Abstract:
A personal vehicle system including a control system and at least one wheel motor coupled to the personal vehicle system and subject to control by the control system. A control system for a personal vehicle system including steps for calibrating the control system, where the control system includes a sensor system having load sensors incorporated into the personal vehicle system and also having lean forward and lean backward outputs, a user interface that prompts a user to lean forward and backward and allows a user to input a sensitivity value, and an electronic hardware component for calculating a normalization value where the wheel motor current is controlled as a function of the normalization value.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/841,396 filed on Mar. 15, 2013, which is incorporated by reference it its entirety for all purposes. 
     
    
     TECHNICAL FIELD 
       [0002]    Embodiments related generally to personal transportation systems and methods. 
       BACKGROUND 
       [0003]    Personal powered transportation allows one to travel intermediate distances at a comfortable pace without expending excess energy. One example of such a personal powered transportation system includes an electric long board (which may be similar to an elongated skateboard, which is intended for traveling intermediate distances rather than short distances, and which is intended primarily for transportation rather than the performance of tricks). Existing systems often use motors that are coupled to the wheels with belts or chains, making them susceptible to the elements. Existing systems may only be able to power one wheel on a vehicle leading to poor performance. Also, bulky gears or transmission systems are often used to achieve a variety of speeds. 
         [0004]    Current solutions to personal powered transportation are often overly complex and unreliable. Heavy and bulky designs reduce portability and decrease travel distances between refueling or recharging. Cumbersome control systems are difficult to use and potentially dangerous, often requiring the use of the hands. Further, current solutions visibly stand out from traditional unpowered recreational vehicles. For example, current electric long boards often visually resemble traditional long boards but with bulky, obtrusive additions for controlling and powering the boards. Existing current electric long boards look distinctly different from, and lack the sleek profile of their non-electric long board counterparts. 
       SUMMARY 
       [0005]    Embodiments include systems and methods for users to travel on a powered personal vehicle system. In one embodiment, a personal vehicle system includes a deck having a substantially flat top surface, for which the top surface is substantially flat and is of sufficient area to support two feet of a user, a truck coupled to the deck, in which the truck includes of a first portion coupled to the deck and a second portion that tilts relative to the first portion, and a wheel motor coupled to the second portion of the truck. The personal vehicle system can also have two wheel motors coupled to the second portion of the truck, and can also have a control system configured to coordinate operation of the first wheel motor and the second wheel motor. Such a control system can activate and regulate power input, speed, and torque of the first wheel motor and the second wheel motor as a function of a weight distribution of the user on the deck, and the control system can coordinate the operation of the first wheel motor and the second wheel motor as a function of current. 
         [0006]    According to such embodiments, the personal vehicle system can also have a wireless mobile device and a wireless mobile application executed by the wireless mobile device, in which the wireless mobile application is configured to receive and transmit information from the control system, and the control system provides calibration parameters to the wireless mobile application and the wireless mobile application calibrates the calibration parameters of the control system. In some cases, the personal vehicle system can also have at least one force sensor configured to measure a force or a deck displacement strain, and the force sensors can be embedded in the deck. In some instances, the personal vehicle system includes a control system that is configured to control the first wheel motor and the second wheel motor as a function of a force output signal from the force sensors. 
         [0007]    In another embodiment, a personal vehicle system includes a deck, a truck coupled to the deck, and a wheel motor coupled to the truck. The wheel motor may have a passive cooling system. The passive cooling system includes at least one endcap that rotates about a wheel rotation axis during operation of the wheel motor, and the endcap has at least one fin, according to some embodiments. The personal vehicle system can also have at least three fins, or at least five fins, such that the fins extends in a radial orientation about the wheel rotation axis, and the fins are angularly distributed equally about the wheel rotation axis. The personal vehicle system can also have at least two end caps that each have fins, and the two end caps have an equal number of fins. In some cases, the inner endcap includes more fins than the outer endcap. In some cases, the fins on the inner endcap are smaller than the fins on the outer endcap. In some cases, the personal vehicle system can have a wheel motor including a wheel motor assembly in which the two outermost ends of the wheel motor assembly are enclosed by two endcaps. Further, a single bolt, or a single compression connector, compresses and holds together the endcaps and the wheel motor assembly along the wheel rotational axis. 
