Crash during auto landing: mechanical failure?

Hello, thanks in advance for any help on this log. My own investigation points to a mechanical failure, however, even after the crash, nothing was broken (only fell from ~5 meters), and it even flew in Stabilize mode just fine shortly afterwards.

Genuine PixHawk
Copter 3.2.1 Quad
3DR NEO-7 GPS/Compass module

The crash occurred during the final descent phase of an auto mode landing. The auto mission went well, and in fact so did the previous mission which was carried out immediately prior, including an auto landing. As the copter was coming down, it suddenly rolled hard over and tumbled to the ground.

In the logs, Roll and DesRoll inexplicably diverge. Motor 3 goes full throttle and motor 4 stops. There’s a big magnetic field change. The problem I’m having is that all of these things happen apparently simultaneously, so I’m having difficulty establishing cause and effect.

Given that I couldn’t find an apparent cause in the logs, I was led to suspect something that is not in the logs, i.e. a mechanical problem, but there was nothing apparently wrong with the aircraft. Maybe it’s an intermittent mechanical or component issue, like an ESC overheating or something. Any thoughts?

Again, thanks or any help. Let me know if there’s any other information that I could provide.

Here is an Auto Analysis of your bin file:

Size (kb) 2417.3759765625
No of lines 32496
Duration 0:15:41
Vehicletype ArduCopter
Firmware Version V3.2.1
Firmware Hash 36b405fb
Hardware Type
Free Mem 0
Skipped Lines 0

Test: Autotune = UNKNOWN - No ATUN log data
Test: Balance/Twist = GOOD -
Test: Brownout = GOOD -
Test: Compass = FAIL - Large change in mag_field (171.13%)

Test: Dupe Log Data = GOOD -
Test: Empty = GOOD -
Test: Event/Failsafe = FAIL - ERR found: CRASH
Test: GPS = GOOD -
Test: IMU Mismatch = WARN - Check vibration or accelerometer calibration. (Mismatch: 1.13, WARN: 0.75, FAIL: 1.50)
Test: Parameters = GOOD -
Test: PM = FAIL - 14 slow loop lines found, max 13.60% on line 17273
Test: Pitch/Roll = FAIL - Roll (-100.03, line 31665) > maximum lean angle (45.00)
Test: Thrust = GOOD -
Test: VCC = GOOD -

Looks like you have both Compass and IMU issues.


I would want the esc and motor on the front left thoroughly tested if it was mine.

Motor 3 went to max output which (to me at least) means it wasn’t producing as much thrust as was needed to maintain level attitude. Pixhawk saw that corner dropping so commanded higher throttle to compensate, but if it wasn’t working properly no amount of extra throttle would help.

It’s very close but to me it look’s like the compass upset comes a split second after motor 3 goes to full.

Here is an Auto Analysis of your bin file:


Looks like you have both Compass and IMU issues.

TCIII AVD[/quote]

Ah, yes, I forgot to mention that:
The red flags thrown by MP’s auto analysis (and some other tools I’ve tried) all appear to a result of the crash itself, as far as I can tell. The IMU mismatch, for example, seems to just be the Pixhawk recording the impact (IMU’s are consistent and within vibration limits throughout the rest of the flight), and the compass deviation might be caused by the magnetic field from the sudden motor throttle change.

[quote=“MarkM”]I would want the esc and motor on the front left thoroughly tested if it was mine.

Yes, good thought. I’ve flown the thing (conservatively!) several times since, so perhaps it overheated or something. I’ll have to look into potential causes of intermittent failure of ESC/motors.