub key. 
         FIG. 22  is an exploded view of the caster side base assembly. 
         FIG. 23  is an exploded perspective view of the motor and drive assembly. 
         FIG. 24  is an exploded view of the front wheel assembly on the steering side. 
         FIG. 25  is a top view of the front wheel assembly on the steering side. 
         FIG. 26  is a perspective view of the invention in a fully collapsed and partially disassembled state ready for shipment. 
     
    
    
     REFERENCE NUMBERS 
     
         
           1  Bed (of berries) 
           2  Empty tray 
           3  Full tray 
           4  Solar panel 
           5  First set of racks (for empty trays) 
           5   a  First half (of rack  5 ) 
           5   b  Second half (of rack  5 ) 
           6  Second set of racks (for full trays) 
           7  Rubber strap 
           8  Aperture (in vertical surface of rack  5 ) 
           9  Cross-member 
           10  Vertical post 
           11  Emergency stop 
           12  Button (on emergency stop) 
           13  Strain relief 
           14  Support member 
           15  Bracket 
           16  Tubular extension 
           17  Connecting member 
           18  Rear control box 
           19  Auto mode button 
           20  Time adjustment knob 
           21  Guide handle 
           22  Bracket 
           23  Release handle 
           24  Bolt 
           25  Twist throttle 
           26  Mud scraper 
           27  Rear wheel 
           28  Gear box 
           29   a  Inner drive tube 
           29   b  Outer drive tube 
           30  Cylindrical cover 
           31  Motor 
           32  Battery compartment 
           32   a  Battery compartment cover 
           33  Main cross-bar 
           34  Pin 
           35  Aperture (in main cross-bar) 
           36  Main control box 
           37  Battery 
           38  Hinged cover (on battery compartment) 
           39  Auto power knob 
           40  Forward/reverse switch 
           41  Internal harness 
           42  First receptacle 
           43  Second receptacle 
           44  Third receptacle 
           45  Fourth receptacle 
           46  Shaft 
           47  Keyway 
           48  Washer 
           49  Collar 
           50  Wheel hub 
           51  Snap ring 
           52  Drive hub key 
           53  Nut 
           54  Spring 
           55  Washer 
           56  Bolt 
           57  Hub cap 
           58  Internal key (on drive hub key) 
           59  Grip tab (on drive hub key) 
           60  Angle bracket 
           61  Channel bracket 
           62  Steering fork 
           63  Hub cover 
           64  Stop 
           65  Steering sensor 
           66  Hub cap 
           67  Slot (in release handle) 
           68  Roof brace 
           69  Locking bar 
           70  Lock 
           71  Locking bracket 
           72  Locking bar slot 
           73  Solar panel support channel 
           74  Spacer 
       
    
     DETAILED DESCRIPTION OF INVENTION 
     The present invention is a battery-operated cart for facilitating the harvesting of berries and other crops. The invention is smaller and lighter than conventional harvest assist machines, and it is preferably solar-charged. The four-wheel articulated frame of the present invention is more stable than prior art designs, and the frame is also adjustable. 
     A first advantage of the present invention is that it replaces the gas engine with an electric power train. As such, the need for liquid fuel and hydraulic oil is eliminated, thereby reducing the chance of crop contamination. Without a gasoline engine, the 100-hour service interval (typically applicable to conventional harvesting machines) no lunger applies, and the service life of the equipment is extended into the thousands of hours. Furthermore, with optional solar recharging, there is no need for daily recharging of the battery via an electric power source. 
     A second advantage of the present invention is that it is sized appropriately for single- or double-user crews. The invention is also designed so that the width of the machine can be adjusted easily by one or two people. The smaller overall size of the invention means that it has a smaller, lighter footprint than conventional machines. This in turn reduces ground compaction and provides a safer work environment. The smaller size of the machine also means that it can be more easily transported. 
