Analysis of normal force of wheel-sand interaction for planetary rovers with active suspension*

The planetary rover with active suspension can climb steeper slopes and cross bigger obstacles in a wheel-step motion mode, which enables the planetary rover to perform more complex exploration tasks. However, wheel-step motion requires coordinated movement of the suspension and the wheels: the suspension can determine the wheel's sinkage depth and translation speed. Matching up with the wheel rotation speed can actively construct the slip ratio. The forces exerted on the wheels by sand during this process are a key index for motion control. This poses new challenges to existing wheel-sand interaction models. In this paper, dynamic normal force tests are carried out. The dynamic variation of wheel normal force with slip ratio is investigated at different sinkage depths. It is found that the normal force exerted on the wheel increases firstly and then decreases with the slip ratio, and reaches the maximum value near s=0. The distributed stresses of the wheel were analysed by discrete element method (DEM) simulation, and the phenomenon of the distribution stress reconstruction of the wheel is found. Further, by analyzing the local particles in contact with the wheel, it is found that the particle movement direction and morphology vary with slip ratio. The analysis of the wheel’s normal force and the granular material variation with slip ratio provides the basis for establishing a physics-based wheel-sand interaction model.