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Here is LEFTY, a BEAMbot based on Mark Tilden's BEAM sumobot as found in the awesome book: Junkbots, Bugbots and Bots with Wheels. The original design called for a sumobot configuration. I revised it to work as a tabletop roamer. LEFTY uses two whiskers for obstacle touch sensors and a copper probe that detects the edge of a table. When his probe falls off the edge, it completes the circuit and LEFTY executes a left turn. Same deal with his whiskers...when one of them contacts an object, LEFTY ...
This is a companion discussion topic for the original entry at https://community.robotshop.com/index.php/robots/show/beambot-roamer-aka-lefty