A Reduced-Order Resistive Force Model for Robotic Foot-Mud Interactions

Abstract

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.

Figures (11)

• Figure 1: Mud-intrusion experimental setup with a cuboid intruder.
• Figure 2: A typical resistive-force profile (normalized). (a) In normalized process (time) domain. (b) In normalized intrusion-depth domain. Shaded regions demonstrate one-standard deviation from 3 trials. (c) The necking of mud that leads to a cohesive suction force during the withdraw process.
• Figure 3: Schematics of 1D foot/mud interaction models using combinations of visco-elasto-plastic elements for the (a) Intrusion and (b) Withdrawal process.
• Figure 4: The mud resistive-force model diagram. A switch is used for regulating the mud velocity $\dot{z}_m$ to interpret necking after significant yielding.
• Figure 5: Calibration of the scaling factor $\lambda$. (a) Sliding experiment setup schematics. (b) Calibration results.