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update? - not really, I accidently deleted the youtube link - so I'm fixing it .. This is not a very intelligent, or special robot - it took me long enough, but it was really just for my education etc. This is about 10cm high, it is a clear ball with three servo motors, driven by three 74AC740 ICs. The ICs measure the amount of light coming through an array of sensors on the top, and rotate the balls in a direction and speed proportionally to that. The result is that the ball "drifts" ...
This is a companion discussion topic for the original entry at https://community.robotshop.com/index.php/robots/show/three-wheeling-doover