Multibody Simulation of the Path Tracking Performance of a Hybrid Leg-wheel Ground Mobile Robot

Epi.q Mod 2 is the last prototype of the “Epi.q” mobile robot family, small-scale surveillance and inspection ground mobile robots, with the highest level of modularity and mechanical reconfigurability. The Epi.q locomotion system is characterized by stepping-triple wheel locomotion units, each one actuated by a single motor through an epicyclical mechanism. These locomotion units allow to switch from wheeled locomotion to legged locomotion without control intervention, on the basis of the dynamic conditions. During wheeled locomotion Epi.q Mod 2 has eight wheels in contact with the ground and wheel slippage is unavoidable, therefore the steering behaviour is highly influenced by the vehicle dynamics, not only by its kinematics. Therefore, a multibody model of the robot, including tyre-ground contacts, electrical model of the robot and steering control law has been developed in order to assess the effectiveness of the path tracking strategy in different conditions and in presence of obstacles. Simulation results show that feedforward compensation allows to reduce remarkably the path tracking error.