Is anybody using this function? How does it work? I've read what's in the wiki, and it's really not that helpful.
#define CH7_OPTION CH7_AUTO_TRIM
Allows you to hold trim the accelerometers of the copter when this switch value is high.
I gave it a shot, and set Ch7 option to Auto trim. I took off normally, got into a hover, flipped Ch7 high, hovered for a bit, then turned it off... no change, no idea if it did anything. I'm having trouble getting it to hover completely flat, so I was trying to figure this out.
This will do exactly what your asking. Just fly and maintain the quad a steady as you can in the air. You should eventually be able to let go and it will hover flat. You cannot do this in a windy or turbulent environment though. Your stick input alters the Accel calibration.
This is also available by holding in the Arm command for 15 seconds. It lasts 45 seconds. then times out.
Well, I tried it, but it didn't seem to do anything? Does it matter if I have "armed motors" first?
I armed, took off, flipped Ch7 high, hovered as best I could, flipped Ch7, but could detect no difference.
I tried the ARM command when flying the other day and had a strange situation. When flying normally the copter had a tendency to go forward and right, so I needed stick input to get a normal takeoff, and hold the hover stationary. Then I tried the ARM command for 15 secs, and when taking off stick input was not needed and the copter hovered perfectly. Tried normal takeoff and it was back to leaning forward and right. Tried ARM command 15 secs again and all was perfect. BTW this is not something new in 2.5, I have experienced it before as well. I know my motors are not 100% straight any longer after several crashes could this be causing this behaviour?
Remember that the settings are saved when you de-arm. So you should land and de-arm after 45 secs if you use this method.