Pls help in crash analysis sudden fall from sky⁷

Copter setup/ integration:
All up weight is 2950gms
Motors t-motors 3508
Esc 40amps hobbywing x rotors opto
Propeller 15x5 (t-motors)
telemetry herelink
RC X9D taranis fr sky (tx) {Rx L9R}

As I was flying the copter with herelink I was not happy with the autotune gains.
So on 22-10-2020, I choose to do the gain tuning my taranis while herelink was hooked with the cube for sending/ receiving telemetry data on mission planner running on Windows PC.
As I wanted to Inflight manual tuning I hooked my X9D to my CUBE.
Configured Channel 6 on tx on pod to change value inflight.
I completed my tuning my in stabilize mode step1: Stab roll/pitch kp & step:2 Rate roll/pitch kp.

After tuning and flying for some time in stabilize mode I shifted to Atthold and finally Loiter after 3-5 minutes flying at about 20m-30 away.

So at a height of 40m I flew the copter 300m and then I started flying back suddenly fell from sky.

Log File C:\Users\AG\AppData\Local\Temp\tmpF6F.tmp.log
Size (kb) 41979.3427734375
No of lines 476764
Duration 0:28:42
Vehicletype ArduCopter
Firmware Version V4.0.4
Firmware Hash 40502bd9
Hardware Type
Free Mem 0
Skipped Lines 0
Test: Autotune = UNKNOWN - No ATUN log data
Test: Brownout = GOOD -
Test: Compass = FAIL - WARN: Large compass offset params (X:127.44, Y:-338.08, Z:-2.46)
WARN: Large compass offset in MAG data (X:127.00, Y:-338.00, Z:-2.00)
Large change in mag_field (45.42%)
Max mag field length (561.53) > recommended (550.00)

Test: Dupe Log Data = GOOD -
Test: Empty = GOOD -
Test: Event/Failsafe = FAIL - ERRs found: CRASH FS_THR GPS_GLITCH
Test: GPS = UNKNOWN - join() takes exactly one argument (2 given)
Test: IMU Mismatch = GOOD - (Mismatch: 0.71, WARN: 0.75, FAIL: 1.50)
Test: Motor Balance = GOOD - Motor channel averages = [1348, 1333, 1311, 1309]
Average motor output = 1325
Difference between min and max motor averages = 39
Test: NaNs = FAIL - Found NaN in CTUN.DSAlt

Test: OpticalFlow = FAIL - FAIL: no optical flow data

Test: Parameters = FAIL - ‘MAG_ENABLE’ not found
Test: PM = FAIL - 63 slow loop lines found, max 7.70% on line 248834
Test: Pitch/Roll = UNKNOWN - ‘BarAlt’
Test: Thrust = GOOD -
Test: VCC = UNKNOWN - No CURR log data


Can view your log. Please share the dataflash log if possible

Not able to access log.

Something went wrong, my humble apologies.
I am attaching below fresh upload links of flight log. I have uploaded both Tlogs as well as dataflash log, both on Gdrive as well as drop box.
I hope it works this time



The motors stopped when the copter was still flying.

You can see the radio failsafe was triggered.

I believe it was either the radio or other hardware issue caused the crash.
Can you check what had been set to radio failsafe behaviour in your copter?

The radio was configured as per the link you shared and was tested before takeoff without the propeller as mentioned in copter documentation was working perfectly.
As I mentioned earlier that I had hooked X9D for RC control for manual tuning and Herelink was installed for getting telemetry data. I am suspicious that this might have caused trouble.
so looking at log even I am confused that whether it was a hardware or software fault.
Or was it it the interference in both x9d and herelink as both work on 2.4 ghz that caused a software fault that led to a hardware misinterpretation fault caused a motor cut off while the copter was still flying as you mentioned above.

I don’t think using rc controller for tuning then uses Herelink for actually flight would cause problem. I have seem people doing this without having your current issue.

Interference in x9d and herelink may cause range reduction or instable signal, but in this case rc failsafe should be triggered.

I think this be may worthy asking this on the ardupilot forum, as this seems to be a false crash detection case. There are more software developers that may help you.