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

• A unified gross traction algorithm is proposed for braked, towed, and powered wheels on clay. • The model is developed using the Database Records for Off-road Vehicle Environments. • The algorithm employs the ratio of average contact pressure to cone index. • The new equation can be implemented in off-road mobility models. A characteristic curve is presented for predicting gross traction of a wheel over a range of powered, towed, and braked modes on clay soils for slip ranging from positive 100% powered slip to negative 100% skid slip. The characteristic curve is a unified approach that relates the ratio of the contact pressure of the wheel to soil strength and predicts the gross traction coefficient over a continuous range of slip. The unified equation is defined by five inflection points: maximum/minimum traction, traction at zero slip, max change in traction with slip, and a shape factor coefficient. The inflection points aim to simplify the calibration of gross traction, slip, soil strength, and contact pressure by using functions adaptable to machine learning. The unified equation is comparable to historic traction equations but is unique in its ability to predict asymmetric braking and powered gross traction. The unified equation is supported and substantiated via error analysis by utilizing the Database Records for Off-road Vehicle Environments (DROVE) – a database constructed around the archived laboratory and field tests for wheels and tracks operating on different soils. The accuracy of the proposed model is assessed and compared to other conventional equations such as the Brixius equation and Maclaurin's extension of the Pacejka equation for off-road traction. [ABSTRACT FROM AUTHOR]