     A third advantage of the present invention is that it can be collapsed down significantly or even disassembled to provide extremely tight packaging of multiple machines without requiring tools or long set-up or take-down times. 
     A fourth advantage of the present invention is that the drive hub can be disengaged to allow towing of the machine at slow speeds for short distances. The latter capability is beneficial in the event the machine malfunctions or needs to be moved down field roads at a speed greater than the operating speed of the machine. Because of this towing capacity, more than one machine can be ganged together to allow one machine to tow several others to the operating area from a place of storage. 
     A fifth advantage of the present invention is that it greatly improves serviceability and decreases required maintenance. With an electric drive motor, there are very few wear items on the machines. The electric motors have extremely long service intervals, and the drive gear boxes need only infrequent oil changes (biodegradable oils may be used to eliminate contamination risk). The electrical control system is plug-in, there are no end user serviceable parts, and the package is delivered as a module that can be rapidly swapped for a functioning unit with no tuning or individualization needed. Without solar power, there is a significant reduction in fuel costs. With solar power, fuel costs are effectively eliminated. 
     A sixth advantage of the present invention is that it incorporates a four-wheel configuration, with one furrow-guided (steering) wheel and one trailing swivel (caster) wheel in the front and two driving wheels in the rear. The machine can be easily reconfigured to provide two swivel wheels in the front and a separate operator-guided steering control at the rear, if needed, depending upon the type of crop and field application. 
     A seventh advantage of the present invention is that it is equipped to carry empty picking containers into a field and to store these containers in another location on the machine once they are full of berries. This saves the operator the effort of carrying each full container out of the field or carrying empty containers with him while harvesting. 
     An eighth advantage of the present invention is that it is configured to stay just ahead of the harvester/operator with minimal interaction between the user and the machine. At the end of the picking rows, the machine is easily guided into the next harvest area by the operator and then travels through the harvest area either self-guided or guided manually. To allow the machine to recharge its batteries, the machine is configured to move forward a preset distance at the touch of a button and then wait (while recharging) for another signal from the operator. This allows the machine to stay out of the way of the operator with little interaction or guidance. These and other advantages are discussed more fully below with reference to the figures. 
       FIG. 1  is a perspective view of the present invention shown fully assembled. As shown in this figure, the invention comprises two pairs of front and rear wheels—one on the steering side (the two wheels on the lower right-hand side of the figure) and one on the caster side (the two wheels on the upper left-hand side of the figure). The two steering side wheels are aligned so that the rear wheel is directly behind the front wheel on the steering side, and the rear wheel is directly behind the pivot axis of the front wheel on the casting side. The invention is configured so that the two steering side wheels and the two caster side fall on either side of a bed of berries  1 . As explained below (particularly in connection with  FIG. 13 ), the width of the invention—that is, the distance between the steering side wheels and the caster side wheels—is adjustable. 
       FIG. 1  also shows that the invention is configured to hold both empty  2  and full  3  berry trays. In the embodiment shown in this figure, the invention comprises tiltable solar panels  4  that recharge the batteries that provide power to the two drive motors (see  FIG. 23 ). 
       FIG. 2  is a perspective view of the present invention showing how the empty and full trays are stored on the machine. As shown in this figure, the empty trays  2  are stacked horizontally on top of a first set of racks  5  that are adjustable (see  FIGS. 4A and 4B ). The full trays  3  are stacked vertically on top of a second set of racks  6  that are positioned directly underneath the first set of racks  5 . 
       FIG. 3  is a detail perspective view of the storage racks for the empty trays. In a preferred embodiment, each end of each rack in the first set of racks  5  comprises a rubber strap  7 . In this particular embodiment, one end of the rubber strap  7  is inserted into an aperture  8  on the inside surface of one end of the rack  5 . The rubber strap  7  is then looped around and secured to the outside surface of the same end of the rack  5 . The purpose of these rubber straps  7  is to prevent the stacked empty trays  2  (not shown) from falling off of the racks  5 . The rubber straps  7  work well because they provide enough friction to keep the empty trays  2  on the racks  5  while still allowing them to be easily removed from the racks  5 . The present invention is not limited to any particular method keeping the empty trays  2  on the racks  5 . 
