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Experimental Nonlinear Control of a Helicopter Unmanned Aerial Vehicle (UAV) Open Access


Other title
control theory
unmanned vehicles
Type of item
Degree grantor
University of Alberta
Author or creator
Godbolt, Bryan M.
Supervisor and department
Alan Lynch (ECE)
Examining committee member and department
Martin Jagersand (Computing Science)
Kimon Valavanis (University of Denver)
Tongwen Chen (ECE)
Bob Koch (Mechanical Engineering)
Department of Electrical and Computer Engineering
Control Systems
Date accepted
Graduation date
Doctor of Philosophy
Degree level
Helicopter Unmanned Aerial Vehicles (UAVs) present a challenging control problem since their dynamics are nonlinear, underactuated and non-minimum phase. Although it is inherently an applied research field, due to the difficulty of building and maintaining an experimental platform relatively few experimental results exist in the literature. The approach followed in this thesis is to combine rigorous analysis with thorough experimental testing. This testing ensures validity of the designs. We present our experimental platform which is designed to be flexible so that it can accommodate nonlinear control research. Existing accounts of helicopter testbeds focus on hardware details. Since autopilot software design and development also requires a significant investment, we describe our implementation which has been released as open source for the benefit of the community. Due to the intractability of existing helicopter models, many control designs use non-physical inputs. We propose simple, invertible expressions relating the non-physical inputs to the physical inputs. In particular, modelling of the main rotor typically results in complicated expressions with extensive state dependence. While it is unlikely that angular velocity has a significant influence on the thrust, we show using experimental results that previous attempts to simplify this expression using a hover assumption are invalid during vertical flight. The platform is validated using a model-based PID control law. This control is derived using passivity to ignore nonlinear terms which do not affect stability. Among the class of vehicles with similar flight capabilities, helicopters possess a coupling between the rotational inputs and translational dynamics which is unique. This coupling is sometimes referred to as the Small Body Force (SBF) and is ignored in the literature for controller synthesis. We derive an experimentally-validated control design which accounts for the effect of the tail rotor in the SBF. In addition, we show why the contribution of the main rotor flapping in the SBF cannot be compensated using the same approach, and give a robustness analysis of their effect on the closed-loop. Finally, based on recent results we propose a control design which accounts for state constraints by enforcing bounds on translational velocity and roll-pitch travel.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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