An Open-Source Benchmarking Platform for Coaxial Rotor Systems

A project log for OmniRotor: An Agile, Coaxial, All-Terrain Vehicle

A coaxial, versatile, modular, tilt-rotor, all-terrain vehicle that can apply its full thrust in any direction.

Joao BuzzattoJoao Buzzatto 10/16/2021 at 20:230 Comments

Small scale, electric, Vertical Take-Off and Landing (VTOL) Unmanned Aerial Vehicles (UAVs) have been extremely popular in robotics, and roboticists prefer such vehicles because they integrate sophisticated small electric sensors, complex control algorithms, and they are mostly aimed at autonomous systems applications. UAV concepts have also grown in variety and complexity, both in terms of design and automation, but also aerodynamically. Aerodynamics research, however, is not the focus of the robotics community. So complex aerodynamic systems are usually treated in a simplified manner, often operating in sub-optimal conditions and not enough research effort is put towards improving them. This is particularly evident in multirotor vehicles with coaxial rotors, where each motor/propeller pair is still treated as a single rotor (as in the PX4 and ArduPilot flight stacks, for example). Such rotor configurations is generally used in applications requiring high thrust but small vehicle footprint, such as in aerial manipulation, drone delivery, and to enable the development of new vehicle concepts, such as the Omnirotor presented in this project. Due to their heavy load capacity and rotor redundancy, coaxial multirotor systems are also employed in manned multirotor and transport applications  (see EHang, Airspeeder, and DCL's Big Drone), or even for the exploration of Saturn’s moon Titan. But despite the large range of applications and the potential of coaxial rotor systems, there are very few works that focus on studying them and on how to improve them.

Figure 1: The benchmarking platform designed to test coaxial rotors systems used on multirotor UAVs. Each side of the testing rig is equipped with force and torque sensors for measurements on one axis. Individual motor speed, applied voltage, and consumed electric current are also measured. Everything is integrated and controlled by a LabView interface, where both closed and open-loop experiments can be programmed.

As part of the Omnirotor project, we also developed an open-source benchmarking platform for coaxial rotor systems that allows us to analyse and improve their efficiency. The platform is highly automated and allows for fast, extensive experiments measuring thrust, torque, motor speed, applied voltage, and electric current consumed by each rotor. Further details will follow on the next logs.