Very interesting I think I have the same issue but on APM 2.6 with 3.2 firmware flying a big 810 frame in Y6B.
I added a new camera today and had a test flight that went ok but had some glitchy video so I landed to look for bad connections. Then when I tried to take off again the friggin machine went nuts. One of the motors spooled up really aggressively in Stabilize and then it appeared to want to flip on slight accelleration.Tried to take off on PosHold but it seemed pretty unstable and I stopped it just short of falling over. Another attempt in Stabilize caused it to fall over forward. It was on the lawn so there wasn't any damage I could see.
I decided to stop trying and inspect the machine but everything looks fine. Tomorrow I will try the acc calibration and see what happens. I also downloaded the firmware upgrade to 3.2.1 so hoping that helps.
It worries me a little because I have never had any problems taking off or flying since I got the machine running 3.1.5 firmware. This is now new better firmware and nearly caused me to crash a machine that has never even tipped over.
I hope someone has some insight into this.
I think that i have the same issue, occasionally when i change the battery the quad flies, but its impossible to make a second flight and sometimes when the drone flies normal after some time flying the speed of one or two motors decreases and the drone falls.
I sent the info and a log to the 3DR support, because i thought that there was a bad sensor, but they told me that my pixhawk is ok. Respect to the backup power im only using the 3dr power module.
My config is Pixhawk, dji E300 (motor, esc, props) and Turnigy 9x with a 3DR ppm encoder.
Hopefully someone from 3dr will reply here...
I know this is a very old thread that I started but i still face this issue occasionally. Was wondering of others are also facing this issue?
If it happens again, Ill upload the logs here.
Yes it happened to me to, CX20 with APM 2.6, I would calibrate then take off, land, take off but would go sideways and crash mainly, recalibraite and repeat all the above steps. I heard that removeing the jp1 jumper and powering the board that way would help but nothing changed, I changed APM but that was today, not tried it yet.