Open-Loop Linear Model Identification of aMultirotor Vehicle with Active Feedback Control

As multirotor vehicles become integrated into the national airspace for applications such as package delivery and videography, it is important that the inner-loop control system be robust and able to meet ever-demanding performance constraints. To achieve high bandwidth control designs, it is necessary to have accurate and high bandwidth open-loop models. In this Paper, a linear state-space model of the open-loop dynamics of a hex-configuration multirotor vehicle was identified from flight tests conducted with an active feedback controller. The system identification methodology and initial model structure were formed and informed by an analytical model, which incorporated a propeller aerodynamics model derived using blade element theory. The methodology for identification of the open-loop model involved the combined application of manual pilot inputs and automated multisine inputs added to the output of the controller. The effectiveness of the model's predictive capability was shown with a validation flight test with simultaneous excitation of the four input axes and an independent flight test for validation of the heave model. The final model structure, which incorporated axis-lumped first order dynamics to represent the propulsion system dynamics, was found to be generalizable to various traditional coplanar multirotor configurations.