Position Control of an Unmanned Autonomous Helicopter Using Robust Backstepping

In this paper, a robust control strategy applied on a small helicopter is proposed. An approximate small-scale helicopter model with decoupled dynamics is adopted for the controller design which uses the backstepping method based on the Lyapunov function. The Lyapunov function is used to show the robustness of the proposed control method under conditions of wind gusts. Finally simulation results, which show the effectiveness of the proposed controller and its ability to cope with external wind gusts on a plant model, are presented. Among the variety of unmanned aerial vehicles (UAVs), unmanned autonomous helicopters (UAHs) are a class of pilot-less vehicles which have unique aerodynamic and propulsion characteristics. These propulsion characteristics enable them to perform vertical takeoff and landing (VTOL). In addition to the ability of VTOL, unmanned helicopters can also hover at a desired height for extended periods of time, fly forwards, backwards and laterally and perform extremely agile manoeuvres at both high and low airspeeds. In addition to the above advantages, small UAHs cost less, can be used for dangerous operations and are easy to operate; therefore, they are suitable for various applications. The special capability of an UAH to hover, takeoff and land on rough terrain give it an advantage over an unmanned fixed-wing aircraft, which requires a runway for takeoff and landing. Nevertheless, helicopters are highly nonlinear and complex systems, and inherently unstable by nature. This behavior makes controlling a small UAH a very challenging job, especially in situations of rapid combat, high crosswinds or low light. The presence of wind disturbances, measurement errors, and model and parameter uncertainties poses further complications in the control design. Therefore, robustness is one of the critical issues, which must