Pixhawk 1 quad in posHold - drifting

There is just poor tuning.
You need to start with the MissionPlanner Initial Parameters section, put in your prop size and battery cell count - also select the “Suggested settings” then accept everything it offers.
Set you flight modes to: Stabilise, AltHold, Loiter.
Then have a separate switch for RTL.

Also definitely set:

ARMING_CHECK,1
INS_LOG_BAT_MASK,1
INS_LOG_BAT_OPT,4
LOG_BITMASK,180222

Don’t disable any arming checks, just work through whatever prevents arming.
Really we only need the ability to disable an arming check in case you know there is a faulty or misconfigured component to be ignored until you get a chance to fix it.

Now work through the