Unmanned Aerial Vehicles (UAVs) have become more and more popular, and how to control them has become crucial. Although there are many different control methods that can be applied to the control of UAVs, nonlinear control techniques are more practical since the nonlinear features of most UAVs. In this thesis, as the first main contribution, three widely used nonlinear control techniques including Feedback Linearization Control (FLC), Sliding Mode Control (SMC), and Backstepping Control (BSC) are discussed, investigated, and designed in details and flight-tested on a unique quadrotor UAV (Qball-X4) test-bed available at the Networked Autonomous Vehicles (NAV) Lab in Concordia University. Each of these three control algorithms has its own features. The advantages and disadvantages are revealed through both simulation and experimental tests. Sliding mode control is well known for its capability of handling uncertainty, and is expected to be a robust controller on Qball-X4 UAV. Feedback linearization control and backstepping control are considered a bit weaker than sliding mode control. A comparison of these three controllers is carried out in both theoretical analysis and experimental results under same fault-free flight conditions. Testing results and comparison show the different features of different control methods, and provide a view on how to choose controller under a specific condition. Besides, safety and reliability of UAVs have been and will always be a critical issue in the aviation industry. Fault-Tolerant Control (FTC) has played an extremely important role towards UAVs’ safety and reliability and the safety of group people if an unexpected crash occurred due to faults/damages of UAVs. Therefore, FTC has been a very active and quickly growing research and development field for UAVs and other safety-critical systems. Based on the use of sliding mode control technique, referred to as Fault-Tolerant SMC (FT-SMC) have been investigated, implemented, flight-tested and compared in the Qball-X4 test-bed and also simulation environment in both passive and active framework of FTC in the presence of different actuator faults/damages, as the second main contribution of this thesis work.
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