       FIG. 4A  is a perspective view of the empty tray storage assembly of the present invention shown with the storage racks in a first position, and  FIG. 4B  is a perspective view of the empty tray storage assembly of the present invention shown with the storage racks in a second position. As shown in these two figures, the width of the first set of racks  5  is adjustable. Each rack  5  comprises a first half  5   a  and a second half  5   b . The first and second halves  5   a ,  5   b  each comprises two planar surfaces, one horizontal and one vertical, joined together at a ninety (90)-degree angle. The rubber straps  7  discussed above are preferably situated on the ends of the vertical surfaces. The horizontal surface of each rack is bolted to two cross-members  9 , which in turn are secured to vertical post  10 . The horizontal surface of the rack is preferably secured to the cross-members  9  with bolts. The cross-members  9  comprise a plurality of bolt holes, which allow the width of each rack to be adjusted. 
       FIG. 5A  is a perspective view of the present invention shown without any empty or full trays and with the solar panels tilted for transport. As noted above, the solar panels  4  are preferably tiltable. Tilting of the solar panels  4  to a more vertical orientation than that shown in  FIG. 1  may be desired for transporting the invention from field to field. Tilting of the solar panels in this manner reduces the possibility of damage to the solar panels  4  during transit, and it also reduces the air pressure underneath the solar panels that attempts to lift them upward when they are in a relatively horizontal position and moving at an appreciable speed. 
       FIG. 5B  is a detail view of the solar panel tilt mechanism. This figure shows how the angle of the solar panels  4  is adjusted. As shown in this figure, the vertical post  10  is pivotaliy attached to a roof brace  68 . The top end of the vertical post  10  is secured (in this case with a pin  34 ) to a solar panel support channel  73  located directly underneath the solar panel  4 . To adjust the position of the solar panel  4 , the pin  34  is removed, the top end of the vertical post  10  is moved to a different set of holes in the solar panel support channel  73 , and the pin  34  is reinserted. 
       FIG. 6  is a detail perspective view of the emergency stop. In a preferred embodiment, the invention comprises an emergency stop  11  on each of the four corners of the cart. The emergency stop  11  comprises a button  12  that, if pressed, will cut all power to the cart. In  FIG. 6 , the strain relief  13  to the right of the button  12  is a conduit for the wires that connect the emergency stop  11  to the power source. 
       FIG. 7  is a partial exploded view of the caster side of the present invention. This figure shows the steering side of the invention in an assembled state and the caster side of the invention in an exploded view. As shown in this figure, the second set of trays  6  is bolted to a support member  14  situated above each of the wheels and also to brackets  15  that are welded or otherwise secured to tubular extensions  16  that protrude laterally from a connecting member  17  that extends between the two support members  14 . The emergency stop  11  on the rear end of the caster side (left-hand side of  FIG. 7 ) is preferably bolted to the underside of the outer corner of the tray  6 . Note that three of the emergency stops are visible in this figure; however, there are preferably four emergency stops, one on each corner of the machine (the fourth one is not visible in this figure, but it is visible in  FIG. 9 ). 
       FIG. 8  is a detail perspective view of the rear control box. The rear control box  18  is preferably situated underneath the tray  6  on the rear end of the steering side. The rear control box  18  comprises an emergency stop  11 , an auto mode button  19 , and a time adjustment knob  20 . When pressed, the auto mode button  18  causes the machine to enter “auto” mode from manual mode. When in “auto” mode, the machine will move forward at a pre-determined speed, (this is discussed in connection with  FIG. 15 ) for a given time interval. The time adjustment knob  20  adjusts the time interval (i.e., the amount of time) during which the cart will move forward (or backward) when the auto mode button is pressed. The machine is programmed so that it will automatically revert to manual mode after the designated time interval. 
