Novel Model-Based Control Mixing Strategy for a Coaxial Push-Pull Multirotor

A Coaxial push-pull multirotor is a Vertical Take-Off and Landing (VTOL) Unmanned Aerial Vehicle (UAV) having 2n (n ∈ IN*) rotors arranged in n blocks of two coaxial contrarotating rotors. A model-based control allocation algorithm (mixer) for this architecture is proposed. The novelty of the approach lies in the fact that the coaxial aerodynamic interference occurring between the pairs of superimposed rotors is not neglected but rather nonlinear empiric models of the coaxial aerodynamic thrust and torque are used to build the mixer. Real flight experiments were conducted and the new approach showed promising results.

I. Introduction

Underactuated multirotors are the most widely used Vertical Take-Off and Landing (VTOL) Unmanned Aerial Vehicles (UAV) both for research and industrial applications due to their easy integration and high versatility. The quadcopter is the precursor of these UAVs and remains the most popular one. However, in order to meet increasing safety and payload requirements, new multirotor configurations with more than four motors have been tested and used over the recent years (like hexarotors [1], [2] and octorotors [3]–[5]). One interesting property of underactuated multirotors is that regardless of the number and disposition of the motors, they can be controlled in the same way, using four control inputs corresponding to the total thrust force and to three torques around the three body axes, as long as these control efforts are dispatched to the motors according to the rotors configuration. The algorithm in charge of this allocation is commonly called mixer.