Skid-steered vehicles are often used as outdoor mobile robots due to their robust mechanical structure and high maneuverability. Sliding, along with rolling, is inherent to general curvilinear motion, which makes both kinematic and dynamic modeling difficult. For the purpose of motion planning, this paper develops and experimentally verifies dynamic models of a skid-steered wheeled vehicle for general planar (2-D) motion and for linear 3-D motion. These models are characterized by the coefficient of rolling resistance, the coefficient of friction, and the shear deformation modulus, which have terrain-dependent values. The dynamic models also include motor saturation and motor power limitations, which enable correct prediction of vehicle velocities when traversing on hills. It is shown that the closed-loop system that results from inclusion of the dynamics of the [proportional-integral-derivative (PID)] speed controllers for each set of wheels does a much better job than the open-loop model of predicting the vehicle linear and angular velocities. For a vehicle turning with small linear and angular accelerations, the model provides accurate predictions of velocities and reasonable predictions of torques. Hence, the closedloop model is recommended for motion planning.

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This paper proposes a new control approach for a robotic walking support system to adapt a user's controlling characteristic. The control approach will be implemented by changing the kinematic structure of the robotic walking support system based on a variable center of rotation. This new control approach aims to help users who have difficulties in controlling their walking support system. In this study, we have a training stage to evaluate and adapt user's controlling characteristics. This will be implemented by allowing the user to follow some training paths. In the event a large path error occurs, a learning algorithm will vary the center of rotation of the support system until the user can successfully follow the training path. The relationship between the user intent in the form of applied force/torque and the new center of rotation will be taken by considering several training paths. This relationship will be used in actual control of the robotic walking support system. Experimentation and evaluation are presented to show the validity of the proposed control algorithm.Index Terms-Robotic walking support system, variable center of rotation.

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