Experimental investigation of traction forces in Touyoura sand using a C-shaped grouser

Abstract

Exploration rovers on Mars and the Moon frequently encounter wheel entrapment in loose terrain due to insufficient traction, which compromises mobility and mission success. Enhancing wheel traction is critical, and the integration of grousers has been empirically demonstrated to improve performance through complex wheel–terrain and grouser–terrain interactions. Traditional measurement methods, such as the bevameter, are designed for heavy vehicles and are less suitable for lightweight planetary rovers. This study introduces a simplified traction measurement prototype utilizing a static shaft connected to a 5-kg load cell and a C-shaped grouser with a width of 90 mm and a physical height of 150 mm with an effective immersion length of 100 mm. During experimental trials, the prototype penetrated Toyoura sand as the wheel advanced, enabling direct traction measurement over a distance of 170 mm. Results indicate that clockwise rotation with the lateral side facing forward generates a traction force of 20.3 N, while a backward orientation yields 22.7 N. The average traction force per grouser cycle ranges from 20.11 to 22.90 N, with a mean of 21.5 N and a standard deviation of 1.3, confirming high reproducibility. The effective attack angle was determined to be 140.16°, facilitating gradual soil shear mobilization without inducing excessive sinkage. These findings suggest that while grouser orientation influences peak forces, the differences remain relatively minor, with the lateral sides primarily serving as structural reinforcement for the C-shaped geometry.