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The First Step Of GD32F103+MPU9150 Quad-Rotor Aircraft: Attitude Fusion Algorithms

Compared with the helicopters, the mechanical structure of the quad-rotor and even the multiple rotor aircraft is simple, flexible and stable. The volume of it can be smaller or larger centainly. It transforms the helicopter’s difficulties of the complex mechanical design to the electronic circuits and algorithms, so the design of the quad-rotor aircraft is easier and much more popular.

The core of the quad-rotor aircraft’s software consists of two parts: attitude fusion algorithms and control algorithms. The cores of the hardware are MCU and sensor. The attitude fusion algorithms is to mix the 3 axis acceleration, the 3 axis angular velocity and the 3 axis magnetic field strength into the quaternion, and then convert the number of quaternion into the Euler angles. Finally, transport the Euler angles to all the motors as controlled quantity to control the attitude of the aircraft. Euler angles include angle Yaw, angle Pitch and angle Roll. AHRS Update is integrated with gyroscopes, accelerometer and magnetometers, while IMU Update is only integrated with gyroscopes and accelerometer. As far as the advantages and disadvantages are concerned, the IMU update algorithm only combines the accelerometer and the data of the gyroscope. It also needs the complementary filtering algorithm to fuse the magnetometer to correct the angle Yaw. Otherwise the aircraft could not find true direction. But there is a problem in this complementary filter. If the range of the angle Yaw is about 0 to 360 degrees, the head of the aircraft will go through 0 degrees (360 degrees) when the head is about 1 degrees north by west to 364 degrees north by east. However, AHRS update can solve this problem very well. But when the sensor is disturbed by a strong peripheral magnetic field, because AHRS update integrates the magnetometer data into all Euler angles, it may lose a full-scale control, and cause the crash.
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