At the beginning of the takeoff my F550 wants to flip backwards (15°). Just in the air it stabilize and hoover with sticks in center position. During the flight everything is OK. I assume that one of the ESC's is not calibrated well. The motors are already changed. Other brands of ESC's have to be calibrated. Is this also possible for the DJI 30A OPTO ESC's and how is the procedure?