BEAMbot Roamer (aka LEFTY)
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 executes a left turn. He doesn't ever turn right...a limitation of this BEAM circuit. And YES...he does fall off the table every now and again. The video tells the story fairly well.
LEFTY is constructed of all scrap components. The only items that were not salvaged are his Solarbotics wheels. Everything else was pulled from something that was no longer working. His chassis is made from an old modem. His slide is an old furniture foot. His canopy is a clear packaging remnant. His gear motors were pulled from a toy my boy no longer enjoys. The driver circuit is constructed from components pulled from a junk VCR and my components stash. His whiskers came from a pretty beat up Parallax BOEbot. I made his other touch sensors from copper wire. An old relay serves as the reverse mechanism. A fairly rewarding build that came in right at $5 bucks.