"I've had similar problems ever since we updated to 2.055, with the problems persisting in 2.1, and seen other users with similar yaw problems (an maybe related roll or pitch problems). 

I was able to get the problem to go away in 2.055 by resetting…"

"If your copter is sitting still, but connected to Mission Planner, does the compass bearing on the heads-up-display continually spin, that is indicate that the copter is spinning even though it's sitting still? "

"When you say that you've done two auto levels in the basement, what exactly do you mean? Did you level using the 'hold yaw left 10 seconds' or did you use 'in-flight leveling' (hold yaw right for 20 seconds)?
Also, have you checked your center of…"

"I would think the easiest way to make a dodecacopter  or hexadecacopter with APM would be to simply use a hex or octo frame (respectively) with props both above and below the arms (i.e., like a y-6, but with 6 or 8 arms instead of 3).

I'm no…"

"Thanks for the suggestions. I re-installed 2.055, cleared eeprom, and re-setup the copter. I also switched power for APM from ESC to a dedicated UBEC, just in case. That seemed to do the trick - yaw drift is gone now.
My guess is that the compass…"

"I'm starting to feel like this is just a conversation with myself. Oh well; posting here what I've learned for posterity and future APM users. 
 
So looking at the code, it does appear that activating auto_trim in channel 7 works exactly the same as…"

"It's the propellers that have to be level. It doesn't matter if the APM, frame, or anything else is level, only the props - after all, it's the props that generate thrust.
There are two ways to set level in the field, which is potentially better…"

"The left stick isn't spring loaded on the m2, whereas it's the right stick that isn't spring loaded on the m1. The non-spring-loaded stick is used for throttle. Ultimately, it's your choice which one you want to use, but most people have the…"

"All,
 
Still having problems getting in-flight leveling to last longer than 13 seconds in my hexacopter. From browsing the forum and the Wiki, it looks like I can set up the software to allow me to turn in-flight leveling on an off using channel 7.…"

"Is your APM connected to the ESC's? If your APM is not connect to the ESCs, then the ESCs will continue to beep non-stop. If that's the case, either learn to live with it (it's annoying, but you don't want your props spinning up when you least…"

"Nope, re-installing the firmware didn't fix the problem....."

"Did you bind the receiver with the transmitter? Even though the receiver came with the transmitter, I still had to bind the Tx/Rx for my Turnigy 9x first."