Discrete Foot Shape Changes Improve Dynamics of a Hopping Robot

Legged locomotion is characterised by a repetitive appearance of impulsive ground collisions which are strongly influencing the locomotion behaviour. The collisions depend on the shape of the contacting foot, but little is known on how the foot needs to be shaped to assist stable and fast locomotion. This paper investigates discrepancies in locomotion dynamics caused by a discrete foot shape change. A curved foot, open-loop controlled hopping robot which can be switched between two foot shape states was built and tested for the experimental investigations. The results indicate that the right timing of foot shape change can induce a variety of locomotion gaits and increase maximal speed by up to 40%, without the shape change doing any positive work on the robot. Three distinct take off cases were identified which depend on the robot’s state and foot shape. The switching between the cases in consecutive hops can explain the observed behaviour qualitatively as presented in this paper