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I named the robot "xi" - pronounced "cross-eye" for reasons which may be a bit embarrassing. Having completed my phototropic robot and went to test it I discovered that the robot would run away from the light as the two motors were supposed to be connected on opposite sides of the IC, instead of re-wiring the project I twisted the photodiodes so they cross each other, giving the appearance of crossed eyes. The robot consists of: two photodiodes (pulled from a VCR), a 7404 IC (Hex Inverter), ...
This is a companion discussion topic for the original entry at https://community.robotshop.com/index.php/robots/show/xi-the-cross-eyed-phototropic-robot