Eliminating Peak Impact Forces by Customizing the Passive Foot Dynamics of Legged Robots

Impact forces are a destructive, yet common occurrence in legged locomotion. Every step produces a collision when the leg’s inertia immediately stops upon ground contact. This results in peak impact forces and high frequency vibrations that resonate through the system, damage components, and complicate control algorithms. Rubber or other damping material is the assumed solution for mitigating these impacts. However, we show the benefit of using foot springs where both stiffness and maximum compression are customized to the leg. Such springs eliminate peak impact forces by gradually bringing the leg’s inertia to rest. The maximum compression point (i.e. a hard stop) then provides a rigid surface during stance. We provide a methodology for designing this passive dynamic foot that is validated through simulation and physical testing. Our results show this methodology reduces rigid body impacts and foot vibrations in a way traditional methods, reliant upon rubber or damping, are yet to achieve.