Evaluation of micro coaxial rotor, single rotor and quad rotor hovering attitude dynamics using system identification

Micro rotorcraft are a subclass of Micro Aerial Vehicles (MAVs) that are rapidly growing in popularity due to their ability to carry out missions and manoeuvre within confined indoor and urban environments. Due to the low cost associated with developing a micro rotorcraft prototype, a large variety of different rotor configurations have been adopted by micro rotorcraft developers. However, there is yet to be a comprehensive quantitative evaluation of how attitude dynamics are affected by different rotor configurations. To address this issue, this study outlines a comprehensive system identification methodology for comparing the dynamics of different rotor configurations; this methodology is demonstrated by applying it to coaxial rotor; single rotor (fixed pitch); and quad rotor configurations. Micro rotorcraft testbeds have been used to experimentally collect flight data in a motion capture laboratory and system identification has been used to obtain validated models for each rotor configuration. A comparison of the frequency response of each model allows their dynamic responses to be evaluated. The single rotor testbed is shown to have similar stability and response speed to the coaxial rotor testbed but has non axis-symmetric dynamics due to the inertia added by its tail boom. The quad rotor testbed is shown to be internally unstable, however, similar attitude dynamics performance to the coaxial and single rotor configurations can be achieved through the implementation of a suitable attitude feedback controller. The methodology and results presented in this study are intended to be used as a reference guide for micro rotorcraft developers to ensure that the most appropriate rotor configuration is selected for a given application. Additionally, the models identified can serve as a basis for further model-based control system development.