Patent Publication Number: US-11660241-B2

Title: Exchangeable universal wheelchair power assist

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 17/696,842 filed Mar. 16, 2022, which is a continuation-in-part of U.S. patent application Ser. No. 17/478,873 filed Sep. 17, 2021, issued as U.S. Pat. No. 11,382,809 on Jul. 12, 2022, which is a continuation of U.S. patent application Ser. No. 17/221,196 filed Apr. 2, 2021, issued as U.S. Pat. No. 11,154,443 on Oct. 26, 2021, which is a continuation-in-part of U.S. patent application Ser. No. 17/169,399 filed Feb. 5, 2021, which is a continuation-in-part of U.S. patent application Ser. No. 16/689,931 filed Nov. 20, 2019, issued as U.S. Pat. No. 10,945,899 on Mar. 16, 2021, which is a continuation-in-part of U.S. patent application Ser. No. 16/395,391 filed Apr. 26, 2019, issued as U.S. Pat. No. 10,517,780 on Dec. 31, 2019, which claims priority to U.S. Provisional Application No. 62/663,289 filed on Apr. 27, 2018, the entire contents of which are incorporated herein by references in their entirety. 
    
    
     BACKGROUND 
     The present application generally relates to a removable power assist for a manual wheelchair, and more particularly relates to a device for converting a manual wheelchair into an electric wheelchair. 
     In 2011, an estimated 2.7 million Americans used a wheelchair on a regular basis; up from 1.8 million in 1995. Based off the 2011 Census, 46,000,000 Americans are disabled and receiving income-based assistance. Of that group, 18.2% report ambulatory difficulty. There is also a population that needs a wheelchair temporarily e.g. 2-12 months and would prefer not to incur the expense of an electronic wheelchair even though it is preferred over a manual wheelchair. 
     Electronic wheelchairs and many of the innovations in the field are very expensive; and there is a significant price gap between the most expensive manual wheelchair and the cheapest electronic wheelchair, which often ranges in the thousands of dollars. Other limitations of electric wheelchairs, in addition to cost, include: portability (foldable); weight; and structural bulk. There are devices on the market for converting manual wheelchairs to electronic wheelchairs but they are flawed so that they cannot be installed by an end user sitting in the chair, are heavy, not portable, have poor surface contact for the propulsion system and/or cannot be disengaged without uninstalling the device from the chair. 
     What is needed is a device for converting a manual wheelchair into a power driven system in a cost effective, portable, easy to install and use, lightweight, alternately convertible from electric to manual without uninstalling the device. The device should be adaptable to existing manual wheelchairs without the need of professional installation. 
     SUMMARY 
     Herein disclosed are apparatus and associated methods related to a wheelchair power assist device configured to be installed, uninstalled and exchanged using an exchange tab welded to a wheelchair, and when installed to switch a motorized friction roller between engaged and disengaged modes with a wheelchair wheel, based on an engagement actuator configured to move the friction roller relative to the wheelchair. The friction roller may be operably coupled with an engagement member configured to move relative to the wheelchair. The engagement member may be moved by an extendable and retractable actuator shaft coupled with the wheelchair. A manual wheelchair may be converted to a powered wheelchair using a motorized friction roller for each wheelchair wheel while leaving an open space behind the wheelchair seating area, advantageously permitting the power assist devices to remain attached to a foldable wheelchair in either folded or unfolded configurations. 
     An exemplary wheelchair power assist apparatus or method implementation in accordance with the teaching of the present disclosure may comprise releasably attaching a wheelchair power assist to a wheelchair using an exchange tab welded to the wheelchair frame. An exemplary implementation may comprise a wheelchair welded to an exchange tab configured to be rotatably coupled with an engagement member. The engagement member may be configured with a movable shaft implemented to move the engagement member relative to the wheelchair as the movable shaft extends or retracts using an engagement actuator. Extending or retracting the movable shaft when the exchange tab is secured to a wheelchair may move the engagement bracket between a disengaged position wherein a friction roller is not in contact with a wheelchair wheel and an engaged position wherein the friction roller is in contact with a wheelchair wheel. Using an exchange tab welded to the wheelchair frame to install, uninstall or exchange a wheelchair power assist may expand a user&#39;s access to wheelchair transportation and permit a user increased freedom to travel. An exemplary exchange tab may be secured to a wheelchair using various techniques that would be known to one of ordinary skill. For example, in addition to or instead of the tab being welded to the wheelchair, an exemplary tab may be glued, screwed, riveted or nailed to the wheelchair. In some implementations the exchange tab may be replaced by a slide together mechanism or a ball mount. Various implementations of the exchange tab mechanism are contemplated as may be known to one of ordinary skill. 
     An exemplary apparatus or method implementation in accordance with the teaching of the present disclosure may relate to a removable power assist for converting a manual wheelchair into an electronic wheelchair, based on configuring a friction roller to releasably engage with a wheelchair wheel, configuring the friction roller when engaged to drive the wheel through a contact surface with the wheel that may be positioned under the wheelchair seating area, or to the side of the wheelchair seating area, or to the underside of an armrest, or in front of a wheelchair wheel, configuring a motor to rotate the friction roller, and moving the wheelchair based on engaging the friction roller and activating the motor to turn the wheel through force by the friction roller against the contact surface with the wheel. Some designs include a lever configured to permit a user seated in the wheelchair to engage or disengage the friction roller. Configuring the friction roller under the wheelchair seating area, or to the side of the wheelchair seating area, or to the underside of an armrest, or in front of a wheelchair wheel may permit wheelchair folding or unfolding without uninstalling the power assist. 
     An exemplary apparatus or method implementation in accordance with the teaching of the present disclosure may relate to a removable power assist for converting a manual wheelchair into an electronic wheelchair, based on configuring a friction roller to releasably engage with a wheelchair wheel, configuring the friction roller when engaged to drive the wheel through a contact surface with the wheel above the wheel center and behind the wheelchair seating area, configuring a motor to rotate the friction roller, and moving the wheelchair based on engaging the friction roller and activating the motor to turn the wheel through force by the friction roller against the contact surface with the wheel. The power assist may include a user-operable lever configured to engage or disengage the friction roller without a user leaving their seated position in the wheelchair. Configuring the friction roller above the wheel center and behind the wheelchair seating area may permit collapsible wheelchair folding or unfolding without uninstalling the power assist. 
     Disclosed are a device and method to convert a manual wheelchair into an electronic wheelchair. In an implementation the device may include a joystick, a communication unit, a motor, a retractable friction roller, an engagement unit and a power source. The joystick may be operably connected to a communication unit. The communication unit may be operably connected to a motor. The motor may include an axle connected to a rotor. The retractable friction roller may be mounted on the axle. The roller may be placed in contact with a wheel of a manual wheelchair. The engagement unit may be attached to the manual wheelchair to detachably attach the friction roller and the wheel. The power source may be operably connected to the motor and the joystick. 
     In accordance with teachings of the present invention a device for converting a manual wheelchair into an electronic wheelchair is provided. Herein described is a manual wheelchair accessory device configured to attach to a manual wheelchair that will convert the manual wheelchair to an electric wheelchair, while still retaining the advantages that manual wheelchairs provide. The device may include an attachable power source affixed to a standard manual wheelchair. 
     In one embodiment, the present invention provides a device having a joystick, a communication unit, a motor, a retractable friction roller, an engagement unit and a power source. The joystick is operably connected to a communication unit. The communication unit is operably connected to a motor. The motor includes an axle connected to a rotor. A retractable friction roller is mounted on the axle. The roller is placed in contact with a wheel of a manual wheelchair. The engagement unit is attached to the manual wheelchair to detachably attach the friction roller to the wheel. The power source is operably connected to the motor and the joystick. 
     In one embodiment, the present invention provides a second motor that is operably connected to a second communication unit and the power source. The second communication unit is operably connected to the joystick. The second motor includes a second axle connected to a second rotor. This embodiment includes a second friction roller that is mounted on the second axle. The second roller is placed in contact with a second wheel of the manual wheelchair to facilitate powered motion. In another embodiment, the joystick may be operably connected to the rotors and is operably programmable to generate commands for the motors. 
     The present invention easily converts a manual wheelchair to a powered, smart wheelchair. Features of the present invention include 1) using the friction roller&#39;s contact to the wheel to generate directed movement; 2) the ability to engage and disengage the friction roller to the wheels of the wheelchair which allows the user to propel the wheelchair with manual propulsion while the device is still attached to the wheelchair—a feature essential if the battery or motor cease to function; 3) the ability to fold the wheelchair with device attached to it without altering the folding of or normal space occupied by a standard manual wheelchair; 4) unit portability. In one embodiment, the device includes a safety guard to prevent a user&#39;s fingers from becoming caught in the motor or the gears. In another embodiment, the motors are bi-directional and independent of one another so that the motor attached to each wheelchair wheel can turn the opposite direction and rotate the wheelchair in place. Using the present invention, both acute and long-term care wheelchair companies and individual users can affordably bring their equipment and standard of care to a higher, professional level. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    illustrates a block diagram of an exemplary device in accordance with an embodiment of the present invention. 
         FIGS.  2 A- 2 E  illustrate side views of an exemplary power assist device attached to a manual wheelchair in accordance with exemplary embodiments of the present invention. 
         FIG.  3    illustrates a top perspective view of an exemplary device implementation attached to the manual wheelchair in accordance with an embodiment of the present invention. 
         FIG.  4    illustrates a perspective view of an exemplary engagement unit in accordance with another embodiment of the present invention. 
         FIG.  5    illustrates a perspective view of the device in accordance with another embodiment of the present invention. 
         FIG.  6    illustrates a perspective view of the device with a protective fender in accordance with another embodiment of the present invention. 
         FIGS.  7 A- 7 B  together illustrate side views of exemplary wheelchair power assist device components. 
         FIG.  8    illustrates a side view of an exemplary wheelchair power assist device operation unit assembly in an exemplary retracted configuration. 
         FIG.  9    illustrates a top perspective view of an exemplary wheelchair with two illustrative power assist devices each configured to drive one of the two depicted wheelchair main wheels. 
         FIG.  10 A  illustrates a rear perspective view of an exemplary wheelchair with two illustrative power assist devices each configured to drive one of the two depicted wheelchair main wheels, with the wheelchair in an exemplary unfolded configuration. 
         FIG.  10 B  illustrates a rear perspective view of an exemplary wheelchair with two illustrative power assist devices each configured to drive one of the two depicted wheelchair main wheels, with the wheelchair in an exemplary folded configuration. 
         FIGS.  11 A- 11 D  illustrate perspective views of an exemplary engagement unit configured in exemplary disengaged and engaged modes. 
         FIGS.  12 A- 12 C  illustrate perspective views of exemplary engagement unit component implementations. 
         FIGS.  13 A- 13 D  depict perspective views of an exemplary engagement and attachment implementation in accordance with the present disclosure. 
         FIGS.  14 A- 14 B  depict outside and inside views of an exemplary engagement and attachment implementation in an exemplary extended mode. 
         FIGS.  15 A- 15 B  depict side views of an exemplary engagement and attachment implementation in exemplary disengaged and engaged modes. 
         FIGS.  16 A- 16 B  depict side views of an exemplary engagement and attachment implementation in accordance with the present disclosure. 
         FIGS.  17 A- 17 B  depict side views of an exemplary engagement and attachment implementation in accordance with the present disclosure. 
         FIGS.  18 A- 18 C  depict side views of an exemplary engagement and attachment implementation in accordance with the present disclosure. 
         FIGS.  19 A- 19 B  depict side views of an exemplary engagement and attachment implementation in accordance with the present disclosure. 
         FIGS.  20 A- 20 C  depict side views of an exemplary engagement and attachment implementation in accordance with the present disclosure. 
         FIGS.  21 A- 21 D  depict various views of an exemplary engagement and attachment implementation in accordance with the present disclosure. 
         FIG.  22    depicts an exemplary front detail view of an exemplary engagement and attachment implementation in accordance with the present disclosure. 
         FIG.  23 A  depicts a top perspective view of an exemplary exchange tab. 
         FIG.  23 B  depicts a side perspective view of an exemplary exchange tab. 
         FIG.  23 C  depicts a side perspective view of an exemplary exchange tab. 
         FIG.  23 D  depicts a front perspective view of an exemplary exchange actuator arrangement. 
         FIG.  23 E  depicts a side view of an exemplary exchange actuator arrangement. 
         FIG.  24    depicts an exemplary wheelchair viewed from a right rear perspective. 
         FIG.  25    depicts an exemplary wheelchair viewed from a right rear perspective. 
         FIG.  26    depicts a partial exploded view of an exemplary wheelchair from a left rear perspective. 
         FIG.  27    depicts an exemplary wheelchair viewed from a top left side perspective. 
         FIG.  28    depicts an exemplary wheelchair viewed from a left side perspective. 
         FIG.  29    depicts an exemplary wheelchair viewed from a left rear top perspective. 
         FIG.  30    depicts an exemplary wheelchair viewed from a left side perspective. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS.  1 - 22    were previously disclosed and  FIGS.  23 - 30    are new. While various embodiments of the present disclosure are disclosed, it should be understood that they are presented as examples only, and are not intended to be limiting. Similarly, the drawings and diagrams depict structural or architectural examples or alternate configurations of the invention, which are provided to aid in understanding the features and functionality of the various embodiments of the invention but are not intended to be limiting. The embodiments and features may be implemented and/or altered in a variety of ways known to those of ordinary skill the art. 
       FIG.  1    illustrates a block diagram of the device  100  in accordance with one embodiment of the present invention. In this embodiment, the device  100  includes a joystick  102 , a retractable friction roller  104 , an engagement unit  106  and a power source  108 . The joystick  102  is operably connected to a communication unit  110 . The joystick  102  is explained in detail in conjunction with  FIGS.  2 A- 2 E  and  FIG.  3    of the present invention. 
     The communication unit  110  is operably connected to a motor  112 . The communication unit  110  is explained in detail in conjunction with  FIGS.  2 A- 2 E  of the present invention. The motor  112  includes an axle  114  and a rotor  116 . The motor  112  is explained in detail in conjunction with  FIG.  3    of the present invention. The axle  114  is shown and explained in detail in conjunction with  FIG.  4    of the present invention. 
     The retractable friction roller  104  is mounted on the axle  114 . During operation of the device  100 , the retractable friction roller  104  is put in contact with at least one wheel  206  (shown in  FIGS.  2 A- 2 E ) of a manual wheelchair  202  (shown in  FIGS.  2 A- 2 E ). The retractable friction roller  104  is explained in detail in conjunction with  FIG.  3    and  FIG.  4    of the invention. 
     The engagement unit  106  is attached to the wheelchair  202  (shown in  FIGS.  2 A- 2 E ) to detachably attach the retractable friction roller  104  and the wheel (shown in  FIGS.  2 A- 2 E ). The engagement unit  106  is explained in detail in conjunction with  FIG.  3   ,  FIG.  4    and  FIG.  5    of the present invention. The power source  108  is operably connected to the motor  112  and the joystick  102 . The power source  108  is shown and explained in detail in conjunction with  FIG.  5    of the present invention. The device  100  converts the manual wheelchair  202  into an automatic wheelchair. 
       FIG.  2 A  illustrates a side view of one embodiment of device  100  attached to a manual wheelchair  202 . The joystick  102  allows the user to control the direction and speed of the motor  112  (shown at least in  FIGS.  1 ,  3 ,  11 A, and  11 B ). In an embodiment, the joystick  102  is attached to an arm  204  of the manual wheelchair  202 . 
     In one embodiment, a user is able to control the direction, movement and speed of the device  100  using the joystick  102 . More specifically, the movement and speed of the wheel  206  of the wheelchair  202  is controlled by user instructions using the joystick  102  and the communication unit  110  (shown in  FIG.  3   ). 
