Landing Energy Management

To survive a fall, an animal or robot must dissipate and/or convert excess impact kinetic energy (KE) while limiting peak forces. Humans do this using a drop landing technique in which leg muscles and knee flexion act as a spring and damper to absorb energy. For high drops, paratroopers and parkour athletes perform landing rolls, which convert KE from vertical to rotational, and extend impact time to reduce peak body loads and dissipate energy. In this study, we investigate the role of leg springs and dampers, body orientation, and geometry on landing energy management. We modeled drop landing using a spring-mass-damper system and corroborated prior literature establishing that peak leg force is minimized when leg damping ratio is near 0.4 and leg spring stiffness is such that the leg spring just reaches maximum compression without exceeding it. To model a landing roll, we replaced the mass with a rigid body in a revolute-prismatic-revolute configuration. We found that with appropriate leg stiffness and body orientation, a passive system can convert 50% of pre-impact KE to rotational KE and maintain a lower peak leg force than drop landing. The result is improved understanding of fall survivability and more rapid and efficient transition to horizontal movement through rolling.