The motion of a differential drive mobile robot with consideration of slip at contact between the wheels and the ground is studied in this work. Traction forces between the wheel and the ground are derived by considering a rigid wheel, rigid ground interaction model and a caster wheel which provides support to the mobile robot during motion. The motion governing equations are determined by incorporating the traction forces. Numerical simulations are conducted to learn the motion behavior of the robot with wheel slip for a range of wheel input torques. Based on the traction force model and observations from numerical simulations, a slip avoidance controller that limits the input torques is developed. Experiments are conducted to verify the characteristics of the dynamic model with slip and the control strategy used to avoid slip. Models that describe the dynamics of a differential drive mobile robot with and without slip are presented and discussed. A traction force model is developed by considering a simple Coulomb friction model. The caster wheel plays an important role in determining the traction forces. The longitudinal and lateral velocities of the wheel are used to compute the longitudinal and lateral forces. Wheel slip occurs if the reaction force exerted by the applied torque is greater than the static frictional force, which is calculated by the proposed model and this limit is used to implement a slip avoidance controller. Numerical simulations and experiments of the system using the proposed traction model reveal that the angular velocity of the wheels is greater than the corresponding linear velocity when slip occurs. The proposed torque limiting controller to avoid slip is also implemented in numerical simulations and experiments. Experimental results show a good correlation with the numerical simulations, thus verifying the approach and the developed dynamic model with wheel slip.Mechanical Engineerin
