Implementation of a Phase Synchronization Algorithm for Multirotor UAVs

Noise generated by small unmanned aerial vehicles has been the objective of research in the past few years. Recent applications of these vehicles, especially those in a multirotor or multi-propeller configuration, include but are not restricted to package delivery, surveillance, mapping, and inspection. However, noise can be a major barrier to public acceptance of these operations. A recent explored alternative is to synchronize the azimuthal position of each propeller. Since the destructive interference is directional, by adjusting the relative offsets of each noise source it is possible to steer the effect into a specific direction of interest. This work presents the implementation of a synchronization algorithm for the azimuthal position of the propeller applied to a small multirotor unmanned aerial vehicle. By considering a virtual reference model for a rotor with a propeller, the controller estimates the difference between the current azimuthal position and the desired one, sending a differential speed command to each rotor to align them with the virtual reference. A fixed azimuthal offset position can be added for each rotor, allowing the synchronization to occur between any combination of actuators. A vehicle configuration with four rotors is used to test and validate the implementation. The synchronization is verified using a high-speed light source measuring equipment as well as by logging data output from the controller and rotors. Lastly, rotor speeds for typical flight conditions of that size of vehicle are tested, and the steady-state performance is presented.