I'm currently working on a (mathematical) presentation dealing with the control and stabilization of a quadrocopter.
For this I would like to present the currently implemented PID controller of the crazyflie, that is give a quick overview of its workings and limitations. Afterwards I'm going to introduce other means of stabilization, e.g. Feedback control.
It would be greatly appreciated if someone could point me to any theoretical work (papers, books, ...) that was used for the implementation of the PID (or did you figure out the parameters just by trial-and-error?

Also I'm particularly interested in a mathematical model of the crazyflie, so if anyone has already done anything related it would be great if you would share your knowledge.

Thanks,
Simon