         [0008]    According to some embodiments, the truck is in thermal communication with the wheel motor. The wheel motor may be a gearless motor or a brushless electric motor. The wheel motor may include a flux canister and a stator, and the average of a first radius of an outer most circumference of the stator with respect to the wheel rotational axis and a second radius of an inner most circumference of the flux canister with respect to the wheel rotational axis is between 30% and 90%, or between 40% and 80%, or between 50% and 75%, or between 55% and 65%, of a third radius of an outermost circumference of the flux canister with respect to the wheel rotational axis. 
         [0009]    In another embodiment, a method for assembling a wheel motor includes sliding the stator shaft of the wheel motor over the truck axle, sliding the wheel motor assembly onto the stator shaft, and compressing the wheel motor with a single compressing connector coupled to the truck axle. The wheel motor assembly may include a stator, an inner endcap, an inner bearing, an outer endcap, an outer bearing, a flux ring, a traction surface, and/or a rotor position sensor. 
         [0010]    In another embodiment, a method for assembling a wheel motor includes sliding a stator shaft over a truck axle, with an inner bearing and an inner endcap forming an inner endcap assembly, sliding an inner endcap assembly onto the stator shaft, a rotor position sensor, and a stator forming a stator assembly, sliding the stator assembly onto the stator shaft, at least one magnet, a flux ring, and a traction surface forming a rotor assembly, sliding the rotor assembly over the stator assembly, an outer bearing, an outer endcap, and a washer forming an outer endcap assembly, sliding the outer endcap assembly onto the stator shaft, and compressing the stator shaft, the inner endcap assembly, the stator assembly, the rotor assembly, and the outer endcap assembly to the truck with a single bolt, or a single compression connector, coupled to the truck axle. Such methods may also include sliding a rotor position sensor onto the stator shaft and inserting a wheel motor wire through the center of the inner bearing and connecting the wheel motor wire to the rotor position sensor. 
         [0011]    In another embodiment, a truck package kit includes components for converting an unpowered personal vehicle to a powered personal vehicle, the truck package kit including a truck assembly, at least one wheel motor attached to the truck, a control system, at least one sensor, and an instruction manual for converting the personal vehicle and calibrating the control system. 
         [0012]    While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  illustrates a side perspective view of a user with a personal vehicle system, according to embodiments of the present invention. 
           [0014]      FIG. 2  illustrates a bottom plan view of a personal vehicle system, according to embodiments of the present invention. 
           [0015]      FIG. 3  illustrates a bottom perspective view of a truck assembly, according to embodiments of the present invention. 
           [0016]      FIG. 4  illustrates an exploded view of the components of the wheel motor, according to embodiments of the present invention. 
           [0017]      FIG. 5A  illustrates a front view of the inner endcap, according to embodiments of the present invention. 
           [0018]      FIG. 5B  illustrates a side view of the inner endcap shown in  FIG. 5A . 
           [0019]      FIG. 6  illustrates a side perspective of a wheel motor, according to embodiments of the present invention. 
           [0020]      FIG. 7  illustrates wireless communication between a control system and a mobile wireless application, according to embodiments of the present invention. 
           [0021]      FIG. 8  illustrates a cross-sectional side view of the personal vehicle system of  FIG. 2  taken along line B-B of  FIG. 2 , showing a position of sensors, according to the embodiments of the present invention. 
           [0022]      FIG. 9  illustrates a cross-sectional front view of the personal vehicle system of  FIG. 2  taken along line A-A of  FIG. 2 , according to the embodiments of the present invention. 
           [0023]      FIG. 10  illustrates a flow chart showing interactions between the mobile wireless application and the control system, according to the embodiments of the present invention. 
           [0024]      FIG. 11  illustrates a main screen of a wireless mobile application, according to the embodiments of the present invention. 
           [0025]      FIG. 12  illustrates a configuration screen of the wireless mobile application, according to the embodiment of the present invention. 
       
    
    
       [0026]    Corresponding reference characters indicate corresponding parts throughout the several views. 
