Abstract:
A modular robot for use as an educational robot system having multiple degrees of freedom and mounting features that allow multiple modules to be assembled with accessories to form a multitude of configurations. Each module is independently mobile and useful when alone or assembled with other modules. An encoder gear and encoder gear track is used to sense multiple degrees of freedom with parallel and perpendicular axis of rotation using a single printed circuit board.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to a reconfigurable modular robot platform. More specifically, the present invention relates to robotic modules which may be reconfigured in multiples in an educational robotic system. 
       CROSS REFERENCE TO RELATED APPLICATIONS 
       [0002]    This application is the U.S. National Stage of International Application No. PCT/US2014/020040, filed on Mar. 3, 2014, which claims the benefit of earlier filed U.S. Provisional Application Ser. No. 61/771,947, entitled MODULAR ROBOT SYSTEM, filed on Mar. 4, 2013, the entire contents of which are incorporated herein by reference for all purposes. 
       BACKGROUND OF THE INVENTION 
       [0003]    A drawback that inhibits wide adoption of robotics in the classroom is the lack of hardware adaptable to a wide range of curriculum, which is still physically manageable in a typical classroom setting. 
         [0004]    Construction kits that disassemble into hundreds of small components are not practical for teaching a classroom of students, relegating robotics to small, after-school groups. Although educational toys are becoming more popular, they offer limited programmability and are bounded by their lack of hardware customizability. 
         [0005]    Also, a drawback to current encoding methods and apparatus used in robot and automation applications is the necessity of multiple, dedicated, printed circuit boards to encode each motor in the robot. 
         [0006]    Provision of encoding for motors is inhibited primarily by cost: Such equipment is expensive, typically needing significant physical space in the system and customized printed circuit boards for each motor in the robot. 
         [0007]    U.S. Pat. No. 6,605,914 to Yim et al., titled “ROBOTIC TOY MODULAR SYSTEM” shows a modular robot which assembles together with other modules. Modules sense the attachment location of other modules, defining the configuration of the assembly of robots. Several accessories are also described. This robot is made up of a single degree of freedom driven by a servo motor. Servo&#39;s typically do not rotate continuously, and those which have been modified to rotate continuously lose the angular sensing capabilities. A single module of this design is not independently mobile, meaning multiple modules must be assembled together in order for the robot to be mobile or achieve basic functionality. 
         [0008]    U.S. Pat. No. 7,013,750 to Kazami et al., titled “UNIT SET FOR ROBOT” shows a unit for constructing a robot with a specific surface profile for the housing having fixed and rotating joints with several accessories described. This modular robot design has two degrees of freedom with axis of rotation which are perpendicular and intersect. There is a limitation to the configurations possible with only this configuration. A single module of this design is not independently mobile, meaning multiple modules must be assembled together in order for the robot to be mobile or achieve basic functionality. Although there are some features on the body for improving stability when attached to another module it&#39;s not possible to attach accessories to the body itself, limiting functionality. 
         [0009]    U.S. Pat. No. 8,175,747 to Lee et al., titled “JOINABLE ROBOT COMPONENT FOR ROBOT TOY, MODIFIABLE ROBOT TOY USING THE JOINABLE ROBOT COMPONENTS, AND CONTROL METHOD THEREOF” shows a toy which can be assembled with accessories to form various configurations. A single module of this design is not independently mobile, meaning multiple modules must be assembled together in order for the robot to be mobile or achieve basic functionality. 
         [0010]    U.S. Pat. No. 6,084,373 to Goldenberg et al., titled “RECONFIGURABLE MODULAR JOINT AND ROBOTS PRODUCED THEREFROM”, discloses a reconfigurable modular drive joint which can be set up in a roll, pitch, or yaw configuration. A single module of this design is not independently mobile, meaning multiple modules must be assembled together in order for the robot to be mobile or achieve basic functionality. 
         [0011]    U.S. Pat. No. 7,747,352 to Raffle et al., titled “PHYSICAL MODELING SYSTEM FOR CONSTRUCTING AND CONTROLLING ARTICULATED FORMS WITH MOTORIZED JOINTS”, discloses a single degree of freedom modular robot and accessories that allow it to be assembled into various configurations. A single module of this design is not independently mobile, meaning multiple modules must be assembled together in order for the robot to be mobile or achieve basic functionality. 
