Dynamics and Control of Tethered Multi-Rotor Unmanned Aerial Vehicles with Switchable Powered and Autorotation Modes

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This research project will promote the progress of dynamic modeling and control design, and advance the national prosperity, welfare and security by increasing both the time aloft and the energy efficiency of tethered unmanned aerial vehicles (UAVs), which are used for surveillance, communication, and sensing. The use of tethered UAVs deserves attention since they can provide a compact, portable, temporary, and rapidly deployable alternative to helicopters or satellites. The presented system, powered through an electrically conductive tether, can increase the time UAVs can remain in the air and reduce the weight of on-board batteries. The project will study the use of suitable blade geometry, a flapping/teetering degree of freedom, and active feedback control with the goal to enhance energy efficiency of a UAV by switching to autorotation when prevailing wind speeds are high. Accordingly, the new design will have the capability of reducing its energy requirement by harnessing wind energy while in operation. The system will be portable, easily deployable, and actively controlled. It will be agile, maneuverable, and its ability to switch between two flight modes will allow robust hovering at desired altitudes and orientations. The project will leverage University of Central Florida iSTEM program to involve women and underrepresented minority students in research activities and enable community outreach via the Orlando Science Center. The project will foster ongoing collaborative research with the energy and power industry and create new collaboration with local industry partners that have business interest in tethered UAVs.The research will make fundamental advances in operation of tethered UAVs by undertaking extensive efforts in dynamic modeling and control design. The two flight modes, their unique set of actuations and inputs, and the distinct aerodynamic characteristics of autorotation, distinguish the control of the system from conventional multi-rotor systems. The system has a Multi-Input Multi-Output structure, alternating causalities, many disturbance sources, a wide array of parameters, and requires active control for delivering the functionalities. The system admits a continuum of equilibria. This research will determine the feasible and optimal subspaces within this equilibrium space where, (1) the momentum theory holds and gives an accurate prediction of the aerodynamics, (2) sufficient lift is generated, and (3) the tether tension is confined within acceptable limits. Stabilization of the system will take fundamentally new directions, involving switched control, uncertainty quantification, and feed-forward actions. During autorotation, differential regenerative braking will be employed for attitude stabilization. Robust autorotation will be achieved by tether length actuation and intermittent mode switching. Thereby energy efficiency and active attitude/altitude control will become integrally coupled. The geometric symmetry of the structure will facilitate control design using reduced-order models while incurring minimal loss of generality.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.