The lowest layer of these robots performs the usual obstacle avoidance behavior. The second layer is much like Allen's; an urge to wander about. The third layer uses the sensors to detect relatively moving objects and causes the robot to be attracted to that object. The first layer regulates how close the robot will get to the target. While the chase behavior is active, the wandering behavior is suppressed.
These robots demonstrated to Brooks and company that the subsumption architecture could be compiled down to the gate level and also that it could run at a clock speed of a few hundred Hertz. This inspired them to automate the compilation process.