A Benchmarking Platform and a Control Allocation Method for Improving the Efficiency of Coaxial Rotor Systems

Coaxial rotors used on multirotor Micro Aerial Vehicles (MAVs) are complex aerodynamic systems that are typically treated in a simplified manner, operating in sub-optimal conditions. In this letter, we propose: i) an open-source benchmarking platform for coaxial rotor systems that allows us to analyse and improve their efficiency and ii) a map of the whole actuation domain of coaxial systems based on extensive experimentation. In particular, we test three systems built using off-the-shelf components and different rotor configurations. Results demonstrate the existence of a maximum efficiency boundary, which covers the whole thrust range of each system. We also analyze how this boundary changes with respect to the rotor configuration. We compare it with the performance of coaxial rotors controlled with the current standard method (i.e., equal commands for both rotors). Finally, we propose a control allocation strategy that improves the efficiency of coaxial rotors by up to 11% over the current industry standard. Implementation on an octocopter with four sets of coaxial rotors validates the proposed methods across two different rotor separation designs and two different payload scenarios.