Toward Establishing a Comprehensive Pressure-sinkage Model for Small Diameter Wheels on Deformable Terrains

Traditional terramechanics theorems utilise pressure-sinkage models based on the assumption that the contact area between a tyre and soil can be approximated as a flat plate. Examples include work by Bekker, Reece, and Ishigami. Recently, the authors have demonstrated that 1) this approximation does not hold for wheels with a diameter less than approximately 50 cm and 2) an improved diameter-dependent pressure-sinkage model can yield more accurate results. In this paper, further improvements to the pressure-sinkage model for small diameter wheels are presented. First the diameter-dependent pressure-sinkage model is augmented with a geometric relationship to account for the normal stress distribution at the wheel-soil interface. Second, the effect of wheel width is investigated. The models are verified with field tests using a man-portable unmanned ground vehicle on wet sand and laboratory experiments on dilative (dry quartz sand) and compactive (kaolin-clay/silt mix) soils. Results indicate that the diameter-dependent pressure-sinkage model outperforms previous models in predicting drawbar pull as a function of slip and that the effect of wheel width on the pressure-sinkage model is highly dependent on the soil type.