       FIG. 9A  is a detail perspective view of the guide handle shown in an up position. As shown in this figure, the guide handle  21  is pivotally attached to a bracket  22  that is situated directly above the outer end of the axle of the front wheel on the steering side—this wheel is referred to as the “steering wheel.” A release handle  23  (also referred to as a “tongue lever”) is also pivotally attached to the bracket  22 . A bolt  24  extends through a tab (not shown) that is welded onto the guide handle  21  and also through a slot  67  in the release handle  23 . When the release handle  23  is pulled upward, the weight of the guide handle  21  causes the bolt  24  to move to the other end of the slot  67 , which in turn allows the guide handle  21  to fall to the ground, as shown in  FIG. 9B . The guide handle  21  should be in a down position before the auto mode button is pressed; in this manner, the machine will be positioned (steered) to move in a straight direction (without turning right or left) during the period of time in which the machine travels in auto mode. In this position, the guide handle  21  keeps the machine moving straight by lying between two raised beds  1 . 
     As noted above, the machine is programmed to automatically revert to manual mode once the pre-programmed time interval (for auto mode) has elapsed. The guide handle  21  can be left in a down position until the operator hits the auto mode button again. Alternately, to use the machine in manual mode (i.e., manual steering), the operator simply lifts the guide handle  21  until the bolt  24  slides back to the other end of the slot  67 , and the guide handle  21  is locked in an up position (as shown in  FIG. 9A ). Note that the guide handle  21  preferably comprises a twist throttle  25  that allows the power (speed) of the machine to be controlled while it is in manual mode. 
     The front wheel on the caster side is referred to as a “caster wheel” because it is neither a steering wheel nor a drive wheel (the two rear wheels are both drive wheels). Rather, the caster wheel simply follows the direction and speed dictated by the steering and power wheels, respectively. 
       FIG. 9C  is a detail side view of the release handle. The release handle “locks” in place when the bolt  24  is positioned within one of the two vertical extensions in the release handle slot  67 . These two vertical extensions allow for two different height adjustments of the guide handle  21 . 
       FIGS. 10 ,  11  and  12  are rear views of the caster side wheel assembly and the steering side wheel assembly shown in a first, second and third relative position, respectively, on the width adjustment tube. Mud scrapers  26  are preferably positioned rearward of each of the two rear wheels  27  (also called the “drive wheels”) for the purpose of scraping mud off of the wheels and to prevent mud from covering the product before it is picked. A gear box  28  is preferably situated on one end of the axle of each of the rear wheels  27 . The gear box  28  is connected to a drive (comprised of an inner drive tube  29   a  and an outer drive tube  29   b ; see  FIG. 22 ) that is preferably enclosed within a cylindrical cover  30  to protect the operators and also to protect the drive from dust and debris. The drive  29  is connected to a motor  31  (see also  FIG. 22 ). The battery compartment  32  is also shown in  FIG. 12 . 
     As illustrated in  FIGS. 10-12 , the distance between the steering side and the caster side of the machine can be adjusted by moving the position of each wheel assembly on the main cross-bar  33  (also referred to herein as the “width adjustment tube”). This is shown more clearly in  FIG. 13 . 
       FIG. 13  is an exploded view of the caster side wheel assembly, the steering side wheel assembly, and the width adjustment tube. The steering side wheel assembly is shown on the right-hand side of this figure, and the caster side wheel assembly is shown in the left-hand side of this figure. The main cross-bar  33  is inserted into the tubular extension  16  on either side of the connecting member  17  on both the steering side wheel assembly and the caster side wheel assembly. The main cross-bar  33  is secured within the tubular extensions  16  with pins  34  that extend through the main cross-bar  33  only (but not through the tubular extensions  16 ) on the outside of each tubular extension  16 . In this manner, the main cross-bar is secured within the tubular extensions  16  but is still allowed to rotate within them. This rotational movement (referred to in the background section above as the “articulated frame”) allows either side of the cart to accommodate undulations (or variations) in the terrain. To move the main cross-bar  33  within the tubular extensions  16  (and thereby increase or decrease the width of the machine), the pins  34  are removed, the main cross-bar  33  is repositioned within the tubular extensions  16 , and the pins  34  are reinserted. The main cross-bar  33  comprises a plurality of apertures  35  into which the pins  34  may be inserted. 
