Effects of Foot Stiffness and Damping on Walking Robot Performance

In this paper, we investigated how the stiffness and damping properties of soft robotic feet affect the stability and energetic economy of bipedal robotic walking. To this end, we manufactured four different spherical feet from the following materials: hollow rubber, Sorbothane, Norsorex, and Neoprene. The materials were specifically chosen to cover a wide range of stiffness and damping values. The impact response of each design was first characterized in a drop test rig. We then evaluated the performance of each foot in an extensive series of walking experiments on the planar bipedal robot RAM one. Our results showed that, at low speeds, the feet with lower damping had a smaller energy cost of walking, possibly due to greater return of mechanical energy at lift-off. However, at speeds above 0.5 ^m\s , the feet with lower damping started to exhibit a bouncing behaviour which led to higher walking instability and increased the energy cost of walking. Additionally, we found the feet with lower stiffness to be more economical across all walking speeds. Our results provide insight into the role of foot properties in bipedal walking and may help with the design of walking robots.