         [0012]    U.S. Pat. No. 6,323,615 to Khairallah et al., titled “MODULAR ARTICULATED ROBOT STRUCTURE”, discloses a modular articulated robot structure. Each module has a single degree of freedom with limited rotation, not allowing for continuous rotation of each joint when modules are assembled. Having module with a single degree of freedom which cannot rotate continuously limits the robot to arm applications and overall mobility to crawling/walking locomotion. In order for the robot to drive as though with wheels for any significant distance it would need a continually rotating degree of freedom. A single module of this design is not independently mobile, meaning multiple modules must be assembled together in order for the robot to be mobile or achieve basic functionality. 
         [0013]    U.S. Pat. No. 6,686,717 to Khairallah et al., titled “MODULAR ARTICULATED STRUCTURE”, discloses additional details regarding a modular articulated robot structure. A riding disc is described for a configuration of this robot, adding a second degree of freedom in the form of a wheel shaped attachment to the end of a module. This configuration is specifically meant for driving with a wheel, but not specifically for attaching to other modules or accessories, limiting functionality. A single module of this design is not independently mobile, meaning multiple modules must be assembled together in order for the robot to be mobile or achieve basic functionality. 
         [0014]    Publication No. EP2531327 to Ryland et al., titled “FOUR DEGREE OF FREEDOM (4-DOF) SINGLE MODULE ROBOT UNIT OR JOINT”, discloses a modular robot which is made up of a center section, two outer sections and two faceplates where the outer sections rotate 180 degrees in reference to the center section and the faceplates rotate continuously in reference to the outer section. 
       SUMMARY OF THE INVENTION 
       [0015]    The present invention relates generally to a reconfigurable modular robot platform. More specifically, the present invention relates to robotic modules which may be reconfigured in multiples in an educational robotic system. 
         [0016]    Modular robots are made up of individual modules which are typically simple in form and capability. Modules can be assembled, connecting together mechanically to form complex robots, or clusters. They can be reconfigured in radically different ways to best suit the desired application, giving them versatility unmatched by application specific robots. 
         [0017]    Presently, teachers wishing to use robots for Science Technology, Engineering, and Math curriculum do not have a turn-key option which is suitable for the classroom environment. Although the Lego Mindstorms and Vex construction kits are extremely flexible they&#39;re also difficult to manage with multiple kids in a busy classroom environment. These construction kits typically have over 500 parts, which means students require close supervision to stay on task, not mix kits, or loose parts. Also, the time and effort required between pulling a construction kit out of the box to getting having a robot that moves in an engaging way is great. There is a steep learning curve that needs to be overcome before it becomes a fun experience for students. Also, these kits are closed source, meaning it&#39;s not possible to modify parts or create new parts that interface with the kit. 
         [0018]    There are wheeled educational robots which are useful for specific curriculum, but their capabilities are limited by their hardware capabilities. Typically these robots are expensive and only have one or two applications, which equates to low teaching value for the cost per student. 
         [0019]    There is a need to provide an educational robot platform that is highly adaptable to a wide array of curriculum and is manageable in a busy classroom environment. 
         [0020]    Additionally, there is a need to provide an educational construction kit which has large components that are easily manageable and not easily lost or mixed up. 
         [0021]    Further, there is a need for an educational robot which enables social interaction between students by allowing robots to be quickly and easily shared and assembled together to form more complex robots to achieve goals set out in curriculum and competitions. In this way modular robots foster 21st century skills like collaboration, creativity and problem solving. 
         [0022]    Herein, the term “module” refers to a robot having multiple degrees of freedom and is assembleable with accessories and other modules. 
         [0023]    Herein, the term “D-shaped housing” refers to the shape of the exterior body of the module which has a D-shaped side profile. 
         [0024]    Herein, the term “degree of freedom” refers to an independently controlled hub which rotates in both directions in reference to the D-shaped housing. 
         [0025]    Herein, the term “hub” refers to a component which is driven by a gearmotor and rotates in reference to the D-shaped housing having a mounting feature facing exterior of the module. 
         [0026]    Herein, the term “fixed hub” refers to a component which can be substituted in the rotating hub location, but is fixed to the D-shaped housing, having the same mounting feature facing the exterior of the module as a hub. 
