Control of a Cheetah Robot in Passive Bounding Gait

Passive dynamics is always one of research emphases of the legged robots. Studies have proved that cheetah robot could achieve stably passive bounding motion under proper initial conditions in the ideal case. However, the actual robot must have energy dissipation because of friction and collision compared with the theoretical model. This paper aims to propose a control method that can drive the cheetah robot running in passive bounding gait. First, a sagittal-plane model with a rigid torso and two compliant legs is introduced to capture the dynamics of robot bounding. Numerical return map studies of the bounding model reveal that there exists a large variety of passively cyclic bounding motions (fixed points). Based on the distribution law of fixed points, an open-loop control method including touchdown angle control strategy and leg length control strategy is put forward. At last, prototype of the cheetah robot is designed and manufactured, and locomotion experiment are carried out. The experiment results show that the cheetah robot can achieve a stable bounding motion at different speeds with the proposed control method.