Dynamic Modeling and Simulation of 4-Wheel Skid-Steering Mobile Robot with Considering Tires Longitudinal and Lateral Slips

Abstract

Skid-steered vehicles are regularly considered for outdoor activities due to their structural robustness and extraordinary maneuverability. Dynamic model of ground vehicles should predict a faithful motion in unknown environments and ability to design a proper controller. The purpose of this paper is to develop a nonlinear model for a 4-wheel skid-steering mobile robot considering dynamic model of tires with all slides. Unlike previous friction models which are considering only frictional forces without tire's slips, the proposed model consists of longitudinal and lateral tires' slips and will be used to predict a real robot's (P3-AT) motion in some specified situations such as moving straight on horizontal and ascent planes and moving on a curve on a horizontal plane. For validation purposes, obtained results will be compared to similar simulations on an Adams/View model. This comparison shows the accuracy of the model. Finally, advantage and disadvantage of the proposed model will be discussed. a distance between center of mass and forward axel (m) b distance between center of mass and behind axel (m) Fx C tire longitudinal stiffness (N/m) x F longitudinal force exerted by the tire on the wheel at the contact point (N) h height of center of mass (m) w I wheel-tire assembly inertia (2 .m kg) ZZ I moment of inertia of total robot about z axis (2 .m kg) L distance between behind axel and forward axel (m) total m total mass of robot (kg) e r effective rolling radius (m) t distance between center of right and left wheels (m) u tire longitudinal compliance or deformation (m) SX V wheel slip velocity (m/s) SX V  contact point slip velocity (m/s) X V wheel center longitudinal velocity (m/s) i X Static force due to robot weight on wheel i in x direction (N) i Y Static force due to robot weight on wheel i in y direction (N) i Z Static force due to robot weight on wheel i in z direction (N)  pitch (rad)  roll (rad)  yaw (rad)  wheel slip '  contact patch slip   tire relaxation length (m)  friction coefficient  wheel angular velocity (rad/s)  contact point angular velocity (rad/s) drive  torque applied by the axle to the wheel (N·m)