A planar hopping robot with one actuator: design, simulation, and experimental results

Animal legs are much more complex than necessary for running on horizontal surfaces. Past research shows that, despite their complexity, they act essentially like simple pogo sticks, or the "spring loaded inverted pendulum" (SLIP). In this paper, the possibility of the realization of a SLIP model using a spring in the leg and only one actuator at the hip is investigated first in numerical simulation and then in experiments. A simple controller results in running at 0.80 m/s (6.7 leg lengths per second). The stability and robustness of the resulting motion is demonstrated.