         [0027]    While the invention is amenable to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described in detail below. The intention, however, is not to limit the invention to the particular embodiments described. On the contrary, the invention is intended to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION 
       [0028]    As shown in  FIGS. 1, 2, 6 and 9 , a personal vehicle system  110  (“PVS”) includes four wheels, two front self-contained, powered wheel motors  220 , and two back wheels  210 . The wheels  210 ,  220  spin about a wheel rotation axis  690  defined by a truck axle  235  that is supported by a truck  230 ,  230 ′. The two trucks  230 ,  230 ′ are attached to opposite ends of a deck  225  creating a stable four wheel vehicle. The top of the deck  950  is substantially flat and is of sufficient area to support a user  120 . In other embodiments the shape and size of the deck vary. The wheels  210 ,  220  support the user  120  above a surface, for example a road, and the PVS  110  allows the user to travel about in a supported and balanced fashion. The user&#39;s  120  right foot  140  and left foot  130  control the steering of the PVS  110  by tilting the deck  225  relative to the trucks  230 ,  230 ′ and wheels  220 ,  210 . The speed, acceleration, and braking of the PVS  110  are determined by the relative deck position and weight distributions between the right foot  140  and left foot  130 . 
         [0029]    In one embodiment, the deck  225  is made from a strong, durable, and light weight carbon fiber. The carbon fiber deck  225  allows the PVS  110  to remain light weight and thin in profile without sacrificing durability or performance.  FIG. 8  show the thin, sleek profile of the PVS  110  as seen from the side, taken along line B-B of  FIG. 2 .  FIG. 9  shows the thin profile of the cross section of the PVS  110  when the deck  225  is cut in half, as taken along line A-A of  FIG. 2 . In other embodiments the deck is made from wood, metal, composite, or a combination of materials. 
         [0030]    In one embodiment the personal vehicle system  110  also includes two wheel motors  220  attached to the front truck  230  and two unpowered wheels  210  attached to the rear truck  230 ′, in another embodiment the two wheel motors are attached to the rear truck and the two unpowered wheels are attached to the front truck. In another embodiment all four wheels are wheel motors, and in another embodiment only one wheel is a wheel motor. The wheel motors  220  each contain an internal electric motor that produces the required force to drive and thus rotate the wheel motors. Further, the wheel motors  220  are operated without belts, gears, or mechanical power couplings connected thereto. The wheel motors  220  can be in a powered or a free state. While in the powered state the wheel motors  220  can provide different levels of torque, acceleration, speed, braking, and regenerative braking. While in the free state the wheel motors  220  act similar to conventional unpowered wheels. 
         [0031]    The wheel motors  220  are powered and controlled through wheel motor wires  50  connected to a control system  280 . The wheel motor wires  50  run from the control system  280 , across the deck  225 , through the truck  230 , and to the wheel motors  220  by running through the wire slot  370  on the truck  230 . The wheel motor wires  50  enter the wheel motor through the center of the inner bearing  2  and along the wire groove  45  on the stator shaft  1 . In one embodiment the wheel motor wires connect to the rotor position sensor  9  and the stator  6 . The control system  280  is housed in the control system port  270  which is a part of the deck  225 . The control system is coupled to the deck  225  with an adhesive technology. In one embodiment the adhesive technology is Velcro or other hook-and-loop type fastener. The control system  280  has a top surface made from a material with a high heat transfer coefficient to remove excess heat, and bottom surface made from an electrically insulating material. In one embodiment the top surface of the control system is made from aluminum and the bottom surface is made from plastic. In one embodiment the control system  280  receives power from one battery  215 ; in another embodiment the control system receives power from two or more batteries  215 . The battery  215  and the control system  280  are connected by wires. The battery  215  is located between the deck  225  and the battery cover  240 . The battery cover  240  provides a watertight chamber for the battery  215 . The control system  280  is also water tight. In one embodiment the battery  215  is a lithium ion battery that can be recharged with a recharging unit or through regenerative braking applied by the wheel motors  220 . In another embodiment the battery is made from a conventional battery technology. One battery  215  can power two wheel motors  220  with a standard weight user  120  over standard terrain for approximately five miles and reach speeds up to twenty miles per hour. 