     In the example depicted by  FIG.  2 A , the exemplary power assist device  100  includes a friction roller configured to drive when engaged the wheel  206 . The friction roller is further described with reference to at least  FIGS.  3 ,  5 - 6 ,  7 A,  9 ,  10 A -B, and  11 A-D. In  FIG.  2 A , the power assist device  100  is attached to the wheelchair  202  above the wheel  206  center and behind the wheelchair  202  seating area. In the example depicted by  FIG.  2 A , the friction roller is configured to drive when engaged the wheel  206  through a friction roller contact surface with the wheel  206  that is above the wheel  206  center and behind the wheelchair  202  seating area. As described in further detail with reference to at least  FIGS.  9 ,  10 A, and  10 B , configuring the friction roller to contact the wheel  206  above the wheel  206  center and behind the wheelchair  202  seating area may leave open the space behind the wheelchair  202  seating area, permitting the power assist device  100  installation and removal from behind the wheelchair  202  while the wheelchair  202  seat is occupied by a person riding in the wheelchair  202 . Leaving open the space behind the wheelchair  202  seating area as a result of configuring the friction roller to contact the wheel  206  above the wheel  206  center and behind the wheelchair  202  seating area may permit folding and unfolding the wheelchair  202  without uninstalling the power assist device  100 . 
     In the example depicted by  FIG.  2 B , the exemplary power assist device  100  includes a friction roller configured to drive when engaged the wheel  206 . In  FIG.  2 B , the power assist device  100  is attached to the upper lateral wheelchair frame support  208 , to position the power assist device  100  in front of the wheel  206  and to the side of the wheelchair  202  seating area. The exemplary wheelchair  202  depicted by  FIG.  2 B  also includes the lower lateral wheelchair frame support  210 , the vertical wheelchair frame support  212 , and arms  204 . 
     In the example depicted by  FIG.  2 C , the exemplary power assist device  100  includes a friction roller configured to drive when engaged the wheel  206 . In  FIG.  2 C , the power assist device  100  is attached to the lower lateral wheelchair frame support  210 , to position the power assist device  100  in front of the wheel  206  and to the side of the wheelchair  202  seating area. The exemplary wheelchair  202  depicted by  FIG.  2 C  also includes the upper lateral wheelchair frame support  208 , the vertical wheelchair frame support  212 , and arms  204 . 
     In the example depicted by  FIG.  2 D , the exemplary power assist device  100  includes a friction roller configured to drive when engaged the wheel  206 . In  FIG.  2 D , the power assist device  100  is attached by power assist bracket  211  to the vertical wheelchair frame support  212 , to position the power assist device  100  in front of the wheel  206  and to the side of the wheelchair  202  seating area. The exemplary wheelchair  202  depicted by  FIG.  2 D  also includes the upper lateral wheelchair frame support  208 , the lower lateral wheelchair frame support  210 , and arms  204 . 
     In the example depicted by  FIG.  2 E , the exemplary power assist device  100  includes a friction roller configured to drive when engaged the wheel  206 . In  FIG.  2 E , the power assist device  100  is attached to the wheelchair  202  below the arm  204 , to position the power assist device  100  above the wheel  206  center and to the side of the wheelchair  202  seating area. The exemplary wheelchair  202  depicted by  FIG.  2 E  also includes the upper lateral wheelchair frame support  208 , the lower lateral wheelchair frame support  210 , and the vertical wheelchair frame support  212 . 
       FIGS.  2 A- 2 E  each depict one side of an exemplary wheelchair  202  implementation according to the present disclosure. In view of the present disclosure it will be understood that the exemplary wheelchair  202  implementations depicted by  FIGS.  2 A- 2 E  are illustrative of a wheelchair  202  having an exemplary power assist device configured on both sides of the wheelchair  202 , for example as described in further detail at least with reference to  FIGS.  3 ,  9 ,  10 A, and  10 B . Multiple power assist devices may be attached to an exemplary wheelchair in multiple ways. For example, a combination of the power assist attachment locations illustrated by  FIGS.  2 A- 2 E  may be configured to attach multiple power assist devices to an exemplary wheelchair. In some designs, the exemplary wheelchair  202  implementations depicted by  FIGS.  2 A- 2 E  may include a power assist device  100  attached to one side of the wheelchair  202  below the arm  204  as depicted by  FIG.  2 E , and the wheelchair  202  may also include a second power assist device  100  attached on the other side of the wheelchair to the wheelchair  202  upper lateral wheelchair frame support  208  as depicted by  FIG.  2 B . In some implementations, one power assist device  100  may be attached to the wheelchair  202  above the wheel  206  center and behind the wheelchair  202  seating area as depicted by  FIG.  2 A , and the wheelchair  202  may also include a second power assist device  100  attached on the other side to the wheelchair  202  lower lateral wheelchair frame support  210 . In an illustrative example, an exemplary wheelchair  202  implementation may include any combination of the power assist device  100  attachment configurations depicted by  FIGS.  2 A- 2 E . Some example wheelchair  202  designs may include more than two power assist devices. For example, a wheelchair  202  may be configured with four power assist devices  100 . In a wheelchair  202  implementation including four power assist devices  100  attached to the wheelchair  202 , each of two wheelchair  202  main wheels may be driven by two friction rollers. In an illustrative example, a wheelchair having multiple power assist devices with multiple friction rollers driving one wheel may have increased load carrying capacity. Some example wheelchair implementations may include power assist devices configured with an engagement unit adapted to engage or disengage multiple friction rollers from one wheel substantially at the same time. For example, multiple friction rollers may be operably linked with a spring-loaded connecting rod to releasably engage or disengage a secondary friction roller from a wheel when the primary friction roller is engaged or disengaged by user operation of an engagement unit. Various exemplary wheelchair implementations may include multiple power assist devices each configured with an independent engagement unit permitting a user to separately and independently engage or disengage multiple friction rollers from one wheel. An exemplary wheelchair implementation configured to permit a user to independently engage or disengage multiple friction rollers from one wheel may permit a user to adapt the wheelchair&#39;s thrust to the load or terrain. For example, a wheelchair could be adapted to carry a heavier load such as additional luggage based on engaging a secondary power assist device including a second friction roller driven by a second motor, to increase thrust to the same wheel already driven by a primary power assist device including a primary friction roller driven by a primary motor. Such an example wheelchair configuration including multiple independently operable motors and friction rollers adapted to drive each wheel may permit a user to operate the wheelchair more effectively in hilly or mountainous terrain based on engaging multiple motors and friction rollers per wheel when needed, and engaging only one motor and friction roller per wheel on less hilly terrain. 
     In an embodiment the communication unit  110  (shown in  FIG.  3   ) and the second communication unit  304  (shown in  FIG.  3   ) is a wired communication unit. Examples of the communication unit  110  (shown in  FIG.  3   ) and the second communication unit  304  (shown in  FIG.  3   ) include but not limited to cables, wires, Bluetooth®, NFC. It would be readily apparent to those skilled in the art that various types of communication unit such as wired or wireless unit may be envisioned without deviating from the scope of the present invention. 
     In one embodiment, the joystick  102  is programmable and enabled to store instructions for controlling the speed and direction of motor  112  (shown in  FIG.  1   ). The joystick  102  receives power from the power source  108  (shown in  FIG.  1   ). The use of a battery operated joystick is known for controlling power wheelchairs. The joystick  102  may be a device that is compatible with commercially available joystick devices designed to be plugged in and disconnected by an end user, to reduce user effort and expense replacing the joystick due to wear and tear through normal use. The joystick  102  may be a Bluetooth® enabled joystick, permitting remote control of the wheelchair within the communication range of the device using a wireless joystick that is not physically installed in the wheelchair. For example, the user riding in the wheelchair may hold a Bluetooth® enabled or wireless joystick  102  in either hand, or in any way that is comfortable or effective, to operate their wheelchair without constraint by a wired or permanently installed joystick. The joystick  102  may include a pop socket ring holder configured to permit a user to effectively manipulate a wireless joystick that is not physically installed in the wheelchair. 
     In one embodiment, the power source  108  is a battery. The batteries may be rechargeable such as but not limited to using an ordinary 110V or 220V charger. Sample batteries that may work with this device include but are not limited to a primary battery (non-chargeable) and secondary batteries such as Lithium-ion (Li-ion), Nickel Cadmium (Ni—Cd), Nickel-Metal Hydride (Ni-MH) and Lead-Acid. 
       FIG.  3    illustrates a top perspective view of the device  100  attached to the manual wheelchair  202  in accordance with an embodiment of the present invention. In this configuration, the retractable friction roller  104  is mounted on the axle  114  (shown in  FIG.  1   ) and rotated by activation of the motor  112 . 
     In one embodiment, the device includes a motor with a friction surface. The motor may be an electric motor. The motor may be an Alternating Current (AC) motor. The motor may be a Direct Current (DC) motor. The DC motor may be a brushless DC motor. The motor may be a speed control motor. The motor may be a geared motor. The motor may be a brushed motor. The motor may be a hub motor. The motor may be a brushless hub motor. The motor may be a worm gear motor. In an illustrative example, the motor may be any other type of motor including, but not limited to, a geared hub motor, a brushed hub motor, a brushless geared hub motor, a brushed geared hub motor, a non-hub motor, or any other similar motor. Hub motors are very common in power wheelchairs but are typically used for separate wheels that contact the ground directly. 
     In the present invention, the retractable friction roller  104  is placed in contact with at least one wheel  206  of the manual wheelchair  202  to rotate the wheel  206  and move the wheelchair  202 . The retractable friction roller  104  rotates the wheel  206  by friction force. This is a unique feature of the present invention. Other devices are commonly based on motor to ground movements, PAW uses a friction roller to the wheel to generate movement. 
     In one embodiment, the retractable friction roller  104  is shaped to have a centerless concave rim housing configured to provide high friction surface facing the wheel  206  of the wheelchair  202 . The centerless concave rim housing acts as a wheel hub to yield a high percentage of surface contact. In one embodiment, the high friction surface of the retractable friction roller  104  faces the wheelchair wheel  206  and is customizable to fit the curve and or size of the wheel  206 . The friction roller  104  may be configured with a rim that is not concave but may comprise a flat surface to engage a wheel. 
     In an embodiment, the material of high friction surface of the retractable friction roller  104  is rubber or polyurethane. However, it would be readily apparent to those skilled in the art that various types of material such as silicone, foam, sand paper, grit tape, sponge-rubber foam etc. may be envisioned without deviating from the scope of the present invention. In another embodiment, the wheels  206  of wheelchair  202  are made using a high friction surface, and the roller  104  is made of steel, aluminum or other similar hardened, textured surface. The friction roller  104  may be configured with a rim having a built-in friction surface. The friction surface may be knurled. The knurled friction surface may be machined. In an embodiment, the friction surface may be machined into the retractable friction roller  104  to provide high friction surface facing the wheel  206  of the wheelchair  202 . The machined surface of the friction roller  104  may be knurled using a straight pattern. However, it would be readily apparent to those skilled in the art that various types of knurling, such as, for example, right hand knurl, left hand knurl, diamond knurl, or the like, of the friction roller  104  high friction surface may be envisioned without deviating from the scope of the present invention. 
     The motor  112  is configured to rotate the retractable friction roller  104 . The retractable friction roller  104  is mounted on the axle  114  (shown in  FIG.  1   ) and the rotor  116  (shown in  FIG.  1   ) rotates the first axle resulting in rotation of the retractable friction roller  104 . In an embodiment, the motor  112  is a brushless DC motor with a friction surface. However, it would be readily apparent to those skilled in the art that various types of motor such as geared hub motor, brushed hub motor, brushed geared hub motor etc. may be envisioned without deviating from the scope of the present invention. 
     In another embodiment, the device  100  further includes a second motor  302  operably connected to a second communication unit  304  and the power source  108  (shown in  FIG.  1   ). The communication unit  110  and the second communication unit  304  are both operably connected to the joystick  102 . In another embodiment, the joystick  102  may further include control buttons  316  operably connected to the motor. The control buttons  316  controls speed of the motor  112  (shown in  FIG.  3   ). 
     The second motor  302  includes a second axle (not shown) connected to a second rotor (not shown). In this embodiment, the device  100  further includes a second friction roller  306  mounted on the second axle (not shown). The second roller  306  is placed in contact with a second wheel  308  of the manual wheelchair  202 . Alternatively, the second roller  306  is mounted to the axle  114  and the motor  112  provides motor torque to rotate the second friction roller  306  and the friction roller  104  (not shown). 
     Similarly, to the retractable friction roller  104 , the second retractable friction roller  306  includes a centerless concave rim housing configured to provide high friction surface facing the second wheel  308  of the wheelchair  202 . The principle and function of the second motor  302  and second friction roller  306  is the same as the motor  112  and retractable friction roller  104  as previously described. 
     In another embodiment of the present invention, the device  100  further includes a second engagement unit  310  attached to the manual wheelchair  202  to detachably attach the second friction roller  306  and the second wheel  308  of the wheelchair  202 . The engagement unit  106  detachably attaches the friction roller  104  and the wheel  206 . The engagement unit  106  and the second engagement unit  310  is attached behind seating area  312  of wheelchair  202  and top of the wheel  206  and the second wheel  308 , respectively. 
       FIG.  4    illustrates perspective view of engagement unit  106  in accordance with another embodiment of the present invention. The engagement unit  106  includes a lever  502  operably connected to a lever mechanism unit  504 , a turnbuckle  506  connected to the lever mechanism unit  504  and an attachment unit  508  operably connected to the turnbuckle  506 . The attachment unit  508  comprises clamps (shown in  FIG.  5   ) and a spring loaded unit (shown in  FIG.  5   ). 
     The retractable friction roller ( 104 , shown in  FIG.  3   ) is operably connected to the turnbuckle  506 . The lever  502  is actuated by the user and results in engaging and disengaging of the retractable friction roller ( 104 , shown in  FIG.  3   ) from the wheel  206 . Thus, the lever  502  results in converting a manual wheelchair into an electronic wheelchair and vice versa. 
     In  FIG.  6    another embodiment of the device  100  is shown with a safety fender  509  also herein referred to as a cover, protective cap and/or shield; which comprises a top, an open bottom, a right side, a left side, a proximal side and distal side wherein each of the four sides has a bottom edge and at least one set of brushes  510  is attached to the bottom edge of the distal side of the safety fender  509  and the safety fender  509  is detachably attached to the wheelchair  202  such as but not limited to attachment by clamps  402  and wherein the safety fender  509  fits over the attachment friction roller  104 . The safety fender  509  may be attached to a motor  112  (depicted at least in  FIG.  3   ). The safety fender  509  may be attached to a second motor  302  (depicted at least in  FIG.  3   ). The safety fender  509  may be attached to a bracket  704  (depicted at least in  FIGS.  7 A- 7 B ). In one embodiment, the at least one set of brushes  510  are positioned on the bottom edge of the distal side of the fender so that the brushes  510  contact the wheel  206  of the wheelchair  202 . In one embodiment, there are at least two sets of brushes  510  with one set of brushes positioned on the bottom edge of the distal side of the fender and the other set of brushes  510  positioned on the bottom side of the bottom edge of the proximal side of the fender. That is in front of and behind the friction roller  104  where friction roller  104  comes into contact with the wheel  206 . It will be apparent to one of ordinary skill in the art that placement of the at least one set of brushes  510  may vary to optimize the contact between the friction roller  104  and the wheel  206 . This is accomplished in part as the at least one set of brushes function to brush away and or clearing debris from coming in between the friction roller  104  and the wheel  206 . 
     In one embodiment, the cover  509  is a protective barrier that shields the top and four sides of the protects the friction roller  104  and axle  114  from environmental exposure, debris and damage. In this regard, the fender  509  may improve the long-term use and function of the device  100  by protecting the friction roller  104  and axle  114  from environmental exposure and preventing environmental debris from impacting or entering into the inner functioning components of the device  100  motor through contact of the wheel  206  with the with the friction roller  104 . The fender  509  is also a safety device. More specifically, the fender  509  improves the safety of the user by preventing clothing, hair, hands and fingers from being caught, snagged or trapped by the device especially as the wheel  206  rotates. 
