Orientation filter and angular rates estimation in monocopter using accelerometers and magnetometer with the Extended Kalman Filter

In monocopter flight, two important parameters are required for control: angular rates and heading direction. Small monocopters fly at a very high speed (more than 600rpm), which can be out of the typical gyroscope limit. Very high speed gyroscopes do exist, but the price is high and it can only measure a single axis rotation. This paper presents an alternative approach to measure angular rates by using three accelerometers. The readings of the accelerometers are subtracted to calculate the angular rates in all three axes (x, y, and z). This paper also proposes to use the Extended Kalman Filter (EKF) to estimate the heading direction based on the magnetometer reading and the angular rates. The angular rates direction is used as the vertical direction reference. The proposed method has been applied on two setups: DC Motor setup (for quantifying the method's performance) and Monocopter setup. In the DC Motor setup, the motor encoder is used as the ground truth for the heading direction. The result is compared with the usual method of using only the magnetometer to obtain the heading direction of monocopters. The EKF result is more accurate and stable even in the presence of strong magnetic disturbances. In addition, the angle of attack and the coning angle can also be determined by the proposed method.