Research on a New Analysis Method of Traction Performance for Variable-Diameter Wheels

Folded variable-diameter wheels used in planetary rovers can save spacecraft volume. Moreover, they can be expanded to improve their mobility on soft soil. However, only a single wheel foot was considered in previous researches on wheel-terrain interaction, which may be inaccurate. Hence, the cycloid motion equations for an unfolded variable-diameter wheel were introduced to obtain the shear displacement of any point on a wheel foot. Then, determining wheel-soil interaction regions was transformed into geometric relationship analysis. Therefore, the simplified model with a single wheel foot was established. Consequently, the traction efficiency achieved the peak when the range of wheel slip rates was 0.15∼0.35. The results shown that increased wheel diameter improved wheel mobility. For a greater sinkage, with the superposition of simplified model, the detailed model based on multiple wheel feet was built. This model got closer to real interaction status. The finite element analysis (FEA) results for the rolling wheel on soft soil were consistent with the theoretical hypotheses. Overall, the simplified model is very efficient, however, the detailed model is more accurate, which provides theoretical references for the control of optimizing wheel mobility. Additionally, this new analysis method developed here can also be applied to other expandable wheels.