Linear Prediction of High-Slip Sinkage for Planetary Rovers' Lugged-Wheels Based on Superposition Principle

Planetary rovers with lugged-wheels are the primary equipment for Mars exploration, and as exploration missions become more complex, rovers are expected move into more challenging terrains. When moving over soft sand or slopes, lugged-wheels experience high slip and heavy sinkage, and an explicit sinkage prediction model for lugged-wheels is not available. This limits the motion control of planetary rovers. Here, we show that wheel sinkage can be divided into static sinkage, rolling sinkage, shearing sinkage, and digging sinkage, based on motion decomposition. Static sinkage is in accordance with the modified Archimedes' theorem, shearing sinkage is proportional to the slip ratio, and digging sinkage is proportional to rim displacement. Furthermore, the superposition principle of sinkage has been proved, and the various types of sinkage were superimposed to obtain an explicit prediction model without terramechanics parameters for lugged-wheels. The single-wheel test proves that the linear model can predict sinkage for slip conditions from 0 to 0.9 with a prediction accuracy of over 90%. The decomposition and modeling of the sub-sinkage further explores the intrinsic of the lugged-wheels' sinkage, and the linear prediction model provides a theoretical basis for high slip control of rovers.