High-fidelity Software-in-the-loop Simulation of a Six-wheel Lunar Rover using Vortex Studio for Output-tracking Control Design

Six-wheel autonomous rovers with skid-steering rear wheels have been designed for Lunar exploration programs due to their lightweight and their enhanced traction and stability. In this paper, a Software-in-the-loop Simulation (SILS) is presented for such a system containing a controller coded in MAT-LAB and a digital twin of the system modeled in Vortex Studio. The controller is developed based on the system's governing equations and static state feedback linearization to perform an output-tracking control task. The equations of motion are derived using Lagrange-d’ Alembert principle subject to ideal nonholonomic constraints and under the point-contact assumption at all wheels. Such simplifying assumptions are commonly considered in proposed control strategies for autonomous rover systems in the literature. The digital twin of the rover is modeled as a multi-body system with realistic parameters moving on 3-dimensional soft/rough terrains with arbitrary tire models provided by Vortex Studio. The results of the developed SILS are compared to those of a 2-dimensional simulation that is fully coded in MATLAB under the simplifying assumptions (ideal plant). This comparison discloses often existing discrepancies between real rover systems and their commonly used mathematical models. This study reveals the effects of isolated physical phenomena, e.g., wheel-slip and tractive force distribution, on the control performance, and can be utilized to design enhanced controllers for rover systems.