Swing angle estimation for multicopter slung load applications

A filtering technique based on a set of recursive equations is analyzed and applied to swing angle estimation for multicopter slung load applications. Starting from the equations of motion of the coupled slung load system, an observation model is derived to autonomously measure the swing angle by means of the data available from the onboard IMU, without the need to rely on extra sensors. Provided the multicopter is subject to known control inputs, data-fusion is performed through a Fading Gaussian Deterministic approach, whose theoretical background was recently investigated by the author. In particular, the algorithm is based on a two-step set of equations derived from the minimization of a cost function where earlier data are progressively de-weighted by a fading factor, making the estimation less prone to problem unknowns. The validity of the approach is investigated by means of numerical simulations, where a tuning criterion is shown to provide the fading factor that best dampens the modeling errors with respect to the measurement noise. Estimated swing angles are then used in a sample feedback control application with the aim to simultaneously perform trajectory tracking and payload swing damping.