Experimental Validation of Energy-Optimal Turning Radii for Skid-Steer Rovers

Abstract

For skid-steer rovers, a point turn consumes a lot of power compared to a straight-line motion. Hence, turning radius, in path planning for this kind of rover, is a factor that should be considered explicitly. In this article, the energy-optimal paths for skid-steer rovers are presented, based on a method using Pontryagin’s minimum principle. The finite number of extremals are compared and an optimal map is generated that shows which path type requires minimum energy depending on start/end pose for a particular example. Moreover, the turns in optimal paths (aside from a small number of special cases where start and end points are extremely close) are to be circular arcs of a particular turning radius, $R',$ equal to half of a skid-steer rover’s slip track. $R'$ is the turning radius at which the inner wheels of a skid-steer rover are not commanded to turn. Experiments with a Husky UGV rover validate the energy-optimality of using $R'$ turns on hard ground. Moreover, the experimental results confirm that circular arc - line - circular arc (CLC) paths save energy compared to point turn - line - point turn (PLP) paths, on both hard ground and sand. It should be noted that PLP is the most commonly used maneuver to go from a starting to an end pose for skid-steer rovers.