Pixhawk Drone flying very abnormally

Hello all!

Urgent help required.

I have made a drone of 650 mm diagonal wheelbase,


Earlier i used a 450mm quad frame to test the system. It was flying ok in stabilize mode but none of the GPS modes were working except RTL. The drone used to start descending when switched to loiter or pos hold mode.

After that I installed the same system on the final 650 mm frame with CF booms & Glass fiber center plates. In first flight, the drone was flying very abnormally but i managed to get it landed safely somehow and tried re-calibrating the radio, compass & accelerometer. When i tried taking off again, it just started flying instantaneously high on a very less throttle value (near 10%-20%). The drone was not at all controllable in the sky and i need to cut the throttle to get it crashed from a small height. I am an experienced flyer and i am flying drones since last 5 years so i can say confidently that there wasn't any piloting problem in this flight.

Following are the parameters of my 650mm drone:

Motor : racerstar 4108
ESC : 6s Opto (simonk firmware)
battery : 6s 35C
Control Unit: Pixhawk + Ublox M8N GPS + Power Module
Tx Rx: Radio link AT10

Firmware: arducopoter v4.0.0

Log files of 2nd flight on 650 mm setup is attached for your reference.

Kindly help me out from this issue. I need this copter ready urgently on priority.
Any help and support is welcome.

Waiting for your valuable suggestions.

Thanks in advance.