Position control of VTOL UAVs using IMU and GPS measurements

We propose a new position control scheme for vertical take-off and landing (VTOL) unmanned airborne vehicles (UAVs). Traditionally, the control schemes for this type of vehicle assume that the system attitude is accurately known (or measured). Unfortunately, there does not exist any sensor that directly measures the orientation of a rigid body. Instead, to obtain the orientation of the aircraft, separately designed attitude-estimation schemes relying, for instance, on an inertial measurement unit (IMU) must be employed. Consequently, one drawback of this common practice, on top of the possible inaccuracies in recovering the systems attitude, is mainly related to the difficulty of proving the stability of the overall closed-loop system (observer-controller). Motivated by this problem, we propose a new position control scheme that does not require the recovery of the system´s attitude. Instead, we rely on a direct use of the vector measurements provided by the IMU. Our approach can efficiently handle large linear accelerations, which is not the case in traditional controllers relying on IMU-based attitude observers that assume that the accelerometer provides a measurement of the gravity vector in the body-attached frame.