The design patented by Mark Tilden and a key curcuit in BEAM Robotics. This analog approach to robotics uses timing cycles as the basis of information in the control of analog robots. A surprising degree of ability results from a very low transistor count. This circuit would be most commonly used in a two motor walker.
The 'suspended bicore' at the top sets the overall pace and drives the front motor. The resistors connecting to the lower bicore set a phase delay of approximately 90°, and drive the rear motor. The timing of the signals stabilizes within the first few cycles.
Sensors can be added to adjust the duty cycle of the square wave to allow, for example, phototropism and other behaviors. A simple analog multiplexer can be added between the bicores to give reversing motion.
To see a bot like this in action you can check out this video (I have no association with the creator). https://www.youtube.com/watch?v=2ZwcM6q7AUM
