Application of a diameter-dependent terramechanics model to small-wheeled unmanned ground vehicles operating on deformable terrain

Applications ranging from planetary exploration to military operations require small unmanned ground vehicles to traverse deformable terrains such as sand or moist earth. Crossing such terrains can be difficult because failure to generate enough traction can result in immobilization and mission failure. Thus, the ability to accurately predict a vehicle´s traction on deformable terrain is critical. Traditionally this has been accomplished via terramechanics based on Bekker theory. However, it has been shown that classical terramechanics loses considerable accuracy when applied to vehicles with wheels less than 50cm in diameter. This paper details the development of a modification to the pressure-sinkage relationship used in Bekker theory that explicitly includes a dependence on wheel diameter. The new model is integrated into a numerical simulation that predicts the tractive performance of an experimental unmanned ground vehicle (UGV). Field tests are performed on sandy terrain, and the results validate the simulated predictions. The new model is found to be significantly more accurate than previous models.