QUAD s 500 Pixhawk 2.4.8 / MP 1.3.58 will not arm

I have run calibrations and motors spin with test, no MP message why arming fails. MP will say armed when Taranis plus throttle down / yaw rt, then goes desarmed before I can throttle up.
How do I post logs for review help and would this be the right place .
Thanks Ken

Have your logging start on power up so you will get the complete picture.
In MP on the messages tab in Flight Data, are you saying there is no message there, or are you referring to no message on the artificial horizon.

On the horizon.
Where do I set logging “at start up”?

Set LOG_DISARMED to 1, run some tests then grab the “bin” log file

log now set LOG_DISARMED
Suggestions for “run Tests”
This is arm try with usb power.
Bin log file voice reports bad “logging” but log shows
\Mission Planner\logs\QUADROTOR\1\2018-08-30 14-01-04.log
Size (kb) 1206.640625
No of lines 15447
Duration 0:00:35
Vehicletype ArduCopter
Firmware Version V3.5.7
Firmware Hash b11c6af3
Hardware Type
Free Mem 0
Skipped Lines 0
Test: Autotune = UNKNOWN - No ATUN log data
Test: Brownout = GOOD -
Test: Compass = WARN - WARN: Large compass offset params (X:-257.00, Y:77.00, Z:-286.00)
WARN: Large compass offset in MAG data (X:-257.00, Y:77.00, Z:-286.00)
mag_field interference within limits (1.03%)

Test: Dupe Log Data = GOOD -
Test: Empty = FAIL - Empty log? Throttle never above 20%
Test: Event/Failsafe = GOOD -
Test: GPS = FAIL - Min satellites: 0, Max HDop: 99.99
Test: IMU Mismatch = GOOD - (Mismatch: 0.19, WARN: 0.75, FAIL: 1.50)
Test: Motor Balance = GOOD - Motor channel averages = [1027, 1027, 1027, 1027]
Average motor output = 1027
Difference between min and max motor averages = 0
Test: NaNs = GOOD -
Test: OpticalFlow = FAIL - FAIL: no optical flow data

Test: Parameters = FAIL - ‘THR_MIN’ not found
Test: PM = GOOD -
Test: Pitch/Roll = GOOD -
Test: Thrust = GOOD -
Test: VCC = FAIL - VCC below minimum of 4.6v (4.48916v)
with usb connection for power up.

I see I have “GPS FAIL”, but pre flight test reports 16 sats and showing position on MP map???

Attache a link to the log file.

This is bad, check your flight controller power source and wiring. Replace if necessary.

This was caused by USB connection. I found will not stay armed was caused by setting “time to disarm .27 sec” or something like that. I can now arm and try to fly to tune and correct other issues if they occur. Ken

Thanks for letting us know that you found a problem and back in action, good luck.