Robust bipedal locomotion on flowable slopes via foot-driven terrain manipulation
2026-07-13 • Robotics
Robotics
AI summaryⓘ
The authors studied how bipedal robots can walk better on loose, sandy slopes by changing how their feet interact with the ground. They discovered that feet with cleats spaced too closely or too far apart performed poorly, causing the robot to sink too much or face too much resistance. By finding the right cleat spacing, the robot could walk on slopes up to 30 degrees without falling. They also designed a foot that can adjust to both hard and loose ground, showing that focusing on foot-ground interaction is a helpful way to improve robot walking.
bipedal robotsgranular terrainterradynamicscleated feetsubstrate yield thresholdrobot locomotionfoot-terrain interactionrobophysical modelflowable surfacesrobot stability
Authors
Deniz Kerimoglu, Junnosuke Kamohara, Jiyeon Maeng, Ziwon Yoon, Seth Hutchinson, Ye Zhao, Daniel I. Goldman
Abstract
Bipedal robots are challenging to control because they operate close to instability, where small variations in foot-terrain contact can rapidly destabilize locomotion. On rigid terrain, bipedal robots mitigate this fragility by using well-established contact mechanics and control strategies. On flowable surfaces such as granular slopes, foot contact can induce large surface deformations and solid-fluid-like transitions, coupling terrain effects with robot dynamics, leading to underperformance or failure. This is partly due to the lack of reliable methods to represent the dynamics of flowable terrain, making it difficult to account for terrain effects in locomotion design. Here, we investigate how controlling terrain response can improve bipedal locomotion on granular slopes by studying the terradynamics of cleated feet, thin plates emanating from the foot soles. Systematic studies of a small-scale (1.4 kg) robophysical biped reveal that cleats with sparse and dense spacing lead to excessive terrain yielding and resistance, respectively, degrading performance and leading to failure. An intermediate cleat spacing distributes interaction forces to maintain substrate stresses near (or below) the yield threshold, enabling walking on granular slopes up to 30 degrees. Guided by these principles, we design a foot that actively adjusts cleat depth and accommodates both rigid and granular terrain. We also demonstrate that the principles of effective foot-terrain interaction translate to a larger (15 kg) autonomous biped. Our study presents an alternative to conventional body-centric robot control approaches, which regulate terrain-induced effects through body motion, by instead regulating terrain interactions through limb-centric approach.