Patent Publication Number: US-10780930-B1

Title: Worm gear drive unit interface and assembly methods

Description:
BACKGROUND 
     Conventionally, vehicles are assembled in two main sections: the “body in white” and the chassis. When these assemblies reach a certain stage of completion, the assemblies are “married” to form a substantially complete vehicle subject to final assembly. This marriage is generally done with the body on an overhead crane system that lowers the body onto the chassis (e.g., the drivetrain and other components) from above. The body is then generally attached to the chassis using multiple fasteners inserted from the bottom and tightened. 
     This configuration requires a great deal of infrastructure. In a production setting, multiple overhead cranes, automated carts, assembly lines, and other heavy machinery is required. In addition, the bolts used to connect assemblies are often visible on the complete vehicle or must be covered with trim (e.g., grommets or plugs) and/or sealed in a separate operation. This requires additional steps and additional components, increasing costs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit of a reference number identifies the figure in which the reference number first appears. The same reference numbers in different figures indicate similar or identical items. 
         FIGS. 1A and 1B  depict a modular vehicle with a main body and removable drive units. 
         FIG. 2A  is a partial cutaway view of a fastening system with a crash structure and drive system installed on a subassembly, in accordance with some examples of the present disclosure. 
         FIG. 2B  is a partial cutaway view of the fastening system with the crash structure and drive system, in accordance with some examples of the present disclosure. 
         FIG. 3A  is a rear perspective view of the drive system, in accordance with some examples of the present disclosure. 
         FIG. 3B  is a front exploded, perspective view of the drive system, in accordance with some examples of the present disclosure. 
         FIG. 4A  depicts a drive interface with an internal drive interface and an external drive interface, in accordance with some examples of the present disclosure. 
         FIG. 4B  depicts a drive interface with two external drive interfaces, in accordance with some examples of the present disclosure. 
         FIG. 4C  depicts another drive interface with two external drive interfaces of the same size, in accordance with some examples of the present disclosure. 
         FIGS. 5A-5C  depict driven gears with large internal, small internal, and external fastener inserts, respectively, in accordance with some examples of the present disclosure. 
         FIG. 6A  is a perspective view of a robotic cart for use with the fastening system, in accordance with some examples of the present disclosure. 
         FIG. 6B  is a side view of the robotic cart for use with the fastening system, in accordance with some examples of the present disclosure. 
         FIG. 6C  is a perspective view of the robotic cart for use with the fastening system with a vehicle support shown separated, in accordance with some examples of the present disclosure. 
         FIGS. 7A and 7B  include a flowchart depicting a method for using the robotic cart with the fastening system, in accordance with some examples of the present disclosure. 
         FIG. 8  is a component level view of an electronic device, such as a propulsion control system, in accordance with some examples of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Examples of the present disclosure relate to systems and methods for assembling and disassembling components in a single operation. In other words, the systems and methods disclosed herein enable components such as, for example, vehicle subassemblies to be installed with fasteners, with the fasteners inserted and torqued in a single operation. The fastening system can also enable the fasteners to be installed using automated systems (e.g., robots and/or automatic torque wrenches), to be substantially hidden from view, and to meet other design criteria (e.g., no fasteners penetrating interior panels). 
     In some examples, the fastening system can be incorporated into the subassemblies themselves. Thus, the fastening system can be included in a crash structure or subframe, for example, and can enable the crash structure or subframe, along with other components, to be easily attached to another subassembly or the body of the vehicle. The fastening system can also enable these same components to be removed from the vehicle by simply reversing the installation procedure. 
     In some examples, the system can include one or more worm drives attached to driveshafts and disposed inside a housing. The worm drives can enable a torquing device, such as an automatic torque wrench, to interface with the driveshafts in a substantially conventional manner i.e., vertically from below the vehicle yet rotate fasteners that are disposed horizontally. In this manner, the fasteners can attach one subassembly to another, for example, such as a drive module to a vehicle body, horizontally. This configuration, in turn, can obviate the need for overhead cranes or gantries, among other infrastructure for assembling and disassembling vehicles. In addition, the system can enable the fasteners to be substantially hidden when installed (without additional procedures or parts) and to utilize blind holes, reducing body penetrations, among other things. 
     For ease of explanation, the systems and methods described below are described in the context of installing and removing drive units from the body of a modular vehicle. One of skill in the art will recognize, however, that these systems and methods are not so limited. Indeed, the systems and methods described herein can be used to assemble and disassemble many different types of components and fasteners without departing from the spirit of the disclosure. The system can be used to fasten transmissions to engines, for example, to install accessories on engines, or to couple and decouple other types of subassemblies and components. Generally, such a system may be employed for any removable subcomponent in a larger assembly. 
     As mentioned above, conventional vehicle assembly lines generally assemble vehicles in one or more subassemblies that are ultimately brought together to form a completed vehicle. Many vehicles are assembled as a “body in white” and a chassis. The body in white refers to the sheet metal components of the vehicle that generally form the body once they have been welded together. The chassis can comprise, for example, a frame, or multiple sub frames, the suspensions components, engine and transmission, exhaust system, and other components. At a predetermined stage of completion, the body in white and the chassis are brought together, generally using a large overhead conveyor system, and bolted, welded, and/or glued to each other. 
     This operation, which is commonly referred to as the “marriage,” requires significant capital investment. In other words, the chassis is typically riding along a large conveyor or assembly line, or on a robotic cart, while the body in white is generally supported by an overhead crane or gantry system. The conveyor and gantry must then be precisely aligned to enable the two main components to be brought together such that the mounting holes and other components are aligned. In addition, the gantry system and conveyors must be sized and shaped to support the components, which can weigh several hundred to several thousand pounds. To this end, infrastructure costs for a new automotive plant generally exceed one billion dollars, representing a significant barrier to entry. 
     In addition to the required infrastructure, vehicles made using traditional manufacturing and assembly processes are difficult to service. Each different vehicle make and model has a different combination of components and assemblies. As a result, stocking all of the required parts for each vehicle can be difficult or impossible. 
     This application, on the other hand, refers to systems and methods that, while suitable for some traditional manufacturing, is suitable for use with modular vehicles. These vehicles can comprise relatively few assemblies, or “modules,” that are then mated during a final assembly step or process. In some examples, the vehicles may be assembled from two main types of modules, for example, a body module and a drive module (e.g., at least one drive module at one end of the body module). Indeed, in some examples, one type of drive module may be used with multiple types of body modules, further reducing complexity. Thus, the vehicle assembly plant can be very simple, compact, and inexpensive to construct and maintain. In addition, inventory management is simplified as the assembly plant need only maintain the few modules used to assemble the vehicle in inventory. 
     The modular construction of the vehicles described herein also greatly improves their serviceability. For instance, in the event of a failure or fault with a component of a module, the module can simply and quickly be removed and replaced with another module. For instance, if a fault occurs with a motor, battery, or other major system of a drive module, the drive module may simply be removed from the vehicle and replaced with another drive module. The replacement of a module may be performed by service personnel, an automated service robot (or robotic cart, as discussed below), or a combination thereof. As shown in  FIGS. 1A and 1B , one solution to reducing capital investment is to use modular manufacturing techniques. As shown, a vehicle  100  can be constructed comprising a body  102 , a first drive unit  104 , and a second drive unit  106 , which can be assembled and disassembled horizontally instead of vertically. In this configuration, the vehicle  100  comprises the body  102 , which can act as a monocoque and passenger compartment, and the drive units  104 ,  106 , which move and steer the vehicle, among other things. The drive units  104 ,  106  can comprise, for example, one or more motors, internal combustion engines, fuel cells (or other power sources), differentials, controllers, steering systems, braking systems, HVAC, etc. The drive units  104 ,  106  and the body  102  can be designed to mate very precisely such that fluids, electronics, HVAC and other functions between the subassemblies can be connected and disconnected using automated equipment and with little, or no, fluid loss. 
     When attaching the drive units  104 ,  106  to the body  102 , it may be desirable, however, to provide a system that enables the use of automated machinery, such as automatic torque wrenches, robots, and/or robotic carts, as discussed below. It may also be desirable for the system to “hide” the fasteners, such that they are not visible during normal use. It may also be desirable to attach the drive units  104 ,  106  to the body  102  without penetrating the passenger compartment. This can reduce water and air infiltration, reduce noise, reduce corrosion, and improve structural rigidity, among other things. It may also be desirable for the system to be able to insert, tighten, and torque the fasteners in a single step to improve efficiency, without the need for grommets, covers, or other accessories. It is to such a system that examples of the present disclosure are primarily directed. 
