A Quasi-Static Approach to Optimize the Motion of an UGV Depending on the Track Profile

Abstract

The aim of this work is to improve the navigation capabilities of an off-road unmanned ground vehicle (UGV) by optimizing the angles between its legs and its body (its configuration angles), as the vehicle travels by a particular track profile. We present a numerical program based on a quasi-static half vehicle model. For a profile entered by the user, the program will be able to calculate how the angles between the legs and the body must vary along the trajectory, so that to maintain the torque on the wheels as constant as possible. Results may be helpful in vehicle control tasks, in particular when passing obstacles efficiently.First of all, some considerations concerning the nomenclature and geometry of the vehicle are presented. Then, the kinematics of the vehicle is exposed starting from the function that defines the profile. We focus on the position and/or trajectories of remarkable points to be employed later. From the kinematics, the quasi-static model is developed and the equations to calculate the forces and torques involved are presented. The algorithm basically calculates the position along the track and the angles between the legs and the body and then, by using the previous equations, finds the optimal values of those angles that satisfy a given condition (as equal to normal forces, torque constancy, minimum torque, etc.)As results, we present the configuration angles that equal to the normal forces on the wheels when the vehicle ascends a ramp, depending on the slope. We also present the optimal configuration angles variation required for the vehicle to pass over a step obstacle. And for a complex profile how the torque changes in function of the angles between the legs.