RIGID WHEEL DESIGN AND EVALUATION FOR LIGHTWEIGHT SNOW ROVER

This paper presents a design approach for rigid wheels operating in highly variable, deformable terrain to improve the mobility, reliability, and efficiency of an autonomous vehicle driving on snow. The longstanding Bekker-Wong theory of terramechanics is used as the basis for the design changes with the wide range of terrain parameters for snow serving as inputs to the models and bounds for the problem. Modifications to the wheel width and diameter are evaluated based on their impacts to the rover as a system, with their effects on torque and drawbar pull being weighed against the resultant modifications in component sizing, rover weight, and energy use. Other factors, not included in the Bekker-Wong models but studied in single-wheel testbed experiments, such as bulldozing resistance and the observed dynamic effects of slip-sinkage, were also considered in the design decisions for the new wheel. Finally, to test these theories and assess the mobility improvements of the new design in situ, a four-wheeled rover, FrostyBoy, was developed for the new wheels and trialed in unmodified snow. While qualitatively showing an improvement in mobility on the Greenland ice sheet, the tests also uncovered dynamic modes of immobilization, in low cohesion, low stiffness snow that are not accounted for in terramechanics theory and require further investigation for trafficability to be maintained in all snow conditions.