After the procedure showed here: http://ardupilot.org/copter/docs/autotrim.html?highlight=autotrim
(Channel 7 switch above 1800, after landing, throttle Zero for at least 1sec, still armed)
the Params in the Full Parameter Tree are still the same as bevore.
It is not described, if we have to disarme bevore switching to 1 or not.
(Pixracer R14)