Linear Expressions of Drawbar Pull and Driving Torque for Grouser-Wheeled Planetary Rovers Without Terrain Mechanical Parameters

Drawbar pull and driving torque are usually applied to characterize the mobility and energy consumption, respectively, of wheeled planetary rovers (WPRs) traversing sandy terrain. Owing to the complexity of the grouser-terrain interaction, neither can be modeled as a closed-form analytical expression of the terrain mechanical parameters. Complexity limits their online applications. Moreover, it is difficult to estimate the terrain mechanical parameters. To solve these issues, based on equivalent wheel sinkage, both the drawbar pull and driving torque can be modeled as a linear function of physically measurable quantities in the absence of terrain mechanical parameters, which is demonstrated using single-wheel experiments conducted with four types of wheels and two sand types. The influence of a sophisticated grouser-terrain interaction on wheel sinkage can be explicitly determined using the linear driving torque model. Furthermore, the validated linear drawbar pull equation is used to estimate the slope-climbing capability of a four-wheeled planetary rover prototype by computing the slope-climbing coefficient, and the relative error can be limited to 10%. In addition, the wheel driving torque of the rover prototype can also be accurately predicted.