bms001:
Please don't take my comments the wrong way, I am not trying to discourage you!
i understand that ,but i was trying to answer your question about being sure in all my trials
i consider it acceptable because it stays (stable) in flight that is not a view point
random faults means the bad signal caused by noise and electrical disfunctionality or human bad interference
and these things happen why to be added to critical PID as parameters?!
(I have already offered a possible explanation twice (but again, without seeing the full code it is a guess). By removing the setpoint you have implicitly made it zero, so your QC wants the rate of rotation to be zero. Your control input affects the motor speed directly - in many ways it's similar to someone hitting the QC on one side as it will cause some rotation. Because the PID setpoint is zero, the QC will try to resist this rotation to bring the actual rotation back to zero. Again, this is a guess and I'm happy to be proven wrong but without any additional information this is what I suspect is happening, and is not a good control method.)
your conclusion is right about how it works, but i dont know why (it is not a good control method)!
if it is flys well and stable and works as the one of (standard PID ), where is the problem?
why to consider a non-happening problem as it happens !?
and i am going to attach the code to see it