Research On The Control Of Chaos In A Small Unmanned Helicopter

In recent years,small unmanned helicopters have been widely used in civil and military fields due to their advantages of high mobility and flexibility.However,small unmanned helicopters have a complex structure,strong nonlinear and coupling,and open-loop instability.At the same time,they are susceptible to the impact of uncertainties,resulting in the fuselage oscillation.Based on the mathematical model of the helicopter,our research group analyzed the dynamic characteristics of the helicopter and found that the angular velocity of the helicopter would generate chaotic oscillations when the counterweight of the helicopter was improper,which would lead to severe shaking of the airframe in practice,and eventually crash out of control.This thesis mainly studies the control of the small unmanned helicopter,especially the control of chaotic oscillation.By reasonable simplification,the mathematical model of helicopter hover and low-speed flight is built,and the dynamics characteristic of the helicopter is analyzed.The chaotic states of the angular velocity will lead to the body extremely unstable,so this thesis designs some sliding mode variable structure controllers(SMCs)and high-order differential feedback controllers(HODFCs)to control the angular velocity of the helicopter.Based on the sliding mode variable structure control strategy,the sliding mode control law of each subsystem of the small unmanned helicopter is designed step by step to realize the tracking control of the helicopter position and attitude.The following conclusions can be obtained from the study on the control of helicopters: prior to chaos of angular velocity appears,the controller can effectively stabilize the occurrence of chaotic oscillation;However,it is unable to stabilize the chaotic oscillation by the controller once chaotic angular velocity occurs.The redesigned angular velocity controller,the chaotic angular velocity is gradually stabilized even if after chaos is generated.Because the sliding mode control relies on an accurate mathematical model,there always is a certain steady-state error after the system is stabilized.The high order differential control strategy is adopted,which does not depend on the accurate mathematical model,this method solves the disadvantage of sliding mode control.The controller of each subsystem of the helicopter is designed step by step to realize the tracking control of helicopter position and attitude.By comparing with sliding mode control,it is shown that the higher-order differential feedback control has stronger adaptability to the change of fuselage structure and stronger robustness to external interference.Once the helicopter has angular velocity chaos,the redesigned angular velocity controller is loaded,and the angular velocity gradually stabilizes,and the steady-state error is eliminated.This thesis builds the experiment platform and the electronic system of the small unmanned helicopter,completes the manual flight test by the experiment platform,realizes the flight control experiment of the high order differential control by applying to the unmanned four-rotor aircraft,and verifies the strong adaptability and robustness of the high order differential controller.