Bipedal robot. Mike Coleman watching a bipedal robot on a slope. This gravity-powered walker may help to improve walking robots and prosthetic legs. It is only stable when it is walking, and falls over if it is stopped. The walker tilts from side to side as it walks, moving in three dimen- sions much like humans. It is mainly made from a toy construction kit. The robot moves despite hav- ing no control system. This shows the importance of gravity, inertia and ground contact in walking. Previously, more emphasis has been placed on ner- vous control. Coleman is an engineering lecturer. Photographed at the Human Power, Biomechanics and Robotics Laboratory at Cornell University, USA.