Terrain-Dependent Intra-Cycle Leg Timing for Effective Locomotion on Granular Slopes

2026-10-02

AI Summary

This study addresses the reduced locomotion efficiency of legged robots on granular inclines caused by diminished shear forces, where the primary mechanism underlying performance degradation remains unclear. By integrating hexapod robot experiments with physics-informed modeling, this work constructs a foot–granule interaction model based on mechanical measurements to predict optimal anchoring timing and stride length, further establishing a failure phase diagram. The findings reveal that delayed anchoring and backward slip, rather than excessive sinkage, constitute the dominant causes of performance loss on slopes. Moreover, this research enables quantitative risk estimation and provides operational guidelines for locomotion on granular inclines, significantly enhancing robotic robustness on deformable sloped terrain.

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.

Problem

• legged robots
• granular slopes
• locomotion failure
• slippage
• sinkage

Innovation

• granular locomotion
• robot-terrain interaction model
• anchoring timing
• failure phase diagrams
• legged robots