PolyBot G2 in a spider configuration with 24 modules.

The second generation of PolyBot is actually just a stepping stone to get to the third generation of PolyBot. The largest functional difference is that G2 modules have the ability to automatically attach and detach from each other, making the system self-reconfigurable. In addition to the ability to reconfigure, these modules are much stronger and carry much more computational power.

PolyBot G2 Module Design

The primary reason this module is considered a step on the way to G3 is the target form factor is a 5 centimeter cube and this module is roughly 11 x 7 x 6 cm. The black cylinder that protrudes outside of the roughly cube shaped module is a brushless DC motor. The 134:1 four stage planetary gear system sits inside the module and takes up to two thirds of the weight. The MicroMo gear motor, although heavy is quite powerful delivering up to 5.6Nm of torque at 60 RPM and the stainless steel sheet structure has a range of motion of +90 to -90 degrees. The combination of sheet steel structure with the strength of the motors poses a slight danger if a finger gets caught near one of the joint limits.

The two connection plates on either side of the module are identical, hermaphroditic and have a 4 way rotational symmetry. Any two connection plates may be attached together at 90 degree increments. Four grooved pins enter four holes and are grabbed by a latching mechanism that is released by a shape memory allow actuator. Each face has a 4 times redundant custom made hermaphroditic electric connectors to enable power and communications to be passed from module to module.

Each module contains a Motorola PowerPC 555 embedded processor with 1 megabyte of external RAM. This is a relatively powerful processor to have on every module and its full processing power has not yet been utilized. The final goal of full autonomy may require the use of these processors and memory, Each module communicates over a semi-global bus using the (controller area network) CANbus standard. Two CANbuses on each module allows the chaining of multiple module groups to communicate without running into bus address space limitations

In G2, the sensing is limited to hall-effect sensors built into the brushless DC motors serving both for commutation as well as joint position with a resolution of 0.45 degrees.

Each module communicates over a semi-global bus using the (controller area network) CANbus standard. Two CANbuses on each module allows the chaining of multiple module groups to communicate without running into bus address space limitations.

G2 Demonstrations

• Snake configuration
• Loop configuration
• Spider configuration
• Self reconfiguration
• Fully automatic docking
• Detachable video camera
• Obstacle course