Failure Mechanisms and Risk Estimation for Legged Robot Locomotion on Granular Slopes

TL;DR

This paper investigates how granular slopes affect legged robot locomotion, providing measurements, a predictive model, and failure risk diagrams to improve safety and robustness on deformable terrains.

Contribution

It introduces a physics-informed model that predicts robot performance and failure risks on granular slopes based on terrain strength and slope angle.

Findings

Shear resistance decreases with slope angle, normal resistance remains stable.

Model predicts anchoring timing, step length, and speed based on terrain properties.

Failure phase diagrams identify sinkage and slippage regimes for risk estimation.

Abstract

Locomotion on granular slopes such as sand dunes remains a fundamental challenge for legged robots due to reduced shear strength and gravity-induced anisotropic yielding of granular media. Using a hexapedal robot on a tiltable granular bed, we systematically measure locomotion speed together with slope-dependent normal and shear granular resistive forces. While normal penetration resistance remains nearly unchanged with inclination, shear resistance decreases substantially as slope angle increases. Guided by these measurements, we develop a simple robot-terrain interaction model that predicts anchoring timing, step length, and resulting robot speed, as functions of terrain strength and slope angle. The model reveals that slope-induced performance loss is primarily governed by delayed anchoring and increased backward slip rather than excessive sinkage. By extending the model to generalized terrain conditions, we construct failure phase diagrams that identify sinkage- and slippage-induced failure regimes, enabling quantitative risk estimation for locomotion on granular slopes. This physics-informed framework provides predictive insight into terrain-dependent failure mechanisms and offers guidance for safer and more robust robot operation on deformable inclines.