       FIGS.  7 A- 7 B  together illustrate side views of exemplary wheelchair power assist device components. In  FIG.  7 A , the exemplary wheelchair power assist device  100  includes the friction roller  104  mounted to the axle  114 . In the depicted example, the friction roller  104  is attached to a motor  112  (depicted at least in  FIG.  3   ) and the motor  112  is attached to the bracket  704 . The friction roller  104  may be attached to the bracket  704 . In the illustrated example, the bracket  704  is configured to attach the motor  112  (depicted at least in  FIG.  3   ) to a wheelchair  202  (depicted at least in  FIG.  3   ) via the attachment unit  508 . The bracket  704  may be configured to attach a second motor  302  (depicted at least in  FIG.  3   ) with a second friction roller  306  (depicted at least in  FIG.  3   ) and second axle  114  (depicted at least in  FIG.  5   ), to adapt another of the two main wheels of an exemplary wheelchair  202  with a second wheelchair power assist device  100 . In the depicted example, the top of the bracket  704  is pivotally coupled with the top of the attachment unit  508 . The top of the bracket  704  may be pivotally coupled with the top of the attachment unit  508  by a swivel pin, for example. In the depicted example, the bottom of the bracket  704  is connected with the turnbuckle  506 . Pivotally coupling the top of the bracket  704  with the top of the attachment unit  508 , and connecting the bottom of the bracket  704  with the turnbuckle  506 , permits the lower portion of the bracket  704  to move relative to the attachment unit  508  in response to operation of the lever  502  by the handle  702 . In the depicted example, moving the lever  502  drives the turnbuckle  506  via the lever mechanism unit  504 , thereby raising or lowering the friction roller  104  to releasably engage the friction roller  104  and a wheel  206  (depicted at least in  FIG.  5   ) via operation of the lever mechanism unit  504 . In the example depicted by  FIG.  7 A , the lower portion of the bracket  704  has been displaced away from the attachment unit  508  by operation of the lever  502 . 
     In  FIG.  7 B , the exemplary wheelchair power assist device  100  operation unit  706  assembly includes the turnbuckle  506  connected to the bracket  704  and the lever mechanism unit  504 . The lever mechanism unit  504  operably couples the lever  502  and handle  702  with the bracket  704  via the turnbuckle  506 , permitting a user to releasably engage a friction roller  104  (depicted at least in  FIG.  7 A ) and a wheel  206  (depicted at least in  FIG.  5   ) via operation of the lever mechanism unit  504 . In the example depicted by  FIG.  7 B , the lower portion of the bracket  704  has been displaced toward the attachment unit  508  by operation of the lever  502 . 
       FIG.  8    illustrates a side view of an exemplary wheelchair power assist device operation unit assembly in an exemplary retracted configuration. In  FIG.  8   , the exemplary wheelchair power assist device operation unit assembly  706  components are shown retracted to collapse the operation unit assembly  706  to facilitate space-efficient storage and transport. In the depicted example, the exemplary wheelchair power assist device operation unit assembly  706  retracted configuration includes the lever  502  and handle  702  coupled via the lever mechanism unit  504  and turnbuckle  506  with the bracket  704  (depicted at least in  FIGS.  7 A and  7 B ) and attachment unit  508 . 
       FIG.  9    illustrates a top perspective view of an exemplary wheelchair with two illustrative power assist devices each configured to drive one of the two depicted wheelchair main wheels. In  FIG.  9   , the exemplary wheelchair  202  includes the main wheels  206  and  308 . In the depicted example, the wheelchair  202  is configured with a wheelchair power assist device operation unit assembly  706  to drive the main wheel  206  via the friction roller  104 . In the illustrated example, the wheelchair  202  is configured with a second wheelchair power assist device operation unit assembly  706  to drive the second main wheel  308  via the second friction roller  306 . Configuring the friction roller  104  and  306  above the respective wheels  206  and  308 , and at the rear of the wheelchair  202 , permits wheelchair power assist device installation and removal from behind the wheelchair while the wheelchair  202  seat is occupied by a person riding in the wheelchair  202 . While riding in the wheelchair  202 , a person riding may releasably engage power assist to the wheel  206  by operating the lever  502  (depicted in  FIGS.  7 A and  7 B ) of the wheelchair power assist device operation unit assembly  706 . The person while riding in the wheelchair  202  may releasably engage power assist to the second wheel  308  by operating the lever  502  (depicted in  FIGS.  7 A and  7 B ) of the second wheelchair power assist device operation unit assembly  706 . When power assist to the wheels is disengaged by operation of the lever  502 , the friction rollers  104  and  306  disengage from the respective wheelchair  202  wheels  206  and  308 , and the wheelchair  202  operates normally with manual propulsion by the user turning the wheels  206  and  308  by hand. The person riding in the wheelchair  202  under manual propulsion may engage power assist to the wheels  206  and  308  by operating the lever  502 , to engage the friction rollers with the wheels. 
       FIG.  10 A  illustrates a rear perspective view of an exemplary wheelchair with two illustrative power assist devices each configured to drive one of the two depicted wheelchair main wheels, with the wheelchair in an exemplary unfolded configuration. In  FIG.  10 A , the exemplary wheelchair  202  is a collapsible wheelchair depicted in an illustrative unfolded configuration. In the depicted example, the friction roller  104  is configured to drive the wheel  206  by an exemplary power assist device (depicted for example by  FIGS.  1 - 6 ,  7 A -B, and  8 - 9 ). In the illustrated example, the second friction roller  306  is configured to drive the second wheel  308  by an exemplary second power assist device (depicted for example by  FIGS.  1 - 6 ,  7 A -B, and  8 - 9 ). In the depicted example, the friction rollers  104  and  306  are configured above the respective wheels  206  and  308 , and behind the wheelchair  202  seating area  312 . In the illustrated example, configuring the friction rollers  104  and  306  above the respective wheels  206  and  308 , and behind the wheelchair  202  seating area  312 , permits folding and unfolding the collapsible wheelchair  202  while the power assist devices remain installed, as a result of leaving open the space  1005  between the power assist devices. The friction rollers  104  and  306  may be disposed above the center of the respective wheels  206  and  308 , between the respective wheel centers and the tops of the wheels, or above the wheels as depicted, to facilitate leaving open the space  1005  and permit folding and unfolding the collapsible wheelchair  202  while the power assist devices remain installed. In the illustrated example, the space  1005  is also left open as a result of the power assist device design that includes separate and distinct power assist devices each configured to drive one of the wheels  206 ,  308 , without power assist device components occupying the space  1005 . The wheelchair  202  may be folded while the power assist remains installed or attached to the wheelchair  202 , independent of whether the power assist is engaged or disengaged, without affecting the folding action of the wheelchair  202 , as a result of leaving the space  1005  open between the two power assist devices each configured to drive one of the wheels  206  and  308 . 
       FIG.  10 B  illustrates a rear perspective view of an exemplary wheelchair with two illustrative power assist devices each configured to drive one of the two depicted wheelchair main wheels, with the wheelchair in an exemplary folded configuration. In  FIG.  10 B , the exemplary wheelchair  202  is a collapsible wheelchair depicted in an illustrative folded configuration. In the depicted example, the friction rollers  104  and  306  are configured above the respective wheels  206  and  308 , and behind the wheelchair  202  seating area  312 . In the illustrated example, the collapsible wheelchair  202  has been folded while the power assist devices remained installed. This facilitation may be a result of the depicted power assist design, that leaves open the space  1005  between the power assist devices and behind the wheelchair  202  seating area  312 , without power assist device components occupying the space  1005 . 
       FIGS.  11 A- 11 D  illustrate perspective views of the exemplary engagement unit  106  (also depicted at least by  FIGS.  1 ,  3 , and  4   ) implementation in accordance with the present disclosure.  FIG.  11 A  is a side perspective view of the engagement unit  106  depicted in an exemplary disengaged mode.  FIG.  11 B  is a side perspective view of the engagement unit  106  illustrated in an exemplary engaged mode.  FIG.  11 C  is a rear perspective view of the engagement unit  106  depicted in an exemplary disengaged mode.  FIG.  11 D  is a rear perspective view of the engagement unit  106  depicted in an exemplary engaged mode. 
     In the examples depicted by  FIGS.  11 A- 11 D , the engagement unit  106  includes the lever  502  operably connected to the lever mechanism unit  504 . The depicted friction roller  104  is configured with the friction surface  1105  (depicted by  FIGS.  11 C and  11 D ) designed to provide high friction with the wheel  206  when the friction roller  104  is in contact with the wheel  206 . 
     In the illustrated examples, the lever mechanism unit  504  is attached to the motor  112  bracket to engage and disengage the friction roller  104  friction surface  1105  and the wheel  206 . In the illustrated examples, the friction roller  104  includes the concave rim housing  1110  (depicted by  FIGS.  11 C and  11 D ) designed to fit the wheel  206  and function as a wheel hub to yield a high percentage of surface contact between the friction roller  104  and the wheel  206 . The concave rim housing  1110  may be a centerless concave rim housing. In  FIG.  11 D , the friction roller  104  is depicted engaged with the wheel  206  at an exemplary point on the contact surface  1115  between the wheel  206  and the friction roller  104 . 
     In the depicted examples, moving the lever  502  drives the lever mechanism unit  504 , thereby raising or lowering the friction roller  104  to releasably engage the friction roller  104  and the wheel  206  via operation of the lever mechanism unit  504 . In the example depicted by  FIG.  11 A , the upper portion of the bracket  704  has been displaced toward the attachment unit  508  by operation of the lever  502 . In the example illustrated by  FIG.  11 B , the upper portion of the bracket  704  has been displaced away from the attachment unit  508  by operation of the lever  502 . 
     In the illustrated examples, the exemplary engagement unit  106  includes a mechanical one button engage and disengage attached to the motor, to raise or lower the friction roller  104  and releasably engage the friction roller  104  and the wheel  206 . The mechanical engage and disengage unit may comprise an engagement actuator  1200 . Exemplary engagement actuator  1200  implementations may comprise, for example, an exemplary linear actuator  1205  (depicted by  FIG.  12 A ), an exemplary linear slide rail  1210  (depicted by  FIG.  12 B ), an exemplary linear screw rail, or an exemplary push/pull solenoid  1215  (depicted by  FIG.  12 C ). 
     With reference to  FIG.  1   , in an embodiment of the present invention, the power source  108  is a battery. The batteries are chargeable using an ordinary 110V or 220V charger. Examples of battery include but not limited to primary battery (non-chargeable) and secondary batteries such as Lithium-ion (Li-ion), Nickel Cadmium (Ni—Cd), Nickel-Metal Hydride (Ni-MH), and Lead-Acid. 
       FIG.  5    illustrates perspective view of the device  100  in accordance with another embodiment of the present invention. The attachment clamps  402  and a spring loaded unit  404  engage and disengage the retractable friction roller  104  and the wheel  206 . 
     With reference to  FIG.  1   , the friction roller  104  is mounted on the axle  114 . In an embodiment of the present invention, the friction roller  104  has an opening to receive the axle  114 . The axle  114  is a cylindrical elongated rod to pass through the opening to rotate the friction roller  104  on receiving motor torque from the rotor ( 116 , shown in  FIG.  1   ). 
     Examples of the attachment unit  508  are simple mechanical devices such as but not limited to spring, screw clamp, mechanical coupling, latch, rod clamp, rail clamp, light, round center mount, mount bracket, pole clamp, pipe clamp, quick release clamp, rack clamp mount, bolt, screw, or handlebar clamp mount on the backrest frame of wheelchair  202  and provides contact between the friction roller  104  and the wheelchair wheel  206 , respectively. Various exemplary attachment unit  508  implementations may include any fastener adaptable to mount the device to the wheelchair. 
       FIGS.  13 A- 13 D  depict perspective views of an exemplary engagement and attachment implementation in accordance with the present disclosure.  FIG.  13 A  depicts one side of the exemplary engagement and attachment implementation including the engagement actuator  1200  operably coupled with the attachment member  508  and the engagement member  704  to move the engagement member  704  relative to the attachment member  508 . In the depicted implementation, the attachment member  508  is a bracket which may hereinafter be referred to as an attachment bracket  508 . In the depicted implementation, the clamp  1305 , the clamp fastener  1310 , the collar  1315 , and the adapter plate  1320  are configured to removably secure the attachment bracket  508  to an exemplary wheelchair  202  (in an illustrative example, at least a portion of an exemplary wheelchair  202  is depicted at least in  FIGS.  2 A- 2 E,  3 ,  9 ,  10 A- 10 B,  14 A- 14 B,  15 A- 15 B,  16 B,  17 B,  18 C,  19 B,  20 A- 20 C,  21 A- 21 D,  22 , and  24 - 30   ). In the depicted implementation, the engagement member  704  is a bracket which may hereinafter be referred to as an engagement bracket  704 . The engagement bracket  704  implementation depicted by  FIG.  13 A  and throughout the present disclosure may include the motor mount holes  1325   a,b,c,d  illustrated at least by  FIGS.  13 C,  16 A,  18 A and  23 D . In the depicted implementation, the attachment bracket  508  includes the attachment bracket  508  first end  1335  and the attachment bracket  508  second end  1340 . In the depicted implementation, the engagement bracket  704  includes the engagement bracket  704  first end  1345  and the engagement bracket  704  second end  1350 . In the depicted implementation the engagement actuator  1200  movable shaft  1330  is connected to the engagement bracket  704  and the attachment bracket  508 . The engagement actuator  1200  movable shaft  1330  is configured to move the engagement bracket  704  relative to the attachment bracket  508  as the movable shaft  1330  extends or retracts using the engagement actuator  1200 . In the depicted implementation, the engagement bracket  704  first end  1345  is rotatably coupled with the attachment bracket  508  first end  1335 , to permit the engagement bracket  704  to move relative to the attachment bracket  508 . In an illustrative example, extending or retracting the movable shaft  1330  may move the engagement bracket  704  relative to the attachment bracket  508  between a disengaged position wherein a friction roller is not in contact with a wheelchair  202  wheel and an engaged position wherein the friction roller is in contact with the wheelchair wheel, as depicted and described at least with reference to  FIGS.  15 A- 15 B . In an illustrative example, an exemplary implementation may comprise at least a first engagement member  704  and a first attachment member  508  configured to drive a wheelchair first wheel using a first friction roller and a first motor; and a second engagement member  704  and a second attachment member  508  configured to drive a wheelchair second wheel using a second friction roller and a second motor, in accordance with what has been described hereinabove. In the implementation depicted by  FIGS.  13 A- 13 B , the adapter plate  1320  secures the collar  1315  to position the collar  1315  opening central axis substantially perpendicular to the attachment bracket  508  length to permit attaching the collar  1315  to a horizonal portion of a wheelchair. In the implementation depicted by  FIGS.  13 C- 13 D  the collar  1315  is secured to the attachment bracket  508  second end  1340  without the use of an adapter plate and with the collar  1315  opening central axis substantially parallel to the attachment bracket  508  length to permit attaching the collar  1315  to a vertical portion of a wheelchair. In the implementation depicted by  FIG.  13 C , the attachment bracket  508  is a U-shaped bracket with walls running the length of the bracket, with the engagement actuator  1200  centrally connected within the attachment bracket  508  walls and an inside surface of the engagement bracket  704 . In the implementation depicted by  FIG.  13 D , the engagement actuator  1200  is connected to the outside of one side of the attachment bracket  508  and the outside of the engagement bracket  704 . 
       FIGS.  14 A- 14 B  depict outside and inside views of an exemplary engagement and attachment implementation with the movable shaft  1330  in an exemplary extended mode.  FIG.  14 A  depicts the exemplary engagement and attachment implementation from an outside point of view looking into the wheelchair  202 .  FIG.  14 B  depicts the exemplary engagement and attachment implementation from an inside point of view underneath the wheelchair  202 . 
       FIGS.  15 A- 15 B  depict side views of an exemplary engagement and attachment implementation in exemplary disengaged and engaged modes. The implementation depicted by  FIGS.  15 A- 15 B  includes the first engagement member  704  and a first attachment member  508  (not visible) configured to drive the wheelchair  202  first wheel  206  using the first friction roller  104  and the first motor  112 ; and, the second engagement member  704  and the second attachment member  508  configured to drive the wheelchair  202  second wheel  308  using the second friction roller  306  and the second motor  302 . In the implementation depicted by  FIGS.  15 A- 15 B , the first friction roller  104  is operably coupled with the first engagement bracket  704 , wherein the first friction roller  104  comprises the first centerless concave rim housing  1110  comprising a first friction surface; the first motor  112  is operably coupled with the first friction roller  104 ; and a first engagement actuator  1200  (not visible) is connected to the first attachment member  508 , wherein the first engagement actuator  1200  comprises a movable shaft  1330  (not visible) configured to move the first engagement member  704  relative to the first attachment member  508  between a disengaged position (depicted at least by  FIG.  15 A ) wherein the first friction roller  104  is not in contact with the wheelchair  202  first wheel  206  and an engaged position (depicted at least by  FIG.  15 B ) wherein the first friction roller  104  is in contact with the wheelchair  202  first wheel  206 . In the implementation depicted by  FIGS.  15 A- 15 B , the second friction roller  306  is operably coupled with the second engagement bracket  704 , wherein the second friction roller  306  comprises the second centerless concave rim housing  1110  comprising a second friction surface; the second motor  302  is operably coupled with the second friction roller  306 ; and the second engagement actuator  1200  is connected to the second attachment bracket  508 , wherein the second engagement actuator  1200  comprises the movable shaft  1330  configured to move the second engagement bracket  704  relative to the second attachment bracket  508  between a disengaged position (depicted at least by  FIG.  15 A ) wherein the second friction roller  306  is not in contact with the wheelchair  202  second wheel  308  and an engaged position (depicted at least by  FIG.  15 B ) wherein the second friction roller  306  is in contact with the wheelchair  202  second wheel  308 . In the depicted implementation the wheelchair  202  is a foldable wheelchair, and the first motor  112 , the first friction roller  104 , the first attachment bracket  508 , the first engagement bracket  704 , the second motor  302 , the second friction roller  306 , the second attachment bracket  508 , and the second engagement bracket  704  may remain attached to the foldable wheelchair  202  when the foldable wheelchair  202  is in a folded or unfolded configuration, as a result of the open space  1005  located behind the seating area of the foldable wheelchair  202  that is configured to accommodate the depicted components. 
