Toward innate leg stability on unmodeled and natural terrain: Quadruped walking

A legged system that can negotiate moderately uneven terrain without human intervention or a vision-based control system can allow those resources, if available, to be concentrated on high-level tasks. This paper presents results of preliminary research on the application of a Force Threshold-based Position (FTP) Controller on an upright quadruped system blindly walking on irregular terrain. The algorithm requires no interleg communication, such as needed for a multi-leg Jacobian, or inertial sensing of the body. Instead, each leg relies upon local feedback and simple time triggers for gait phasing. Results are shown for sagittal plane implementation in a dynamics-based simulator, while an experimental system is being designed for further testing. Concurrent research applies the FTP controller to a sprawled-leg hexapod system in hopes of extracting general leg control principles for innate stability over moderate terrain.