A Steering Control Method Applicable to an Eight-Wheeled Planetary Laboratory

In the future planet exploration mission, the eight-wheeled Planetary Mobile Laboratory (PML) has enough carrying and driving capacity to meet the needs of the mission, but it is prone to serious lateral slip during high-speed steering due to large inertia. Modern technology has made it possible to realize eight-wheel independent steering of a four-axle vehicle, but to make the whole vehicle more stable in the steering process, it is necessary to effectively control the steering angle of each wheel. To reduce the lateral offset of the eight-wheeled PML during steering, this paper proposes a novel rear axle steering feed-forward controller. First, a mathematical model of the steering control of the four-axle vehicle is established. The kinematic equations of Ackermann steering for the whole vehicle are derived, and based on this, the equations of feed-forward zero side-slip steering control for the third and fourth axes are derived. Then, a zero-slip steering control strategy is designed, in which the first and second axes are controlled using the Ackermann steering principle, and the third and fourth axes are controlled by feed-forward control to eliminate the lateral deflection of the body's center of mass. After that, a multi-body dynamics model of the PML is constructed in the open-source platform Chrono to evaluate the turning radius of the vehicle under this control method and optimize the steering angle ratios of the third and fourth axes. Finally, a Double Lane Change (DLC) simulation experiment is conducted on the loose terrain of the planet's surface to compare the dynamic performance of the vehicles with the controller designed in this paper and with the 100% Ackermann steering strategy respectively under different driving speeds, which verifies the effectiveness of the control strategy. This study provides an advanced steering control strategy to improve the steering stability of the PML at high speeds, ensuring that it can steer smoothly on the planet's surface.