Analysis of Angle of Attack for Efficient Slope Ascent by Rovers

Abstract

What direction should a rover drive to efficiently ascend slope of loose soil? To explore the lunar poles, rovers will need to traverse craters where high slip will hamper progress. Because of limited energy, rovers need to find efficient routes to traverse such sloped terrain. It is an open question whether efficient and successful slope-ascending is achieved in loose soil by driving directly uphill or in a diagonal cross-slope direction. In this thesis, the influence of the rover’s angle of attack on slope-ascent performance was analyzed based on a slope-ascent rover model that consists of force equilibrium conditions and terramechanics-based wheel–soil interaction. The terramechanic model was validated in single-wheel experiments. Rover slip, uphill velocity, and power efficiency were predicted and associated with the angle of attack. Analysis shows the ascent in the direct uphill direction results in most effective motion, in terms of velocity and power efficiency, on most of the slopes analyzed even if the vehicle longitudinal slip can be reduced by decreasing the angle of attack. The analysis also indicates that a rover can diagonally ascend steep slopes where it cannot drive directly up if the rover can generate sufficient lateral grip against downhill slides. Slope-ascent experiments using a rover were conducted to experimentally evaluate the effect of the angle of attack. The test results validated the model-based analysis and the usefulness of the proposed slope-ascent model. A strategy to select slope-ascending routes is proposed based on the model and experiment based analysis. The utility of the route selection method was demonstrated in simulations on various slopes and for different rovers. The findings in this research are useful to develop path planning strategies and also to develop locomotion configuration and controls which can have high slope-ascent capability.