AutoTrim was started by holding the yaw stick while arming

What ArduPilot says:

• AutoTrim start

The yaw stick was held fully right for 10 seconds in Stabilize: the first 2 arm the copter, and 8 more start this. For 25 seconds of flight ArduPilot now shifts its idea of level towards wherever you hold the roll and pitch sticks, then saves it as AHRS_TRIM_X and AHRS_TRIM_Y: a cure for a steady drift in still air. It begins counting only once the copter has taken off, and is dropped (“AutoTrim cancelled”) if you leave Stabilize, land or disarm before the end.

What to do, most likely first

1. The stick was held too long while arming, by accident.

   FixLet the yaw stick go as soon as the motors start. To stop a trim that has begun, change mode or land before the 25 s are up: nothing is saved.

2. You meant it: the copter drifts in still air.

   FixDo it in calm air only, and hold the copter in one place with the sticks for the whole 25 s.

4.7 has no stick gesture for this: there AutoTrim is started from a switch with RCn_OPTION 182 (“AutoTrim running”).

Parameters to look at

Where to do it:Setup & Tuning Guide