Towards bipedal running as a natural result of optimizing walking speed for passively compliant three-segmented legs

Elasticity in conventionally built walking robots is an undesired side-effect that is oppressed as much as possible because it makes control very hard, and thus complex control algorithms must be used. The human motion apparatus, in contrast, shows a very high degree of flexibility with suffcient stability. In this research we investigate how elasticities and damping can sensibly be used in humanoid robots to improve walking capabilities. A modular robot system consisting of rigid segments, joint modules and adjustable elastic strings spanning one or more joints is used to configure a human-like biped. In parallel, a complex simulation model of the robot has been established. Walking motion is gained by oscillatory out-of-phase excitations of the hip joints. An optimization of the walking speed has been performed by improving the viscoelastic properties of the leg and identifying the appropriate hip control parameters. Experiments on the real robot very well matched the numerical results. At higher speeds, transitions from walking to running are found in both the simulation as well as in the robot