       FIGS.  16 A- 16 B  depict side views of an exemplary engagement and attachment implementation in accordance with the present disclosure. In  FIG.  16 A , the depicted exemplary engagement and attachment implementation comprises the engagement bracket  704  having a length not more than half the attachment bracket  508  length. In the depicted implementation, the engagement actuator  1200  is secured directly to the attachment bracket  508  substantially at a mid-point of the attachment bracket  508  length and the engagement bracket  704  first end  1345  is rotatably coupled with the attachment bracket  508  first end  1335 . In the depicted implementation, the engagement bracket  704  second end  1350  is displaced relative to the attachment bracket  508  mid-point as the movable shaft extends or retracts. In the depicted implementation, the collar  1315  is secured directly to the attachment bracket  508  second end  1340  with the collar  1315  opening central axis parallel to the attachment bracket  508  length.  FIG.  16 B  depicts the exemplary engagement and attachment implementation illustrated by  FIG.  16 A  configured on one side of the exemplary wheelchair  202  proximal with the wheelchair  202  first wheel  206 . 
       FIGS.  17 A- 17 B  depict side views of an exemplary engagement and attachment implementation in accordance with the present disclosure. In  FIG.  17 A , the depicted exemplary engagement and attachment implementation includes the attachment bracket  508 , engagement bracket  704 , and engagement actuator  1200  features described with reference to  FIG.  16 A , and the implementation depicted by  FIG.  17 A  further comprises the collar  1315  is secured to the adapter plate  1320  connected to the attachment bracket  508  second end  1340  with the collar  1315  opening central axis perpendicular to the attachment bracket  508  length.  FIG.  17 B  depicts the exemplary engagement and attachment implementation illustrated by  FIG.  17 A  configured on one side of the exemplary wheelchair  202  proximal with the wheelchair  202  first wheel  206 . 
       FIGS.  18 A- 18 C  depict side views of an exemplary engagement and attachment implementation in accordance with the present disclosure. In  FIGS.  18 A- 18 C , the depicted exemplary engagement and attachment implementation includes attachment bracket  508 , engagement bracket  704 , and engagement actuator  1200  features similar to those features described with reference to  FIG.  17 A . In the implementation depicted by  FIGS.  18 A , the engagement actuator  1200  is secured directly to the attachment bracket  508  at the attachment bracket  508  first end  1335 , and the engagement bracket  704  first end  1345  is rotatably coupled with the attachment bracket  508  substantially at a mid-point of the attachment bracket  508  length. In the depicted implementation, the engagement bracket  704  second end  1350  is displaced relative to the attachment bracket  508  first end  1335  as the movable shaft  1330  extends or retracts. In the implementation depicted by  FIG.  18 A , the attachment bracket  508  is a U-shaped bracket with walls running the length of the bracket, with the engagement actuator  1200  centrally connected within the attachment bracket  508  walls and an inside surface of the engagement bracket  704 . In the implementation depicted by  FIG.  18 B , the engagement actuator  1200  is connected to the outside of one side of the attachment bracket  508  and the engagement bracket  704 .  FIG.  18 C  depicts the exemplary engagement and attachment implementation illustrated by  FIG.  18 A  configured on one side of the exemplary wheelchair  202  proximal with the wheelchair  202  first wheel  206 . 
       FIGS.  19 A- 19 B  depict side views of an exemplary engagement and attachment implementation in accordance with the present disclosure. In  FIGS.  19 A- 19 B , the depicted exemplary engagement and attachment implementation includes the attachment bracket  508 , engagement bracket  704 , and engagement actuator  1200  features described with reference to  FIG.  18 B . The implementation depicted by  FIG.  19 A  further comprises the collar  1315  is secured to the adapter plate  1320  connected to the attachment bracket  508  second end  1340  with the collar  1315  opening central axis perpendicular to the attachment bracket  508  length.  FIG.  19 B  depicts the exemplary engagement and attachment implementation illustrated by  FIG.  19 A  configured on one side of the exemplary wheelchair  202  proximal with the wheelchair  202  first wheel  206 . 
       FIGS.  20 A- 20 C  depict side views of an exemplary engagement and attachment implementation in accordance with the present disclosure. In  FIGS.  20 A- 20 C , the depicted exemplary engagement and attachment implementation includes attachment bracket  508 , engagement bracket  704 , and engagement actuator  1200  features similar to those features described hereinabove. The implementation depicted by  FIGS.  20 A- 20 C  further comprises the engagement bracket  704  rotatably secured at one end of the attachment bracket  508 , wherein the engagement bracket  704  rotates between a position substantially parallel to the attachment bracket  508  and a position substantially perpendicular to the attachment bracket  508 . The engagement bracket  704  may rotate through more than 90 degrees relative to the attachment bracket  508 , as the engagement bracket  704  moves between exemplary engaged and disengaged positions. In some implementations, the engagement bracket  704  may rotate up to 360 degrees relative to the attachment bracket  508 . In the depicted implementation the engagement actuator  1200  is disposed at an angle relative to the attachment bracket  508 , to cause the engagement bracket  704  to rotate relative to the attachment bracket  508  as the moveable shaft  1330  extends or retracts. In the implementation depicted by  FIGS.  20 A- 20 C , the attachment bracket  508  is secured to the exemplary wheelchair  202  by the two collars  1315 .  FIG.  20 A  depicts the exemplary engagement and attachment implementation in an illustrative engaged mode.  FIG.  20 B  depicts the exemplary engagement and attachment implementation in an illustrative intermediate position between the engaged mode depicted by  FIG.  20 A  and the retracted mode depicted by  FIG.  20 C . 
       FIGS.  21 A- 21 D  depict various views of an exemplary engagement and attachment implementation in accordance with the present disclosure. In  FIGS.  21 A- 21 D , the depicted exemplary engagement and attachment implementation includes the attachment bracket  508 , engagement bracket  704 , and engagement actuator  1200  features in accordance with what has been described hereinabove. The implementation depicted by  FIGS.  21 A- 21 D  further comprises the engagement bracket  704  is configured with a slot (visible at least in  FIGS.  21 C and  21 D ) wherein the slot is adapted to subsume a portion of the attachment bracket  508  and wherein the engagement bracket  704  slides along the attachment bracket  508  length as the engagement bracket  704  moves relative to the attachment bracket  508 . In the implementation depicted by  FIGS.  21 A- 21 D , the engagement bracket  704  slides along the attachment bracket  508  length as the moveable shaft  1330  extends or retracts. In the implementation depicted by  FIGS.  21 A- 21 D , the attachment bracket  508  is secured to the exemplary wheelchair  202  by the two collars  1315 .  FIG.  21 A  depicts the exemplary engagement and attachment implementation in an illustrative engaged mode.  FIG.  21 B  depicts the exemplary engagement and attachment implementation in an illustrative retracted mode side view.  FIG.  21 C  depicts a front perspective view of the illustrative retracted mode depicted in a side view by  FIG.  21 B .  FIG.  21 D  depicts a side detail view of the exemplary engagement and attachment implementation in an illustrative disengaged mode. 
       FIG.  22    depicts an exemplary front detail view of an exemplary engagement and attachment implementation in accordance with the present disclosure. In  FIG.  22   , the exemplary engagement actuator  1200  is powered and controlled through the engagement actuator electrical connection  2210 . The engagement actuator  1200  may be controlled by an engage button accessible to a user of the wheelchair  202 . The engage button may be configured to control the engagement actuator  1200  using the engagement actuator electrical connection  2210 . In the depicted implementation, the engagement actuator  1200  is secured to the adapter plate  1320  by the engagement actuator adapter securing screw  2215 . In the depicted implementation, the collar  1315 , the upper engagement actuator collar securing screw  2205 , and the lower engagement actuator collar securing screw  2220  secure the adapter plate  1320  to the wheelchair  202 . 
       FIG.  23 A  depicts a top perspective view of an exemplary exchange tab  2300  implementation.  FIGS.  23 B and  23 C  depict side perspective views of the exemplary exchange tab  2300  implementation illustrated by  FIG.  23 A . In  FIGS.  23 B and  23 C , the exchange tab  2300  comprises the tab mount holes  2305 . The tab mount holes  2305  may be configured in various numbers or shapes in various locations of the exchange tab  2300 . The exchange tab  2300  may comprise metal, fiberglass, composite, or other material. 
       FIG.  23 D  depicts a front perspective view of an exemplary exchange actuator arrangement. In  FIG.  23 D , the exemplary exchange actuator arrangement comprises the exchange tab  2300 . In the implementation depicted by  FIG.  23 D  the tab mount holes depicted by  FIGS.  23 B and  23 C  are disposed in alignment with the engagement member mount holes  2310  configured in the engagement member  704 . In the implementation depicted by  FIG.  23 D  the engagement member  704  comprises the motor mount holes  1325   a,b,c,d  illustrated at least by  FIGS.  13 C,  16 A and  18 A . In the implementation depicted by  FIG.  23 D  the engagement actuator  1200  comprises the movable shaft  1330 . The movable shaft  1330  is connected to the engagement member  704 . In the depicted implementation, the adapter plate  1320  is operably connected to the engagement actuator  1200 . In the depicted implementation, the collar  1315  is configured to removably secure the adapter plate  1320  to an exemplary wheelchair  202  (in illustrative examples, at least a portion of an exemplary wheelchair  202  is depicted at least in  FIGS.  2 A- 2 E,  3 ,  9 ,  10 A- 10 B,  14 A- 14 B,  15 A- 15 B,  16 B,  17 B,  18 C,  19 B,  20 A- 20 C,  21 A- 21 D,  22 , and  24 - 30   ). The engagement actuator  1200  movable shaft  1330  is configured to move the engagement member  704  relative to a wheelchair  202  as the movable shaft  1330  extends or retracts using the engagement actuator  1200 . In the depicted implementation, the engagement member  704  is configured to be rotatably coupled with the exchange tab  2300 . The exchange tab  2300  may be secured to a wheelchair  202 . The depicted implementation configures the engagement member  704  to rotate about a central axis through the tab mount holes  2305  as the movable shaft  1330  is extended or retracted. In an illustrative example, extending or retracting the movable shaft  1330  when the exchange tab  2300  is secured to a wheelchair  202  may move the engagement bracket  704  relative to the exchange tab  2300  and wheelchair  202 . For example, extending or retracting the movable shaft  1330  when the exchange tab  2300  is secured to a wheelchair  202  may move the engagement bracket  704  between a disengaged position wherein a friction roller is not in contact with a wheelchair  202  wheel and an engaged position wherein the friction roller is in contact with a wheelchair  202  wheel, as depicted and described at least with reference to  FIGS.  15 A- 15 B .  FIG.  23 E  depicts a side view of the exchange actuator arrangement shown in  FIG.  23 D . 
       FIG.  24    depicts an exemplary wheelchair viewed from a right rear perspective. In the implementation depicted by  FIG.  24    the exemplary wheelchair  202  comprises the exchange tab  2300 . The exchange tab  2300  may be welded to the wheelchair  202 . In the depicted implementation the wheelchair  202  comprises the wheel  206  and the arm  204 . 
       FIG.  25    depicts an exemplary wheelchair viewed from a right rear perspective. In the implementation depicted by  FIG.  25    the exemplary wheelchair  202  comprises the two exchange tabs  2300 . In the depicted implementation the two exchange tabs  2300  are welded to the back of the wheelchair  202  at either side of the seating area  312 . In the depicted implementation the wheelchair  202  comprises the wheel  206  and the second wheel  308 . 
       FIG.  26    depicts a partial exploded view of an exemplary wheelchair and exemplary exchange actuator arrangement components viewed from a left rear perspective. The example depicted by  FIG.  26    shows the wheel  206  disposed on the right side of the wheelchair  202 . The example depicted by  FIG.  26    shows the exemplary exchange actuator arrangement components comprising the exchange tab  2300  in an exemplary position to facilitate mounting the exchange tab  2300  to the left side of the wheelchair  202 . In the example depicted by  FIG.  26    the exemplary exchange actuator arrangement components further comprise the engagement member  704 , the collar  1315 , the adapter plate  1320  and the engagement actuator (depicted for example at least in  FIGS.  23 D and  23 E ). In the depicted example the engagement actuator further comprises the movable shaft  1330 . In the example depicted by  FIG.  26    the exemplary exchange actuator arrangement components are shown in an exemplary position to be configured to enable the second motor  302  and the second friction roller  306  to drive a second wheel (not shown). In the depicted example the second wheel (depicted for example at least by  FIGS.  25  and  27    with reference to second wheel  308  therein) would be disposed on the opposite side of the wheelchair  202  from the depicted wheel  206 . 
       FIG.  27    depicts exemplary wheelchair  202  viewed from a top left side perspective. In the example depicted by  FIG.  27    the exchange tab  2300  is secured to the left side of the wheelchair  202 . In the depicted example the exemplary exchange actuator arrangement is shown in an illustrative position to permit mounting the engagement member  704  to the exchange tab  2300 . An exemplary wheelchair  202  may be configured with two exchange actuator arrangements similarly positioned with one exchange actuator arrangement at each side of the wheelchair. Configuring a wheelchair with two exchange actuator arrangements similarly positioned with one at each side may permit selectively and independently engaging and disengaging two friction rollers with two respective wheelchair wheels while leaving an open space behind the seating area  312 . In an illustrative example the open space behind the seating area  312  may permit folding a foldable wheelchair while the devices described herein remain installed on the wheelchair. 
       FIG.  28    depicts the exemplary wheelchair shown by  FIG.  27    viewed from a left side perspective. 
       FIG.  29    depicts an exemplary wheelchair viewed from a left rear top perspective. In the implementation depicted by  FIG.  29    the collar  1315  is secured to the wheelchair  202  and the collar  1315  is secured to the adapter plate  1320 . In the depicted implementation the engagement member  704  is engaged with and in position to be secured to the exchange tab  2300 . The engagement member  704  may be secured with the exchange tab  2300  using a locking pin or similar mechanism. In the depicted implementation the engagement actuator  1200  includes a movable shaft (depicted for example at least in  FIG.  28   ) configured to move the engagement member  704  relative to the wheelchair  202  as the movable shaft extends or retracts using the engagement actuator  1200 . 
       FIG.  30    depicts the exemplary wheelchair shown by  FIGS.  27 - 29    viewed from a left side perspective. 
     In an illustrative example the engagement member  704  may be rotatably coupled with the exchange tab  2300  using a removable securing device such as a spring-loaded retractable pin or similar mechanism, permitting a user to remove and reinstall a user&#39;s wheelchair power assist device from their wheelchair. For example the spring-loaded retractable pin or similar mechanism may be inserted through the tab mount holes  2305  and the engagement member mount holes  2310  to releasably couple the engagement member  704  with the exchange tab  2300  welded to the wheelchair. 
     In illustrative examples, by disconnecting the collar  1315  from their wheelchair, a user of a wheelchair power assist device in accordance with the present disclosure may exchange their wheelchair power assist device for another wheelchair power assist device while keeping their wheelchair, using the exchange tab  2300  welded to the wheelchair to disconnect the engagement member  704  from an exemplary wheelchair. The user may, for example, install a new, upgraded, restored or refurbished wheelchair power assist device in exchange for their old wheelchair power assist device. Alternatively, a user may exchange their wheelchair configured with the exchange tab  2300  welded to the wheelchair, while keeping their wheelchair power assist device. 
