Crash Analysis please

Hi folks!

I experienced a flyaway this evening and am VERY lucky to have missed a parked car by about 3 feet!

When attempting to arm my quad, I was getting a “Bad Compass Health” warning that kept me from arming my quad. After several attempts on starting and restarting, I VERY STUPIDLY disabled the Compass arming check (note: I have done this a few times before and did not have any problems, so I am not sure if this is exactly what caused the fly away). After disabling the Compass on the arming check, I armed the copter in stabilize mode and took off to about 15 feet, I then switched to Auto and the quad just flew away and crashed on the street. Was hoping if someone could analyze my log to determine the cause of the crash and/or confirm or deny the bad compass health was actual the cause of the crash.


Well, your MAG.MagX,Y,Z did not log anything - most likely you did not had an working magnetometer at all.

  • reading the compass then would give VERY bad data.
    A multirotor depends very much on magnetometer for assisted flight.

As you discovered yourself; safety check on ArduCopter are there for a reason, this is some of the big differences between serious autopilots and toys.
Disabling them may be necessary for complex operations (like when you need to take off from a somewhat magnetic steel surface(ship), or other lots of iron in ground) - then we take off in stabilize , and always try the UAV very well while airborne in f.eksample Loiter , before using AUTO, or expecting a mission.

It’s not very good idea to disable mag checks, and then switch to a mode that needs that data.

If you did not chose to switch to RTL, but Stabilize, you would be able to save the day.
Make sure you learn to fly well in stabilize, do not be dependent on assisted modes, if you felt comfortable in stabilized, you’d switch to that in a situation where you suspected AP’s ability.

Thanks for the response. Yes, I learned the hard way not to disable any pre-arm checks. But in my still learning of quads, I mistakenly assumed that the compass was more for nose heading while the GPS was more for position. I am VERY lucky to have only damaged my quad and lipo and nothing else. A mistake I will never make again. I am comfortable flying in any mode as I fly helis and planes as well, but I seem to have be startled by what was happening that I switched to RTL in a panic. The second it crashed, I asked myself “why in the hell did you not switch to stabilize mode?”

I always (well, except for this one time…but always will from now on) take off in stable mode, switch to loiter, RTL and then launch again in stable, then Auto, but for some stupid reason, I didnt that time.

Again, I feel very fortunate to have this learning experience that it didnt hurt any one or anything

Yep :slight_smile:
BTW: If I ever in doubt if a multirotor can be put in navigation modes , like if it is a newly built, recalibrated, or took of from places like those described above, then I do this procedure to make sure:

Stabilize mode, fly ~5m/s heading north , switch to loiter watch stop:
(expect clean , no toiletbowl effect or overshoot to one side, then return)
-repeat same for west,south,east so the UAV does prove it stops precisely regardless where north is.
if it does that, magnetometer and navigation works fine, and you can observe that closely in a very limited airspace.