Dynamical modeling and simulation of the four-wheel micro rover in sandy terrain

With the arrival of low cost launch options, space exploration has become accessible and affordable, attracting many researchers and start-ups. This has led to more difficult mission opportunities, becoming possible for research organizations such as the development of resource prospecting rovers for environments such as the lunar surface. With this in mind, Tohoku University's "Space Robotics Laboratory", in collaboration with ispace, is currently developing a lunar rover for the Google Lunar XPRIZE competition, which aims to be used for resource prospecting in future mission. Uncertainties are inherent in space development as single point failures can hinder the rover's mobility performance in a space environment and lead to mission failure. One of the most important locomotive factors is the wheel-soil interaction under rough terrain with loose soil, where wheel slippage has been a recurring issue. Our objective is to enable straight traversal under sloped terrain. Given that drift is inevitable, a new locomotive method is proposed. This is essential for rover teleoperation to reach the destination as quickly and safely as possible. In this paper, a simulator for dynamics of a four-wheeled vehicle is developed. The dynamics of the wheel are formulated based on well-known terramechanics theories. To match the model with the experimental data from the single wheel testing, we have tuned the parameters that are dominant elements in the equation, which is the shear deformation modulus. Once the wheel-soil characteristics are determined, the dynamic model is translated into the fourwheel rover case. We have performed several traversal runs on different inclined testbeds under controlled conditions to validate the simulator's accuracy. Furthermore, we have determined the straight horizontal traversal motion by orienting the rover's attitude for specific slopes, and we have evaluated its consistency with the experimental data.