     To this end, a fastening system  108  can be used to horizontally couple the drive units  104 ,  106  to the body  102 . As shown, the fastening system  108  can be attached to the drive units  104 ,  106  and can be substantially hidden from view in the assembled state. As mentioned above, the fastening system  108  can include one or more driveshafts, disposed vertically below the vehicle  100 . The fastening system  108  can also include one or more spur gears, straight, spiral, or hypoid bevel gears, and related mechanisms to turn fasteners, with the fasteners disposed horizontally in the fastening system  108 . In some examples, the fastening system can include worm drives due to their ability to transmit higher torque loads when compared to other gear types. This can enable the fastening system  108  to horizontally attach the drive units  104 ,  106  to the body (or vice-versa). The fastening system  108  can enable relatively conventional torquing devices, with vertical orientation, to be converted to improved modular, horizontal assembly procedures. In addition, the fastening system  108  and fasteners can be substantially hidden from view when assembled, obviating the need for additional steps or parts (e.g., seals or aesthetic covers). 
     As shown in  FIG. 1B , in some examples, jack stands, blocks, or internal air or hydraulic jacks  110  can be used to support the body  100  when one or more of the drive units  104 ,  106  is removed. In other words, the vehicle  100  is normally supported on the wheels  112  in the assembled state. Thus, in some examples, the jacks  110  can be used to support the body  102  when the drive units  104 ,  106  are removed. In other examples, as discussed below with reference to  FIGS. 6A-6C , a robotic cart  600  with a separable vehicle stand  604  can be used to support the body  102 . 
     As shown in  FIG. 2A , examples of the present disclosure can comprise a fastening system  108  for attaching subassemblies during vehicle production. The fastening system  108  can enable a first subassembly  202  (e.g., the drive units  104 ,  106 , discussed above) to be attached to a second subassembly  204  (e.g., the body  102 ) with a plurality of fasteners  206  in a horizontal manner, such that the fasteners  206  are not visible in the installed position. As shown, in some examples, the fastening system  108  can be attached to the first subassembly  202  to enable the first subassembly  202  to be easily attached to the second subassembly  204 , or vice-versa. 
     As shown in  FIG. 2B , the fastening system  108  and can also comprise a housing  208  and a drive system  210 . The housing  208  can comprise a casting or extrusion suitable to attach the fastening system  108  to one of the subassemblies  202 ,  204  and can house the drive system  210 . When used on a vehicle  100 , for example, the housing  208  may not only house the drive system  210 , but may also act as part of the crash structure for the vehicle  100 . Thus, the housing  208  can act as a crumple zone and can include internal structure, such as ribs  208   a , for example, configured to deform in response to a predetermined crash force. This can enable the housing  208  to absorb crash energy, rather than transferring this energy to the vehicle  100 . The housing  208  can be replaced separately to minimize repair costs. 
     In other example, the housing  208  can instead (or in addition) support a separate crumple zone or crash structure on a surface facing an external portion of the vehicle  100 . Thus, additional crash structures can be bolted or bonded to an external surface of the housing  208 , for example. This may prevent damage to the drive system  210  and other components, further reducing repair costs. 
     In some examples, as shown in  FIG. 2A , the fastening system  108  can be attached to a subframe  212 , such as a subframe for supporting the drive units  104 ,  106 . Thus, the fastening system  108  can be used to attach the drive units  104 ,  106  to the body  102  (depicted more generically as subassembly  204 ). Though, as discussed above, the fastening system  108  is not so limited and can be used on other components of the vehicle  100 , other vehicles, or other machines or components. 
     Thus, turning one or more driveshafts  214  on the drive system  210  can rotate a series of mechanisms to rotate one or more fasteners  206  to detachably couple the first subassembly  202  to the second subassembly  204 . As shown, in some examples, the driveshaft(s)  214  can rotate a worm gear configured to change the direction of rotation from a first orientation (e.g., vertically below the vehicle  100 ) to a second orientation (e.g., horizontally to the ground). The fastening system  108  can include a variety of drive interfaces configured to interface with a variety of torquing devices. The fastening system  108  can also include a variety of fastener drives to tighten and loosen multiple types and sizes of fasteners. 
     In some examples, to aid installation, the fasteners  206  can be captured between the drive system  210  and the housing  208 . In other words, the fastener  206  can pass through an aperture in the housing  208  that is sized to enable the shaft of the fastener to pass through, but not the head of the fastener  206 . As discussed below, the fastening system  108  can then be spring-loaded to promote extension of the fastener  206  of the fastening system (e.g., the driven gear  308 , discussed below) from the housing  208 . In this manner, the fasteners  206  can remain with the fastening system  108  when the subassembly  202  is removed, for example, to prevent loss or damage. In addition, upon reassembly of the components  202 ,  204 , the fasteners are readily available for installation and are constantly driven into a respective receiving assembly. In some examples, such a spring assembly may promote alignment of multiple fasteners  206  driven by the drive system  210 . The spring assembly can also provide inward force on the fasteners  206  to ensure thread engagement upon reassembly. In some examples, as shown in  FIG. 3B , below, the fastener  206  can also be tapered to provide additional alignment between the fastener  206  and the respective receiver in the subassembly  102 ,  104 ,  106 . 
     As shown from the rear in  FIG. 3A  and from the front and exploded in  FIG. 3B , the drive system  210  can comprise the first driveshaft  214 , second driveshaft  302 , worm shaft  304 , worm gear  306 , and driven gear  308  for each fastener  206 . As shown in  FIG. 3A , the drive system  210  contains provisions for two fasteners  206  (e.g., two sets of gears  304 ,  306 ,  308 ), but the fastening system  108  can be used with more or less fasteners  206  by adding or removing components. 
     As shown, the driveshaft(s)  214 ,  302  can be engaged with the worm shaft(s)  304  to enable the fasteners  206  to be tightened from an angle that is substantially perpendicular to the fastener  206 . Thus, the driveshafts  214 ,  302  can be located vertically beneath (or above) the vehicle  100 , with the fasteners  206  disposed in a substantially horizontal manner inside the fastening system  108 . In other words, in the orientation shown in  FIGS. 3A and 3B , the worm shaft  304  can covert rotary motion about the y-axis, for example, into rotary motion about the x-axis. 
     Thus, while tightening tools (e.g., torque wrenches) can be inserted into the driveshafts  302  in the conventional manner e.g., vertically from below the vehicle  100 —the fasteners  206  can be tightened into the subassembly  204  horizontally. This enables the fasteners  206  to be located inside the housing  208  and, when tightened, inside the subassembly  204  such that they are substantially hidden from view. In addition, the use of a simple seal  322  (e.g., a lip seal, as shown in  FIG. 3B ) between the driveshaft(s)  214 ,  302  and the housing  208 , for example, can enable the fasteners  206  to be substantially sealed from the elements. Thus, the fasteners  206  are hidden and protected without the need for additional steps or components during assembly, increasing productivity and reducing costs. 
     As shown in  FIGS. 3A and 3B , when two fasteners  206  are employed, the drive system  210  can comprise one driveshaft  214  ( FIG. 3A ) or two driveshafts  214 ,  302  ( FIG. 3B ), two worm shafts  304 , two worm gears  306 , and two driven gears  308 . In some examples, as shown in  FIG. 3A , the drive system  210  can include a single driveshaft  214  coupled to both worm shafts  304  to enable both fasteners  206  to be tightened at the same time and with the same tool. This may be useful when fastener torque is less critical, for example, or when the conditions can be controlled such that each fastener  206  receives substantially the same fastening torque. 
     In other examples, as shown in  FIG. 3B , the drive system  210  can include separate driveshafts  214 ,  302 , one for each worm shaft  304 . Thus, in this configuration, the outer driveshaft  214  can turn the lower worm shaft  304   a , while the inner driveshaft  302  can turn the upper worm shaft  304   b . In this manner, each fastener  206  can be independently tightened and torqued. In some examples, the driveshafts  214 ,  302  can be concentric such that an inner driveshaft  302  rotates inside an outer driveshaft  214 . In this configuration, the driveshafts  214 ,  302  can also comprise separate drive interfaces  310   a ,  310   b  to enable each driveshaft  214 ,  302  to be driven independently. 
     As shown, in some examples, rather than using a single worm shaft  304  that spans a significant portion of the driveshaft&#39;s length, the drive system  210  can comprise a single, short worm shaft  304  for each fastener  206 . In some examples, the drive system  210  can also include a drive housing  312  for each worm shaft  304 . The drive housing  312  can be designed to not only house the drive system  210 , but to act as a structural and/or crash member for the drive module  104  or vehicle  100 . 
     The drive housing  312 , in turn, can include one or more bushings or bearings  314  to reduce the flex of driveshaft(s)  302  proximate the worm shaft  304 . Thus, the drive housing  312  can include an upper bearing  314   a , disposed above the worm shaft  304 , for example, and a lower bearing  314   b  disposed below the worm shaft  304 . Of course, depending on the size of the drive system  210 , more or less bearings  314  can be used. 
