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Planetary surfaces are covered with soft soil. So the wheels for exploration rovers easily slip and lose the traction force. Understanding the interaction between wheel and soft soil is important for traction control to make rovers travel long distances efficiently. The interaction between wheel and soft soil has been studied in the field of terramechanics. Since terramechanics-based wheel model considers only the static state of wheel sinkage, the wheel model is not applicable to the dynamic sinkage. Therefore the authors deal with the problems of wheel sinkage and slip. The traction mechanics in the dynamic sinkage is important in order to predict the wheel motion when the sinkage becomes to be the static state. This paper presents a terramechanics-based wheel dynamics model with consideration of the dynamic sinkage. This paper also proposes dynamic wheel models for solving the problem of wheel sinkage and a shear deformation model for solving the problem of wheel slip. This paper evaluates the proposed models by simulation study. The simulation results show that the proposed models are able to solve these problems and they are applicable to the dynamic wheel sinkage.

Soil-tire system interaction is a fundamental and important research topic in terramechanics. In this paper, the authors applied a 2-D finite element, discrete element method (FE-DEM), using FEM for the tire and the bottom soil layer and DEM for the surface soil layer. Satisfactory performance analysis was achieved. In this study, to clarify the capabilities and limitations of the method for soil-tire interaction analysis, the tractive performance of real automobile tires with 2 different tread patterns—smooth and grooved—was analyzed by FE-DEM, and the numerical results compared with the experimental results obtained using an indoor traction measurement system. The analysis of tractive performance could be performed with sufficient accuracy by the proposed 2-D dynamic FE-DEM. FE-DEM obtained larger drawbar pull for a tire with a grooved tread pattern, which was verified by the experimental results. Moreover, the result for the grooved tire showed almost the same gross tractive effort and similar running resistance as in experiments. However, for a tire with smooth tread pattern, the analyzed gross tractive effort and running resistance behaved differently than experimental results, largely due to a difference in tire sinkage in FE-DEM.