Differential Flatness of Quadrotor Dynamics Subject to Rotor Drag for Accurate Tracking of High-Speed Trajectories

• Published in: IEEE robotics and automation letters Vol. 3; no. 2; pp. 620 - 626
• Main Authors: Faessler, Matthias, Franchi, Antonio, Scaramuzza, Davide
• Format: Journal Article
• Language: English
• Published: Piscataway IEEE 01.04.2018; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Acceleration; Aerial systems; Aerodynamics; Computational modeling; Computer Science; Control methods; Control systems; Control theory; differential flatness; Drag; Drag coefficients; dynamics; Feedback control; Feedforward control; mechanics and control; Nonlinear control; Nonlinear feedback; Optimization; quadrotor control; Robotics; Rotary wing aircraft; Rotors; Tracking errors; Trajectories; Trajectory; Trajectory tracking
• ISSN: 2377-3766; 2377-3766
• DOI: 10.1109/LRA.2017.2776353

In this letter, we prove that the dynamical model of a quadrotor subject to linear rotor drag effects is differentially flat in its position and heading. We use this property to compute feedforward control terms directly from a reference trajectory to be tracked. The obtained feedforward terms are then used in a cascaded, nonlinear feedback control law that enables accurate agile flight with quadrotors. Compared to the state-of-the-art control methods, which treat the rotor drag as an unknown disturbance, our method reduces the trajectory tracking error significantly. Finally, we present a method based on a gradient-free optimization to identify the rotor drag coefficients, which are required to compute the feedforward control terms. The new theoretical results are thoroughly validated trough extensive comparative experiments.