     The housing  208  can be shaped and sized to house drive system  210 , which includes the worm shaft  304  and the worm gear  306 . As shown, the housing  208  can comprise a substantially cylindrical portion to house the worm shaft  304  and a substantially circular portion to house the worm gear  306 . The housing  208  may also include seals, grease fittings, and other components suitable to maintain and service the components  304 ,  306 ,  308  of the drive system  210 . 
     The combination of the bearings  314 , drive housing  312 , and worm shafts  304  can substantially eliminate flexing of the worm shafts  304  with respect to the worm gears  306 . This reduces friction and wear on both gears  304 ,  306 . This also enables more accurate torque measurement when torquing the fasteners  206  during assembly. This configuration also enables the driveshafts  302  (as opposed to the worm shafts  304 ) to be somewhat flexible since they are not required to locate the worm shafts  304 . In this manner, slight misalignments between the driveshafts  302  and any drive tools (e.g., a robotic torque wrench) can be absorbed by the driveshafts  302 , further reducing wear on the gears  304 ,  306 . Thus, while a slight misalignment between a torque wrench and the drive system  210  may cause one, or both driveshafts  214 ,  302  to bow slightly, for example, the alignment between the worm shafts  304  and the worm gears  306  is maintained. 
     As shown, the worm gear  306  can be rotated by the worm shaft  304 , while the driven gear  308  can be turned by the worm gear  306 . Thus, the worm gear  306  can comprise a complementary tooth pattern to the worm shaft  304  to turn the direction of rotation of the driveshafts  214 ,  302  through approximately 90 degrees. The worm gear  306  can also comprise internal teeth suitable to engage with the external teeth of the driven gear  308 . As briefly noted above, such a worm gear combination may enable high torques to be transferred, though other suitably sized gear configurations could also be used. 
     Thus, the driven gear  308  is turned by the worm gear  306  and, in turn, turns the fastener  206 . To this end, the driven gear  308  can include an interface  316  to rotate, tighten, and torque the fasteners  206 . As shown, in some examples, the interface  316  can simply comprise and appropriately sized hole in the driven gear  308  (e.g., a hex, 8-point, or 12-point “socket”). In other examples, as discussed below, the driven gear  308  can include an insert, or adapter, to enable a single type or size of driven gear  308  to be adapted to multiple types and sizes of fasteners  206 . In still other examples, to reduce complexity, the worm gear  306  can drive the fastener  206  directly obviating the need for the driven gear  308 . 
     In some examples, to facilitate maintenance and repair, the drive system  210  can also comprise a removable cover  318  and a spring  320 . As shown, in some examples, the cover  318  can be removable to provide access to the worm gear  306 , driven gear  308 , and other fastening system  108  components. This can enable the components  304 ,  306 ,  308  to be inspected, cleaned, lubricated, and/or replaced without completely disassembling the drive system  210  (or the fastening system  108  or removing it from the vehicle  100 ). In addition, in the event of a failure of the drive system  210  such as, for example, a broken gear  304 ,  306 ,  308  or a jammed or cross-threaded fastener  206 , the cover  318  and spring  320  can be removed from the rear of the fastening system  108 . Once removed, the worm gear  306  and/or driven gear  308 , for example, can also be extracted through an appropriately sized aperture  312   a  in the drive housing  312  to enable the drive system  210  to be serviced in situ. 
     Significantly, in some examples, the driven gear  308  can be removed through the aperture  312   a  to enable a manual socket to be inserted through the drive housing  312  and the worm gear  306 . Thus, a manual ratchet or wrench can be used to extract the fastener  206 , for example, for replacement and/or drive the fastener  206  directly into or out of the respective receiving region. This may be because the fastener  206  is damaged, cross-threaded, corroded, or has simply reached the end of its service life (i.e., it has been retorqued a predetermined number of times. Thus, the fastener  206  can be removed and replaced without removing the fastening system  108  from the vehicle  100  and without disturbing the setup (e.g., backlash) between the worm shaft  304  and worm gear  306 . In addition, the drive unit  104 ,  106  can be removed from the vehicle  100 , for example, despite a mechanical failure. 
     As shown in  FIG. 4A , in some examples, the ends of the driveshafts  214 ,  302  can be substantially coplanar. In this configuration, to enable each driveshaft  214 ,  302  to be turned separately, the inner driveshaft  302  can comprise an internal drive interface  402  such as, for example, an internal hex (e.g., Allen®), internal Torx®, square drive, or another type of internal drive interface  402 , while the outer driveshaft  214  can comprise an external drive interface  404 , such as an external hex, external 12-point, or another external drive interface  404 . This may enable a dual (concentric) torque wrench, for example, to tighten both fasteners  206  separately, but at the same time. In addition, this configuration can shorten the overall length of the driveshafts  214 ,  302  and thus, the drive system  210 . In other words, the internal drive interface  402  enables the inner driveshaft  302  to be turned even though the internal driveshaft  302  and external driveshaft  214  terminate at the same point (i.e., they are not the same length, but their ends are flush), reducing the overall length required for the driveshafts  214 ,  302 . 
     As shown in  FIG. 4B , in other examples, both driveshafts  302  can comprise external drive interfaces  404 , with the inner driveshaft  302  being longer than the outer driveshaft  214  to enable access to both drive interfaces  404 . In this configuration, the first drive interface  404   a  for the inner driveshaft  302  can comprise a smaller, external hex or 12-point, for example, which can be turned with a smaller, standard depth socket. The second drive interface  404   b  for the outer driveshaft  214 , on the other hand, can comprise a larger, external hex or 12-point, for example, which can be driven with a larger, deep socket. Regardless, the separate driveshafts  214 ,  302  can enable each fastener  206  to be tightened and torqued independently, if desired. In some examples, the inner driveshaft  302  can also include an internal drive interface  402  to provide redundancy and/or improved access, as necessary. 
     As shown in  FIG. 4C , in other examples, the inner driveshaft  302  and the outer driveshaft  214  can have the same size external interface  404   b ,  406 . In this configuration, the first drive interface  406  for the inner driveshaft  302  can comprise the same size external hex or 12-point, for example, which can be turned with the same socket or driver as the outer drive shaft  214 . Thus, both the first drive interface  406  and the second drive interface can be driven with the same, deep socket. This can be used when there is an acceptable range of torques for each fastener  406  (e.g., less precision is required) or by adjusting the length or thread pitch of the fasteners  406 , for example, to achieve the desired torques. 
     As mentioned above, in some examples, the interface  316  molded directly into the driven gear  308  can turn the fasteners directly. In other examples, the interface  316  can be molded directly into the worm gear  306 , obviating the need for the driven gear  308  (though this may affect serviceability). In still other examples, as shown in  FIGS. 5A-5C , the driven gear  308  can include a fastener insert  502 , disposed inside the interface  316 , to adapt the driven gear  308  to a variety of fastener sizes and/or types. Thus, the interface  316  of the driven gear  308  can comprise, for example, a hex (shown), 12-point, spline, or other drive to couple with the fastener insert  502 . The fastener insert  502 , in turn, can comprise a fastener drive  504 ,  508  configured to rotate a fastener and can include a complementary external surface  506  e.g., sized and shaped to fit inside the interface  316 . 
     Each fastener insert  502  can comprise a fastener drive  504  sized and shaped to rotate a specific size and type of fastener. Thus, the fastener inserts  502  can comprise, for example, external fastener drives  504   a ,  504   b  ( FIGS. 5A and 5B , respectively) for external fasteners like hex bolts. The fastener inserts  502  can also comprise internal fastener drives  508  ( FIG. 5C ) for internal fasteners like Allen® or internal Torx® bolts. 
     As shown, a large fastener insert  502   a  can include a large, external fastener drive  504   a  for turning large, external fasteners (e.g., large hex bolts). Similarly, a small external fastener insert  502   b  can include a small, external fastener drive  504   b  to turn smaller external fasteners (e.g., small hex bolts). Thus, while the fastener inserts  502   a ,  502   b  are externally the same size and configured to fit inside the driven gear  308 , the fastener drives  504  can be different sizes for different sized fasteners. 
     In addition, as shown in  FIG. 5C , the fastener insert  502   c  can also comprise an internal fastener drive  508  to drive internal fasteners in this case an Allen® bolt. Thus, the internal fastener drive  508  can be sized and shaped to fit different sized (e.g., ¼″, ½″, 5 mm, 6 mm, 7 mm, etc.) and different style (e.g., Torx®, Allen®, splined, square drive, star, flat head, Phillips, etc.) internal fasteners. Thus, by simply changing out the fastener inserts  502 , the fastening system  108  can be adapted to different sizes and types of fasteners. 
     This modular configuration can also enable the driven gear  308  and the fastener insert  502  to be made of different materials to, for example, reduce fastener damage, improve wear characteristics, reduce friction, and/or reduce noise. Thus, the fastener insert  502  can comprise nylon, for example, or another softer material to substantially prevent any coatings (e.g., zinc chromate) on the fastener from being removed during tightening and removal procedures. Thus, the fastener insert  502  can comprise a polymer, for example, while the driven gear  308  can comprise a metal. The fastener insert  502  can also comprise a hard material to reduce wear on the fastener insert  502 , while enabling a softer material to be used for the driven gear  308  to reduce wear on the drive gear  306 . Other combinations are also possible. 