         [0027]    Herein, the term “mounting feature” refers to a method of fastening to a surface, releasably or permanently, using screws, snap connectors or any other fastening method. 
         [0028]    Herein, the term “controller” refers to a electronic device located on the robot which can come loaded with a program, or be programmed by an external device such as a computer, tablet or smartphone. The control can be programmed through an electrical connection or wireless communication such as Bluetooth or ZigBee. The controller can receive and execute commands through an electrical connection or wirelessly for remote control. 
         [0029]    Herein, the term “battery” refers to a power source capable of powering the controller and gear motors of the system. 
         [0030]    Herein, the term “gearmotor” refers to an actuator that is connected to a pivot mechanism to supply operational power for rotation. 
         [0031]    Herein, the term “connector plate” refers to a component which is capable of permanently or temporarily fastening to the mounting feature, whether using hooks, snap features, screws, or any other fastening method. 
         [0032]    Herein, the term “bridge plate” refers to a component which connects two modules together in a way other than hub to hub. Bridge plates can have multiple mounting features distributed in multiple configurations and at various angles depending on the desired application. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    The aspects of the present invention will be apparent upon consideration of the following detailed description taken in conjunction with the accompanying drawings, in which like referenced characters refer to like parts throughout, and in which: 
           [0034]      FIG. 1  is a perspective view of one example embodiment of a robotic module having two degrees of freedom with parallel axis of rotation; 
           [0035]      FIG. 2  is a disassembled perspective view of one example embodiment for a robotic module having two degrees of freedom with parallel axis of rotation; 
           [0036]      FIG. 3  is a disassembled perspective view of the drive unit of one example embodiment having two degrees of freedom with parallel axis of rotation; 
           [0037]      FIG. 4  is a disassembled perspective view of the controller unit of one example embodiment having two degrees of freedom with parallel axis of rotation; 
           [0038]      FIG. 5  is a disassembled perspective view of the hub of one example embodiment having two degrees of freedom with parallel axis of rotation; 
           [0039]      FIG. 6  is a disassembled perspective view of the hub of one example embodiment having two degrees of freedom with parallel axis of rotation; 
           [0040]      FIG. 7  is a cross sectional view of the hub of one example embodiment having two degrees of freedom with parallel axis of rotation; 
           [0041]      FIG. 8  is a perspective view of one embodiment of a robotic module having two degrees of freedom with perpendicular axis of rotation; 
           [0042]      FIG. 9  is a top view of one embodiment of the robotic module having two degrees of freedom with perpendicular axis of rotation; 
           [0043]      FIG. 10  is a disassembled perspective view of one example embodiment for a robotic module having two degrees of freedom with perpendicular axis of rotation; 
           [0044]      FIG. 11  is a disassembled perspective view of the drive unit of one example embodiment having two degrees of freedom with perpendicular axis of rotation; 
           [0045]      FIG. 12  is a disassembled perspective view of the controller unit of one example embodiment having two degrees of freedom with perpendicular axis of rotation; 
           [0046]      FIG. 13  is a disassembled perspective view of one example embodiment of the hub; 
           [0047]      FIG. 14  is a disassembled perspective view of one example embodiment of the hub; 
           [0048]      FIG. 15  is a disassembled perspective view of one example embodiment of the fixed hub; 
           [0049]      FIG. 16  is a disassembled perspective view of one example embodiment of the fixed hub; 
           [0050]      FIG. 17  is a perspective view of one embodiment of invention robotic module having three degrees of freedom; 
           [0051]      FIG. 18  is a disassembled perspective view of one example embodiment for a robotic module having three degrees of freedom; 
           [0052]      FIG. 19  is a disassembled perspective view of the drive unit of one example embodiment having three degrees of freedom; 
           [0053]      FIG. 20  is a disassembled perspective view of the control circuit of one example embodiment having three degrees of freedom; 
           [0054]      FIG. 21  is a disassembled perspective view of a robotic module having two degrees of freedom with parallel axis of rotation attached to wheels using connector plates; 
           [0055]      FIG. 22  is a perspective view of a robotic module having two degrees of freedom with parallel axis of rotation attached to wheels using connector plates; 
           [0056]      FIG. 23  is a disassembled perspective view of several robotic modules of one example embodiment having two degrees of freedom with parallel axis of rotation attached to each other and wheels using connector plates and a bridge plate; 
           [0057]      FIG. 24  is a side view of several robotic modules of one example embodiment having two degrees of freedom with parallel axis of rotation attached to each other and wheels using connector plates and a bridge plate; 
           [0058]      FIG. 25  is a disassembled perspective view of several robotic modules of one example embodiment having two collinear degrees of freedom attached to each other and bridge plates using connector plates; 
           [0059]      FIG. 26  is a perspective view of several robotic modules of one example embodiment having two degrees of freedom with parallel axis of rotation attached to connector plates and bridge plates to form a dog configuration; 
           [0060]      FIG. 27  is a disassembled perspective view of one example embodiment having two degrees of freedom with perpendicular axis of rotation where the hubs with encoder gear tracks, encoder gears, motors, printed circuit board and encoders which have been isolated from the rest of the module to show an encoding method. 
