Propeller Thrust Identification and Calibration for High-Precision Control of a Quadrotor Unmanned Aerial Vehicle

Quadrotors are becoming a major platform for both industrial and research activities, increasing the requirements for precise and dynamic control. Best control can be achieved by directly controlling the individual rotor thrust forces, which, during flight, can only be estimated. An identification of the thrust generation mechanism, and subsequent exploitation of this relation in the quadrotor's command chain is therefore crucial. In this work, the relationship between a given angular velocity command and actual thrust of each individual rotor is modeled as a Wiener model, consisting of a linear dynamic first-order plus time delay element and a static nonlinear second order polynomial. Parameters are identified experimentally using a propeller thrust scale and measurements of the true rotor speed. In addition, an inflight calibration procedure is proposed for compensation of varying system and environment parameters. The command structure is then implemented on a quadrotor employed with a flatness-based controller, and indoor flights in a tracking cell show a low mean error of 0.2m/s(2) between commanded and true acceleration. The simplicity and accuracy of this approach motivates the application to quadrotors with all kinds of controllers to increase their performance during dynamic maneuvers.