Trunk Pitch Oscillations for Energy Trade-offs in Bipedal Running Birds and Robots

TL;DR

This paper analyzes how trunk pitch oscillations influence energy efficiency in bipedal running birds and robots, proposing control strategies to optimize locomotion energetics based on a biomechanical model.

Contribution

It introduces a biomechanical model and control strategies to leverage trunk pitch motions for energy-efficient bipedal locomotion in birds and robots.

Findings

Trunk pitch oscillations can reduce energy fluctuations in locomotion.

Control strategies can minimize work done by hips and legs.

Insights can inform design of energy-efficient legged robots.

Abstract

Bipedal animals have diverse morphologies and advanced locomotion abilities. Terrestrial birds, in particular, display agile, efficient, and robust running motion, in which they exploit the interplay between the body segment masses and moment of inertias. On the other hand, most legged robots are not able to generate such versatile and energy-efficient motion and often disregard trunk movements as a means to enhance their locomotion capabilities. Recent research investigated how trunk motions affect the gait characteristics of humans, but there is a lack of analysis across different bipedal morphologies. To address this issue, we analyze avian running based on a spring-loaded inverted pendulum model with a pronograde (horizontal) trunk. We use a virtual point based control scheme and modify the alignment of the ground reaction forces to assess how our control strategy influences the trunk pitch oscillations and energetics of the locomotion. We derive three potential key strategies to leverage trunk pitch motions that minimize either the energy fluctuations of the center of mass or the work performed by the hip and leg. We suggest how these strategies could be used in legged robotics.