I have a stock ArduCopter frame with ArduCopter 2.0.55. I have enabled the mag, and it's soldered as described in the wiki.
It hovers very stable, and yaw is not drifting. However, when I apply yaw input with the rudder stick, the quad yaws in the wrong direction.
It looks correct in the radio calibration in the mission planner. Moreover, it arms when I move the rudder stick to the right. Hence, I don't think I should reverse the rudder channel.
That can sometimes seem the case for small yaw movements if the motors are a little askew. Does it still do that if you move the yaw stick a bit more?
Upon inspection, I saw that one of the arms were a liiittle bit twisted. It was barely visible. I have twisted it back and will try again. I will also try to move the stick a bit more (I was very careful in the sticks).
I will try again and report back! I need to order a new propeller, though, as the landing after the last attempt was less than optimal ;-)
Ok, I tried again now. What happens is:
1. I take off and hover. It hovers nicely without any drift
2. I apply some slight left rudder. Now the copter starts rotating to the right.
3. I apply even more left rudder. Now the copter rotates the correct direction (left)
4. Moving the rudder stick to the right works fine - the copter rotates to the right.
5. After this has happened, the copter yaw starts drifting to the left without input.
I have checked all the arms and motors -- they have no visible bends or twists.
Anything else I can try?
Correction: forget about point 5. It seems to have disappeared in 2.1.
After a few flights, it got much better. Compass offsets, perhaps?
Yes, the in air compass calibration takes a minute or two in the air.