Saturday, May 26, 2007

A Chain Reconfiguration Robot

PolyBot G2 spider
PolyBot G2 with 24 modules in a four-legged spider configuration.

PolyBot is made up of many repeated modules. Each module is virtually a robot in and of itself having a computer, a motor, sensors and the ability to attach to other modules. In some cases, power is supplied off board and passed from module to module. These modules attach together to form chains, which can be used like an arm or a leg or a finger depending on the task at hand.

This is the most versatile form of modular reconfigurable robot that we have shown so far. We have demonstrated a wide variety of tasks from moving boxes to riding a tricycle.

PolyBot Design

PolyBot has gone through many variations with three basic generations.

Generation I

G1 modules as snake The first generation of PolyBot has the basic ideas shared in all the generations of repeated modules being about 5 cm on a side. The modules are built up from simple hobby RC servos, power and computation are supplied offboard. The modules are manually screwed together, so they do not self-reconfigure. The G1 modules showed the first instance of simple reconfiguration for locomotion in 1997. This design has been made available to other researchers, most notably the NASA snakebot (so far).

Generation I version 4 (g1v4)

G1v4 module This module was made to be a testbed for adding sensors and for testing the functionality of various configurations. Although it is not self-reconfigurable, it is very easy to manually reconfigure with a simple push and a twist. These modules do have a simple 8-bit processor and batteries on board.

Generation I version 5 (G1v5)

G1v5 module This version was built after the second and third generations and took the learning from building the G2 and G3 versions further. It is more reliable than the G2 and G3 versions, and more robust and scalable than any of the other G1 versions. This comes primarily from using more robust servos with more reliable output stages and using a higher voltage power bus. The increased robustness was demonstrated at an IROS03 tutorial putting the modules in the clumsy hands of robotics researchers.

Generation II

G2 moduleThis generation of PolyBot includes onboard computing (Power PC 555) as well as the ability to reconfigure automatically via shape memory alloy actuated latches. Docking of the chains is aided by infrared emitters and detectors. The black cylinder sticking out of the module is the motor. The motor with gearbox is about 5 times stronger than the G1 modules.

Generation III

G3 module

The first prototypes of the Generation III (G3) have been constructed as of December 2001. A short run of 200 modules is in progress. The modules are very similar to G2 using the same processor but has the following exceptions

Fit inside 5x5x5 cm box
Approximately 1/2 weight and volume of G2
Lower power than G2
Integrated active brake
More sensors G2

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