Feedforward control design for a four-rotor UAV using direct and indirect methods

To calculate feedforward control strategies by means of dynamic optimization procedures, the alternatives of direct and indirect methods are compared in this paper. The direct optimization approaches that are considered in this paper make use of the Hermite-Simpson method and of the Legendre Pseudospectral method as underlying discretization strategies. Their description is followed by a short introduction to the maximum principle of Pontryagin, i.e., the indirect method. All procedures are employed to compute feedforward control sequences for the flight control of a four-rotor UAV, which is an unstable, nonlinear multi-input multi-output system. The optimization results are compared with respect to their accuracy and applicability.