An empirical study of the terramechanics of small unmanned ground vehicles

A critical component of remote terrestrial and planetary exploration is understanding how terrain properties affect rover mobility. Bekker theory has long been used successfully in this regard for the analysis of large vehicles. In recent years, the semi-empirical formulae contained within Bekker theory have also been applied to small UGVs. Bekker himself noted, however, that his formulae offer significantly less accurate predictions for vehicles with wheel diameters and normal loading lower than 50 cm and 45 N, respectively. This has been shown to lead to errors in the prediction of tractive performance. The results of this paper show that Bekker theory yields under-estimates of small wheel sinkage and resistances. The consequences of such errors are severe, as they could potentially lead to unexpected rover immobilization. With increasing numbers of small UGVs being used in planetary, research and military roles, it is crucial to investigate the source of these errors. This paper details an empirical approach to characterizing small vehicle wheel sinkage and its impact on vehicle-terrain models.