Disturbance observer-based control schemes for quadrotors – a tutorial

This paper presents a short tutorial introduction to disturbance observer-based control approaches for the quadrotors. With this tutorial, researchers, engineers and students would be able to implement disturbance observer-based model-in-loop simulations and experiments more easily to design robust autopilot system for the quadrotors. To achieve this, first of all, the modeling and controlling of a quadrotor are explained and all linear disturbance observer-based control approaches in the literature are adapted in its overall nonlinear architecture. Disturbance observer-based control design steps are given in detail by design challenges. To show their disturbance rejection capabilities and practical applicability, two flight simulation scenarios are carried out. For all simulation cases, we only take into account the external disturbances in rotational motions. While we give the attitude trajectory commands to quadrotor attitude control architecture in the first scenario, we issue both way-point and trajectory commands to an outer loop controlling the translational motions in the second one. Presented disturbance observer-based control approaches have successfully completed the given reference commands in the presence of the external disturbances even under the measurement noise. Moreover, simulation experiments have shown that UDEBC approach transmits the external disturbance and measurement noise effects to the actuators directly. As a result, for UDEBC approach, it should be kept in mind that flight accidents may occur due to excessive ESC heating. Baseline attitude controller without disturbance observer-based control approach have failed to follow the given reference commands. The simulation studies have also proved the practical applicability of these methods, which are successful even under measurement noise.