       FIG. 14A  is an exploded view of the battery compartment of the present invention. The battery compartment  32  preferably houses a main control box  36  and a plurality of batteries  37 . The present invention is battery-powered, but the invention is not limited to any particular number or type of batteries. The battery compartment  32  preferably comprises a hinged cover  38  that allows access to the main control box  36 . In this embodiment, the battery compartment  32  is situated underneath the connecting member  17  on the steering side of the machine. 
       FIG. 14B  shows the battery compartment from a different perspective. This figure shows the locking bar  69 , one end of which extends through a locking bar slot  72  in the first battery compartment cover  32   a . The locking bar  69  extends through the battery compartment on top of the batteries  37 . A lock  70  is situated on the other end of the locking bar  69 , and this lock  70  locks onto a locking bracket  71  on the underside of the second battery compartment cover  32   a . The lock  70  is accessible only through the hinged cover  38  on the battery compartment  32 . 
       FIG. 15  is a detail perspective view of the main control box. As shown in this figure, the main control box  36  plugs into a first receptacle  42  that is part of the internal harness  41  (see  FIG. 16 ). The main control box  36  houses the motor control system and preferably comprises an auto power knob  39  that controls the power (speed) of the machine in auto mode. The main control box  36  also preferably comprises a forward/reverse switch  40  that allows the operator to put the machine in forward or reverse. 
       FIG. 16  is a partial exploded view of the main control box and batteries showing the internal harness. The internal harness  41  comprises a first receptacle  42  into which the main control box is plugged. It also comprises a second receptacle  43  for the wiring to the motor and solar panels on the caster side of the machine, a third receptacle  44  for the wiring to all buttons and sensors (the steering sensor is discussed in connection with  FIG. 24 ), and a fourth receptacle  45  for the wiring to the motor and solar panels on the steering side of the machine. 
       FIG. 17  is a detail perspective view of the locking hub assembly shown with the hubs engaged, and  FIG. 18  is a detail perspective view of the locking hub assembly shown with the hubs disengaged.  FIG. 19  is an exploded view of the locking hub assembly. As shown in  FIG. 19 , the gear box  28  comprises a shaft  46  with a keyway  47 . The locking hub assembly comprises (working outward from the gear box shaft  46 ) a washer  48 , a bushing  49 , a wheel hub  50 , a washer  48 , a snap ring  51 , a drive hub key  52 , two nuts  53 , a spring  54 , a washer  55 , a bolt  56  and a hub cap  57 . 
     When fully assembled, the first washer  48  goes onto the shaft  46 , the bushing  49  is inserted into the wheel hub  50 , and the bushing  49  and wheel hub  50  are positioned around the shaft  46 . The next washer  48  is also positioned on the shaft  46  inside of the wheel hub  50 . The snap ring  51  holds all of these pieces on the shaft  46 . The drive hub key  52  is situated between the shaft  46  and the wheel hub  50 . The wheel hub  50  has an inside diameter that is larger than the outside diameter of the shaft  46 , and the wheel hub  50  has an internal hex profile that corresponds to the external hex profile of the drive hub key  52  (see  FIG. 21 ). The internal key  58  on the drive hub key  52  fits into the keyway  47  on the gear box shaft  46 . The bolt  56  holds the spring  54  against the drive hub key  52 . The spring  54  holds the drive hub key  52  in the wheel hub  50 . The bolt  56  screws into the (threaded) center of the outward end of the gear box shaft  46 . The hub cap  57  is press fit into the drive hub key  52 . 
