Motion-control-based analytical model for wheel-soil interaction mechanics of lunar rover

Abstract

During rover lunar exploration missions (such as China's “Chang'e”), rovers are required to move autonomously on the loose lunar soil. Control methods based on the rigidity hypothesis can hardly be expected to satisfy these requirements practically so wheel-soil interaction mechanics should be taken into account. The currently used integral model based on wheel-soil interaction mechanics, however, is complicated, and it cannot be directly applied to the design of a lunar rover's controller. This paper presents a new simplified method of determining the wheel-soil interaction of lunar rovers by introducing a normal stress factor and the ratio of the forward region to the rear region, based on an analysis of the integral model and lunar soil parameters. As an example, numerical analysis is performed for a lunar rover wheel with a width of 165 mm and a radius of 135 mm. Based on a slip ratio as high as 0.4 and an entrance angle that varies from 10° to 40°, the results show that the maximum errors of the model for the calculation of normal force and drawbar pull force are less than 2%, while the maximum error of resistance torque is approximately 5%. When designing a rover's controller, the relationship between the driving torque of wheel T and the drawbar pull of wheel FDP is T = FDPr according to the rigidity hypothesis, a relationship that contradicts the terramechanics model. The proposed simplified model, which is verified by experiments, provides an important basis for the design of a control algorithm for a lunar rover that takes into account lunar wheel-soil interaction mechanics.