Body Lift and Drag for a Legged Millirobot in Compliant Beam Environment

TL;DR

This study measures and analyzes the lift and drag forces on a legged millirobot navigating through compliant beam environments, revealing how body forces influence locomotion efficiency and suggesting design improvements.

Contribution

It introduces a method to measure body interaction forces in cluttered terrains and demonstrates how these forces affect robot locomotion, providing insights for improved robot design.

Findings

Negative lift can enhance traction in dense terrains.

Body-beam forces significantly influence small robot locomotion.

A half-ellipsoid shape reduces drag and improves movement efficiency.

Abstract

Much current study of legged locomotion has rightly focused on foot traction forces, including on granular media. Future legged millirobots will need to go through terrain, such as brush or other vegetation, where the body contact forces significantly affect locomotion. In this work, a (previously developed) low-cost 6-axis force/torque sensing shell is used to measure the interaction forces between a hexapedal millirobot and a set of compliant beams, which act as a surrogate for a densely cluttered environment. Experiments with a VelociRoACH robotic platform are used to measure lift and drag forces on the tactile shell, where negative lift forces can increase traction, even while drag forces increase. The drag energy and specific resistance required to pass through dense terrains can be measured. Furthermore, some contact between the robot and the compliant beams can lower specific resistance of locomotion. For small, light-weight legged robots in the beam environment, the body motion depends on both leg-ground and body-beam forces. A shell-shape which reduces drag but increases negative lift, such as the half-ellipsoid used, is suggested to be advantageous for robot locomotion in this type of environment.