         [0032]    The control system  280  is an electronic hardware component and software assembly that both sends output signals via wiring to the wheel motors  220  and receives input signals from the wheel motors  220 . The control system  280  is replaceable to allow for maintenance, repair, and upgradability. The control system  280  is pre-programmed to allow for plug and play operability and can automatically recognize connected wheel motors. The control system has multiple connection ports that allow for multiple wheel motors or wheel motor axle assemblies to be connected to the control system. In one embodiment the control system can connect to four wheel motors or two wheel motor axle assemblies. The control system  280  coordinates the operations of the two wheel motors  220  and also synchronizes the two wheel motors  220  so that the PVS  110  can be properly controlled. By varying current, the control system  280  regulates the torque, rotational speed, ground speed, acceleration, and deceleration of the wheel motors  220 . In one embodiment in which two wheel motors  220  are coupled to the same truck  230 , the control system is able to independently control each wheel motor  220 . The wheel motors  220  send operating parameters, for example temperature, motor serial number, motor ID, rotor position and rotational speed (e.g. rpm) back to the control system  280 . The control system  280  determines the operations of the wheel motors based on calibration parameters and force output signals received from force sensors  250 ,  250 ′ (“sensor”) embedded in the deck  225 . In one embodiment the PVS  110  has four sensors  250 ,  250 ′ embedded in the deck  225 , two sensors  250  near the front of the deck and two sensors  250 ′ near the rear of the deck; in other embodiments there may be one sensor, two sensors, three sensors, or more than four sensors. Sensors  250 ,  250 ′ may be embedded or otherwise concealed within the deck  225  in order to create a more aesthetic appearance, and so as to not interfere with the user&#39;s feet  130 ,  140 . 
         [0033]    The sensors  250 ,  250 ′ measure force. In one embodiment the force measured by the sensors  250 ,  250 ′ is a load or weight. In another embodiment the force measured by the sensors  250 ,  250 ′ is deck displacement strain in the deck material. The sensors  250 ,  250 ′ may be load cells, strain gauges, or other suitable technology. The varying amount of force applied to the different sensors  250 ,  250 ′ is based on the user&#39;s  120  weight distribution and foot placement with respect to the deck  225 . If more force is detected by the front sensors  250  in comparison with the back sensors  250 ′ the control system  280  activates motion or acceleration of the wheels motors  220 . If the reverse is true, the control system  280  deactivates the wheel motors  220  or initiates deceleration, braking, or stoppage. If no weight or force is detected on the front sensors  250  (e.g., the user  120  is no longer on the PVS  110 ) the control system  280  signals the wheel motors  220  to apply full braking until they stop. 
         [0034]    The calibration parameters of the control system  280  and hence the performance of the wheel motors  220  are based on the weight and technical level of the user and can be adjusted to set a limit on the maximum speed or to optimize battery life. The weight and technical level of the user can be inputted manually or wirelessly into the control system  280 . The data can be manually entered into the control system  280  using input controls  205  and a digital display  290 . The data can be wirelessly entered into the control system  280  using a wireless mobile device  700  executing a wireless mobile application  710 . Two-way communication between the wireless mobile device  700  and the control system  280  is achieved directly through Bluetooth or another wireless technology, and/or is achieved indirectly via a network  720 , such as the Internet. The wireless mobile application  710  can display on the mobile device  700  real-time parameters from the wheel motors  220  and the control system  280 , for example wheel motor temperature, wheel motor serial numbers, wheel motor ID numbers, battery life, and rotational speed (e.g. rpm). Using the data from the control system  280  and the wheel motors  220 , the wireless mobile application  710  calculates one or more of average speed, top speed, travel time, travel distance, battery time remaining, maximum distance on remaining battery charge, average distance on remaining battery charge, and in combination with a GPS application, estimated time of arrival. 
         [0035]    The control system  280 , in combination with the embedded sensors  250 ,  250 ′, permits the user  120  to control the PVS  110 , including forward motion, braking, forward acceleration, and turning, without the use of any hands, and without the use of any handlebars or any handheld or hand-controlled mechanism, simply by shifting the weight balance among the right and left feet  140 ,  130 . 