       
    
    
       [0061]    While the invention will be described and disclosed in connection with certain preferred embodiments and procedures, it is not intended to limit the invention to those specific embodiments. Rather it is intended to cover all such alternative embodiments and modifications as fall within the spirit and scope of the invention. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0062]      FIG. 1  shows one embodiment of the robotic module  100  of the present invention. A housing consisting of 102 and 104, which may be comprised of any numerous known plastic materials. The materials used in the housing and other parts may be made from injection molded plastic or other materials such as sheet-cut or molded plastic, metal, paperboard, or wood. There is a mounting feature formed into the front face of the housing shown in this embodiment as being made up of four threaded holes  106 , four slots  108 , and four indentations  110 . The four threaded holes  106  are designed to receive a #6-32 screw for releasably fixing accessories. The slots  108  and indentations  110  are designed to mate with a connector plate  1302 , described later. This connector plate allows modules to quickly snap together while taking up very little space between modules. This mounting feature is also present on the hub  400 . 
         [0063]      FIG. 2  shows a disassembled perspective view of a two degree of freedom module with parallel axis of rotation showing a drive unit  200  a controller unit  300  and two hubs  400 . The controller unit has two encoders  302  with an encoder gear  304  that mates with the encoder track  418  on the back of the hub  400 . The encoder gear floats between the printed circuit board  306  and the top surface of the motor  202  shown as surface  118  and  120 . This offers support for the encoder gear ensuring that it stays aligned and correctly engaged with the encoder gear track  418 . The hubs  400  are shown assembled, however, in order for them to interface with the housings they need to be assembled around the housing so the housing wall  114  runs along the track formed by the front of the hub  402  and the back  408 , described in more detail in  FIG. 5 . The hubs are made of a dissimilar material from the housings in order to aid in smooth rotation. For this embodiment the housings are made from ABS and the hub front and back from Delrin, which provides a low friction interface. Motor  202  is a brushed DC motor with plastic gearing and offset output available from Pololu.com, item number  1118 . 
         [0064]      FIG. 3  shows a disassembled perspective view of a two degree of freedom module showing a drive unit  200 . Two motors  202  attach to the motor carrier  204 . The non-rotating ledge of the motor  216  engages with the hoop  208  and snaps into place with features  210 . A battery  206  attaches to the underside of the motor carrier  204  using double sided tape. 
         [0065]      FIG. 4  depicts one exemplary embodiment of controller unit  300  with printed circuit board  306 , two encoders  302  and encoder gears  304 . The encoder gear  304  has a shaft  312  which mates with the encoder gear hole  318 . The rounded feature  314  of the encoder gear fits inside  308  helping to center it. The encoder gear teeth  316  match up with the encoder gear track  418  shown in  FIG. 6 . The hole  310  is not populated with an encoder or encoder gear because this printed circuit board is currently configured for a module with two hubs with parallel axis of rotation. This printed circuit board can be used for a module with hubs collinear or perpendicular, shown in later figures. Also, in one exemplary embodiment, a single controller unit  300 , or even one printed circuit board, can be used to encode and drive multiple degrees of freedom. 
