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make a multipurpose humanoid robot, this approach chooses from among the multitude of possible bodily designs the best one to do a specific job. ACM R-1, for instance, is ideally shaped to explore un- derground pipes, if not for much else.

While Hiroses robots are not humanoid, they maintain a fixed form. But there is a more radical approach to locomotion and bodily design: robots with no permanent legs or arms, no fixed bodily con- figuration, that dynamically change their shape and means of locomo- tion to meet the needs of the moment. One version of these reconfigurable robots, called PolyBots, is being developed by Mark Yim,Ying Zhang, and David Duff of the Palo Alto Research Center. These researchers contrast the fixed assembly-line world of industrial robots with the shifting demands and terrain of the real world and envision a robot that could

shape itself into a loop and move by rolling like a self-propelled tank tread; then . . . form a serpentine configuration and slither under or over ob- stacles . . . then . . .morphinto a multilegged spider, able to stride over rocks and bumpy terrain.

The key to this flexibility is to construct the robot from individual modules of only one or two types, but numbering in the hundreds and potentially in the millions.

One PolyBot under study, dubbed G2, has modules, each a cube 5 centimeters (2 inches) on a side, that can automatically connect with each other to form long strings. There are two types of modules: motion units, which use a hinge moved by an electric motor to inch along the floor, and node units,which have multiple attachment points so that other modules can branch off in different directions. Each module houses a powerful computer-processing chip with a lot of memory, giving the robot an intelligence that distributes instructions and data throughout its structure, including commands that synchro- nize the motion hinges so that the entire PolyBot moves.

With its many motors, sensors, and computer chips, Polybot re- quires a good deal of electrical power, and battery life is a problem. Also, programming PolyBot becomes a struggle, according to the re- searchers, when many modules (units have been made with up to 100

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