         [0036]      FIGS. 10, 11, and 12  further show the interactions between the control system  280 , wireless mobile application  710 , sensors  250 ,  250 ′ and the wheel motors  220 . The main screen  1100  of the wireless mobile application  710  shows outputs and calculation derived from such outputs received from the control system  280  (for example, battery life  1120  and miles per hour  1110  of the PVS  110 ; other values can be shown by clicking on different areas of the PVS diagram). In one embodiment the main screen  1100  allows for one touch wireless communication with the control system  280  via the wireless button  1130 . The configuration button  1200 ′ leads to the configuration screen  1200 . On the configuration screen  1200 , the sensitivity slider  1210  adjusts the sensitivity value  1060  of the control system  280 . The calibration button  1220  starts a calibration algorithm which records a lean back calibration value  1070  and lean forward calibration value  1080  based on the feedback from the sensors  250 ,  250 ′. In one embodiment, when the calibration button  1220  is activated the user  120  is instructed to lean forward on the PVS  110  and the control system records a lean forward calibration value  1080  based on outputs from the sensors  250 ,  250 ′; then the user  120  is instructed to stand centered on the PVS  110 ; then the user  120  is instructed to lean back on the PVS  110  and the control system records a lean back calibration value  1070 . With the calibration parameters the control system  280  is able to control the PVS  110  while in operation by the user  120 . While in operation the sensors  250 ,  250 ′ send a force sensor value  1000  to the control system  280 . The control system  280  runs the force sensor value  1000  through a box car moving average filter  1010 , then subtracts the lean back calibration value  1020 , then divides the remaining value by the (lean forward calibration value minus the lean back calibration value) divided by two hundred ( 200 ), which may be done for normalization. The normalized value is then capped be a saturation limit  1040  which uses the sensitivity value  1060  to ensure that the wheel motors  220  do not obtain a speed higher than desired by the user  120 . The value capped by the saturation limit  1040  is converted to a motor current command  1050  which is sent to the wheel motors  220 . Via the control system  280  the wheel motors  220  and control system  280  send outputs to the wireless mobile application (see  1090 ). Examples of outputs to the wireless mobile application  710  include: wheel motor speeds, wheel motor temperatures, wheel motor errors, wheel motor rotor position, wheel motor currents, battery charge values, and force sensor values. In one embodiment the control system  280  runs calculations, for example the calculations process shown by  FIG. 10 , at a frequency of ten hertz. 
         [0037]    In some cases, a truck package kit may be provided in order to retrofit an existing conventional or non-powered PVS. Such a kit may include at least one truck assembly, where the control system and at least one sensor are integrated into a truck; at least one wheel motor; and an instruction manual. The truck package kit allows for the modification of different types of personal vehicles, for example unpowered skateboards. The instruction manual aids in the use of the kit, describing how to convert an unpowered vehicle and how to calibrate the control system. In another embodiment, a truck package kit includes: at least one truck, at least one wheel motor, a control system, at least one sensor, and an instruction manual. 
         [0038]    As shown in  FIGS. 2 and 3 , the front and rear trucks  230 ,  230 ′ are composed of several components. The truck  230  is composed of a first portion  320  which is coupled to the deck  225 , and a second portion  310 . The trucks  230 ,  230 ′ are coupled to the deck  225  with truck bolts  295 . In other embodiments the trucks are coupled to the deck in other ways. The second portion  310  tilts or pivots with respect to the first portion  320  about a truck pivot  330 . Wheels  210  or wheel motors  220  are mounted on the truck axle  235  which is rigidly and/or fixedly coupled to the second portion  310 . Tilt performance is controlled and improved by two truck springs  340  which are coupled to the first portion  320  and the second portion  310 , and which serve to bias the second portion  310  toward a “wheels straight” position in the absence of turning forces. In other embodiments, fewer than two springs, more than two springs, or other biasing technologies may be used to bias the second portion  310  toward the “wheels straight” position. The tilt of the trucks  230 ,  230 ′ (which is based on the user&#39;s  120  left to right weight distribution) allows the PVS  110  to be steered left or right. When the PVS  110  is turning, two wheel motors coupled to the same truck cover different amounts of distance and therefore spin at different speeds. The control system  280  allows the two wheel motors to operate at different speeds by maintaining substantially equal force for each wheel motor. Operating the two wheel motors at substantially equal force allows for traction control by preventing excess wheel slippage and spin outs. The independent operation of the two wheel motors allows the PVS  110  to smoothly turn either left or right. The base damper  350  further improves performance and control of the PVS  110 . 