     In some scenarios an exchange depot may provide user access to exchangeable wheelchair power assist devices. For example a user having a wheelchair power assist device configured in a wheelchair with exchange tabs  2300  welded to their wheelchair may visit a wheelchair power assist exchange depot to exchange their wheelchair or their power assist device for similar devices pre-positioned at the exchange depot. Some exchange depot implementations may comprise automated storage facilities configured to scan a digital identification from a user&#39;s wheelchair power assist device or a user&#39;s wheelchair. For example, a unique digital identification may be encoded in a chip embedded in the wheelchair or in the wheelchair power assist device. The encoded digital identification may be embedded in one or more engagement member  704  of a wheelchair power assist device. The encoded digital identification may be embedded in an exchange tab  2300  welded to a wheelchair. An exemplary component part such as for example an engagement member  704 , exchange tab  2300 , or wheelchair may be configured with other forms of identification such as a Vehicle Identification Number (VIN) or other identifiers. The VIN may be printed on a label or tag affixed to the component. The VIN may be embossed or engraved on or into the component. In some implementations an exchange depot may be configured to use a database to store encoded digital identification codes or other identifiers uniquely associated with particular devices and users. 
     In an illustrative example a user may subscribe for an exchange renewal or upgrade permitting the user to travel with their wheelchair power assist without bringing their wheelchair, and plan to visit an exchange facility to obtain a wheelchair upon arrival. For example, a traveling user may fly with their wheelchair power assist device but without bringing their wheelchair or batteries for the power assist. In this example, the user may visit an exchange depot upon arrival and present their wheelchair power assist device having an encoded digital identification embedded in an engagement member  704  to the automated exchange for scanning. In one example the automated exchange may use a database to associate the encoded digital identification with an exchange account of the user and determine the user account is authorized for charged battery and wheelchair rental and return. The exchange may dispense a wheelchair and batteries by unlocking a cabinet preloaded with a suitable wheelchair and batteries for the user&#39;s wheelchair power assist device, and the user may go on their way with their powered wheelchair after installation. In an illustrative example the user may return the wheelchair and batteries to the exchange facility and continue their journey while travelling with their wheelchair power assist device. In some examples a user may travel with their wheelchair having the encoded digital identification associated with their exchange account embedded in one or more exchange tab  2300  welded to the user&#39;s wheelchair. In such a scenario, the user may travel with their wheelchair and rent or exchange a wheelchair power assist device for use with their wheelchair, using the exchange tab  2300  to facilitate connecting and disconnecting the wheelchair power assist device. Using encoded digital identification embedded in components of the wheelchair power assist or an exchange tab may reduce a user&#39;s effort accessing wheelchair-based transportation by permitting users to travel without batteries or a wheelchair for their power assist device and obtain those items from an exchange facility upon reaching an intermediate destination. Embedding the encoded digital identification in components of the wheelchair power assist or an exchange tab may prevent fraudulent use and theft of a user&#39;s equipment based on providing a permanent identification more difficult to destroy than identification such as a barcode label that may be removed or a serial number that may be ground or scraped off. 
     In an illustrative example, an exchange depot may provide user access to a wheelchair configured with the power assist devices. For example a user having a manual wheelchair without the wheelchair power assist device configured may visit an exchange depot to exchange the user&#39;s manual wheelchair for another manual wheelchair provided by the exchange depot, with the power assist device configured in the manual wheelchair provided by the exchange depot. In another example a user having a manual wheelchair with the power assist device configured may visit an exchange depot and exchange the user&#39;s manual wheelchair and power assist device for a new wheelchair provided by the exchange depot with a new power assist device configured for any reason. 
     An exemplary exchangeable wheelchair power assist may achieve various advantageous technical effects as a result of a wheelchair and power assist that are exchangeable in various configurations, including but not limited to a wheelchair alone, a wheelchair with the power assist device, or the power assist device alone. For example an exchangeable wheelchair power assist implementation may reduce a user&#39;s effort accessing wheelchair transportation based on providing the user access to a power assist or wheelchair prepositioned at geographically distributed exchange depot locations. Some exchangeable wheelchair power assist implementations may improve a user&#39;s quality of life by simplifying a wheelchair user&#39;s travel planning and increasing their mobility. For example a wheelchair user may be able to travel greater distances, travel more frequently or more often based on traveling with only their wheelchair or only their wheelchair power assist. Such an exemplary user may, for example, travel with only their power assist and obtain a wheelchair to use temporarily with their power assist. Alternatively the user may, for example, travel with only their wheelchair and obtain a power assist to use temporarily with their wheelchair. Some example implementations may reduce a wheelchair user&#39;s uncertainty about maintenance or repair and reduce their worry about being stranded with an inoperative wheelchair. For example, such a user may find their wheelchair or power assist in need of maintenance or repair and visit an exchange depot to swap out the wheelchair alone, the wheelchair with the power assist device, or the power assist device alone, and be on their way with a functional power assisted wheelchair. 
     An exemplary wheelchair or power assist may be swapped at any facility, locker, or exchange depot. The exchange depot may be a facility having prepositioned wheelchairs and power assist devices implemented in accordance with the present disclosure. The user may be a veteran having a standard manual wheelchair. The exchange depot may be, for example, a facility operated by an entity such as the Veterans Administration (VA). The veteran may go to any VA location having an exchange depot and swap their standard manual wheelchair without the power assist device for a new wheelchair with the power assist device already installed/ready to go. Should that new wheelchair with power assist device installed have any customer service issues, the user may go back to their local VA or any VA and swap their unit out for an entirely new wheelchair with the device installed. 
     In an illustrative example, an exchange depot may be a facility equipped with wheelchairs and power assist devices prepositioned in lockers. The lockers may be configured with sensors implemented to scan or read identification from a wheelchair or power assist, an embedded computing device/controller, network connectivity, and locks operable by the computing device/controller to release or open one or more locker. In an illustrative example identification numbers or codes may be embedded in one or more component part of an exemplary wheelchair, exchange tab, or power assist device, in accordance with the teaching of the present disclosure. A cloud-connected database may be operably coupled with the computing device via a network such as the public internet. In some scenarios the database may be configured with identification numbers or codes that are also embedded in one or more component part of an exemplary wheelchair, exchange tab, or power assist device. A user may have an account comprising a subscription for exchangeable wheelchair power assist services. However the user involved in an exemplary exchange may be any user, not exclusively the wheelchair user. Some exchange depot facilities may be configured with a computing device/controller configured to accept payment and establish an initial account for a new user. The user account and subscription for exchangeable wheelchair power assist services may be stored in the database. The user account and subscription stored in the database may be associated in the database with the identification numbers or codes that are also embedded in particular components assigned to or subscribed for by the user. In an exemplary scenario a user may visit an exchange depot and present a component of their wheelchair or power assist device to be scanned by a sensor to read the embedded identification code. The facility may comprise a plurality of lockers each retaining a wheelchair or a power assist device. In an illustrative example the computing device/controller may send the identification code to a server connected to the database. The server may use the database to identify the user account associated with the particular wheelchair, exchange tab, or power assist device identified by the identification numbers or code scanned by the sensor, based on associating the user account with the scanned identification numbers or code. The user account may comprise a user subscription authorizing a new wheelchair for the user&#39;s power assist, or a new power assist for the user&#39;s wheelchair. Upon determining the user is authorized for a new wheelchair or a new power assist the computing device/controller may open one or more locker to permit the user to access the wheelchair or power assist. The user may take the wheelchair or power assist received from the locker. The computing device/processor may update the database to associate the user account with the scanned identification numbers or code of particular components received from the locker by the user. The user may return wheelchair or power assist components by placing the wheelchair or power assist components that the user previously possessed into respective storage lockers. The computing device/controller may update the database to indicate the exchange depot location where the returned wheelchair or power assist components are stored. The computing device/controller may update the user account in the database to indicate the returned wheelchair or power assist components are no longer possessed by the user. 
     The total weight for the entire device  100  is approximately 20 pounds. It is expected that the speed is 0-5 MPH adjustable, maximum carrying capacity of up to 260 pounds, with a maximum incline up to 10 degrees. In one embodiment, the product is classified as a Class 1 device under FDA Code of Federal Regulations Title 21 Subpart D Section 890.3910. In another embodiment, the device  100  is exempt from needing direct FDA approval, but would require a 510(k) license. In another embodiment, the device  100  is not classified as a medical device and is exempt from needing FDA approval. 
     It would be readily apparent to those skilled in the art that second retractable friction roller; second engagement unit; and second motor performs exactly same functions as described in the description for retractable friction roller; engagement unit; and motor respectively. 
     In other embodiments one of ordinary skill in the art will be able and may make changes to the size and materials of the friction roller; the size and type of motor or battery used; and/or the type of controller or joystick; and the size and type of attachment devices used to fix the device to the manual wheelchair such as but not limited to a screw clamp. In one embodiment a casing for each of the two units may be added for safety, convenient travel and appearance. In another embodiment, the device may be used as a power assist to any object that is traditionally transported on wheels via manual propulsion, such as baggage carts. 
     Some wheelchair power assist device designs may be adapted with a sensor, and configured to automatically stop the wheelchair in an emergency situation detected based on information captured by the sensor. For example, an exemplary wheelchair may be configured to determine the speed of the wheelchair relative to the ground based on sensor data, compare the detected speed to a predetermined maximum safe speed, and automatically mitigate the unsafe speed based on stopping a motor, reducing the speed of a motor, or reversing a motor. The speed sensor may be, for example, a shaft encoder configured in a wheel. The speed sensor may be a Time of Flight (ToF) sensor pointed forward from the wheelchair passenger, in line with the direction the passenger would typically face. 
     Various wheelchair power assist device implementations may include an emergency kill switch configured to permit a user to manually stop the wheelchair in an emergency situation detected by the user. For example, the joystick may be configured with a button adapted to stop the motor to prevent serious injury or damage in an emergency situation. The switch may be configured as a dead-man switch, which would have to be actively engaged by a user seated in the chair for the wheelchair power assist to move the wheelchair. In some cases, the dead-man switch may be implemented with a key lock configured to prevent the motor from activating unless the key is present and turned to the activate position. The dead-man switch may be a weight sensor configured in the wheelchair seat, to prevent motor activation unless body weight of at least a predetermined threshold weight is detected in the wheelchair seat. The threshold weight may be configurable to a specific numeric weight, or to a weight selectable from a range of weights. The dead-man switch may be configured to stop the motor if the wheelchair passenger leaves the wheelchair seat. 
     Some wheelchair power assist device designs may include one or more handle configured to permit a user to grasp the one or more handle while carrying the device. The one or more handle may me rotatably secured with swivels to reduce the user&#39;s effort balancing the load while carrying the device. The one or more handle may be configured with a latch mechanism to secure the handle in the wheelchair power assist device when the handle is not in use. 
     In some wheelchair power assist device implementations, lights may be configured on the front or back of the device. The lights may be warning lights, configured to be visible to others not riding in the wheelchair. The lights may be headlights such as spotlights or floodlights, configured to improve the effective vision of the person riding in the wheelchair. Warning lights may be various colors and may be configured to blink or flash in various patterns to warn others or make the wheelchair more visible to others. Headlights or spotlights may be configured with a swivel mount permitting the wheelchair passenger to manually direct light in a direction of interest. In an illustrative example, the light swivel mount direction may be adjustable in pan and tilt modes under control of motors governed by the joystick. 
     Various wheelchair power assist device power source designs may include an interchangeable battery replacement system configured to adapt batteries of various diverse form factors and electrical connection geometries to a common form factor designed to electrically connect to and power the wheelchair. 
     In an illustrative example, some wheelchair power assist device designs may be adapted with an electronic engage and disengage (described with reference to at least  FIGS.  12 A-C ). Some electronic engage and disengage implementations may be configured to be activated using a push button, switch, speech, and via Bluetooth®. Various electronic engage and disengage designs may be integrated with a communication unit to permit operation of the electronic engage and disengage via a joystick. For example, the communication unit may be configured to activate the electronic engage and disengage in response to a predetermined joystick motion pattern. In an illustrative example, the predetermined joystick motion pattern may be programmed into the communication unit by a user. In this example, the communication unit may be configured to activate the electronic engage and disengage in response to the communication unit recognizing the predetermined joystick motion pattern programmed by the user. In some examples, the electronic engage and disengage may be configured to be activated by the communication unit in response to predetermined voice command received by a microphone configured with the communication unit. The predetermined voice command may include a recorded voice command selected by a user. In an illustrative example, the electronic engage and disengage may be configured to be activated via Bluetooth®. For example, the user&#39;s mobile device may be configured with a mobile application designed to link via Bluetooth® with the wheelchair communication unit, and provide a user interface adapted to controlling the wheelchair systems including motors and the electronic engage and disengage. For example, a user by operating the mobile application could activate the electronic engage and disengage, and control motor speed, to facilitate control of the wheelchair. In various designs, a wheelchair speech control interface may be implemented in a mobile application to permit the user to control the wheelchair with verbal commands received by the user&#39;s mobile device. 
     Potential limitations include the following: the device may not work if the maximum weight limit is exceeded; the maximum incline is exceeded; the friction roller is not engaged properly to the powertrain; operation on wet surfaces due to slippage, operation on ice, sand, or oily surfaces, if the battery, motor, or grip components are damaged, if the wheels are locked or do not freely rotate, or if operated in excessive heat. 
     In an aspect, a method to convert a manual wheelchair ( 202 ) to an electronic wheelchair is disclosed, the method comprising: operably connecting a joystick ( 102 ) to a communication unit ( 110 ); operably connecting the communication unit ( 110 ) to a motor ( 112 ); connecting an axle ( 114 ) to a rotor ( 116 ); connecting the motor ( 112 ) to the axle ( 114 ); mounting a retractable friction roller ( 104 ) on the axle ( 114 ); configuring the retractable friction roller ( 104 ) with a centerless concave rim housing ( 1110 ) designed to provide a high friction surface ( 1105 ) when the friction roller ( 104 ) is placed facing and in contact with a wheel ( 206 ); placing the retractable friction roller ( 104 ) in contact with a wheel ( 206 ) of a manual wheelchair ( 202 ); attaching to the wheelchair ( 202 ) an engagement unit ( 106 ) configured to detachably attach the retractable friction roller ( 104 ) and the wheel ( 206 ); and operably connecting a power source ( 108 ) to the motor ( 112 ) and the joystick ( 102 ). 
     The method may further comprise attaching the friction roller ( 104 ) to the motor ( 112 ) and attaching the motor ( 112 ) to a bracket ( 704 ) operably coupled via a lever mechanism ( 504 ) with a lever ( 502 ) to releasably engage the friction roller ( 104 ) and a wheel ( 206 ) in response to operation of the lever ( 502 ). 
     The method may further comprise configuring a safety fender ( 509 ) to detachably attach to the wheelchair ( 202 ), wherein the safety fender ( 509 ) fits over the retractable friction roller ( 104 ) when the safety fender ( 509 ) is attached to the wheelchair ( 202 ). 
     The method may further comprise attaching at least one set of brushes ( 510 ) to the safety fender ( 509 ), wherein the at least one set of brushes ( 510 ), when attached to the safety fender ( 509 ), are in contact with the wheel ( 206 ), and wherein the safety fender ( 509 ) comprises a top, an open bottom, a right side, a left side, a proximal side and a distal side, wherein each of the sides has a bottom edge and the at least one set of brushes ( 510 ) is attached to the bottom edge of the distal side of the safety fender ( 509 ). 
     The method may further comprise configuring the engagement unit ( 106 ) with a lever ( 502 ); operably connecting the lever ( 502 ) to a lever mechanism unit ( 504 ); and operably connecting the lever mechanism unit ( 504 ) to the motor ( 112 ) bracket. 
     The method may further comprise configuring the engagement unit ( 106 ) with a lever ( 502 ); operably connecting the lever ( 502 ) to a lever mechanism unit ( 504 ); operably connecting the lever mechanism unit ( 504 ) to a turnbuckle ( 506 ); and operably connecting the turnbuckle ( 506 ) to an attachment unit ( 508 ). 
     The method may further comprise configuring the attachment unit ( 508 ) with a spring loaded unit ( 404 ); operably connecting the spring loaded unit ( 404 ) to the retractable friction roller ( 104 ); and operably connecting a clamp ( 402 ) to the spring loaded unit ( 404 ). 
