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134 Biomimetics: Biologically Inspired Technologies

candidate controllers were evaluated by trying them out on the robot in a cage, and measuring
fitness using a camera that tracks the red ball on the foot of one of the legs of the machine (see inset
in Figure 4.2b for a view from the camera). Snapshots from one of the best evolved gates are
shown in Figure 4.2c. Walker et al. (2004) provide a review of controller evolution on both
simulated and physical machines.

Figure 4.2 (See color insert following page 302) Evolving a controller for physical dynamic legged machine.
(a) The nine-legged machine is powered by 12 pneumatic linear actuators arranged in two Stewart platforms. The
controller for this machine is an open-loop pattern generator that determines when to open and close pneumatic
valves. (b) Candidate controllers are evaluated by trying them out on the robot in a cage, and measuring fitness
using a camera that tracks the red foot (see inset). (c) Snapshots from one of the best evolved gates. (From Zykov,
V., Bongard, J., Lipson, H., (2004) Evolving dynamic gaits on a physical robot, Proceedings of Genetic and
Evolutionary Computation Conference, Late Breaking Paper, GECCO’04. With permission.)