Design of feedback control for quadrotors considering signal transmission delays

For quadrotor types of unmanned aerial vehicles (UAVs), existence of transmission delays caused by wireless communication is one of the critical challenges. Estimation of the delays and analysis of their effects are not straightforward for designing controllers. An estimation method is introduced using experimental data and analytical solutions of delay differential equations (DDEs). Collected altitude responses in the time domain are compared to the predicted ones obtained from the analytical solutions. The Lambert W function-based approach for first-order DDEs is used for such analysis. The dominant characteristic roots among infinite number of roots are obtained in terms of coefficients and the delay. The effects of the time delay on the responses are analysed through the locations of the characteristic roots in the complex plane. Based on the estimation result, proportional plus velocity controllers are proposed to improve transient altitude responses.