  This work presents the coordinated motion control and obstacle-crossing
problem for the four wheel-leg independent motor-driven robotic systems via a
model predictive control (MPC) approach based on an event-triggering mechanism.
The modeling of a wheel-leg robotic control system with a dynamic supporting
polygon is organized. The system dynamic model is 3 degrees of freedom (DOF)
ignoring the pitch, roll and vertical motions. The single wheel dynamic is
analyzed considering the characteristics of motor-driven and the Burckhardt
nonlinear tire model. As a result, an over-actuated predictive model is
proposed with the motor torques as inputs and the system states as outputs. As
the supporting polygon is only adjusted at certain conditions, an event-based
triggering mechanism is designed to save hardware resources and energy. The MPC
controller is evaluated on a virtual prototype as well as a physical prototype.
The simulation results guide the parameter tuning for the controller
implementation in the physical prototype. The experimental results on these two
prototypes verify the efficiency of the proposed approach.