         [0066]      FIG. 5  shows a hub having a front half  402  which faces toward the outside of the module and a back half  408  facing toward the inside of the module.  402  has a mounting feature consisting of four threaded holes  106 , four slots  108  and four indents  110 . Four square nuts  404  provide a metal thread for the four screw holes  106 . The nuts are sandwiched between  402  and  408 . The four screws  406  pass through four holes  416  in  408  and mount to the back of  402  to hold the assembly together. 
         [0067]      FIG. 6  is the same assembly as  FIG. 5 , but from another angle, exposing the rear features of  402  and  406 . The step  424  creates the groove which the D-shaped housing features  114  run along, acting like a bearing for axial, rotary and torsional forces. Feature  430  in the back of  402  receives the square nut  404 . The encoder track  418  is concentric to the hub and mates with encoder gear  304 . There are an equal number of female slots on the track  418  as there are male teeth on the encoder gear  304 . The center of the hub has a feature  426  which mates with the hub of the gearmotor drive shaft  206 . This feature  426  protrudes through the hole  420  in the back half  406 . Finally, four screws  408  mount in feature  422 . 
         [0068]      FIG. 7  shows a cutaway view of the hub  400  where the slot formed by the front  402  and back  406  half of the hub forms a slot which engages with hole features  114  in the D-shaped housing. This view also shows clearly that the shaft mating feature  426  extends past the encoder track. Also, the nut  404  is sandwiched between the two halves. 
         [0069]      FIG. 8  shows an embodiment of the module where the hub axes are perpendicular and introduces the concept of a fixed hub. This configuration has a hole in the housing which has a connector  502 . This connector offers an I2C buss to power and control accessories such as range finders, tactile switches, or whatever the user desired. The plug is shown here as a standard phone jack. There are also holes in the housing for three buttons  504  for user interface. There&#39;s also a sticker  508  on the housing with graphics  510  showing the use of each button. The module is recharged and can be programmed or controlled using a USB plug  506  and there is a hole in the housing to allow access. The sides of the housing are numbered  512  to identify the hub locations to make it easier to identify orientation for programming. There is a marker  514  on the housing which shows the vertical position for the hub vertical indicator  818 . These two features are used to help align the hub when calibrating the zero location of the robot. A rounded ridge  518  runs along the outer rim of the housing and protrudes out to help protect the body surface finish, buttons and plugs from wear and tear of standard operation. The fixed hub  900  curves inward, shown by dotted lines  902 , and mates flush with the housing. Fixed hub  900  is meant to blend in to the housing whereas hub  800  stands out by protruding from the housing and being a dissimilar color, texture and material to help it stand out as a moving element. 
         [0070]      FIG. 9  is a top down view of  500  which shows the symmetry of hub  522  and fixed hub  524 . Even though the fixed hub does not rotate it has the same mounting features and surface location of that of a hub to help symmetry when assembling. In this embodiment X and Y are equal, which also improves symmetry when assembling. However, it is not required to have symmetry to successfully assemble with other modules or accessories. The housing is translucent and a multicolor LED  724  lights up the internal surface of the housing causing the module to glow, emanating approximately from the location of  520 . 
         [0071]      FIG. 10  is a disassembled view of  500  showing a drive unit  600 , controller unit  700 , hub  800 , fixed hub  900  and housing components. The housing for this embodiment is made up of five components which snap together. The top  528  and bottom snap into the sides  532  and  536  using the snap features  542  and  544 . Sides  532  and  536  are mirror images of each other. The front housing  534  has a lip  554  extending out along its edges which fits in the groove  552  of the side housing components as well as a groove in the top and bottom housing components. The features  720  of the controller unit  700  fits into the mounting feature  546  in the side housing components, and feature  722  fits in slot  558  of the top housing  528 . The feature  620  of the drive unit  600  fit into the mounting feature  550  of the side housing components, and feature  622  fits in slot  538  of the bottom housing  530 . The feature  548  shows one of three features where the fixed hub tabs  910  mount to the side housing  532 . 
         [0072]      FIG. 11  shows a disassembled view of the drive unit  600  where two motors  202  are mated with the carrier  604 . This drive unit design accommodates both the parallel and perpendicular axis of rotation configuration of the module. The gearmotor  202  body feature  626  mates with motor carrier feature  616 , while the rest of the gearmotor interfaces with feature  614 . A snap feature  608  secure the motor. The battery  206  is affixed to the bottom of the carrier with double sided tape or epoxy. Feature  620  mates with feature  550  of the housing  536  and  622  mates with feature  538  and  540  of the module housing  530  to mount the carrier. The vertical tab  624  pushes against the bottom of the controller unit  700  to support it when the user pushes a plug into 502. 
