Design And Research Of Control Mechanism Of The Small-scale Unmanned Helicopter

The small-scale unmanned helicopter has the characteristics of vertical take-off and landing,hovering,low-speed cruising,high mobility,and so on,so it is widely used in various fields.Different from the general unmanned aerial vehicle,the helicopter needs a special control mechanism,namely the swashplate mechanism,to realize the collective control and the cyclic control of the main rotors,so as to realize the control of the helicopter flight attitude.An accurate kinematic model of the control mechanism used on the small-scale unmanned helicopter is very important to solve the inputs of actuators.And the corresponding dynamic model is helpful for the design of the flight control system of the small unmanned helicopter.The helicopter control mechanism is actually a parallel mechanism with multi-loop chains,and the nonlinear relationship between the input and the output is very complex.Therefore,it is very difficult to establish the kinematic model and dynamics model for such a multi-body system.In this paper,the available limbs of the control mechanism are analyzed in detail by using Lie Group based on the helicopter control characteristics.Then,a flybar-less control mechanism with three rotary servo motors for a small unmanned helicopter is proposed by choosing the reasonable limb.Then the degree of freedom of the mechanism is verified to be correct by using screw theory.Based on the parallel manipulators concepts,a complete and accurate kinematic model is established,and the nonlinear inverse kinematics relationship between the pitch angles of the main rotors and the inputs of the control mechanism is derived.The velocity and acceleration of the mechanism are analyzed,and the jacobian matrix of each component is derived.Based on the precise kinematic model,the genetic algorithm is used to optimize the size of the mechanism.The principle of virtual work is employed to solve the inverse dynamics of the swashplate mechanism.After derivation of jacobian matrices for each component,the complete inverse dynamic solution of the control mechanism is obtained.Furthermore,an integrated actuating system model for the helicopter is established by combining the dynamic model of the main rotors and the dynamic model of the actuators.In order to verify the correctness and effectiveness of the mathematical model,the rigid body model of the control mechanism is built in Recurdyn and the mathematical model is built in Matlab.The proposed model is proved to be correct and effective by comparing the calculation results with the simulation results.Combined with the command allocation,a series of simulations for load analysis of actuators are performed.From the perspective of the entire simulation process,the equilateral triangle arrangement of these three actuators realizes a uniform distribution of the load,and the control mechanism can realize the changes in both the collective and cyclic pitch angles of the main rotor blades.