Hello,
In my experience, the reboot is usually due to the high current demanded by the motor, it could reduce the battery voltage below the one needed by the 5V regulator. You cannot see it in the log because the pixhawk is rebooted and a short period of time before the reboot is not recorded in the SD or sent to the ground station. I can see in the photo that the battery cables are blue and brown , have they a proper section? too thin wires can have a large voltage drop.
I would try to test it again with the propeller removed, the motor should ask far less current, if the pix does not reboot, the only difference is the current demanded by the motor.
good luck!
I forgot to add that maybe the battery is faulty. I have experienced this problem with MANY batteries, they were ok, but then the next summer one cell isdead, and the symptom is precisely a lower voltage or increased internal resistance, that lower the voltage more than usual with high current demands.
Adolfo.
I tested with propeller removed
No short circuit risk if I test with 8AH 60C lipo ?
Is the lipo for my big big flying wing 
Only the voltage, number of cells, matters - provided the battery has enough capacity to supply the required current.
So I test with this lipo (same voltage, more amps) ?
Yes - a battery just needs ability to supply current (amps) that devices draw or the voltage will drop.
It’s the voltage that will kill things if it’s too high (or sometimes if it’s too low)
Same problem, esc throttle range calibration ?
Someone seems to have the same issue with this power board
: https://www.rcgroups.com/forums/showthread.php?2987782-Lowest-priced-Pixhawk%21-Radiolink-Mini-PIX-F4-Fc/page8
solder the motor wires directly on Vbat can solve the issue ?
I soldered motor dires directly to vbat, but nothing change
ESC Calibration problem ?
I tried with usb wire plugged, no reboot.
I retried without usb cable, reboot
Nothing powered with mini pix excepted mini pix himself
Radiolink power hub is 5V 2.5A able
ESC directly soldered on VBAT
Replace original capacitor by 1000uF 25V solve the problem for me