         [0073]      FIG. 12  shows a disassembled view of the controller unit  700 , which is split into two boards,  702  and  704 . The encoders  302  and encoder gears  304  are in the perpendicular axis of rotation configuration. The standard phone jack connector  710  is used for I2C communication with accessories and protrudes through the housing. Two sockets  712  mate with pins  714  making an electrical connection between boards and offering some mechanical stability. There are three buttons  716  on the vertical board as well as a USB plug  718 . A multicolor LED is located on the main board  724 . The main board  702  has features  722  and  720  which mate with the housing of the robot. 
         [0074]      FIG. 13  shows a disassembled view of the hub made up of a front half  802  which faces outward and a back half  804  which faces inward to the module and are assembled with four screws  806 . The square nuts of the previous embodiment are replaced with acorn nuts  808  because they have a blind threaded hole. If a screw was inserted into the square nut and torqued down hard it could damage the internal structure of the hub or module. An acorn nut provides a blind threaded hole. There is a finger  810  which extends from the back half of the hub  804  which and touches the top of the nut to stop it from rattling, while still offering clearance needed for manufacturing tolerance stack-up. Four tabs  812  mate with feature  822  of  FIG. 14  to help center the two halves of the hub and keep them from rotating apart from each other. In a similar way, feature  814  helps keep the two halves of the hub concentric when they mate with the outer half  802 . There is a marking  816  in the center of the hub that defines the positive direction of rotation to the user. The direction is right-hand-rule and the same for all hubs. A marker  818  shows the zero location of the hub. There are also marks  832  in 45 degree increments. 
         [0075]      FIG. 14  is the same embodiment as  FIG. 13 , but from another angle showing the underside of  802  and  804 . You can see where the tab  812  mates with the hub at  822  and the rounded feature  814  with the internal edge  830 . The encoder gear track  826  is concentric with the hub. Also, the mounting location  828  for the acorn nut  808  is hexagonal in the hub front. Finally, there is a hole  820  where the hub front  802  protrudes through hub back  804 . 
         [0076]      FIG. 15  shows a disassembled view of the fixed hub which is made up of a front half  902  and back half  904 . The back half has three tabs  910  which extend out from the circular profile to mate with the housing features  548 . The profile of  902  curves down, shown in dotted lines  914 , from the mounting feature plane to a narrow edge which mates with the housing having a minimal seam. Four screws  806  mount the two halves together sandwiching four nuts  808  inside. 
         [0077]      FIG. 16  is the same embodiment as  FIG. 15 , but from a different angle that shows that there is no mounting feature for the motor drive shaft  206 . Also, there is no encoder gear track on  904 . 
         [0078]      FIG. 17  shows an embodiment of a three degree of freedom module having three hubs  400 . The D-shaped housing is made up of two halves,  1002 . There are also mounting features formed into the housing, two threaded holes  1006 , two slots  1008  and one indent  1010 . The third hub  400  is not visible on the far side of the module. 
         [0079]      FIG. 18  shows a disassembled view of the three degree of freedom module. Again, the hubs  400  are shown assembled, but they would instead sandwich the hole features in  1002  for operation. For the front hub  400  there is a partial hole  1012  in each of the housing halves for the hub to mount. A drive unit  1100  and controller unit  1200  are also shown. 
         [0080]      FIG. 19  shows a disassembled view of the drive unit  1100  which has three motors  202  fastened to the carrier  1102 . The controller unit  1200  fits behind the front motor and in front of the side motors. The front motor passes through slot  1210  of the board and the mounting hook  1104  of the motor carrier passes through feature  1212  of the board. The side encoder gears  304  are stabilized by the motor housing surface  1106  and  1108 . 
         [0081]      FIG. 20  shows a disassembled view of the printed circuit board  1202  with three encoders  302 . Two encoder gears  304  mount to the side encoders and interface with the encoder gear track of the hub. The encoder shaft reducer  1208  mates the rear shaft of the front motor  202  to the center encoder. In this way, it&#39;s possible to encode multiple degrees of freedom as long as the axis of rotation is perpendicular or parallel. The hole  1210  fits around the front gearmotor  202  and feature  1212  allows clearance for the front motor mounting hook  1104  to pass through. 
