Stable and robust autonomous dynamic locomotion is demonstrated experimentally in a four and a six-legged robot. The Scout II quadruped runs on flat ground in a bounding gait, and was motivated by an effort to understand the minimal mechanical design and control complexity for dynamically stable locomotion. The RHex 0 hexapod ms dynamically in a tripod gait over fiat and badly broken terrain. Its design and control was motivated by a collaboration of roboticists, biologists, and mathematicians, ...