My copter disarms after 2 seconds it arms. It seems when throttle is at zero it disarms. I have 3.6.4 firmware arducopter. Is this normal?
There is a parameter for that DISARM_DELAY. But the default is 10s so something else may be going on.
have you tried doing individual motor tests on the bench? I had something similar happen and it ended up being a motor with a bad solder joint that was causing it to hang up and act weird. fixed the solder and it worked after that