Soil Kinematics Under Rigid Wheels

In recent years, the need for reliable modeling tools for lightweight robotic systems deployed on various terrains has spurred research efforts into development of vehicle terrain interaction (VTI) models. This paper presents an analysis of rigid wheels - dry sand interaction and compares experimental results with predictions from established terramechanics theory. A novel experimental setup, based on sensing elements placed on the wheel surface, allows inference of normal and tangential stress at the wheel-terrain interface. A particle image velocimetry (PIV) analysis is used to study the soil kinematics under the wheel. The analysis of stress profiles shows that stress patterns under lightweight vehicle wheels conform reasonably well to established terramechanics theory developed for heavy vehicles. For the wheel under investigation, the stress distribution had minor variation along wheel width for low slip conditions. The wheel model proposed by Wong and Reece was analyzed in light of the stress and soil kinematics measurements available. It was found that, by appropriately characterizing the model coefficients c1 and c2, and understanding the physical meaning of the shear modulus kx, it is possible to obtain torque, drawbar force, and sinkage predictions within 11% (full scale error) of experimental data.