pid regulator tune by responce.

Hello. In embedded code i realize PID-regulator to attitude control for quadrotor. The output of PID-controller ( C ) is input of plant model ( P ). To manage closed-loop the output of P is input of C. Like here: http://ctms.engin.umich.edu/CTMS/index.php?example=Introduction&section=ControlPID

PID-regulator is:

C = pid(10,450,10,0,0.002);

Coefficients of C is estimated and modelled in Matlab by experiment with a quadrotor. The problem that there is not stability. The reason is incorrect experiment that give me incorrect P model. So the transfer function of P is unknown. There is known output of system. See picture in attachment. The input of system is zero. So my answer how to estimate transfer function of P by known transfer function of C and output of system. Function tfest() wan't work because there is must be step input.