         [0039]    As shown in  FIGS. 3, 4, 5   a ,  5   b , and  6 , the wheel motors  220  are wheels with an internal self-contained electric motor. The wheel motors  220  do not require external motors, external belts or chains, external gears or gear systems, external transmissions, or power couplings. In one embodiment the wheel motors  220  are both gearless and brushless electric motors. In one embodiment the wheel motors  220  are comprised of a wheel motor assembly including a non-rotational stator shaft  1  which prevents the stator  6  from turning, an inner bearing  2 , an inner endcap  4 , a rotor position sensor  9 , magnets  17  which are fixed to the inside of a flux ring  3 , a traction surface  22  which surrounds the flux ring  3  (see  FIG. 8 ), an outer endcap  5 , an outer bearing  11 , a washer  12 , and a compressing connector  20 , such as a nut, for example. The inner endcap  4  and the outer endcap  5  enclose the two outermost ends of the wheel motor assembly. The traction surface  22  provides adequate friction with the travel surface. In one embodiment the traction surface  22  is rubber. The rotor position sensor  9  communicates with the control system  280  through connecting wires. The rotor position sensor  9  monitors the position and rotational velocity (e.g. in rotations per minute or rpm) of the rotating magnets  17 . In one embodiment the rotor position sensor is a hall effect and/or hall sensor. In one embodiment, the stator shaft  1  is prevented from rotating on the truck axle  235  by a pin  35 ; where the pin is inserted or flexibly coupled with a pin hole  360  on the axle  230  and a pin grove  40  on the stator shaft  1 . In other embodiments the stator shaft is prevented from rotating by other mechanical means. A single compressing connector  20  in combination with the stator shaft  1  compresses the components of the wheel motor  220  by coupling the compressing connector  20  to the truck axle  235 . In one embodiment the truck axle is threaded and the compressing connector is a nut. In another embodiment the truck axle has a hollow and threaded center core and the compressing connector is a bolt. Using only one compressing connector  20  to compress the wheel motor  220  allows for an efficient, compact, lightweight, watertight, and dust tight design. The stator shaft  1 , stator  6 , and rotor position sensor  9  form the non-rotating stator assembly (“stator assembly”). The magnets  17 , flux ring  3 , traction surface  22 , inner endcap  4 , and the outer endcap  5  form the rotating rotor assembly (“rotor assembly”). In one embodiment the wheel motor  220  is assembled by inserting the stator shaft  1  over a truck axle  235 , inserting the inner bearing  2  over the stator shaft  1 , inserting the inner endcap  4  over the stator shaft  1 , inserting the rotor position sensor  9  over the stator shaft  1 , inserting the stator  6  over the stator shaft  1 , inserting the magnets  17 , flux ring  3 , and traction surface  22  over the stator  6 ; inserting the outer endcap  5  over the stator shaft  1 , inserting the outer bearing  11  over the stator shaft  1 , and compressing the components with a washer  12  and single compressing connector  20  where the compressing connector  20  couples to the truck axle  235 . 
         [0040]    The wheel motor  220  operates by passing electrical current through electrically conductive wiring in the stator  6  which generates a magnetic field. In one embodiment the stator is a three phase stator. The magnetic field exerts a magnetic force on the magnets  17  causing the magnets  17 , which are part of the rotating rotor assembly, to spin. A small gap between the stator  6  and the magnets  17  called a flux gap prevents the non-rotating stator assembly and the rotating rotor assembly from touching. The inner bearing  2  and the outer bearing  11  help maintain the proper position between the non-rotating stator assembly and the rotating rotor assembly. While in operation the inner bearing  2  and the outer bearing  11  reduce the friction between the moving and stationary parts of the motor. For maximum efficiency the flux ring  3  may be made out of a magnetically conductive material, according to some embodiments. The flux ring  3  may also be made from a strong and durable material as it provides structural support for the wheel motor, according to some embodiments. 
         [0041]    To maximize power, torque, efficiency, and durability of the wheel motor  220 , the wheel motor  220  benefits from proper cooling. Magnets in wheel motors operate more efficiently at cooler temperatures. In one embodiment, the magnets  17  are permanent magnets that lose efficiency at high temperature, for example temperatures exceeding eighty degrees Celsius; further extended exposure to excess heat may in some cases damage the magnets  17  and reduce their lifespans. The wheel motor  220  uses two forms of passive cooling. The flux gap between the stator  6  and the magnets  17  prevents efficient heat transfer between the stator assembly and the rotor assembly. Therefore, both the stator assembly and the rotor assembly may include separate passive cooling mechanisms. The stator assembly is in conductive thermal communication with the truck axle  235  and the truck  230 . The truck axle  235  and the truck  230  are made of a material with a high heat transfer coefficient, which allows the truck axle  235  and the truck  230  to act as heat sinks for the stator assembly. 