     This configuration can provide additional modularity. In other words, the driven gear  308  can be a standard size with a standard sized interface  316 . The fastener inserts  502 , in turn, can each comprise a standard external surface  506  and a different sized fastener drive  504 , or “socket,” for a specific size and/or style of fastener. So, for example, the large fastener insert  502   a  can comprise a 12 mm fastener drive  504   a  and the small fastener insert  502   b  can comprise an 8 mm fastener drive  504   b . Of course, these sizes a purely exemplary and other sizes are possible. Indeed, as mentioned above, the fastener inserts  502  can also comprise either external drives (hex, 12-point, etc.) or internal drives (e.g., Allen®, Torx®, etc.), as desired. 
     In this manner, the fastening system  108  can be substantially standardized and can be used on vehicles  100  with multiple sizes or styles of fasteners  206  or on multiple different types of vehicles serviced in the same facility. In some examples, the fastening system  108  can include multiple sizes suitable to service a range of fastener sizes. In other words, the fastening system  108  can include, for example, a small, medium, and large size, with each fastening system  108  suitable to a range of fastener sizes (e.g., 4-8 mm, 10-12 mm, and 14-16 mm, respectively). Thus, each fastening system  108  includes appropriately sized (and torque rated) components  214 ,  302 ,  304 ,  306 ,  308  and a plurality of fastener inserts  502  sized and shaped for the range of covered fasteners  206 . 
     As shown in  FIGS. 6A-6C , the fastening system  108  can be used in conjunction with a robotic cart  600 . Thus, the robotic cart  600  can be used, for example, to remove the subassemblies  104 ,  106  from the body  102  for maintenance and repair, among other things. The robotic cart  600  can comprise, for example, a main body  602  and a vehicle stand  604 . The main body  602  can comprise, for example, one or more drive systems  606 , each comprising one or more motors/transmissions, and a plurality of wheels, rollers, casters, or another suitable component. 
     The drive systems  606  can comprise any type of motor suitable to move the cart  600  and/or the subassemblies  104 ,  106  throughout a service facility, for example, or an assembly plant. In some examples, the drive systems  606  can comprise for example, direct drive electric motors (i.e., without using transmissions), electric motors acting through transmissions, servo motors, or another type of electric motor. In other examples, the drive systems  606  can comprise pneumatic or hydraulic motors power by a pump that is itself driven by a central electric motor, internal combustion engine, fuel cell, etc. 
     Regardless, the main body  602  can comprise one or more docking pins  608  and one or more torquing devices  610 . The torquing devices  610  can comprise any of a variety of automated/robotic torque-controlled screwdrivers and nutdrivers, such as those commonly used on vehicle assembly lines. The docking pins  608  can comprise pins, cups, latches, or other suitable interface to enable the cart  600  to securely lift and move the drive units  104 ,  106 . Thus, in some examples, the docking pins  608  can simply comprise pins, for example, that are sized and shaped to be inserted into complementary holes in the drive units  104 ,  106 . In other examples, the docking pins  608  can comprise cups or holes, for example, into which complementary hemispheres or pins in the drive units  104 ,  106  can be received. The docking pins  608  and their respective complementary receiving portions on the drive units  104 ,  106  may be sized and shaped to promote alignment. Thus, the docking pins  608  can serve to locate, align, and/or provide fixturing between, for example, the cart  600  and the vehicle  100 . 
     The main body  602  can also comprise one or more torquing devices  610  configured to interface with the fastening system  108 . Thus, the torquing device  610  can comprise, for example, a mechanical or electronic torque wrench configured to tighten and loosen the fasteners  206  to enable the drive units  104 ,  106  to be installed and removed from the vehicle  100 . The torquing devices  610  can comprise automatic electric or hydraulic torque wrenches, for example, configured to tighten the fasteners  206  to one or more preset tightening torques or torque-to-yield (TTY) settings. The torquing devices  610  can also be used to loosen the fasteners  206  to enable the drive units  104 ,  106  to be removed. 
     As mentioned above, in some examples, the fastening system  108  can comprise multiple driveshafts  302  to enable the fasteners  206  to be tightened, loosened, and torqued independently. In this configuration, the torquing device  610  can comprise complementary torque wrenches. So, for example, in the case of concentric driveshafts  214 ,  302 , discussed above, the torquing device  610  can include a first torque wrench for the inner driveshaft  302  and a second torque wrench for the outer driveshaft  214 , with the appropriate tool on each torquing device  610  for the respective driveshaft  302 . Of course, in some examples, the torquing device  610  can include a single torque wrench with multiple heads, concentric heads, or other devices, for this purpose. 
     In some examples, the torquing devices  610  can be moved in one or more axis to enable the torquing devices  610  to be aligned with the driveshafts  214 ,  302 . The torquing devices  610  can be moved back and forth or side-to-side, for example, to center the torquing devices  610  on the driveshafts  214 ,  302 . The torquing devices  610  can also be moved vertically from a lowered position ( FIG. 6A ) to a raised position ( FIG. 6C ) to enable the cart  600  to engage with the driveshafts  214 ,  302 . 
     In some examples, the cart  600  can also include an upper stanchion  612  including one or more additional docking pins  608 . As before, these docking pins  608  can be, for example, pins, cups, latches, or other devices suitable to engage with the drive units  104 ,  106 . The upper stanchion  612  can support an upper portion of the drive units  104 ,  106  to substantially prevent the drive units  104 ,  106  from rolling, tipping, or otherwise falling, off the cart  600 . This can provide additional security when the cart  600  removes, installs, and transports the drive units  104 ,  106  during operation. 
     In some examples, such as for vehicles  100  with moveable suspensions, the upper stanchions  612  can be fixed. In this configuration, the cart  600  can be positioned under the vehicle  100  with the docking pins  608  aligned with the pickup points on the vehicle  100 . The vehicle  100  can then alter its suspension to first provide clearance for the cart  600  and then lower onto the cart  600 . 
     In other examples, such as for vehicles  100  with fixed suspensions, the upper stanchions  612  can be moveable. The upper stanchions  612  can be mounted on actuators  612   a  such as, for example, pneumatic or hydraulic rams, linear actuators, or screw drives to enable the cart  600  to lift the vehicle  100 . In this configuration, the cart  600  can be positioned under the vehicle  100  with the docking pins  608  aligned with the pickup points on the vehicle  100  and the upper stanchions  612  can be moved from a lowered position ( FIG. 6C ) to a raised position ( FIG. 6A ), as shown by Arrow A, to raise the vehicle  100  off the ground. 
     In some examples, the upper stanchions  612  can also include additional torquing devices  610 . Thus, raising the upper stanchions  612  can enable the torquing devices  610  to engage with fasteners  206  on the drive module  104 ,  106  or other subassemblies. Of course, while shown vertically oriented, in some examples, the torquing devices  610  can be disposed horizontally on the ends of the upper stanchions  612  to tighten horizontal fasteners  206 . 
     The cart  600  can also include the vehicle stand  604 . As shown in  FIG. 6C , the vehicle stand  604  can be detachable from the main body  602 , as shown by Arrow B, and can support the vehicle  100  when one, or both, of the drive units  104 ,  106  is removed. To this end, the vehicle stand  604  can include one or more docking pins  608  and a foot  614 . As before, the docking pins  608  can be, for example, pins, cups, latches, or other devices, but in this case, can be suitable to engage with complementary pickup points on the body  102  (i.e., as opposed to the drive units  104 ,  106 ). In other words, because the body  102  is normally supported by the wheels of the vehicle  100 , when a drive unit  104 ,  106  is removed, it may be necessary to support the body  102  until a drive unit  104 ,  106  is reinstalled. 
     In some examples, such as when the cart  600  is used on vehicles  100  with active suspensions, the foot  614  can be a simple pin or bar. Thus, the cart  600  can move under the vehicle  100 , the vehicle  100  can alter its suspension (lowering the vehicle  100  onto the cart  600 ), and the vehicle  100  can simply rest on the vehicle stand  604 . In this configuration, as the cart  600  removes the drive unit  104 ,  106  from the vehicle  100 , the vehicle stand  604  can detach from the cart  600  to support the vehicle  100 . When the cart  600  returns with the drive unit  104 ,  106  (or a replacement drive unit  104 ,  106 ), the drive unit  104 ,  106  can be reinstalled and the suspension altered to raise the vehicle  100  off of the cart  600 . The vehicle stand  604  can then be reattached to the cart  600  for removal to another location. This process is described in more detail below with respect to  FIGS. 7A and 7B . 
