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This paper presents a practical design approach to the stabilization of a three degrees of freedom (3-DOF) RC helicopter. First, the nonlinear model of the RC helicopter is constructed. To facilitate control design, a simplified version of the nonlinear model is derived. A Takagi-Sugeno fuzzy model is then constructed to represent the simplified nonlinear model. The control purpose is to stabilize the RC helicopter while taking into account practical performance considerations in terms of good speed of response and small control effort. To achieve the control objective, we impose a decay rate condition to ensure a good speed of response and an input constraint condition to avoid actuator saturations in the control design. Both conditions are represented in terms of linear matrix inequalities (LMIs). By simultaneously solving them, we render a stabilizing fuzzy controller that achieves good speed of response with small control effort. However, the controller designed for the simplified model can not always stabilize the original nonlinear model due to discrepancies introduced via the simplification process. To overcome this limitation, we design a robust fuzzy controller to compensate for the modeling discrepancies. The resulting robust stability condition with good speed of response is represented in terms of LMIs. By simultaneously solving this condition together with an input constraint condition, we arrive at a robust stabilizing fuzzy controller that achieves good speed of response without actuator saturations. Both simulation and experimental results are included to demonstrate the viability and applicability of the approach.
Date of Publication: March 2004