Advance Modeling of a Skid-Steering Mobile Robot for Remote ...

2.2 Generalized Modeling 25quence on robot vibrations is considered. Conversely, for remote telepresence applications,jerky motion and vibrations are usually not negligible as the robot is often required to performsharp movements, like swiveling in place, and the remote user continuously needs fullcontrol of the robot and clear vision of the environment.In order to provide a dynamic model reproducing the real robot jerky motion and large amplitudevibrations, we need to include the roll and pitch motion and a more accurate modelof reaction forces. In particular, an accurate model of the reaction forces will be deeply discussedin Chapter 3 and 6.1, while a generalized 3D dynamic model of skid-steering motionis provided in this section, considering the reaction forces as unknown functions. As therobot is allowed to freely move in a 3D space, Assumption 1,5,6 considered in the previoussection will not hold in the following, while Assumption 2,3,4 still hold.We first consider a 4-wheels skid-steering vehicle moving freely in the 3D space, as depictedin Figure 2.5.Figure 2.5: Three dimensional SSMR kinematics.To describe motion of the robot it is convenient to define an local frame attached to itwith origin in its CoM. We assume that q = [X T Θ T ] T = [X Y Z φ ψ θ] T denotesthe generalized coordinate vector, where X, Θ determine respectively the CoM positionand the orientation of the local frame with respect to the inertial frame, using theRoll (rotation around the z-axis about φ), Pitch (rotation around the y-axis about ψ) andYaw (rotation around the x-axis about θ) angles as representation of the orientation. Let