     In other examples, such as on vehicles  100  with conventional (non-active) suspension systems, the foot  614  can comprise, for example, a hydraulic, pneumatic, or electric jack to enable the vehicle  100  to be lifted to remove the drive units  104 ,  106 . Thus, as shown in  FIG. 6C , for example, the foot  614  can move vertically, as shown by Arrow C, up and down from a retracted position ( FIG. 6A ) to an extended position ( FIG. 6C ) to support the body  102 . In some examples, the vehicle stand  604  and foot  614  can be substantially self-contained. In other words, the vehicle stand  604  can comprise an internal battery and the foot  614  can comprise an electric jack to raise the vehicle. In this manner, fewer, or no, connections are needed between the main body  602  and the vehicle stand  604 . In this configuration, the main body  602  and vehicle stand  604  may nonetheless be wirelessly connected (e.g., using Bluetooth® or Wi-Fi) to enable signaling between various components. 
     In other examples, the cart  600  can comprise, for example, electrical, pneumatic, and/or hydraulic (e.g., “dry-break”) connections between the cart  600  and the vehicle stand  604  to enable the cart  600  to power the vehicle stand  604 , yet enable the vehicle stand  604  and cart  600  to separate. Thus, the cart  600  can position itself under the vehicle  100 , the foot  614  can extend, and the cart  600  can disconnect from the vehicle stand  604 . The cart  600  can then remove the drive unit  104 ,  106  from the vehicle  100  for service, repair, or replacement, leaving the body  102  resting on the vehicle stand  604  (and foot  614 ). 
     In still other examples, the cart  600  can include a moveable suspension. In this configuration, the drive system  606 , for example, can be mounted on an actuator to enable the cart  600  to be moved up and down. The drive system  606  can be mounted on airbags, for example, or linear actuators to move between a lowered position and a raised position. In this manner, the cart  600  and the foot  614  can both lift the vehicle  100  to a predetermined height to enable the drive unit(s)  104 ,  106  to be removed. 
     The cart  600  can also include a propulsion control system  616  and a plurality of sensors  618  to enable the cart  600  to properly locate the vehicle  100 , position itself under the vehicle  100 , locate the drive interfaces  310 , and locate any pickup points on the vehicle  100 , etc. The sensors  618  can include, for example, one or more image sensors  618   a , radio distance and ranging (RADAR) sensors  618   b , and/or laser distance and ranging (LIDAR) sensors  618   c  mounted on the cart  600 . The sensors  618  can also comprise a global positioning system (GPS), inertial measurement unit (IMU), accelerometers, gyrometers, and other sensors. The sensors  618  can be arranged in a predetermined pattern, for example, in order to provide a desired area of coverage for the area proximate, and under, the vehicle  100 . In some examples, as shown, the sensors  618  can be disposed in a pattern that enables approximately 360-degree coverage around the cart  600 . This can enable the cart  600  to detect objects regardless of which direction the cart  600  is traveling (e.g., to, or from, the vehicle  100 ). This can also enable the cart  600  to detect objects approaching from the sides of the cart  600  (e.g., another cart  600  or a worker in a service facility). Other patterns and arrangements of the sensors  618  are contemplated. 
     The image sensors  618   a  may be any known types of digital image sensors, digital or analog cameras, and/or digital or analog video cameras. The image sensors  618   a  may be high dynamic range (HDR) cameras, for example, to provide improved accuracy of the images. In some examples, the image sensors  618   a  may include one or more of light-sensitive cameras, range sensors, tomography devices, RADAR, and/or ultra-sonic cameras. Other suitable types of imagers are contemplated. The imager sensors  618   a  may be selected to provide two-dimensional (2-D) image data, two and a half-dimensional (2.5d, or depth maps), and/or three-dimensional (3D) image data, image sequences, gray scale (or intensity) image data, and/or color image data. In some examples, the imager sensors  618   a  may be selected to provide depth data, absorption data, and/or reflectance data. 
     As shown, the example sensors  618  may be mounted to a portion of the cart  600  that provides a line-of-site view of a portion of the area around the cart  600 , with at least a portion of the sensors  618  pointed in, or moveable to, the direction of travel and at least a portion of the sensors  618  pointed in, or moveable to, the upward-looking position. This can enable the cart  600  to safely travel through a maintenance facility, for example, and to properly position itself underneath the vehicle  100  for maintenance. The sensors  618  may be located separately from one another and on different parts of the cart  600 , as shown, or incorporated into one or more sensor arrays. 
     The sensors  618  can enable the cart  600  to position itself properly underneath the vehicle  100 , among other things. To this end, the vehicle  100  and/or surrounding environment can include fiducials configured to be identified by the sensors  618 . In some examples, the pickup points on the vehicle  100  and/or disposed about the environment of the vehicle, can include bar codes, artificial reality tags, QR codes, retroreflectors, etc., for example. In some examples, sensor fusion (e.g. using SLAM, Kalman filters, bundle adjustment, etc.) to predict a pose of the cart  600  can be used to accurately localize the cart  600  and plan a trajectory to mate with the vehicle  100 . In other examples, the image sensors  618   a  can be used to identify the pickup points and other features of the vehicle  100  for this purpose. The process of localizing the cart  600  is described in more detail below with reference to  FIGS. 7A, 7B, and 8 . 
     In some examples, rather than being robotic, the cart  600  can be controlled by a worker using a remote control or a handle  620  on the cart. The handle  620  can act as a joystick, for example, to enable the worker to maneuver the cart  600  into place under the vehicle  100 . In some examples, the sensors  618  can include lights to indicate which way the cart  600  needs to be moved to align with the vehicle  100  or a fiducial. In other examples, the cart  600  can include an LCD screen, or other display, to provide directions to the worker. 
     The cart  600  can also comprise a torque control system  622 . The torque control system  622  can provide control for the positioning and operation of the torquing devices  610 . The torque control system  622  can receive various sensor inputs to enable the torquing devices  610  to be centered on the driveshafts  214 ,  302  and then raised into engagement. The torque control system  622  can also control the torque applied through the drive system  208  by the torquing devices  610 . Thus, the torque control system  622  can receive inputs from torque sensors, position encoders, and other sensors to provide the desired torque on the fasteners  206 . 
     The torque control system  622  can also ensure the fasteners  206  are properly removed during disassembly. This can be achieved by detecting a torque spike, for example, to “break the fastener  206  loose” followed by a predetermined number of turns on the fastener  206 . Thus, the torque control system  622  may turn the fastener  406  eight times (or whatever number is required) to remove the fastener  406 , plus another two turns to ensure the fastener  406  is completely removed. 
     As shown in  FIG. 6C , in some examples, the vehicle stand  604  can be detachably coupled to the main body  602  using one or more latches  622 . In some examples, the latches  622  can comprise, for example, mechanical latches. Thus, the latches  622  can comprise, for example, screw drives, cam locks, retractable hooks, or other mechanism suitable to mechanically couple the vehicle stand  604  to the main body  602 . In other examples, the latches  622  can comprise electronic latches such as, for example, electromagnets, linear actuators, screw drives, etc. In either case, the latches  622  can be remotely activated to enable the cart  600 , the vehicle  100 , or a central control to provide a signal to cause the vehicle stand  604  to couple to, or decouple from, the vehicle  100 . 
     In some examples, one or more fiducials  624  can be placed on the ground in the service area. For automated vehicles, for example, the vehicle  100  can positioning itself over the fiducial  624  for service. The cart  600  can then position itself using the fiducial  624 . In this manner, the cart  600  and the vehicle  100  can be properly located using the same frame of reference. The cart  600  can position itself (or a sensor  618 ) over the fiducial  624 , for example, and then engage with the vehicle  100 . 
     In some examples, the vehicle stand  604  can also include a plurality of casters  626 , rollers, wheels, or other device to enable the vehicle  100  to be moved when one, or both, of the drive modules  104 ,  106  is removed. The drive modules  104 ,  106  may be removed to recharge or replace batteries, for example, while the body  102  may be wheeled into the body shop to repair dents or dings obtained during use. The casters  626  can enable multiple repairs to be provided at the same time, among other things. 
     In some examples, the vehicle stand  604  can also comprise one or more lifting points  628 . The lifting points  628  can enable the body  102  to be safely lifted with a crane or other device to enable the body to be moved, lifted, and/or rotated to facilitate service. In some examples, the vehicle stand  604  can include two lifting points sized and shaped to accept, for example, the tines of a forklift for easy maneuvering. 
     As shown in  FIGS. 7A and 7B , examples of the present disclosure can also comprise a method  700  of using the fastening system  108  in conjunction with the robotic cart  600 . The cart  600  can be used to remove and replace drive units  104 ,  106  for maintenance operations, battery swaps, and reconfigurations, among other things. Thus, and in general, the cart  600  can approach the vehicle  100 , align with the vehicle  100  and drive unit  104 ,  106 , remove or decouple the fasteners  206 , and then remove the drive unit  104 ,  106  from the vehicle  100 . For modular vehicles  100 , the cart  600  can then replace the same drive unit  104 ,  106  (e.g., after service or repair), for example, or replace the drive unit  104 ,  106  with a new drive unit  104 ,  106  that has already been recharged, serviced, or repaired. 
