Adiguzel, F., and T. V. Mumcu. “Robust Discrete-Time Nonlinear Attitude Stabilization of a Quadrotor UAV Subject to Time-Varying Disturbances”. Elektronika Ir Elektrotechnika, vol. 27, no. 4, Aug. 2021, pp. 4-12, doi:10.5755/j02.eie.28916.