         [0042]    Further, convective cooling is achieved as the PVS  110  moves and air passes over the truck  235 . In one embodiment the trucks  230 ,  230 ′ are made of aluminum. The rotating rotor assembly, which includes the magnets  17 , is cooled by convective cooling which is assisted by the inner endcap  4  and the outer endcap  5 . The magnets  17  and the flux ring  3  are in conductive thermal communication with both the inner endcap  4  and the outer endcap  5 . The flux ring  3  is made from a material with a high heat transfer coefficient. In one embodiment the flux ring  3  is made from aluminum or iron. The endcaps  4 ,  5  are made from a material with a high heat transfer coefficient, and include at least one fin  510 . As the wheel motor  220  spins, the endcaps  4 ,  5  spin with the flux ring  3  and the magnets  17 . The spinning of the endcaps  4 ,  5  and the attached fins  510 , which extend in a radial orientation from the wheel rotational axis, increases convective cooling from the endcaps  4 ,  5 . The profile of the fins  510  increases convection by increasing the movement and turbulence of the surrounding air. The fins  510  also increase the surface area of the endcaps  4 ,  5  which increases heat dissipation. In one embodiment multiple fins  510  are located on each endcap  4 ,  5  and the fins  510  are equally distributed angularly along the radius of the endcap  4 ,  5  to improve heat dissipation. In one embodiment there are an equal number of fins  510  on inner endcap  4  and the outer endcap  5  so that heat transfer and cooling of the magnets  17  is substantially equal along the length of the wheel rotational axis  690  (see  FIG. 6 ) of the wheel motor. According to other embodiments, the inner endcap  4  has more fins  510 , and/or smaller fins  510 , than the fins  510  on the outer endcap  5 . As illustrated in  FIG. 5 , divots  520  in the endcaps  4 ,  5  provide additional cooling benefits and reduce the weight of the endcaps  4 ,  5 . In one embodiment the endcaps  4 ,  5  and the fins  510  are made from aluminum. According to some embodiments, one or more fins  510  are substantially straight along a radius of the endcap  5 . According to other embodiments, one or more fins  510  have varying geometries; for example, one or more fins  510  may be curved over part of or their entire lengths. 
         [0043]    As shown in  FIGS. 4 and 6 , a wheel motor  220  is most efficient and produces the most torque when the ratio of the length of the torque arm of the wheel motor, compared to the length of the total wheel radius of the wheel motor, approaches one. The magnets  17 , flux ring  3 , and traction surface  22  form the rotating flux canister (“flux canister”). A first radius  625  is the distance between outermost circumference of the stator  620  and the wheel rotational axis  690 . A second radius  615  is the distance between the innermost circumference of the flux canister  610  and the wheel rotational axis  690 . A third radius  605  is the distance between the outermost circumference of the flux canister  600  and the wheel rotational axis  690 . The gap or area between outer surface  610  and inner surface  600  may be referred to as the flux gap. The length of the torque arm is the average of the length of the first radius and the length of the second radius. In one embodiment the length of the torque arm is the distance between the middle of the flux gap and the wheel rotational axis  690 . The length of the total wheel radius is the length of the third radius. By constructing the wheel motor  220  out of strong, durable materials, using a one bolt  20  assembly, and by utilizing the two passive cooling systems, the wheel motor  220  is able to be compactly designed. The compact design of the wheel motor  220  allows the ratio of the length of torque arm compared to the length of the total wheel radius to approach one. In one embodiment the length of the torque arm (average of lengths  605  and  615 ) is at least 59% the length of the total wheel radius  605 . In other embodiments, the length of the torque arm (average of lengths  605  and  615 ) is between 30% and 90%, or 40% and 80%, or 50% and 75%, or 55% and 65% of the length of the total wheel radius  605 . 
         [0044]    Various modifications and additions can be made to the exemplary embodiments discussed without departing from the scope of the present invention. For example, while the embodiments described above refer to particular features, the scope of this invention also includes embodiments having different combinations of features and embodiments that do not include all of the described features. Accordingly, the scope of the present invention is intended to embrace all such alternatives, modifications, and variations as fall within the scope of the claims, together with all equivalents thereof.