Collaborative Research: Spherical Sailing Omnidirectional Rovers (SSailORs) for Sustainable, Persistent, and Autonomous Characterization of Remote Environments

This research project will establish the first spherical wind-powered rover capable of moving in all directions, thereby enabling an unprecedented level of persistence (defined as the ability to execute a mission without stopping to recharge) and autonomy (defined as the ability to operate without human intervention). Analogous to how modern sailboats leverage lifting sails and keels, centerboards, or other vertically oriented foils to enable upwind motion, Spherical Sailing Omnidirectional Rovers (SSailORs) will use lifting sails and a directionally constrained hull to achieve the same result. Specifically, the lifting sails will enable forward thrust even when moving in an upwind direction. The directionally constrained hull will enable significant lateral resistance when the hull heels (tilts) due to the lateral force from the wind, thereby resisting sideslip. While preliminary investigations of the SSailOR indeed confirm its ability to move in all directions under different slopes, the robust achievement of these capabilities across a wide variety of operating regimes (characterized by different wind and terrain, for example) requires a delicate balance between several features related to both the physical design and control system. Achievement of this balance through a formal physical system and control co-design process represents the centerpiece of the research plan. The resulting designs will be validated through a progressive experimental campaign, including wind tunnel testing, dynamic characterization in a controlled environment, and dynamic characterization in North Carolina’s Outer Banks. The research activities will be complemented by outreach activities with both the Engineering Place at NC State University and the University of Michigan Engineering On-Ramp.To achieve robust omnidirectional mobility and optimize the expected performance of SSailORs, the project will pursue a combined physical and control system co-design process that is centered around a unique characterization termed the stochastic velocity polar (SVP). This characterization statistically quantifies the achievable speed of the rover along any direction relative to the wind direction, over a specified set of terrain types and grades. The SVP will first be parametrically characterized based on longitudinal, lateral, and heel (rotational) characterizations of the SSailOR. After this, a sequential plant-controller co-design process will be used to maximize an objective function that statistically characterizes the scientific information that can be gathered from a candidate design and controller, subject to chance constraints. Following the sequential co-design process, a stochastic reachability-based co-design process will be used to refine the design over a reduced design space. The co-design work will be complemented with an experimental plan that begins with static wind tunnel tests aimed at validating and refining the SSailOR model. This will be followed by controlled dynamic testing, with the primary goal of demonstrating upwind mobility in a constant wind field, and will culminate with testing in the Outer Banks, to demonstrate that upwind mobility is preserved in realistic, time-varying wind conditions and inconsistent terrain.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.