This is something I built a while ago. I won't call it a robot as it's very limited in its function - It only knows about FORWARD! It was just an idea which I wanted to build something around. The 'brain' is a latching relay, which once pulsed, retains the state it's just changed to, so it's effectively a 'relay with a memory'.
This was built almost entirely from things I had lying around - I only had to buy the relay. The servo has the electronics bypassed so it's just a motor and a gearbox.
The circuit operation is simple enough. It's essentially an electro-mechanical flip-flop. As the motor arm reaches the endstop one way, it hits the microswitch which energises the relay and reverses the current to the motor, setting it running the other way until the arm hits the endstop . . . . .
And the name? Well, I'm an old prog rock fan at heart.