Design And Control Method Research Of Fully-Actuated Tilting Rotor Hexacopter

The traditional multirotor is an underactuated nonlinear system with strong coupling of position and attitude,the position movement in any direction must be achieved by changing the attitude,which seriously affects the maneuverability of the UAV and restricts the realization of the aerial interaction task of the UAV.In order to solve the above problems,a fully actuated tiltable hexacopter is designed in this thesis to achieve decoupled control of the UAV’s attitude and position,which is based on a positive tetrahedral frame with power units evenly distributed in three-dimensional space.Based on this platform,a nonsingular terminal sliding mode controller based on geometric control and a backstepping terminal sliding mode controller based on linear extended state observer(LESO)with finite time convergence are designed to realize stable control of UAVs in fixed state and variable tilt state.The specific research contents are as follows:1)A fully actuated tiltable hexacopter is proposed,and its structure design and physical prototype are carried out.The parameters of power unit and moment of inertia of the designed UAV are measured by building an experimental platform for model parameter measurement,which provides experimental support for the design and simulation of UAV controller.2)The mathematical model of the fully actuated tiltable hexacopter is constructed,and the mapping relationship between the force and torque of the UAV and the actuator is established by analyzing the transformation relationship between the UAV coordinate systems,and the control distribution matrix of the UAV is derived.Based on the control distribution matrix,a general method for judging the driving characteristics of multi-rotor UAV is proposed,and then the driving characteristics of the UAV under fixed and tiltable states are analyzed.3)Considering the finite time convergence and singularity of traditional sliding mode control,the nonsingular terminal sliding mode controller is used to design the controller,and the control law of the fully driven UAV is designed in combination with the geometric control theory,so as to realize the large attitude angle and high maneuverability flight of the UAV.Aiming at the nonlinear control allocation matrix with parameters of fully actuated tiltable hexacopter,the nonlinear control allocation problem is linearized by linearization method.Considering the complexity of the control problem of fully actuated tiltable hexacopter,the effectiveness of the control algorithm is verified by the simulation experiments with fixed and tiltable state UAVs.The simulation results show that the proposed control framework can effectively control the fixed state UAV,but for the tiltable UAV,there are still large steady-state errors and jitter in the control process due to the uncertainties and disturbances caused by the additional tilting mechanism.4)To address the problems of steady-state error and jitter in the control process of fully actuated tiltable hexacopter due to the uncertainties and disturbances caused by the additional tilting mechanism,the backstepping method is combined with a terminal sliding mode controller and a finite time control method,while LESO is introduced to improve the robustness and rapidity of the system.The simulation results show that the backstepping terminal sliding mode controller based on linear extended State observer(LESO-BSTSMC)is effective for the fully actuated tiltable hexacopter.