Publication news

A unified equation for predicting traction for wheels on sand over a range of braked, towed, and powered operations

George L. Mason, James M. Williams, Farshid Vahedifard, Jody D. Priddy
Journal of Terramechanics, Volume 79, 2018, Pages 33-40, ISSN 0022-4898,

Abstract: Vehicle traction between the wheel and the ground surface is a critical design element for on-road and off-road mobility. Adequate traction in dry sand relates to the vehicle’s ability to negotiate deserts, sand dunes, climb slopes, and ingress/egress along beaches. The existing traction equations predict values for only one mode of operation (braked, towed, or powered). In this article, we propose a unified algorithm for continuous prediction of traction over a range of braked, towed, and powered operations for wheels operating on sand. A database of laboratory and field records for wheeled vehicles, entitled Database Records for Off-road Vehicle Environments (DROVE), was used to develop the proposed algorithm. The algorithm employs the ratio of contact pressure to cone index as a primary variable to develop fitting parameters for a relationship between slip and traction. The performance of the algorithm is examined versus the measured data and is also compared against two alternative equations. The new equation showed higher correlation and lower error compared to the existing equations for powered wheels. The proposed equation can be readily implemented into off-road mobility models, eliminating the need for multiple traction equations for different modes of operation.

Keywords: Off-road mobility; Sand; Traction; Vehicle Terrain Interface (VTI) model; Database Records for Off-road Vehicle Environments (DROVE)