hello everybody I confused about quad-copter model identification , since the quad is unstable in open loop ,then how can I identify it since is unstable? But if I add a controllers in loop of system and re-identify the new global system in close loop ; then how can I extract the quad-copter original model from a close loop model which contain the controllers function? I am so confused about that .  

  or  do not I need to the controller , I am only need to record the reference data (input to plan) (coming from Joystick ) and the  output data (coming from quad-copter) , in this case the controllers will be I , by manipulating the reference (input to plan) according to (what I see) quad-copter situation?