In-situ wheel sinkage estimation under high slip conditions for grouser-wheeled planetary rovers: Another immobility index

Abstract

Loose sandy terrain is more likely to induce high slip, making it the most hazardous type of area for grouser-wheeled planetary rovers to traverse. To prevent successfully landed planetary rovers from getting trapped, the rover slip ratio is always selected as a key getting trapped index. Wheel sinkage increases dramatically with slip ratio under high slip conditions, and even though a small uncertainty in the estimated slip ratio could cause a large error in the estimated wheel sinkage. Wheel sinkage contributes directly to entrapment, and thus should also be selected as another important immobility index. Because of the severe soil particle flow caused by the grouser digging effect, the performance of the traditional wheel sinkage estimation algorithm is not acceptable in this context. This study proposes an algorithm to estimate wheel sinkage in-situ using physically measurable quantities, which is validated using single-wheel experiments. Based on the experimental results, the maximum relative error of the estimated wheel sinkage can be reduced from 205% to 14%. The estimated wheel sinkage is then used to compute the drawbar pull to further validate its accuracy, and the maximum relative error of the estimated drawbar pull can be limited to 6%.