A Three-Dimensional Passive-Dynamic Walking Robot with Two Legs and Knees

TLDR

Passive‑dynamic walking has long been used to study animal locomotion and design anthropomorphic robots, but existing three‑dimensional devices have not achieved human‑like motions, operating mainly in two dimensions or as stiff‑legged waddles. The authors built an 85‑cm‑tall, two‑legged robot that retains McGeer’s simple, knee‑flexing, gravity‑powered design while adding curved feet, a compliant heel, and mechanically constrained arms to produce a stable, human‑like gait. The robot weighs 4.8 kg, walks at 0.51 m s⁻¹ down a 3.1° slope while consuming 1.3 W, demonstrating that passive dynamics can yield efficient, human‑like walking and guiding future simple robot designs.

Abstract

The authors have built the first three-dimensional, kneed, two-legged, passive-dynamic walking machine. Since the work of Tad McGeer in the late 1980s, the concept of passive dynamics has added insight into animal locomotion and the design of anthropomorphic robots. Various analyses and machines that demonstrate efficient human-like walking have been developed using this strategy. Human-like passive machines, however, have only operated in two dimensions (i.e., within the fore-aft or sagittal plane). Three-dimensional passive walking devices, mostly toys, have not had human-like motions but instead a stiff legged waddle. In the present three-dimensional device, the authors preserve features of McGeer’s two-dimensional models, including mechanical simplicity, human-like knee flexure, and passive gravitational power from descending a shallow slope. They then add specially curved feet, a compliant heel, and mechanically constrained arms to achieve a harmonious and stable gait. The device stands 85 cm tall. It weighs 4.8 kg, walks at about 0.51 m/s down a 3.1-degree slope, and consumes 1.3 W. This robot further implicates passive dynamics in human walking and may help point the way toward simple and efficient robots with human-like motions.