Design And Experimental Study Of Main Rotor System Of A Coaxial Helicopter For Mars Exploration

Traditional Mars exploration methods mainly include orbiter surround and rover patrol,whose imaging clarity and detection range are limited by the complex environment on the surface of Mars.The successful flight of the NASA’s Ingenuity helicopter on the surface of Mars in 2021 indicates that the Mars rotorcraft will be used as a new aerial exploration platform to effectively expand human Mars detection capabilities.Due to the low atmospheric density of Mars and the communication delay between the Earth and Mars,the main rotor system as the power source of the aircraft needs to have strong propulsion capabilities,high flight efficiency,and autonomous flight control functions.This paper proposes a main rotor system of the Mars coaxial helicopter.The main rotor mechanism parameters are optimized based on the coaxial rotor aerodynamic model and hover experiment.The hardware circuit and control algorithm of the drive and control unit are designed,and finally,the driving and control performance has been verified by flight test.The rotor is modeled as a pair of rigid beams rotating around spring hinges,and the blade flapping equation and the mathematical model of the main rotor hub force are established.The equation shows that the higher hinge stiffness is beneficial to increase the aerodynamic response speed of the aircraft in the Martian atmosphere.Based on this,the rigid hinge rotor configuration is selected.The model shows that the vertical and horizontal periodic pitch change of the upper rotor and the lower rotor can change the pitch and roll motions.Based on this decoupling,a distributed attitude control method with four manipulation variables is selected.According to the requirements of compactness,high efficiency,and high reliability,two separate motors are chosen to directly drive the upper rotor and the lower rotor,thus completing the overall design of the main rotor mechanical system and electronic control system.A coaxial dual-rotor vertical flight aerodynamic model is established based on the fluid continuity equation,the momentum and energy equation,and the slipstream theory.The power load was used to measure the propulsion capability and the quality factor to measure the flight efficiency.The hover characteristic experiment of the coaxial rotor is carried out to optimize the mechanical parameters such as the collective angle of the rotors and the distance between the rotors based on the index.A rotor blade with a trapezoidal shape near the root and a hyperbolic shape near the tip is selected,and the main rotor mechanical body structure is designed in detail based on the optimal parameters.The propulsion motor drive circuit and the attitude sensing interface circuit are designed according to the overall architecture of the main rotor electronic system,the main rotor power supply circuit.The joint inertial measurement unit and the laser altimeter pose calculation program are designed based on the Kalman filter algorithm.In order to design the main rotor attitude control algorithm,a linearized model of attitude adjustment in hovering is established based on the rigid body dynamics equation of the aircraft and the main rotor hub force mathematical model.The dynamic characteristics of the hover model are analyzed through the relative gain vector and singular value decomposition method.According to the dynamic characteristics of the model,a pitchroll control law with full state feedback and input feedforward is proposed,a yaw control method based on speed following and total distance following is proposed,and a closedloop control algorithm of the main rotor attitude is designed in combination with the attitude calculation program.The open-loop pitch and roll tests are carried out in order to verify the main rotor attitude adjustment model.It is found that the fuselage’s heading angle output lags behind the control input by about 143°,which is 4% different from the theoretical prediction.An attitude closed-loop control test is carried out to verify the attitude closed-loop control algorithm,which find that the pitch and roll angle control errors of the main rotor are within 2.4°,and the yaw angle control error is within 4.2°.The main rotor system has achieved a flight with a load of 2 kg in a simulated Martian environment,which verifies the driving and control performance of the main rotor system.