STABLE CONTROL OF A SIMULATED ONE-LEGGED RUNNING ROBOT WITH HIP AND LEG COMPLIANCE

We present a control strategy for a simplified model of a one-legged r unning robot which features compliant elements in series with hip and leg actuators, For this model, proper spring selection and initial con ditions result in ''passive dynamic'' operation close to the desired m otion, without any actuation, However, this motion is not stable, Our controller is based on online calculations of the desired passive dyna mic motion which is then parametrized in terms of a normalized ''locom otion time.'' We show in simulation that the proposed controller stabi lizes a wide range of velocities and is robust to modeling errors, It also tracks changes in desired robot velocity and remains largely pass ive despite a fixed set of springs, masses, and inertias. Comparisons of simulated runs with direct hip actuation show 95% hip actuation ene rgy savings at 3 m/s. Such energy savings are critical for the power a utonomy of electrically actuated legged robots.