     At  702 , therefore, the cart  600  can approach the vehicle  100  and position itself in the appropriate location proximate a first end  750  of the vehicle  100 . So, for example, the cart  600  can approach the vehicle  100  using one or more of the sensors  618  to determine its position relative to the vehicle  100 . Once the cart  600  is with a predetermined distance from the vehicle  100  (e.g., 3 or 5 feet), the cart  600  can reduce its speed for final positioning. 
     In some examples, the cart  600  can, at least partially, be manually positioned. In other words, rather than being entirely robotic, the cart  600  can be manually pushed into place by a worker, for example, or controlled by a worker with a remote control. In this configuration, the worker can guide the cart  600  into and approximate location beneath the vehicle  100  pending final positioning. 
     At  704 , the cart  600  can begin final positioning under the vehicle  100 . In some examples, this can include switching from forward-looking sensors  618  to upward- or downward-looking sensors  618 . In other examples, the cart  600  can locate fiducials, holes, pins, or other locators on the vehicle  100  or on the ground beneath the vehicle  100  using the one or more of the sensors  618 . Thus, the cart  600  can move to align the docking pins  608  with the appropriate pick-up points on the vehicle  100 . The process of localizing the cart  600  is described in more detail below with reference to  FIG. 8 . 
     In other examples, the cart  600  can be manually maneuvered (i.e., by hand or with a remote control) into place by a worker. Thus, the cart  600  can include lights or a digital display, for example, to indicate which direction the cart  600  needs to be moved to be properly aligned with the vehicle  100  based on the sensor data. So, for example, the cart  600  can include four lights (right, left, forward, and backward) or arrows on an LCD screen, for example, to enable the worker to precisely located the cart  600  underneath the vehicle  100 . 
     In some examples, in the operation  704 , the cart  600  can also establish communications between the cart  600  and the vehicle  100 . In some examples, the cart  600  can communicate with the vehicle  100  via a wireless connection (e.g., using Bluetooth® or Wi-Fi). In other examples, the cart  600  can communication with the vehicle  100  using a wired connection. Thus, as discussed above, a docking pin  608  on the cart  600 , for example, can include a plug suitable to interface with a complementary plug on the vehicle  100 . 
     In still other examples, the vehicle  100  and the cart  600  may be in communication with a central control (e.g., a central computer or cloud service) associated with the maintenance facility. Thus, each component  100 ,  600  can be in communication with the central control and providing status messages as the method  700  progresses. The central control can, in turn, provide commands to the components  100 ,  600  to perform various actions, as necessary. 
     Regardless of the method of communication, in some examples, the vehicle  100  can open hatches  752 , covers, or other access panels as necessary to enable the cart  600  to access one or more pickup points or fasteners  206  on the vehicle  100  and/or drive unit  104 ,  106 . Thus, as shown, the vehicle  100  may open a rear hatch  752 , as shown by Arrow D, to enable the upper stanchions  612  to be positioned below pickup points on the top of the drive unit  104 ,  106 . 
     At  706 , for vehicles  100  with active suspensions, airbags, or otherwise moveable suspension components, the vehicle  100  can raise or lower the front suspension  754 , as shown by Arrow E. In some examples, the vehicle  100  may perform this act in response to the cart  600  attaining a predetermined orientation, or pose, relative to the vehicle  100  (i.e., the vehicle  100  sensing the cart  600  is in the proper position). In other examples, the vehicle  100  may perform this act in response to a signal from the cart  600  or the central control. The vehicle  100  may first raise the suspension, for example, to provide additional clearance for the cart  600  and then lower the suspension to “squat” onto the cart  600 . 
     As shown, raising the suspension on the vehicle  100  effectively lowers the vehicle  100  onto the cart  600 . As mentioned above, in this configuration, the foot  614  can be substantially passive and can simply support the weight of the vehicle  100  when the drive unit  104 ,  106  is removed. In this configuration, therefore, as the body  102  lowers onto the foot  614 , the foot  614  is trapped between the body  102  and the ground  756  and supports the vehicle  100 . In some examples, the foot  614  can include a spring or shock, for example, that compresses as the body  102  is lowered to provide some cushion to the body  102 . 
     In some examples, to provide additional clearance underneath the vehicle  100 , the front suspension may initially lower (raise the vehicle  100 ) and then raise (lower the vehicle  100 ). So, when the vehicle  100  is placed into service mode, for example, the vehicle  100  may automatically raise slightly (e.g., 1-6″) to increase clearance under the vehicle  100 . In response to subsequently receiving a signal from the cart  600  or a central control, for example, the vehicle  100  can then lower onto the cart  600  raising the wheels off the ground. 
     For vehicles  100  with conventional, or passive, suspensions, the cart  600  and/or the foot  614  can include a jack to raise the first end  750  of the vehicle  100  slightly. This can enable the wheels  758  to be raised slightly off the ground  756  to enable the drive unit  104 ,  106  to be removed. In this configuration, the foot  614  can also support the body  102  as the drive unit  104 ,  106  is removed. As mentioned above, however, in this configuration, the foot  614  and/or the cart  600  can include a jack that uses hydraulic power, electric power, pneumatic power, or a combination thereof to lift the drive unit  104 ,  106  and/or body  102  to facilitate the removal of the drive unit  104 ,  106  from the body. 
     At  708 , regardless of the lift mechanism, the torquing devices  610  on the cart  600  can engage with the drive interface(s)  310  on the fastening system  108 . In some examples, the cart  600  the torquing device(s)  610  can already be properly located when the cart  600  located itself beneath the vehicle  100 . In other words, the act of the cart  600  engaging with the vehicle  100  e.g., the vehicle  100  lowering on to the cart  600  or the cart  600  raising to meet the vehicle  100  engages the torquing devices  610  with the drive interface(s)  310  at the same time. 
     In other examples, the cart  600  can simply raise the torquing device(s)  610  (on the cart  600  and/or the upper stanchions  612 ) into place, as shown by Arrow F, with the torquing device(s)  610  having been previously located in the x- and y-axes by virtue of the cart  600  locating itself beneath the vehicle  100 . In still other examples, the torquing device(s)  610  may include additional sensors to position and/or fine tune the location of the torquing device(s)  610  with respect to the drive interface(s)  310 . Thus, the torquing device(s)  610  may move slightly fore and aft, left and right, and/or vertically to engage the drive interface(s)  310 . 
     Once engaged, the torquing devices  610  can loosen the fasteners  206 , which connect the drive unit  104 ,  106  to the body  102 . To this end, the torquing device(s)  610  can rotate the driveshaft(s)  214 ,  302  (via the drive interface(s)  310 ) as necessary to remove the fasteners  206  (i.e., ultimately via the interface  316  or fastener inserts  502 ). Thus, the torquing device(s)  610  can rotate the fastener(s)  206  clockwise or counter-clockwise (for reverse thread) to remove the fastener(s)  206  from the body  102 . As discussed above, in some examples, the fastener(s)  206  can be captured inside the fastening system  108  e.g., between the driven gear  308  and then housing  208  and can remain with the drive unit  104 ,  106  in mechanical engagement with the interface  316 . 
     At  710 , the cart  600  can lower the foot  614  (if applicable) and disengage from the vehicle stand  604 . As discussed above, in some examples, the cart  600  can lower the foot  614 , as shown by Arrow G, to support the body  102  when the drive unit  104  is removed. In addition, the cart  600  can include fasteners, latches  622 , or other mechanisms to enable the cart  600  and the vehicle stand  604  to be detachable. This may be in response to a signal from the cart  600 , vehicle  100 , or central control to the vehicle stand  604 . This can enable the vehicle stand  604  to separate from the main body  602  of the cart  600 . At this point, the cart  600  can support the drive unit  104  while the foot  614  can support the body  102  of the vehicle  100 . 
     At this stage, having separated from the vehicle stand  604 , the cart  600  may slightly lower for clearance and can begin to move slowly backwards, as shown by Arrow H, to remove the drive unit  104 ,  106  from the body  102 . In some examples, the cart  600  may continue to scan the body  102  with the sensors  618  to avoid collisions between the cart  600  and/or drive unit  104 ,  106  and the body  102 . The cart  600  may also proceed at a first predetermined speed (e.g., less than 1 MPH) until the cart  600  and/or the drive unit  104 ,  106  has moved a first predetermined distance from the body  102 . 