     The method may further comprise operably connecting a second motor ( 302 ) to a second communication unit ( 304 ) and the power source ( 108 ), and operably connecting the second communication unit ( 304 ) to the joystick ( 102 ). 
     The method may further comprise configuring the joystick ( 102 ) to be operably programmable to generate commands for operating the motor ( 112 ) and the second motor ( 302 ). 
     The method may further comprise connecting the second motor ( 302 ) to a second axle ( 114 ), and connecting the second axle ( 114 ) to a second rotor ( 116 ). 
     The method may further comprise mounting a second retractable friction roller ( 306 ) on the second axle ( 114 ), and placing the second roller ( 306 ) in contact with a second wheel ( 308 ) of the manual wheelchair ( 202 ). 
     The method may further comprise configuring the second retractable friction roller ( 306 ) with a centerless concave rim housing ( 1110 ) designed to provide a high friction surface ( 1105 ) facing the second wheel ( 308 ) of the manual wheelchair ( 202 ). 
     The method may further comprise attaching the second friction roller ( 306 ) to the top of the second wheel ( 308 ) behind the seating area ( 312 ). 
     The method may further comprise attaching the second friction roller ( 306 ) to the front of the second wheel ( 308 ) under the seating area ( 312 ). 
     The method may further comprise attaching the second friction roller ( 306 ) to the second wheel ( 308 ) using the arm ( 204 ) of the wheelchair ( 202 ). 
     The method may further comprise attaching a second engagement unit ( 310 ) to the manual wheelchair ( 202 ), wherein the second engagement unit ( 310 ) is configured to detachably attach the second friction roller ( 306 ) and the second wheel ( 308 ) of the wheelchair ( 202 ). 
     The method may further comprise configuring the second engagement unit ( 310 ) with a second lever ( 502 ); operably connecting the second lever ( 502 ) to a second lever mechanism unit ( 504 ); and operably connecting the second lever mechanism unit ( 504 ) to the second motor ( 302 ) bracket. 
     The method may further comprise configuring the second engagement unit ( 310 ) with a second lever ( 502 ); operably connecting the second lever ( 502 ) to a second lever mechanism unit ( 504 ); operably connecting the second lever mechanism unit ( 504 ) to a second turnbuckle ( 506 ); and operably connecting the second turnbuckle ( 506 ) to a second attachment unit ( 508 ). 
     The method may further comprise configuring the second attachment unit ( 508 ) with a second spring loaded unit ( 404 ); operably connecting the second spring loaded unit ( 404 ) to the second retractable friction roller ( 306 ); and operably connecting a second clamp ( 402 ) to the second spring loaded unit ( 404 ). 
     The method may further comprise attaching the friction roller ( 104 ) to a motor ( 112 ) and attaching the motor ( 112 ) to a bracket ( 704 ) operably coupled via a turnbuckle ( 506 ) with a lever ( 502 ) to releasably engage the friction roller ( 104 ) and a wheel ( 206 ) in response to operation of the lever ( 502 ). 
     The method may further comprise attaching the friction roller ( 104 ) to the top of the wheel ( 206 ) behind the wheelchair ( 202 ) seating area ( 312 ). 
     The method may further comprise attaching the friction roller ( 104 ) to the front of the wheel ( 206 ) under the wheelchair ( 202 ) seating area ( 312 ). 
     The method may further comprise attaching the friction roller ( 104 ) to the wheel ( 206 ) using the arm ( 204 ) of the wheelchair ( 202 ). 
     The method may further comprise attaching the friction roller ( 104 ) to an upper lateral wheelchair frame support ( 208 ). 
     The method may further comprise attaching the friction roller ( 104 ) to a lower lateral wheelchair frame support ( 210 ). 
     The method may further comprise attaching the friction roller ( 104 ) to a vertical wheelchair frame support ( 212 ). 
     In an aspect, a method to move a wheelchair ( 202 ) is disclosed, the method comprising: configuring a friction roller ( 104 ) to releasably engage with a wheel ( 206 ) of a wheelchair ( 202 ), based on attaching the friction roller ( 104 ) to the wheelchair ( 202 ); configuring the friction roller ( 104 ) to drive when engaged the wheel ( 206 ) through a contact surface ( 1115 ) with the wheel ( 206 ) above the wheel ( 206 ) center and behind the wheelchair ( 202 ) seating area ( 312 ); configuring a motor ( 112 ) to rotate the friction roller ( 104 ); and moving the wheelchair ( 202 ) based on engaging the friction roller ( 104 ) and activating the motor ( 112 ) to turn the wheel ( 206 ) through force by the friction roller ( 104 ) against the contact surface with the wheel ( 206 ). 
     The method may further comprise configuring a second motor ( 302 ) to rotate a second friction roller ( 306 ) configured to drive a second wheel ( 308 ) through a contact surface ( 1115 ) with the second wheel ( 308 ) above the second wheel ( 308 ) center and behind the wheelchair ( 202 ) seating area ( 312 ), based on attaching the second friction roller ( 306 ) to the wheelchair ( 202 ). 
     The method may further comprise folding the wheelchair ( 202 ) while the friction roller ( 104 ) remains attached to the wheelchair ( 202 ) and the second friction roller ( 306 ) remains attached to the wheelchair ( 202 ). 
     The method may further comprise disengaging, by a user remaining seated in the wheelchair ( 202 ) seating area ( 312 ), the friction roller ( 104 ). 
     In another aspect, a method to move a wheelchair ( 202 ) is disclosed, the method comprising: configuring a friction roller ( 104 ) to releasably engage with a wheel ( 206 ) of a wheelchair ( 202 ), based on attaching the friction roller ( 104 ) to the wheelchair ( 202 ); configuring the friction roller ( 104 ) to drive when engaged the wheel ( 206 ) through a contact surface ( 1115 ) with the wheel ( 206 ) in front of the wheel ( 206 ) under the wheelchair ( 202 ) seating area ( 312 ); configuring a motor ( 112 ) to rotate the friction roller ( 104 ); and moving the wheelchair ( 202 ) based on engaging the friction roller ( 104 ) and activating the motor ( 112 ) to turn the wheel ( 206 ) through force by the friction roller ( 104 ) against the contact surface ( 1115 ) with the wheel ( 206 ). 
     The method may further comprise configuring a second motor ( 302 ) to rotate a second friction roller ( 306 ) configured to drive a second wheel ( 308 ) through a contact surface ( 1115 ) with the second wheel ( 308 ) in front of the second wheel ( 308 ) under the wheelchair ( 202 ) seating area ( 312 ), based on attaching the second friction roller ( 306 ) to the wheelchair ( 202 ). 
     In another aspect, a method to move a wheelchair ( 202 ) is disclosed, the method comprising: configuring a friction roller ( 104 ) to releasably engage with a wheel ( 206 ) of a wheelchair ( 202 ), based on attaching the friction roller ( 104 ) to the wheelchair ( 202 ); configuring the friction roller ( 104 ) to drive when engaged the wheel ( 206 ) through a contact surface ( 1115 ) with the wheel ( 206 ) in front of the seating area ( 312 ) using the arm ( 204 ) of the wheelchair ( 202 ); configuring a motor ( 112 ) to rotate the friction roller ( 104 ); and moving the wheelchair ( 202 ) based on engaging the friction roller ( 104 ) and activating the motor ( 112 ) to turn the wheel ( 206 ) through force by the friction roller ( 104 ) against the contact surface ( 1115 ) with the wheel ( 206 ). 
     The method may further comprise configuring a second motor ( 302 ) to rotate a second friction roller ( 306 ) configured to drive a second wheel ( 308 ) through a contact surface ( 1115 ) with the second wheel ( 308 ) in front of the seating area ( 312 ) using the arm ( 204 ) of the wheelchair ( 202 ), based on attaching the second friction roller ( 306 ) to the wheelchair ( 202 ). 
     In another aspect, a method is disclosed to convert a manual wheelchair ( 202 ) to an electronic wheelchair, the method comprising: operably connecting a joystick ( 102 ) to a communication unit ( 110 ); operably connecting the communication unit ( 110 ) to a motor ( 112 ); connecting an axle ( 114 ) to a rotor ( 116 ); connecting the motor ( 112 ) to the axle ( 114 ); configuring a retractable friction roller ( 104 ) with a centerless concave rim housing ( 1110 ) designed to provide a high friction surface ( 1105 ) when the friction roller ( 104 ) is placed facing and in contact with a wheel ( 206 ); mounting the retractable friction roller ( 104 ) on the axle ( 114 ); attaching to the wheelchair ( 202 ) in front of the wheel ( 206 ) and below the seating area ( 312 ) an engagement unit ( 106 ) configured to detachably attach the retractable friction roller ( 104 ) and the wheel ( 206 ); and operably connecting a power source ( 108 ) to the motor ( 112 ) and the joystick ( 102 ). 
     The method may further comprise configuring the engagement unit ( 106 ) with a lever ( 502 ); operably connecting the lever ( 502 ) to a lever mechanism unit ( 504 ); and operably connecting the lever mechanism unit ( 504 ) to a motor ( 112 ) bracket ( 704 ). 
     The method may further comprise operably connecting a second motor ( 302 ) to a second communication unit ( 304 ) and the power source ( 108 ), and operably connecting the second communication unit ( 304 ) to the joystick ( 102 ). 
     The method may further comprise configuring the joystick ( 102 ) to be operably programmable to generate commands for operating the motor ( 112 ) and the second motor ( 302 ). 
     The method may further comprise connecting the second motor ( 302 ) to a second axle ( 114 ), and connecting the second axle ( 114 ) to a second rotor ( 116 ). 
     The method may further comprise mounting a second retractable friction roller ( 306 ) on the second axle ( 114 ), and placing the second retractable friction roller ( 306 ) in contact with a second wheel ( 308 ) of the manual wheelchair ( 202 ). 
     The method may further comprise configuring the second retractable friction roller ( 306 ) with a centerless concave rim housing ( 1110 ) designed to provide a high friction surface ( 1105 ) facing the second wheel ( 308 ) of the manual wheelchair ( 202 ). 
     The method may further comprise attaching the second retractable friction roller ( 306 ) in front of the second wheel ( 308 ) and below the seating area ( 312 ). 
     The method may further comprise attaching a second engagement unit ( 310 ) to the manual wheelchair ( 202 ), wherein the second engagement unit ( 310 ) is configured to detachably attach the second retractable friction roller ( 306 ) and the second wheel ( 308 ) of the manual wheelchair ( 202 ). 
     The method may further comprise configuring the second engagement unit ( 310 ) with a second lever ( 502 ); operably connecting the second lever ( 502 ) to a second lever mechanism unit ( 504 ); and operably connecting the second lever mechanism unit ( 504 ) to a second motor ( 302 ) bracket ( 704 ). 
     The method may further comprise attaching the retractable friction roller ( 104 ) to the motor ( 112 ) and attaching the motor ( 112 ) to a bracket ( 704 ) operably coupled via a lever mechanism ( 504 ) with a lever ( 502 ) to releasably engage the friction roller ( 104 ) and a wheel ( 206 ) in response to operation of the lever ( 502 ). 
     The method may further comprise attaching the retractable friction roller ( 104 ) to the top of the wheel ( 206 ) behind the wheelchair ( 202 ) seating area ( 312 ). 
     The method may further comprise placing the retractable friction roller ( 104 ) in contact with a wheel ( 206 ) of the manual wheelchair ( 202 ). 
     In another aspect is disclosed a method to move a wheelchair ( 202 ) comprising: configuring a retractable friction roller ( 104 ) to releasably engage with a wheel ( 206 ) of a wheelchair ( 202 ), based on attaching the retractable friction roller ( 104 ) to the wheelchair ( 202 ); configuring the retractable friction roller ( 104 ) to drive when engaged the wheel ( 206 ) through a contact surface ( 1115 ) with the wheel ( 206 ) above the wheel ( 206 ) center and to the side of the wheelchair ( 202 ) seating area ( 312 ); configuring a motor ( 112 ) to rotate the retractable friction roller ( 104 ); and moving the wheelchair ( 202 ) based on engaging the retractable friction roller ( 104 ) and activating the motor ( 112 ) to turn the wheel ( 206 ) through force by the retractable friction roller ( 104 ) against the contact surface ( 1115 ) with the wheel ( 206 ). 
     The method may further comprise configuring a second motor ( 302 ) to rotate a second retractable friction roller ( 306 ) configured to drive a second wheel ( 308 ) through a contact surface ( 1115 ) with the second wheel ( 308 ) above the second wheel ( 308 ) center and to the side of the wheelchair ( 202 ) seating area ( 312 ), based on attaching the second retractable friction roller ( 306 ) to the wheelchair ( 202 ). 
     Attaching the second retractable friction roller ( 306 ) to the wheelchair ( 202 ) may further comprise attaching the second retractable friction roller ( 306 ) to the front of the second wheel ( 308 ) under the wheelchair ( 202 ) seating area ( 312 ). 
     Attaching the second retractable friction roller ( 306 ) to the wheelchair ( 202 ) may further comprise attaching the second retractable friction roller ( 306 ) to the second wheel ( 308 ) using an arm ( 204 ) of the wheelchair ( 202 ). 
     The method may further comprise folding the wheelchair ( 202 ) while the retractable friction roller ( 104 ) remains attached to the wheelchair ( 202 ) and the second retractable friction roller ( 306 ) remains attached to the wheelchair ( 202 ). 
     Attaching the retractable friction roller ( 104 ) to the wheelchair ( 202 ) may further comprise attaching the retractable friction roller ( 104 ) to the front of the wheel ( 206 ) under the wheelchair ( 202 ) seating area ( 312 ). 
     Attaching the retractable friction roller ( 104 ) to the wheelchair ( 202 ) may further comprise attaching the retractable friction roller ( 104 ) to the wheel ( 206 ) using an arm ( 204 ) of the wheelchair ( 202 ). 
     Apparatus and associated methods relate to a removable power assist for converting a manual wheelchair into an electronic wheelchair, based on configuring a friction roller to releasably engage with a wheelchair wheel, configuring the friction roller when engaged to drive the wheel through a contact surface with the wheel that may be positioned under the wheelchair seating area, or to the side of the wheelchair seating area, or to the underside of an armrest, or in front of a wheelchair wheel, configuring a motor to rotate the friction roller, and moving the wheelchair based on engaging the friction roller and activating the motor to turn the wheel through force by the friction roller against the contact surface with the wheel. Some designs include a lever configured to permit a user seated in the wheelchair to engage or disengage the friction roller. Configuring the friction roller under the wheelchair seating area, or to the side of the wheelchair seating area, or behind the wheelchair seating area, or to the underside of an armrest, or in front of a wheelchair wheel may permit wheelchair folding or unfolding without uninstalling the power assist. 
     In an aspect, an exemplary apparatus kit may comprise: a first retractable friction roller configured to releasably engage with a wheelchair first wheel, wherein the first retractable friction roller includes a high friction surface configured on the first retractable friction roller to drive the wheelchair first wheel when the first retractable friction roller is engaged with the wheelchair first wheel through a contact surface with the wheelchair first wheel that is disposed behind a wheelchair seating area; a first engagement unit configured to be attached to a manual wheelchair, wherein the first engagement unit is configured to detachably attach the first retractable friction roller and the wheelchair first wheel; and a first motor configured to rotate the first retractable friction roller and move the manual wheelchair with force by the first retractable friction roller through the contact surface with the wheelchair first wheel. 
     The apparatus kit may further comprise a second retractable friction roller configured to releasably engage with a wheelchair second wheel, wherein the second retractable friction roller includes a high friction surface configured on the second retractable friction roller to drive the wheelchair second wheel when the second retractable friction roller is engaged with the wheelchair second wheel through a contact surface with the wheelchair second wheel that is disposed behind the wheelchair seating area; a second engagement unit configured to be attached to the manual wheelchair, wherein the second engagement unit is configured to detachably attach the second retractable friction roller and the wheelchair second wheel; and a second motor configured to rotate the second retractable friction roller and move the manual wheelchair with force by the second retractable friction roller through the contact surface with the wheelchair second wheel. 
     The apparatus kit may further comprise the contact surface with the wheelchair first wheel configured to be disposed above the wheelchair first wheel center. 
     The apparatus kit may further comprise the contact surface with the wheelchair second wheel configured to be disposed above the wheelchair second wheel center. 
