Locomotion

Passive Dynamics

Passive dynamics refers to the motion a mechanism exhibits under gravity and its own inertia, without actuation or control. Tad McGeer's passive dynamic walkers of 1990 descended shallow slopes with a strikingly human-like gait using no motors at all, demonstrating that morphology alone can generate stable locomotion. Designers exploit passive dynamics through careful mass distribution, compliant elements, and natural oscillation frequencies to reduce actuation effort.

Why it matters for physical AI

Exploiting a body's natural dynamics rather than fighting them is central to energy-efficient legged locomotion, and it motivates hardware-software co-design in which controllers work with the mechanism's intrinsic behavior.