Research Of Attitude Control System For Quad-Rotor Aircraft

In recent years, with the development of Micro-Electro Mechanical System (MEMS) technology, aircraft technology has made great progress, and been widely used in the civilian and military fields. Different from traditional helicopter, Quad-Rotor aircraft, with four cross-shaped propellers, can only realize various actions through to change the speed of the propeller. Because it is six degrees of freedom of the VTOL aircraft and is ideal for flight in the static or quasi-static condition, the research of Quad-Rotor aircraft has great practical significance. As typical nonlinear system, attitude control of Quad-Rotor aircraft has always been a hot topic and difficulty. Combined with microelectronics and classical filter theory, an attitude control system of Quad-Rotor aircraft has been designed in this work, which mainly consists of hardware and software design, and attitude algorithm.In aspect of hardware design, based on modular design, hardware system is composed of the sensor module, power management module, processor module, serial communication module, remote control module. Sensor module composed of three sensors, respectively, gyroscope and accelerometer, digital compass, barometer, which are responsible for collecting aircraft attitude data and transferring data to the controller module through the I2C bus. As the core of system, controller module is responsible for collecting data, processing algorithm and coordinating control of each module. Serial communication module is mainly used to communicate with the host computer and debug in the stationary state of the vehicle. Remote control module is used to send remote control signals through RC interface. Power management module includes a lithium 11.1V battery, and power conversion circuits. The system’s power is supplied by the power management module during flight.In aspect of software design, similarly based on the idea of modular design, software design of the system is composed of four main modules, namely:the system initialization module, data communication module, data acquisition and processing module, attitude control module. Initialization module of the system is responsible for initializing each peripheral controller, communication protocol and control algorithm parameters. Data communication module is mainly for data transmission between the various parts, including the wireless communications of remote control, I2C communication of sensors and serial communication of host computer. Data acquisition and processing module is responsible for data acquisition and processing through the accelerometer, gyroscope, digital compass and barometer. Attitude control module, according to the collected data of attitude, is used to run the attitude control algorithm, and calculate the control signal of each channel transmitted to the motor drive to change the motor speed.In aspect of the attitude algorithm of Quad-Rotor aircraft, Kalman filter (Kalman Filter) and EKF (Extended Kalman Filter) have been expounded. The sensor measurement model and the dynamic model of system have been established. Based on the model, these two algorithms are being simulation analysis and experimental data show that the Extended Kalman Filter algorithm has faster convergence, smaller error, and better robustness. Therefore the Extended Kalman Filter has been used to integrate attitude data. Meanwhile, based on the hardware platform of the attitude system for Quad-Rotor aircraft, the classic PID control algorithm has been used to control the actual attitude angle and the expected attitude angle of the aircraft, which forms a closed loop negative feedback to make the system stable by tuning aircraft’s PID parameters.