     The apparatus kit may further comprise each of the first retractable friction roller and the second retractable friction roller configured with a centerless concave rim housing. 
     The apparatus kit may further comprise a joystick configured to be operably connected to at least one communication unit, wherein the at least one communication unit is configured to be operably connected to the first motor and the second motor, and wherein the joystick is configured to be operably programmable to generate commands for operating the first motor and the second motor; and a power source configured to be operably connected to the first motor, the second motor, and the joystick. 
     The apparatus kit may further comprise the contact surface with the wheelchair first wheel disposed above the wheelchair first wheel center, and wherein the contact surface with the wheelchair second wheel is disposed above the wheelchair second wheel center. 
     In another aspect, an exemplary apparatus kit may comprise: a joystick configured to operably connect to a communication unit, the communication unit configured to operably connect to a first motor; said first motor comprising a first axle configured to connect to a first rotor; a first retractable friction roller comprising a centerless concave rim housing configured to provide a high friction surface facing a wheelchair first wheel of a manual wheelchair; wherein said first retractable friction roller is configured to mount on the first axle and to contact the wheelchair first wheel of the manual wheelchair; a first engagement unit configured to attach to the manual wheelchair and to detachably attach the first retractable friction roller and the wheelchair first wheel; and a power source configured to operably connect to the first motor and the joystick. 
     The apparatus kit may further comprise a second motor configured to operably connect to the communication unit and the power source. 
     The apparatus kit may further comprise a second axle configured to connect to a second rotor. 
     The apparatus kit may further comprise a second retractable friction roller configured to mount on the second axle, and to contact a wheelchair second wheel of the manual wheelchair. 
     The apparatus kit may further comprise a second engagement unit configured to attach to the manual wheelchair to detachably attach the second friction roller and the wheelchair second wheel of the manual wheelchair. 
     The apparatus kit may further comprise a second centerless concave rim housing configured to provide a high friction surface facing the wheelchair second wheel of the manual wheelchair. 
     The joystick may be operably configured to generate commands for the first motor. 
     The joystick may be operably configured to generate commands for the second motor. 
     The first retractable friction roller may be configured to contact the wheelchair first wheel behind a seating area of the manual wheelchair. 
     The second retractable friction roller may be configured to contact the wheelchair second wheel behind a seating area of the manual wheelchair. 
     The apparatus kit may further comprise a first lever configured to operably connect to a first lever mechanism unit; said first lever mechanism unit configured to operably connect to a first turnbuckle; and said first turnbuckle is configured to operably connect to a first attachment unit. 
     The apparatus kit may further comprise a second lever configured to operably connect to a second lever mechanism unit; said second lever mechanism unit configured to operably connect to a second turnbuckle; and said second turnbuckle configured to operably connect to a second attachment unit. 
     The apparatus kit may further comprise a first spring-loaded unit configured to operably connect to the first retractable friction roller; and a first clamp configured to operably connect to the first spring-loaded unit. 
     The second attachment unit may further comprise: a second spring-loaded unit configured to operably connect to the second retractable friction roller; and a second clamp configured to operably connect to the second spring-loaded unit. 
     The apparatus kit may be configured with a plurality of friction rollers disposed to contact a single wheel. In such a design, the plurality of friction rollers may have respective contact surfaces configured to contact the single wheel at different respective contact surfaces with the single wheel. In an illustrative example, an implementation may comprise first, second, third or more apparatus kits providing multiple points of contact on a single wheel wherein each apparatus kit is configured with a respective friction roller disposed to contact the wheel at different respective contact points between the friction rollers and the wheel. 
     In another aspect, an exemplary apparatus may comprise: a first friction roller ( 104 ) operably coupled with a first engagement member ( 704 ), wherein the first friction roller ( 104 ) comprises a centerless concave rim housing ( 1110 ) comprising a friction surface ( 1105 ); a first motor ( 112 ) operably coupled with the first friction roller ( 104 ); and a first engagement actuator ( 1200 ) connected to a first attachment member ( 508 ), wherein the first engagement actuator ( 1200 ) comprises a movable shaft ( 1330 ) configured to move the first engagement member ( 704 ) relative to the first attachment member ( 508 ) between a disengaged position wherein the first friction roller ( 104 ) is not in contact with a wheelchair ( 202 ) first wheel ( 206 ) and an engaged position wherein the first friction roller ( 104 ) is in contact with the wheelchair ( 202 ) first wheel ( 206 ) at a point of contact ( 1115 ) between the first friction roller ( 104 ) friction surface ( 1105 ) and the wheelchair ( 202 ) first wheel ( 206 ), and wherein the point of contact ( 1115 ) is disposed behind a seating area ( 312 ) of the wheelchair ( 202 ). 
     The apparatus may further comprise the first attachment member ( 508 ) is removably secured to the wheelchair ( 202 ) to position the first friction roller ( 104 ) centerless concave rim housing ( 1110 ) friction surface ( 1105 ) to drive the wheelchair ( 202 ) first wheel ( 206 ) by force from the first motor ( 112 ) through the point of contact ( 1115 ) between the first friction roller ( 104 ) friction surface ( 1105 ) and the wheelchair ( 202 ) first wheel ( 206 ) when the first engagement member ( 704 ) is in the engaged position. 
     The apparatus may further comprise: a second friction roller ( 306 ) operably coupled with a second engagement member ( 704 ), wherein the second friction roller ( 306 ) comprises a centerless concave rim housing ( 1110 ) comprising a friction surface ( 1105 ); a second motor ( 302 ) operably coupled with the second friction roller ( 306 ); and a second engagement actuator ( 1200 ) connected to a second attachment member ( 508 ), wherein the second engagement actuator ( 1200 ) comprises a movable shaft ( 1330 ) configured to move the second engagement member ( 704 ) relative to the second attachment member ( 508 ) between a disengaged position wherein the second friction roller ( 306 ) is not in contact with the wheelchair ( 202 ) second wheel ( 308 ) and an engaged position wherein the second friction roller ( 306 ) is in contact with the wheelchair ( 202 ) second wheel ( 308 ) at a point of contact ( 1115 ) between the second friction roller ( 306 ) friction surface ( 1105 ) and the wheelchair ( 202 ) second wheel ( 308 ) and wherein the point of contact ( 1115 ) is disposed behind the seating area ( 312 ) of the wheelchair ( 202 ). 
     The apparatus may further comprise the second attachment member ( 508 ) is removably secured to the wheelchair ( 202 ) to position the second friction roller ( 306 ) centerless concave rim housing ( 1110 ) friction surface ( 1105 ) to drive the wheelchair ( 202 ) second wheel ( 308 ) by force from the second motor ( 302 ) through the point of contact ( 1115 ) between the second friction roller ( 306 ) friction surface ( 1105 ) and the wheelchair ( 202 ) second wheel ( 308 ) when the second engagement member ( 704 ) is in the engaged position. 
     The apparatus may further comprise the movable shaft ( 1330 ) connected to the first engagement member ( 704 ), wherein the movable shaft ( 1330 ) is extendable and retractable and configured to move the first engagement member ( 704 ) relative to the first attachment member ( 508 ) based on extending or retracting the movable shaft ( 1330 ). 
     The apparatus may further comprise the first motor ( 112 ) operably coupled by a first axle ( 114 ) with the first friction roller ( 104 ). 
     The apparatus may further comprise the first motor ( 112 ) operably coupled by a first rotor ( 116 ) with the first axle ( 114 ). 
     The first attachment member ( 508 ) may be a bracket having a first end ( 1335 ), a second end ( 1340 ), and a length between the first end ( 1335 ) and the second end ( 1340 ), and wherein the first attachment bracket ( 508 ) is removably secured to the wheelchair ( 202 ). 
     The first engagement member ( 704 ) may be a bracket having a first end ( 1345 ), a second end ( 1350 ), and a length between the first end ( 1345 ) and the second end ( 1350 ), and wherein the first engagement bracket ( 704 ) is operably coupled with the first attachment bracket ( 508 ). 
     The first attachment bracket ( 508 ) may be disposed substantially horizontally and parallel with respect to a surface on which the wheelchair ( 202 ) would rest. 
     The first attachment bracket ( 508 ) may be disposed substantially vertically and perpendicular with respect to a surface on which the wheelchair ( 202 ) would rest. 
     The first attachment bracket ( 508 ) first end ( 1335 ) may be removably secured by a clamp ( 1305 ) to the wheelchair ( 202 ). 
     The first attachment bracket ( 508 ) second end ( 1340 ) may be removably secured by a collar ( 1315 ) to the wheelchair ( 202 ). 
     The collar ( 1315 ) may be coupled by an adapter plate ( 1320 ) with the first engagement actuator ( 1200 ) and the movable shaft ( 1330 ) may be coupled with the first engagement bracket ( 704 ), wherein the adapter plate ( 1320 ) may have a planar surface disposed in a plane substantially parallel to the first attachment bracket ( 508 ) length. 
     The collar ( 1315 ) may comprise at least one half-collar ( 1315 ). 
     The collar ( 1315 ) may have a central opening having a central axis disposed substantially parallel with the first attachment bracket ( 508 ) length. 
     The collar ( 1315 ) may have a central opening with a central axis disposed substantially perpendicular with the first attachment bracket ( 508 ) length. 
     The collar ( 1315 ) may be connected to a structural member of the wheelchair ( 202 ) that is substantially horizontal and parallel with respect to a surface on which the wheelchair ( 202 ) would rest. 
     The collar ( 1315 ) may be connected to a structural member of the wheelchair ( 202 ) that is substantially vertical and perpendicular with respect to a surface on which the wheelchair ( 202 ) would rest. 
     The first engagement bracket ( 704 ) length may be approximately the first attachment bracket ( 508 ) length. 
     The first engagement bracket ( 704 ) length may be not more than half the first attachment bracket ( 508 ) length. 
     The first engagement bracket ( 704 ) length may be any length relative to the first attachment bracket ( 508 ) length. 
     The first engagement bracket ( 704 ) first end ( 1345 ) may be rotatably coupled with the first attachment bracket ( 508 ) to displace the first engagement bracket ( 704 ) second end ( 1350 ) away from the first attachment bracket ( 508 ) as the first engagement bracket ( 704 ) moves to the engaged position. 
     The first engagement bracket ( 704 ) first end ( 1345 ) may be rotatably coupled with the first attachment bracket ( 508 ) to rotate about the first attachment bracket ( 508 ) first end ( 1335 ). 
     The first engagement bracket ( 704 ) first end ( 1345 ) may be rotatably coupled with the first attachment bracket ( 508 ) at a point between the first attachment bracket ( 508 ) first end ( 1335 ) and the first attachment bracket ( 508 ) second end ( 1340 ) to rotate about said point. 
     The first engagement bracket ( 704 ) may be configured with a slot adapted to subsume a portion of the first attachment bracket ( 508 ) wherein the first engagement bracket ( 704 ) slides along the first attachment bracket ( 508 ) length as the first engagement bracket ( 704 ) moves relative to the first attachment bracket ( 508 ). 
     The first engagement actuator ( 1200 ) and the second engagement actuator ( 1200 ) may be linear actuators. 
     The apparatus may further comprise a second movable shaft ( 1330 ) connected to the second engagement member ( 704 ), wherein the second movable shaft ( 1330 ) is extendable and retractable and configured to move the second engagement member ( 704 ) relative to the second attachment member ( 508 ) based on extending or retracting the second movable shaft ( 1330 ). 
     The apparatus may further comprise the second motor ( 302 ) operably coupled by a second axle ( 114 ) with the second friction roller ( 306 ). 
     The apparatus may further comprise the second motor ( 302 ) operably coupled by a second rotor ( 116 ) with the second axle ( 114 ). 
     The second attachment member ( 508 ) may be a bracket having a first end ( 1335 ), a second end ( 1340 ), and a length between the first end ( 1335 ) and the second end ( 1340 ), and wherein the second attachment bracket ( 508 ) is removably secured to the wheelchair ( 202 ). 
     The second engagement member ( 704 ) may be a bracket having a first end ( 1345 ), a second end ( 1350 ), and a length between the first end ( 1345 ) and the second end ( 1350 ), and wherein the second engagement bracket ( 704 ) is operably coupled with the second attachment bracket ( 508 ). 
     The second attachment bracket ( 508 ) may be disposed substantially horizontally and parallel with respect to a surface on which the wheelchair ( 202 ) would rest. 
     The second attachment bracket ( 508 ) may be disposed substantially vertically and perpendicular with respect to a surface on which the wheelchair ( 202 ) would rest. 
     The second attachment bracket ( 508 ) first end ( 1335 ) may be removably secured by a clamp ( 1305 ) to the wheelchair ( 202 ). 
     The clamp ( 1305 ) may be a spring, screw clamp, mechanical coupling, latch, rod clamp, rail clamp, light, round center mount, mount bracket, pole clamp, pipe clamp, quick release clamp, rack clamp mount, bolt, screw, handlebar clamp mount, or other suitable fastener as may be known to one of skill in the art. 
     The second attachment bracket ( 508 ) second end ( 1340 ) may be removably secured by a collar ( 1315 ) to the wheelchair ( 202 ). 
     The collar ( 1315 ) may be coupled by a second adapter plate ( 1320 ) with the second engagement actuator ( 1200 ) and the second movable shaft ( 1330 ) may be coupled with the second engagement bracket ( 704 ), wherein the second adapter plate ( 1320 ) has a planar surface disposed in a plane substantially parallel to the second attachment bracket ( 508 ) length. 
     The collar ( 1315 ) may comprise at least one half-collar ( 1315 ). 
     The collar ( 1315 ) may further comprise a central opening having a central axis disposed substantially parallel with the second attachment bracket ( 508 ) length. 
     The collar ( 1315 ) may further comprise a central opening with a central axis disposed substantially perpendicular with the second attachment bracket ( 508 ) length. 
     The collar ( 1315 ) may be connected to a structural member of the wheelchair ( 202 ) that is substantially horizontal and parallel with respect to a surface on which the wheelchair ( 202 ) would rest. 
     The collar ( 1315 ) may be connected to a structural member of the wheelchair ( 202 ) that is substantially vertical and perpendicular with respect to a surface on which the wheelchair ( 202 ) would rest. 
     The second engagement bracket ( 704 ) length may be approximately the second attachment bracket ( 508 ) length. 
     The second engagement bracket ( 704 ) length may be not more than half the second attachment bracket ( 508 ) length. 
     The second engagement bracket ( 704 ) length may be any length relative to the second attachment bracket ( 508 ) length. 
     The second engagement bracket ( 704 ) first end ( 1345 ) may be rotatably coupled with the second attachment bracket ( 508 ) to displace the second engagement bracket ( 704 ) second end ( 1350 ) away from the second attachment bracket ( 508 ) as the second engagement bracket ( 704 ) moves to the engaged position. 
     The second engagement bracket ( 704 ) second end ( 1345 ) may be rotatably coupled with the second attachment bracket ( 508 ) to rotate about the second attachment bracket ( 508 ) first end ( 1335 ). 
     The second engagement bracket ( 704 ) second end ( 1345 ) may be rotatably coupled with the second attachment bracket ( 508 ) at a point between the second attachment bracket ( 508 ) first end ( 1335 ) and the second attachment bracket ( 508 ) second end ( 1340 ) to rotate about said point. 
     The second engagement bracket ( 704 ) may be configured with a slot adapted to subsume a portion of the second attachment bracket ( 508 ) wherein the second engagement bracket ( 704 ) slides along the second attachment bracket ( 508 ) length as the second engagement bracket ( 704 ) moves relative to the second attachment bracket ( 508 ). 
     The apparatus may further comprise a programmable joystick ( 102 ) configured to govern the operation of the first motor ( 112 ) and the second motor ( 302 ). 
     The apparatus may further comprise an engage button configured to activate the first engagement actuator ( 1200 ) and the second engagement actuator ( 1200 ) and thereby move the first engagement member ( 704 ) and the second engagement member ( 704 ). 
     The engage button may be configured on the wheelchair ( 202 ) in a location accessible to a user seated in the wheelchair  202  seating area ( 312 ). 
     The engage button may be configured in an arm ( 204 ) of the wheelchair ( 202 ). 
     The engage button may be configured with a wireless connection to an engagement actuator electrical connection ( 2210 ) designed to control one or more engagement actuator ( 1200 ). 
     The apparatus may further comprise an electrical power source configured to operably power the first engagement actuator ( 1200 ), the second engagement actuator ( 1200 ), the first motor ( 112 ), the second motor ( 302 ), and the engage button. 
