Passive-dynamic leg design for agile robots

The spring-mass locomotion paradigm is showing great promise as a template for agile and efficient robots. Efficiency and stability are enabled by the passive generation of locomotion patterns, rather than enforced by the control system. However, as leg designs develop more articulation and complexity, a problem arises: how do we implement a chosen set of passive dynamics in complex hardware? We present compliance and impact inertia analyses in a “visually tactile” way, allowing complex and redundant mechanism designs to be easily evaluated. The patterns shown here begin a framework for the comprehensive design of agile, highly dynamic robots.

I. Introduction

Humans and other animals have the remarkable ability to negotiate an unknown and changing environment, not only without falling, but also with a level of efficiency currently unmatched in existing robotic systems. Literature suggests that a large portion of this agility is due to the natural behavior of the animal's body in addition to neurological feedback control [1]–[3]. Morphology and materials of limbs (their mass, elasticity of tendons, lever arms between joints, etc) can enable efficient and immediate feedback control and stabilization at the hardware level [4]. Using this hardware-in-the-loop control premise, natural looking walking and running gaits can emerge from the “natural” (“free”, or “passive”) dynamics of the mechanism, as seen in McGeer's original passive dynamic mechanisms [5].