Abstract: A general method of kinematical modeling for all-terrain mobile robots is proposed. The robot is treated as a series-parallel multi-rigid body system. A series sub-system is formed from each wheel-terrain contact point to the robot body through compliant joints. Planar slips including forward slip, side slip and steering slip are considered by building instantaneous coordinate frame at each wheel-terrain contact point, and a closed velocity chain is developed for each series sub-system. In each closed velocity chain, the velocity relationship between the rigid body motion of the robot and the steering, and driving rates of the wheels can be directly written out at the axle center of each driving wheel. The whole kinematics equation of the robot body can be achieved by combining the velocity equation of each closed velocity chain. By using this kinematics modeling method which considers both planar slips of each driving wheel and the effects of terrain profile, velocity equations can be easily developed for an all-terrain mobile robot. As long as the structure parameters of the robot are known, the kinematical equations of the robot body will be easily achieved, and also the forward and inverse kinematics are convenient to solve by using this method. The example of applying this method to a six-wheeled all-terrain mobile robot shows its merits of generality, definite physical meaning and concise derivation process.

Key words: All-terrain wheeled mobile robots, Kinematics, Modeling, Passive compliant mechanism