Modeling of Skid-steered Wheeled Robotic Vehicles on Sloped Terrains

Skid-steered robots are commonly used in outdoor applications due to their mechanical simplicity, high maneuverability, and robustness. The maneuverability of these robots allows them, under ideal conditions (e.g., flat terrain and powerful actuators), to perform turning maneuvers ranging from point turns to straight line motion. However, sloped terrain, terrain with high friction, or actuator torque and power limitations can limit the achievable turning radii. This work presents the analysis and experimental verification of a dynamic model for skid-steered autonomous ground vehicles equipped with non ideal (i.e., torque and power limited) actuators and moving on sloped terrains. The experimental results show that the model is able to predict motor torques for the full range of turning radii on flat ground, i.e., from point turns to straight line motion. In addition, it is shown that the proposed model is able to predict motor torques (including motor saturation) and minimum turn radius as a function of terrain slope, vehicle heading, terrain parameters and actuator characteristics. This makes the model usable for curvilinear motion planning tasks on sloped surfaces.