Toward the Design of a Kangaroo-Inspired Robot

In this paper we report on the design and fabrication of a Kangaroo-inspired running robot. The goal was to develop a robotic platform to understand the effects of the leg dynamics on the stability of running gaits. Specifically, we studied the effect of the leg posture and compliance on the self-stability characteristic of spring mass running gait. In our design, we tuned the leg compliance and leg resting posture and studied their effect on the stability performance of the system. The design of this platform was carried out based on the well-known Spring Loaded Inverted Pendulum (SLIP) as a first stage reduced order model. After that, we modeled the segmented leg with a rotational spring at the knee and studied the effect of the spring stiffness and resting posture of the leg on the self-stability of the system. Then, to be able to manage the whole energy level of the system and in order to transition to different energy levels, we expanded the model to a hip-actuated system in which the body can apply hip torque during the stance phase. For the flight phase swing leg control policy, we followed the simple constant angle of attack strategy in which the system lands with a constant leg orientation. The results showed that if the leg posture and compliance were chosen properly, the self stability of the system improves and a simple hip torque controller can manage the energy transitioning in a robust way with high convergence rate.