Legged robots are well-suited for broad exploration tasks in complex environments with yielding terrain. Understanding robotic foot-terrain interactions is critical for safe locomotion and walking efficiency for legged robots. This paper presents a reduced-order resistive-force model for robotic-foot/mud interactions. We focus on vertical robot locomotion on mud and propose a visco-elasto-plastic analog to model the foot/mud interaction forces. Dynamic behaviors such as mud visco-elasticity, withdrawing cohesive suction, and yielding are explicitly discussed with the proposed model. Besides comparing with dry/wet granular materials, mud intrusion experiments are conducted to validate the force model. The dependency of the model parameter on water content and foot velocity is also studied to reveal in-depth model properties under various conditions. The proposed force model potentially provides an enabling tool for legged robot locomotion and control on muddy terrain.

翻译：腿足式机器人非常适合在复杂环境中进行广域探索任务，尤其是在具有可变性地形的场景中。理解机器人足部与地形的相互作用对于确保其安全运动和行走效率至关重要。本文提出了一种用于机器人足部-泥浆相互作用的降阶阻力模型。我们聚焦于机器人在泥浆上的垂直运动，并构建了一个粘-弹-塑性类比模型以描述足部与泥浆之间的相互作用力。该模型明确讨论了泥浆的粘弹性、拔出时的黏附吸力及屈服等动态行为。通过与干/湿颗粒材料的对比，我们开展了泥浆侵入实验以验证该力模型的准确性。此外，还研究了模型参数对含水量和足部速度的依赖性，以揭示模型在不同条件下的深层特性。所提出的力模型有望为泥泞地形上腿足式机器人的运动与控制提供有效工具。