     At  712 , once the cart  600  and/or the drive unit  104 ,  106  have reached the first predetermined distance from the body  102 , the cart  600  may raise slightly and accelerate to a second predetermined speed (e.g., 1, 2, 3, 5, etc. MPH) to move the drive unit  104 ,  106  throughout the service facility. As discussed above, in some examples, the drive unit  104 ,  106  can be exchanged for a drive unit  104 ,  106  that had been, for example, repaired or recharged. In other examples, the drive unit  104 ,  106  can be removed to enable it to be repaired or to provide access to the body  102 , or other components, for service and repair, as necessary. 
       FIGS. 7A and 7B  are flow diagrams of illustrative processes illustrated as a collection of blocks in a logical flow graph, which represent a sequence of operations that can be implemented in hardware, software, or a combination thereof. In the context of software, the blocks represent computer-executable instructions stored on one or more computer-readable storage media that, when executed by one or more processors, perform the recited operations. Generally, computer-executable instructions include routines, programs, objects of interest, components, data structures, and the like that perform particular functions or implement particular abstract data types. The order in which the operations are described is not intended to be construed as a limitation, and any number of the described blocks can be combined in any order and/or in parallel to implement the processes. 
     For example, while shown removing the drive unit  104 ,  106  from the body  102 , the cart  600  can also be used to reinstall the drive unit  104 ,  106  to the body  102  by essentially reversing the order of the steps. In addition, the cart  600  can also be used to install and remove different subassemblies and assemblies from different types of machines and mechanisms. Thus, the description of the method  700  above is intended to be illustrative, as opposed to limiting. 
       FIG. 8  is a component level schematic view an example of an electronic device. For ease of explanation, the electronic device is described in terms of the functions of the propulsion control system  616 . One of skill in the art will recognize, however, that the electronic device can be used for many other functions in the vehicle  100  or cart  600 , for example, with minor modification. Indeed, a similar electronic device can comprise a component of the torquing devices  610  or other electronic components for use with the systems  108 ,  600  and method  700  described herein. In some examples, the propulsion control system  616  can comprise a dedicated electronic device, such as a dedicated microcontroller. Other components of the cart  600 , however, can comprise an electronic device with multiple functions such as, for example, a cell phone, smart phone, laptop, tablet, or another electronic device that comprise a number of components to gather data, communicate, and maneuver, among other things. 
     The propulsion control system  616  for the cart  600  can comprise memory  802  configured to include computer-executable instructions including at least an operating system (OS)  804  for receiving data and controlling the drive system(s)  606 , sensors  618 , and other components. The OS  804  can also make calculations (e.g., calculate the current distance between the vehicle  100  and the cart  600 ), communicate with other components in the vehicle  100  (e.g., to open the hatch  752 ), the torquing devices  610 , and other components. The memory  802  can also include a localization module  806 , a drive unit data  808 , a torque data  810 , and a vehicle support data  812 . 
     The localization module  806  can receive sensor data from the sensors  618  on the cart  600  to calculate precise trajectories at a given frequency to maneuver the cart  600  safely through an environment (e.g., a maintenance facility or assembly plant), as described herein. Such a trajectory may correspond to a series of poses (i.e. position and orientation), linear and angular velocities, as well as linear and angular accelerations for the cart  600 . In turn, such trajectories may be translated to control steering angles and torque and/or braking applied by the drive system(s)  606  on the cart  600 . 
     The localization module  806  can receive current sensor data from the sensors  618 . As mentioned above, this can include, for example, a variety of data from imagers (e.g. RGB cameras, RGB-D cameras, greyscale cameras, etc.), LIDAR, RADAR, GPS, and other sensors to localize the cart  600  (i.e. provide a position and/or orientation) relative to a map and relative to the vehicle  100 . This can also include inputs from, for example, wheel encoders, gyroscopes, magnetometers, accelerometers and/or IMUs to provide linear acceleration and angular velocities. Deviations from an expected trajectory may then be measured from a measured position and/or orientation when localizing to position the cart  600  near to, and then under, the vehicle  100  being serviced. 
     In some examples, the cart  600  and/or the vehicle  100  can be positioned using one or more fiducials on the floor or walls of the service facility. In this configuration, the vehicle  100  can moved into the service facility and position itself relative to the fiducials (e.g., with a particular fiducial directly underneath a predetermined sensor on the vehicle  100 ). The cart  600  can then use the same fiducial(s) to precisely locate itself underneath the vehicle  100  in a similar manner. This positioning may also be supplemented with additional sensors (e.g., high-resolution video cameras) to confirm the positioning of the cart  600 . 
     The memory  802  can also include the drive unit data  808 . The drive unit data  808  can include location and tightening data for the various drive units  104 ,  106  being serviced. The drive unit data  808  can comprise, for example, the location of the drive interface(s)  310 , including, for example, their location relative to the body  102  or drive units  104 ,  106 , the height from ground, and other relevant information. The drive unit data  808  can also include the type of drives used on the drive interface(s)  310  such as, for example, internal or external drive interfaces, size, type (e.g., hex or Torx®), etc. In facilities that service multiple types of vehicles  100  or drive units  104 ,  106 , the drive unit data  808  can also include this data about each type of drive unit  104 ,  106 , vehicle  100 , version, build number, and other variations. 
     The memory  802  can also include the torque data  810 . The torque data  810  can include data about torque specifications and procedures to control the torquing devices  610 . Thus, the torque data  810  can include torque values for each type or size of fastener  206 , each drive unit  104 ,  106 , each vehicle  100 , etc. Thus, some drive units  104 ,  106  can include multiple fastener sizes, for example, each requiring a separate torque value. Other drive units  104 ,  106  may require a torquing sequence e.g., torque to 15 ft. lbs., then 45 ft. lbs., and then 75 ft. lbs. Similarly, some drive units  104 ,  106  may have torque-to-yield (TTY) fasteners  206  e.g., torque to 45 ft. lbs. and then turn an addition 90 degrees or other torquing procedures. In addition, many fasteners  206  can only be torqued once (e.g., TTY fasteners), while others can be only torqued a finite number of times, before they must be replaced. Thus, the torquing procedures, torque values, number of times the fastener has been torqued, and related data can be stored and updated in the torque data  810 . 
     The memory  802  can also comprise a vehicle support data  812  to control the foot  614  and/or latches  622  on the vehicle stand  604 . Depending on the type of latches  622  used, for example, the vehicle support data  812  can comprise a driver for a linear actuator, electromagnet, servo motor, or other suitable actuator. The vehicle support data  812  can also include data regarding the weight of the body  102 , for example, and the location of various significant points on the body  102  for one or more vehicles  100 . The vehicle support data  812  can include, for example, the location of various pickup points on the vehicle  100  to enable the cart  600  to align itself and the docking pins  608 , among other things. The vehicle support data  812  can also include the location of jacking points on the body  102  to enable the vehicle stand  604  to be properly located under the body  102 . This can reduce damage to the body  102  (e.g., the floor pans or pinch welds) caused by improper placement of the vehicle stand  604 . 
     Of course, in some examples, rather than being stored in the propulsion control system  616 , the localization module  806 , drive unit data  808 , torque data  810 , vehicle support data  812 , and other functions, or portions thereof, can be located on another component, such as the central control or another remote server, for example, and accessed by the propulsion control system  616  via a communication network. 
     The propulsion control system  616  can also include one or more processors  814 , removable storage  816 , non-removable storage  818 , transceiver(s)  820 , output device(s)  822 , and input device(s)  824 . In some implementations, the processor(s)  814  can comprise a central processing unit (CPU), a graphics processing unit (GPU), or both a CPU and a GPU, or any other sort of processing unit, including, but not limited to ASICs, FPGAs, microcontrollers and the like. The processor(s)  814  can be responsible for running software on the propulsion control system  616 , including the OS  804  and other modules, and to interpret and send messages to the central control, if applicable. In some examples, the processor(s)  814  can also perform calculations and provide instructions based on the current localization data, torque data, etc. 
     The propulsion control system  616  can also include additional data storage devices (removable and/or non-removable) such as, for example, memory chips, magnetic disks, optical disks, or tape. Such additional storage is illustrated in  FIG. 8  by removable storage  816  and non-removable storage  818 . The removable storage  816  and non-removable storage  818  can store the various modules, programs, and algorithms for the OS  804  and other modules. 
     Non-transitory computer-readable media may include volatile and nonvolatile, removable and non-removable tangible, physical media implemented in technology for storage of information, such as computer readable instructions, data structures, program modules, or other data. The memory  802 , removable storage  816 , and non-removable storage  818  are all examples of non-transitory computer-readable media. Non-transitory computer-readable media include, but are not limited to, RAM, ROM, electronically erasable programmable ROM (EEPROM), flash memory or other memory technology, compact disc ROM (CD-ROM), digital versatile discs (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other tangible, physical medium which can be used to store the desired information and which can be accessed by the propulsion control system  616 . Any such non-transitory computer-readable media may be part of the propulsion control system  616  or may be a separate device (e.g., a jump drive) or a separate data or databank (e.g., at a central server). 