     The invention is designed so that the two rear/drive wheels can be disengaged from the gear box/drive motor for towing purposes. To disconnect the rear wheel from the gear box, the operator would grab hold of the grip tabs  59  on the drive hub key  52 , pull the drive hub key  52  outward and rotate it approximately thirty (30) degrees until the hex portion of the drive hub key  52  is resting on top of the wheel hub  50 , as shown in  FIG. 18 . This action disengages the key  58  on the drive hub key  52  from the keyway  47  on the gear box shaft  46 . This action requires the operator to counteract the force of the spring  54 . The spring  54  also serves to maintain the drive hub key  52  in the position shown in  FIG. 18  until the operator twists the drive hub key  52  and releases it back to the position shown in  FIG. 17 . 
       FIG. 20  is a front perspective view of the drive hub key, and  FIG. 21  is a rear perspective view of the drive hub key. As shown in these two figures, the drive hub key  52  comprises an internal key  58  that extends inward toward the center of the drive hub key and a plurality of grip tabs  59  situated around the perimeter of the drive hub key. The assembly shown in  FIG. 19  applies to both of the rear/drive wheels. 
       FIG. 22  is an exploded view of the caster side base assembly. The left-hand side of this figure shows the motor and drive assembly, which includes the motor  31 , inner drive tube  29   a , outer drive tube  29   b , cylindrical cover  30  (for the inner and outer drive tubes), spacer  74 , and gear box  28  discussed above.  FIG. 23  is an exploded perspective view of the motor and drive assembly. 
     The right-hand side of  FIG. 22  shows the front caster wheel (non-steering side) assembly. Note that the front caster wheel assembly preferably comprises a rotatable angle bracket  60  that allows the front caster wheel to swivel/cast freely. 
       FIG. 22  also shows the two channel brackets  61  that are welded to the top surface of the connecting member  17 . The vertical posts  10  described in connection with  FIGS. 4A and 4B  fit into these channel brackets  61 . 
       FIG. 24  is an exploded view of the front wheel assembly on the steering side. This figure shows the steering fork  62  with bracket  22 . As described above in connection with  FIG. 9A , both the guide handle  21  and the release handle  23  are attached to the bracket  22 . The front wheel assembly further comprises a hub cover  63  with two stops  64  (only one of which is visible in this figure), a steering sensor  65  and a hub cap  66 . The steering sensor  65  senses the position of the steering fork assembly and varies power to one or the other of the motors  31  to facilitate a turn. 
       FIG. 25  is a top view of the front wheel assembly on the steering side. This figure shows the steering fork assembly in the position shown in  FIG. 24 , that is, with the front steering wheel oriented so that the machine will travel straight and not turn. The dotted lines in  FIG. 25  illustrate the possible path of rotation of the steering fork. Note that the stops  64  allow the steering fork to rotate ninety (90) degrees in either direction (from the position shown in  FIG. 25 ); in other words, the steering fork may rotate a full one hundred eighty (180) degrees. The purpose of the stops  64  is to prevent over-rotation of the steering fork. 
       FIG. 26  is a perspective view of the invention in a fully collapsed and partially disassembled state ready for shipment. In this figure, the main cross-bar  33  has been removed from the tubular extensions  16  and the two sides (steering and caster) of the machine placed next to each other. The solar panels  4  have been tiled so that they are relatively horizontal. The first set of trays  5  have been unbolted from the cross-members  9  and stacked together horizontally. The guide handle  21  has been detached (unbolted) from the rest of the machine, and the vertical posts  10  (see  FIG. 4 ) have been decoupled from the channel brackets  61  (see  FIG. 22  ) on the connecting members  17 . In this configuration, the invention can fit easily into a crate for shipment or storage. 
     Although the preferred embodiment of the present invention has been shown and described, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from the invention in its broader aspects. The appended claims are therefore intended to cover all such changes and modifications as fall within the true spirit and scope of the invention.