     The apparatus may further comprise an electrical power source configured to operably power the first engagement actuator ( 1200 ), the second engagement actuator ( 1200 ), the first motor ( 112 ), the second motor ( 302 ), the engage button, and a programmable joystick ( 102 ). 
     The apparatus may further comprise an electrical power source configured to operably power the first engagement actuator ( 1200 ), the second engagement actuator ( 1200 ), the first motor ( 112 ), the second motor ( 302 ), the engage button, a programmable joystick ( 102 ), a communication unit  110 , and a second communication unit  304 . 
     The electrical power source may be a battery. 
     The battery may be rechargeable. 
     The rotational movement of the apparatus may charge the battery. 
     The rechargeable battery may be recharged using electric energy harvested by a generator powered by rotation of one or more wheelchair wheel. 
     The rechargeable battery may be recharged using electric energy from a generator powered by one or more wheelchair wheel rotating while the one or more wheelchair wheel is in contact with a surface supporting the wheelchair. 
     The rechargeable battery may be recharged using electric energy harvested from solar energy. 
     The solar energy may be supplied by one or more solar cell configured in the wheelchair. 
     The solar energy may be supplied by one or more solar panel not attached to the wheelchair. 
     The one or more solar panel may be a portable solar charging station. 
     The one or more solar panel may comprise a solar panel external to the wheelchair, said wheelchair configured to operably connect to the solar panel to charge the battery. 
     The solar panel may be operably connected to the wheelchair. 
     The wheelchair ( 202 ) may be a foldable wheelchair, and the apparatus may further comprise an open space ( 1005 ) located behind the seating area ( 312 ) of the foldable wheelchair ( 202 ), and wherein the first motor ( 112 ), the first attachment member ( 508 ), the first engagement member ( 704 ), the second motor ( 302 ), the second attachment member ( 508 ) and the second engagement member ( 704 ) remain attached to the foldable wheelchair ( 202 ) when the foldable wheelchair ( 202 ) is in a folded or unfolded configuration. 
     An exemplary apparatus may comprise: a first friction roller ( 104 ) operably coupled with a first engagement member ( 704 ), wherein the first friction roller ( 104 ) comprises a centerless concave rim housing ( 1110 ) comprising a friction surface ( 1105 ); a first motor ( 112 ) operably coupled with the first friction roller ( 104 ); and a first engagement actuator ( 1200 ) configured to be connected to a wheelchair ( 202 ), wherein the first engagement actuator ( 1200 ) comprises a movable shaft ( 1330 ) configured to move the first engagement member ( 704 ) relative to the wheelchair ( 202 ) between a disengaged position wherein the first friction roller ( 104 ) is not in contact with a wheelchair ( 202 ) first wheel ( 206 ) and an engaged position wherein the first friction roller ( 104 ) is in contact with the wheelchair ( 202 ) first wheel ( 206 ) at a point of contact ( 1115 ) between the first friction roller ( 104 ) friction surface ( 1105 ) and the wheelchair ( 202 ) first wheel ( 206 ), wherein the point of contact ( 1115 ) is disposed behind a seating area ( 312 ) of the wheelchair ( 202 ), wherein the movable shaft ( 1330 ) is connected to the first engagement member ( 704 ), and wherein the movable shaft ( 1330 ) is extendable and retractable and configured to move the first engagement member ( 704 ) relative to the wheelchair ( 202 ) based on extending or retracting the movable shaft ( 1330 ). 
     The apparatus may further comprise the first engagement member ( 704 ) is configured to be removably secured to a first exchange tab ( 2300 ) configured to be welded to the wheelchair ( 202 ) to position the first friction roller ( 104 ) centerless concave rim housing ( 1110 ) friction surface ( 1105 ) to drive the wheelchair ( 202 ) first wheel ( 206 ) by force from the first motor ( 112 ) through the point of contact ( 1115 ) between the first friction roller ( 104 ) friction surface ( 1105 ) and the wheelchair ( 202 ) first wheel ( 206 ) when the first engagement member ( 704 ) is in the engaged position. 
     The apparatus may further comprise: a second friction roller ( 306 ) operably coupled with a second engagement member ( 704 ), wherein the second friction roller ( 306 ) comprises a centerless concave rim housing ( 1110 ) comprising a friction surface ( 1105 ); a second motor ( 302 ) operably coupled with the second friction roller ( 306 ); and a second engagement actuator ( 1200 ) configured to be connected to the wheelchair ( 202 ), wherein the second engagement actuator ( 1200 ) comprises a movable shaft ( 1330 ) configured to move the second engagement member ( 704 ) relative to the wheelchair ( 202 ) between a disengaged position wherein the second friction roller ( 306 ) is not in contact with the wheelchair ( 202 ) second wheel ( 308 ) and an engaged position wherein the second friction roller ( 306 ) is in contact with the wheelchair ( 202 ) second wheel ( 308 ) at a point of contact ( 1115 ) between the second friction roller ( 306 ) friction surface ( 1105 ) and the wheelchair ( 202 ) second wheel ( 308 ) and wherein the point of contact ( 1115 ) is disposed behind the seating area ( 312 ) of the wheelchair ( 202 ). 
     The apparatus may further comprise the second engagement member ( 704 ) is configured to be removably secured to a second exchange tab ( 2300 ) configured to be welded to the wheelchair ( 202 ) to position the second friction roller ( 306 ) centerless concave rim housing ( 1110 ) friction surface ( 1105 ) to drive the wheelchair ( 202 ) second wheel ( 308 ) by force from the second motor ( 302 ) through the point of contact ( 1115 ) between the second friction roller ( 306 ) friction surface ( 1105 ) and the wheelchair ( 202 ) second wheel ( 308 ) when the second engagement member ( 704 ) is in the engaged position. 
     The apparatus may further comprise the first motor ( 112 ) operably coupled by an axle ( 114 ) with the first friction roller ( 104 ). 
     The apparatus may further comprise the first motor ( 112 ) operably coupled by a rotor ( 116 ) with the axle ( 114 ). 
     The apparatus may further comprise the second motor ( 302 ) operably coupled by an axle ( 114 ) with the second friction roller ( 306 ). 
     The apparatus may further comprise the second motor ( 302 ) operably coupled by a rotor ( 116 ) with the axle ( 114 ). 
     The first engagement member ( 704 ) may be a bracket having a first end ( 1345 ), a second end ( 1350 ), and wherein the first engagement bracket ( 704 ) is configured to be removably secured with the first exchange tab ( 2300 ). 
     The first engagement member ( 704 ) first end ( 1345 ) may be removably secured to the first exchange tab ( 2300 ). 
     The first exchange tab ( 2300 ) may be welded to the wheelchair ( 202 ). 
     The first engagement member ( 704 ) second end ( 1350 ) may be operably coupled by a collar ( 1315 ) to the wheelchair ( 202 ). 
     The collar ( 1315 ) may be coupled by an adapter plate ( 1320 ) with the first engagement actuator ( 1200 ) and the movable shaft ( 1330 ) is coupled with the first engagement member ( 704 ) second end ( 1350 ). 
     The collar ( 1315 ) may be connected to a structural member of the wheelchair ( 202 ) that is substantially horizontal and parallel with respect to a surface on which the wheelchair ( 202 ) would rest. 
     The first engagement member ( 704 ) first end ( 1345 ) may be rotatably coupled with the first exchange tab ( 2300 ) to rotate about the first engagement member ( 704 ) first end ( 1345 ). 
     The second engagement member ( 704 ) may be a bracket having a first end ( 1345 ), a second end ( 1350 ), and wherein the second engagement bracket ( 704 ) is configured to be removably secured with the second exchange tab ( 2300 ). 
     The second engagement member ( 704 ) first end ( 1345 ) may be removably secured to the second exchange tab ( 2300 ). 
     The second exchange tab ( 2300 ) may be welded to the wheelchair ( 202 ). 
     The second engagement member ( 704 ) second end ( 1350 ) may be operably coupled by a collar ( 1315 ) to the wheelchair ( 202 ). 
     The collar ( 1315 ) may be coupled by an adapter plate ( 1320 ) with the second engagement actuator ( 1200 ) and the movable shaft ( 1330 ) is coupled with the second engagement member ( 704 ) second end ( 1350 ). 
     The collar ( 1315 ) may be connected to a structural member of the wheelchair ( 202 ) that is substantially horizontal and parallel with respect to a surface on which the wheelchair ( 202 ) would rest. 
     The second engagement member ( 704 ) first end ( 1345 ) may be rotatably coupled with the second exchange tab ( 2300 ) to rotate about the second engagement member ( 704 ) first end ( 1345 ). 
     The first engagement actuator ( 1200 ) and the second engagement actuator ( 1200 ) may be linear actuators. 
     The apparatus may further comprise a programmable joystick ( 102 ) configured to govern the operation of the first motor ( 112 ) and the second motor ( 302 ). 
     The apparatus may further comprise an engage button configured to activate the first engagement actuator ( 1200 ) and the second engagement actuator ( 1200 ) and thereby move the first engagement member ( 704 ) and the second engagement member ( 704 ). 
     The apparatus may further comprise an electrical power source configured to operably power the first engagement actuator ( 1200 ), the second engagement actuator ( 1200 ), the first motor ( 112 ), the second motor ( 302 ), and the engage button. 
     The wheelchair ( 202 ) may be a foldable wheelchair, and the apparatus may further comprise an open space ( 1005 ) located behind the seating area ( 312 ) of the foldable wheelchair ( 202 ), and wherein the first motor ( 112 ), the first exchange tab ( 2300 ), the first engagement member ( 704 ), the second motor ( 302 ), the second exchange tab ( 704 ) and the second engagement member ( 704 ) remain attached to the foldable wheelchair ( 202 ) when the foldable wheelchair ( 202 ) is in a folded or unfolded configuration. 
     The apparatus may comprise an encoded digital identification is embedded within the first engagement member ( 704 ), and wherein the digital identification is stored in a database associated with a digital identification of a user of the apparatus. 
     The apparatus may further comprise an encoded digital identification embedded within the first exchange tab ( 2300 ), and wherein the digital identification is stored in a database associated with a digital identification of a user of the apparatus. 
     The apparatus encoded digital identification is embedded within the first engagement member ( 704 ), wherein the encoded digital identification is embedded within the first exchange tab ( 2300 ), and wherein the digital identification is stored in a database associated with a digital identification of a user of the apparatus. 
     The apparatus may comprise an encoded digital identification is embedded within the second engagement member ( 704 ), and wherein the digital identification is stored in a database associated with a digital identification of a user of the apparatus. 
     The apparatus may further comprise an encoded digital identification embedded within the second exchange tab ( 2300 ), and wherein the digital identification is stored in a database associated with a digital identification of a user of the apparatus. 
     The apparatus encoded digital identification is embedded within the second engagement member ( 704 ), wherein the encoded digital identification is embedded within the second exchange tab ( 2300 ), and wherein the digital identification is stored in a database associated with a digital identification of a user of the apparatus. 
     In the foregoing description, it will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the concepts disclosed herein. Such modifications are to be considered as included in the following claims, unless the claims by their language expressly state otherwise. 
     Various changes may be made to the disclosed configuration, operation, and form without departing from the spirit and scope thereof. In particular, it is noted that the respective implementation features, even those disclosed solely in combination with other implementation features, may be combined in any configuration excepting those readily apparent to the person skilled in the art as nonsensical. Likewise, use of the singular and plural is solely for the sake of illustration and is not to be interpreted as limiting. 
     Terms and phrases used in this document, and variations thereof, unless otherwise expressly stated, should be construed as open ended as opposed to limiting. As examples of the foregoing: the term “including” should be read as meaning “including, without limitation” or the like; the term “example” is used to provide exemplary instances of the item in discussion, not an exhaustive or limiting list thereof; the terms “a” or “an” should be read as meaning “at least one,” “one or more” or the like; and adjectives such as “conventional,” “traditional,” “normal,” “standard,” “known” and terms of similar meaning should not be construed as limiting the item described to a given time period or to an item available as of a given time, but instead should be read to encompass conventional, traditional, normal, or standard technologies that may be available or known now or at any time in the future. 
     Likewise, where this document refers to technologies that would be apparent or known to one of ordinary skill in the art, such technologies encompass those apparent or known to the skilled artisan now or at any time in the future. Furthermore, the use of plurals can also refer to the singular, including without limitation when a term refers to one or more of a particular item; likewise, the use of a singular term can also include the plural, unless the context dictates otherwise. 
     The presence of broadening words and phrases such as “one or more,” “at least,” “but not limited to” or other like phrases in some instances shall not be read to mean that the narrower case is intended or required in instances where such broadening phrases may be absent. Additionally, the various embodiments set forth herein are described in terms of exemplary block diagrams, flow charts and other illustrations. As will become apparent to one of ordinary skill in the art after reading this document, the illustrated embodiments and their various alternatives can be implemented without confinement to the illustrated examples. For example, block diagrams and their accompanying description should not be construed as mandating a particular architecture or configuration. 
     Although the disclosure is described above in terms of various exemplary embodiments and implementations, it should be understood that the various features, aspects and functionality described in one or more of the individual embodiments are not limited in their applicability to the particular embodiment with which they are described, but instead can be applied, alone or in various combinations, to one or more of the other embodiments of the disclosure, whether or not such embodiments are described and whether or not such features are presented as being a part of a described embodiment. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments. 
     It is to be understood that the disclosure of particular features of various implementations in this specification is to be interpreted to include all possible combinations of such particular features. For example, where a particular feature is disclosed in the context of a particular aspect or implementation, or a particular claim, that feature can also be used—to the extent possible—in combination with and/or in the context of other particular aspects and implementations, and in an implementation generally. 
     In the present disclosure, various features may be described as being optional, for example, through the use of the verb “may;” or, through the use of any of the phrases: “in some implementations,” “in some designs,” “in various implementations,” “in various designs,” “in an illustrative example,” or, “for example.” For the sake of brevity and legibility, the present disclosure does not explicitly recite each and every permutation that may be obtained by choosing from the set of optional features. However, the present disclosure is to be interpreted as explicitly disclosing all such permutations. For example, a system described as having three optional features may be implemented in seven different ways, namely with just one of the three possible features, with any two of the three possible features or with all three of the three possible features. 
     In the present disclosure, any method or apparatus implementation may be devoid of one or more process steps or components. In the present disclosure, implementations employing negative limitations are expressly disclosed and considered a part of this disclosure. 
     Where reference is made herein to a method comprising two or more defined steps, the defined steps can be carried out in any order or simultaneously (except where the context excludes that possibility), and the method can include one or more other steps which are carried out before any of the defined steps, between two of the defined steps, or after all the defined steps (except where the context excludes that possibility). 
     Reference throughout this specification to “an implementation” or “the implementation” means that a particular feature, structure, or characteristic described in connection with that implementation is included in at least one implementation. Thus, the quoted phrases, or variations thereof, as recited throughout this specification are not necessarily all referring to the same implementation. 
     Similarly, it should be appreciated that in the above description, various features are sometimes grouped together in a single implementation, Figure, or description thereof for the purpose of streamlining the disclosure. This method of disclosure, however, is not to be interpreted as reflecting an intention that any claim in this or any application claiming priority to this application require more features than those expressly recited in that claim. Rather, as the following claims may reflect, inventive aspects may lie in a combination of fewer than all features of any single foregoing disclosed implementation. Thus, the claims following this Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate implementation. This disclosure is intended to be interpreted as including all permutations of the independent claims with their dependent claims. 
     Elements described herein as coupled or connected may have an effectual relationship realizable by a direct connection or indirectly with one or more other intervening elements. 
     The phrases “connected to,” “coupled to” and “in communication with” refer to any form of interaction between two or more entities, including mechanical, electrical, magnetic, electromagnetic, fluid, and thermal interaction. Two components may be functionally coupled to each other even though they are not in direct contact with each other. The terms “abutting” or “in mechanical union” refer to items that are in direct physical contact with each other, although the items may not necessarily be attached together. 
     Recitation in a claim of the term “first” with respect to a feature or element does not necessarily imply the existence of a second or additional such feature or element. 
     A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. For example, the steps of the disclosed techniques may be performed in a different sequence, components of the disclosed systems may be combined in a different manner, or the components may be supplemented with other components. Accordingly, other implementations are contemplated, within the scope of the following claims.