Passively stable hopping of an articulated leg with a tendon-coupled ankle

Dynamic maneuvers have been successfully implemented on many prismatic legged robots. Systems with articulated legs of significant relative mass pose more of a challenge in part due to the physics of thrusting with rotating limbs, which results in undesired non-vertical impulses, and in part due to the control problem of synchronizing ankle and knee joints. Presented here is an experimental articulated leg system that simplifies the control of an articulated monopod through the use of a joint-coupling tendon. The ankle is coupled to the thigh with an inelastic tendon, which causes automatic horizontal impulse compensation on liftoff for varying knee thrusts. Using a tendon-coupled ankle, stable sustained hopping is achieved for a fixed-torso monopod with a very simple control strategy, and with minimal hip actuator effort, while hopping in place is achieved for short time periods with a bipedal robot with freely pitching torso.