         [0082]      FIG. 21  shows a disassembled view of the two degree of freedom module with parallel axis of rotation. The snap connector  1302  releasably fastens two wheels  1308  to the rotating hubs  400 . Both hubs  100  mate with two snap connectors  1302  which have hooks  1306  and depressible detents which interface with the module&#39;s mounting features and with a wheel  1304  mounting feature  1308 . 
         [0083]      FIG. 22  shows a two degree of freedom module  100  with collinear hubs with two snap connectors and two wheels. The hooks of the snap connector mate with the wheels and it can be seen that the hooks protrude through the wheel  1310 . 
         [0084]      FIG. 23  shows a four wheel drive robot made up of two  1300  assemblies. These modules are connected together using two snap connectors  1302  and a bridge plate  1402 . The modules are acting like an axle for a four wheel drive car. The front mounting feature  1404  of the module does not rotate so the two modules are fixed in relationship to each other. If a three degree of freedom module was used instead it would be possible to turn the modules independently, allowing this vehicle configuration to steer. If a perpendicular axis of rotation module  500  was snapped into the front position with a parallel axis of rotation module  100  in the rear the front module  500  would only have one powered wheel, but it could rotate in reference to the bridge plate  1402  like a tricycle and steer. 
         [0085]      FIG. 24  shows a side view of  FIG. 23 , showing the ground clearance of the robot. 
         [0086]      FIG. 25  shows how a bridge plate  1402  can be used to connect modules together in conjunction with snap connectors  1302 . This configuration is similar to an inchworm in the way it can move. Both hubs  400  are in parallel, which means the lifting torque is doubled, giving it more lifting torque. 
         [0087]      FIG. 26  shows a dog shaped robot made out of parallel axis of rotation modules  100  assembled together using snap connectors and bridge plates. The legs of the dog are made up of assembly  1500  shown in  FIG. 25 . Three modules  100 A,  100 B, and  100 C make up the body segment where  100 B allows the back to twist and the hubs of  100 A and  100 C make up the shoulder of the dog and are connected to the fixed hub of the  1500  assemblies. The same configuration can be made using fewer perpendicular axis of rotation modules. In fact, it would require fewer modules to obtain the same movements because there&#39;s so much redundancy of collinear degrees of freedom in  1600 . However, if perpendicular degree of freedom modules were used they would not have as much lifting torque for the same reason. The same configuration could be recreated using a three degree of freedom module, while increasing the complexity of movement and keeping the same high torque configuration of the legs. 
         [0088]      FIG. 27  shows a disassembled view of the motor  202 , hub  400 , encoder gear  304 , printed circuit board  306 , and encoders  302  isolated from the rest of the module to show the interaction between the encoder gears  304  and the encoder gear track  418 . The encoder gears are sandwiched between the gearmotor  202  and printed circuit board  306  and protrude beyond the board to engage with the encoder gear track  418  on the back of the hub  400 . The encoder gear has the same number of teeth as there are female slots in the encoder gear track  418 , which means when the hub rotates it is translates into an equal angular rotation of the encoder gear which drives the encoder. This is how it&#39;s possible to have absolute encoding and continuous rotation of multiple degrees of freedom in different orientations using only one printed circuit board. 
         [0089]      FIG. 28  shows a serious of motions where one module lifts another module. The surface  1802  of module  100  is fixed so it can lift another module  100 ′ using a pridge connector  1402 . The D-shaped housing of the modules allow for the minimum distant between each hub, shown as distance A. The shorter distance A the shorter the lever arm when one module lifts another module, allowing it to lift a greater payload. This also applies to lifting objects on the D-shaped side of the module. 
         [0090]    Various additional modifications of the described embodiments of the invention specifically illustrated and described herein will be apparent to those skilled in the art, particularly in light of the teachings of this invention. It is intended that the invention cover all modifications and embodiments, which fall within the spirit and scope of the invention. Thus, while preferred embodiments of the present invention have been disclosed, it will be appreciated that it is not limited thereto but may be otherwise embodied within the scope of the following claims.