     In some implementations, the transceiver(s)  820  can include any sort of transceivers known in the art. The transceiver(s)  820  can include, for example, wireless modem(s) to facilitate wireless connectivity between the cart  600  and the torquing devices  610 , vehicle  100 , the Internet, and/or an intranet. Further, the transceiver(s)  820  may include a radio transceiver that performs the function of transmitting and receiving radio frequency communications via an antenna (e.g., cellular, Wi-Fi, or Bluetooth®). In some examples, the transceiver(s)  820  can also include wired transceivers to enable the cart  600  to establish communications between the cart  600  and the vehicle  100  via one or more docking pins  608 , for example, as mentioned above. 
     In some implementations, the output device(s)  822  can include any sort of output devices known in the art, such as the displays (e.g., a liquid crystal display (LCD), light emitting diode (LED) display, or thin film transistor (TFT) screen), a touchscreen display, lights, speakers, a vibrating mechanism, or a tactile feedback mechanism to provide interactive feedback to an operator, a repair technician, etc. In some examples, the output device(s)  822  can play various sounds related to whether the cart  600  is “docked” with the vehicle  100 , the distance between the cart  600  and the vehicle  100 , during loosening or tightening sequences, etc. When removing a drive unit  104 ,  106  from a vehicle  100 , for example, the cart  600  may “beep” when reversing, similar to commercial and construction vehicles. Output device(s)  822  can also include ports for one or more peripheral devices, such as headphones, peripheral speakers, or a peripheral display to provide feedback to operators, service technicians, or assembly line workers, for example. 
     In various implementations, input device(s)  824  can include any sort of input devices known in the art. For example, input device(s)  824  may include a microphone, a keyboard/keypad/touchpad, a touch-sensitive display, a proximity sensor, gyroscope, accelerometer, altimeter, and other sensors. A keyboard/keypad may be a standard push button alphanumeric, multi-key keyboard (such as a conventional QWERTY keyboard), a touchscreen keyboard, or one or more other types of keys or buttons, and may also include a joystick, wheel, and/or designated navigation buttons, or the like. In some examples, the input device(s)  824  can also include communication ports to receive data from service technicians (e.g., for updates), external sensors, or cameras, among other things. 
     The subject matter described above is provided by way of illustration only and should not be construed as limiting. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure. Various modifications and changes may be made to the subject matter described herein without following the examples and applications illustrated and described, and without departing from the spirit and scope of the present invention, which is set forth in the following claims. 
     Example Clauses 
     A. A robotic cart comprising a drive system to move the robotic cart throughout an area, one or more transceivers to send and receive one or more wired and wireless transmissions, memory storing at least a localization module and torque data, one or more inputs to receive data from a user, and one or more processors in communication with at least the one or more transceivers, the memory, and the one or more inputs, the memory including computer executable instructions to cause the one or more processors to receive sensor data from one or more sensors disposed about a robotic cart, determine, using the sensor data, a pose of the robotic cart relative to a vehicle, plan a trajectory of the robotic cart based, at least in part, on the pose, the trajectory causing the robotic cart to align with one or more couplers of the vehicle, cause a drive unit of a robotic cart to move the robotic cart along the trajectory, send a first signal to torquing device on the robotic cart, the first signal causing a torquing device to rotate a drive interface in a first direction to remove a fastener from the vehicle, the fastener detachably coupling a subassembly to the vehicle, and move, using the drive unit, the robotic cart in a second direction away from the vehicle to remove the subassembly from the vehicle. 
     B. The robotic cart of paragraph A, wherein the sensor data comprises sensor data received from an environment proximate the vehicle and the robotic cart, the environment comprising one or more fiducials, and wherein the one or more fiducials comprise one or more artificial reality tags, bar codes, QR codes, or retroreflectors. 
     C. The robotic cart of paragraph A or B, further comprising a vehicle stand detachably coupled to the robotic cart, the computer executable instructions further causing the one or more processors to send a second signal to a latch detachably coupling the vehicle stand to the robotic cart, the second signal causing the latch to decouple the vehicle stand from the robotic cart, and send a third signal to cause a torquing device on the robotic cart to engage with a drive interface of a fastening system on a subassembly of the vehicle, wherein the vehicle stand of the robotic cart remains in place under a body of the vehicle to support the body with the subassembly removed. 
     D. The robotic cart of paragraph A, B, or C, the computer executable instructions further causing the one or more processors to send a fourth signal from the one or more processors to the vehicle stand to cause a portion of the vehicle stand to lower to a ground surface to support the body of the vehicle when the subassembly is removed. 
     E. The robotic cart of paragraph A, B, C, or D, the computer executable instructions further causing the one or more processors to send a second signal to the vehicle, the second signal causing the vehicle to alter a portion of a suspension of the vehicle to raise or lower the vehicle. 
     F. The robotic cart of paragraph A, B, C, D, or E, wherein rotating the drive interface with the torquing device comprises rotating a first driveshaft with a first torque device to remove a first fastener from a body of the vehicle, and rotating a second driveshaft a second torque device to remove a second fastener from the body of the vehicle. 
     G. A method comprising determining a first pose of a robotic cart based, at least in part, on sensor data received from one or more sensors disposed about the robotic cart, moving, using a drive unit, the robotic cart into a second pose relative to a vehicle, the second pose aligning a portion of a main body of the robotic cart with a vehicle stand disposed underneath a body of the vehicle, sending, using a transceiver of the robotic cart, a first signal to cause one or more latches to connect the vehicle stand to the robotic cart, sending, using the transceiver, a second signal to cause a torquing device on the robotic cart to rotate a drive interface of a fastening system of a subassembly of the vehicle in a first direction to tighten a fastener to detachably couple the subassembly to the vehicle, and moving, using the drive unit, the robotic cart in a second direction away from the vehicle. 
     H. The method of paragraph G, further comprising sending a third signal to cause a foot inside the vehicle stand to retract to lower the vehicle. 
     I. The method of paragraph G or H, wherein the sensor data comprises sensor data received from an environment proximate the vehicle and the robotic cart, the environment comprising one or more fiducials, and wherein the one or more fiducials comprise one or more artificial reality tags, bar codes, QR codes, or retroreflectors. 
     J. The method of paragraph G, H, or I, wherein rotating the drive interface with the torquing device comprises rotating an external driveshaft of the fastening system with a first torque device to tighten a first fastener to detachably couple the subassembly to the vehicle, and rotating an internal driveshaft of the fastening system with a second torque device to tighten a second fastener to detachably couple the subassembly to the vehicle. 
     K. The method of paragraph G, H, I, or J, wherein the first torque device tightens the first fastener, the second torque device tightens the second fastener, and the first torque is different than the second torque. 
     L. The method of paragraph G, H, I, J, or K, wherein the robotic cart moves at a first speed when the robotic cart is outside a first distance from the vehicle, and wherein the robotic cart moves at a second speed when the robotic cart is inside the first distance from the vehicle. 
     M. A robotic cart comprising an area for supporting a subassembly when the subassembly is removed from a vehicle, a drive system for moving the robotic cart throughout an environment, and a plurality of sensors to determine a pose of the robotic cart, and a torquing device, sized and shaped to engage with a fastening system of the subassembly of the vehicle, the torquing device rotating a driveshaft of the fastening system about a vertical axis, wherein rotating the driveshaft of the fastening system about the vertical axis causes a fastener of the subassembly to rotate about a horizontal axis, and wherein the fastener detachably couples the subassembly to the vehicle. 
     N. The robotic cart of paragraph M, wherein the torquing device includes a first torque device comprising a first drive interface configured to couple with a first driveshaft of the fastening system, and a second torque device, concentric to the first torque device, comprising a second drive interface configured to couple with a second driveshaft of the fastening system. 
     O. The robotic cart of paragraph M or N, wherein the first drive interface comprises a first external drive interface configured to interface with a first driveshaft of the fastening system, and wherein the second drive interface comprises a first internal drive interface or a second external drive interface to interface with a second driveshaft of the fastening system. 
     P. The robotic cart of paragraph M, N, or O, further comprising one or more couplers to couple with one or more pickup points of the subassembly. 
     Q. The robotic cart of paragraph M, N, O, or P, further comprising an upper stanchion comprising one or more couplers to couple with one or more additional pickup points of the subassembly. 
     R. The robotic cart of paragraph M, N, O, P, or Q, the upper stanchion comprising one or more actuators to move the upper stanchion between a lowered position and a raised position to support the subassembly. 
     S. The robotic cart of paragraph M, N, O, P, Q, or R, further comprising a vehicle stand, detachably coupled to the robotic cart, the vehicle stand including: one or more latches to releasable couple the vehicle stand to the robotic cart, one or more couplers to couple with one or more pickup points of the vehicle, and a foot to engage a body of the vehicle. 
     T. The robotic cart of paragraph M, N, O, P, Q, R, or S, the foot further comprising a jack to lift the body of the vehicle.