Modeling, Control, and Closed-Loop Mobility Characterization of a S pherical S ailing O mnidirectional R over (SSailOR)

Abstract This paper presents a control-oriented dynamic model, controller, and closed-loop mobility characterization for the first wind-powered spherical rover capable of net upwind motion. This device, termed the Spherical Sailing Omnidirectional Rover (SSailOR), incorporates design features within a spherical, terrestrial rover that mimic the role that a centerboard (or keel) and lifting sails play in allowing net upwind motion for sailboats. Specifically, a traction hoop enables significant lateral resistance, thereby providing a nonholonomic constraint in the direction of travel. Lifting sails enables net thrust even when traveling significantly upwind, while also providing heading control. While providing unique capabilities, the SSailOR gives rise to a complex design and control space, where careful model-based design and control are necessary to ensure that the SSailOR can simultaneously (i) make net upwind progress, (ii) respond quickly to wind speed/direction changes, (iii) limit heel angle, and (iv) control its heading. To simultaneously address these challenges, we first present a control-oriented dynamic model. This is followed by the presentation of a combined heading and heel angle controller. Finally, with the dynamic model and control structure in place, we present a detailed closed-loop Pareto analysis, which illustrates the tradeoff between transient and steady-state performance, along with the design features that favor one modality of performance over another.