Crash on launch, Hardware, software or some kind of runtime calibration error?

ArduPlane Plane 3.9
1

Nasty crash on launch, log and even short video (sorry for quality) attached.
This was third flight, Arduplane master and BMI088 IMU
Any Ideas please?

https://mega.nz/#!ydI03CBA!i7MedVsCcxgRzpweAj_SxFoCXs3ejCMhht1ZJEB_ykw

2

without taking a deeper look your horizon strikes at first sight imho:

hor_off
hor_off.jpg720×401 84.8 KB

custom firmware on that board?

3

Not custom fw really , built from master but the Flight controller is our board.

Yes unfortunate I was doing the Launch LOS or it would not have happened as I would have seen the AHI - it was not like that when moments earlier I checked sats etc when the plane was on the ground. I just had no time to disable the FC and save the plane. You don’t expect this after 2 uneventful flights

4

pretty clearly the state estimation was way off. Because you only have 1 IMU we can’t easily see which sensors were off, but the EKF was clearly very unhappy.
Some things from the log:

  • your vibration is way too high. You either haven’t added isolation or the isolation is not adequate. You definitely had clipping, and I am pretty sure you had aliasing as well
  • you have a lot of the arming checks disabled. That is a really bad idea. The arming checks are there to ensure that everything is OK for flight before you takeoff. In this case the EKF was clearly unhappy before takeoff, but the disabled arming checks means that was ignored
  • you have no compass. We can fly with no compass, but we are more reliant on everything else being right when we don’t have a compass, which it wasn’t

If you really don’t want to wait for arming checks then use DCM instead of the EKF. It won’t fly as well, but it is more likely to be ready if you are not willing to wait for the EKF. Set AHRS_EKF_TYPE=0 to use DCM.

5

Great comparison here about DCM vs EKF : Difference between DCM & EKF
I prefer flying with DCM on plane. Is there a way to disable accelerometer in EKF ?

6

Thanks Tridge

  • You mistake vibration for the violent crash inputs, the Plane was only in the Air for 1 sec
    previous flight vibration :-
    image|690x431

  • Only Mag and voltage arm checks are disabled, oh I did uncheck Loggin as it would not read cards, unless I missed something

  • I thought the consensus was to not bother with mag on planes as they are always moving forward and mag is frequently troublesome

  • Arming checks were passed and the buzzer beeped it had just initialized with Level 90deg out when it was picked up from the ground ( AHI was level in goggles when I checked sats and Armed it).
    All I would say is it got Sat lock etc quick and from power up I armed in maybe 15sec , much quicker than anything ever before, should they be left on the ground for longer to fully initalize regardless ?

The mystery to me was the plane was in Stab, but initially flew level for 500ms before rolling 90deg left (like it made no attempt to go to the incorrect level ) and when it did I had less than 500ms and a couple of feet of altitude to switch off the leveling, which is not really enough time :frowning:
If you watch the video, you can see GPS and AHI going all over the place after the crash

photo_2019-08-26_21-33-27
photo_2019-08-26_21-33-27.jpg1280×800 146 KB

7

Anything related here …

8

Any chance your flight controller came loose? I had a friend who double sided taped his FC in his plane, during a level flight it suddenly rolled sharply and crashed. The FC moved inside the airframe, making the FC think the plane itself moved. Seeing the horizon off by so much with the plane level made me think of that.

9

@cyber_06_wolf Not a chance, it is soft mounted on special gyro pads but even the vicious cartwheel crash did not dislodge it .
Unfortunately don’t do simple problems but thanks for the idea :slight_smile: