Hi all,

This is my first post here, I've only been using APM for a few weeks on a DJI F450 Quad and so far it has been going well, until today.  I'm using an rctimer APM 2.5.2 board with the latest firmware v3.0.1

I'd been out flying earlier in the day and was getting some "toilet bowling" when using loiter, when previously my copter had been nice and steady in loiter.  After reading around a bit I decided to recalibrate the compass.  So I went through the live calibration and compassmot - which came out about 58% I think - not great, but not bad, and no worse than the last time I did it.

Went out to test fly in the garden.  Started off in stabilize, all ok, switched to Alt hold, still good, holding altitude well, all behaving very nicely.  I then switched to Loiter and whoosh, the APM applied full throttle and (what I assume was) full pitch back shot over my shoulder and smacked into the back of the house :-(  By some miracle, the copter seems to be ok (and still flies in stabilize), though it did put two nice scratches in the glass in my back door :-O

So, I need a little help triyng to work out what went wrong?  I've attached the logs (my switch to loiter is at line 2246) and a couple of plots I've done.  You can see where it goes totally bonkers immediately after I switch into loiter.  I initially thought that the "problem" was that WPDst=2.5, but after a bit more reading, I see that means that it thought it was 2.5cm from where it should be (have I got that right?).  So that shouldn't have caused any major movements right?

GPS hdop and nsats both look good, so I don't think it was a GPS issue.

The numbers that look odd to me from NTUN rows are PErX and PErY - distance to intermediate target(what do these mean, what are they exaclty?) - and VelX and VelY - velocity estimates, which are huge, and DPit = 45 - is that 45degree pitch back?  Which is what it appeared to do.

Any more ideas why did it did what it did?  

How can I gain some confidence that it's not going to do this again next time I switch to loiter?  

Should I recalibrate everything? gyros, compass, etc.  (I don't see how any of this could be that out given it was flying well in stabilize and alt hold)

Any ideas welcome.



PS: hope I've picked a sensible category.



2013-09-22 18-22 6.log

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  • This happened to me today. I put it in loiter mode to switch to fpv goggles but the quad aggressively went to the right. I switched back to stabilize and took control.

    if i had put the goggles on it would have been a bad crash :(

    logs attached, arducopter version 3.1.1  


    • Hi Rob, hi Kishore,


      @ Kishore: watch for supply voltage: you have 5,4Volts, that is quite high......


      first, looking at Errors, time stamp 16000, i see subsytem 6 error code 1:

      6: Battery failsafe

      ECode 1: battery voltage dropped below LOW_VOLT or total battery capacity used exceeded BATT_CAPACITY

      So, did you activate any supply sensing: low batt or low capacity?

      Volt signal shows near 10V, that should be inspected:

      *)' is your battery weak, or

      *) is the voltage sensor not calibrated?

      Current sensing: is the current sensor calibrated?


      next, Performance Monitor: at 13000 and 16000 NLON and MAXT show activity: program loops exceed processor capacity, due to  ??? whatever.


      remark at CTUN DCrate: at 17000, you do not add throttle, but your desired climb rate raises to 56cm/s, when your waypoint height changes to 8 meters. I think this will not makt your copter instable.

      Logging the motors would help.....



      @ Rob:

      AUTO MODE, my quad raised with full throttle (100% !!!) after some loss in SatCount, induced by heavy roll/nick shaking.  

      Missing GPS position caused GLAT and ILNY distance errors.

      So PERRY started integrating, and when the Sat signals switched back to the "old" values (i suppose), the control reaction ACORRX, ACORRY exeeded normal values.

      On an free area, i landed safe in Stablity mode.


      Why dont i see all the logging values when i select "nearly all" in the MP?


      Greetings, Hans-Jochen

  • Here are the logs.  Thanks so much.

    2013-09-27 16-02 20.kmz

    2013-09-27 16-02 20.log

    2013-09-25 14-07-06.tlog

  • Developer

    By the way 58% compass inteference is at the top end of the "grey zone" which is 30% ~ 60%.  below 30% is ideal.

    Good work on looking into the logs yourself though by the way!  nice.

  • Developer


         It looks like a problem with your GPS.  It only seems to be providing position updates once per second (it should be 5x per second) so that's not enough to keep the inertial navigation estimates from drifting off.  I guess it's not a 3dr GPS so maybe it's the wrong type or maybe it hasn't been loaded with the correct config (the APM actually tries to update the config at startup but perhaps the GPS isn't accepting that for some reason.

         You can see the issue by checking the "Time" column of the GPS messages.  In a good log each time will be increased by 200 from the previous (200ms = 0.2 seconds = 5hz) but this log has them increasing by 1000 with each message.


  • This is quite interesting. You have probably already seen my thread describing a disastrous crash in RTL where the controller asked for (and got) full pitch and throttle despite there being no reason for it to do so.

    From your description your crash sounds similar. However I'm not quite sure - it's a shame there isn't a bit more of the "bad" section of the flight (seeing as your house got in the way!) to be certain. The odd thing with your log is that the PitchIn and RollIn don't seem to follow the DRol and DPit and actual Roll and Pitch. The way i understand it (I may be wrong) is that in a navigation mode on a correctly setup quad with hands off the RC sticks, the DPit, PitchIn, and Pitch values should all track each other. That's what happened in my crash and in other successful flights. So I don't really know why they are different here.

    Nonetheless there have really been quite a few issues now with people having loiter or RTL mode result in a high speed, straight line flyaway. None of them have been answered satisfactorily by anyone, so far as I can see. These threads are just being ignored. 

    If you get any replies at all to this I am sure they will tell you that compassmot of 58% is too high and you should buy an external compass and everybody will live happily ever after. It probably is too high, but I am simply not convinced that is the reason for these problems. Bad compass issues result in toilet-bowling spiral patterns. GPS glitches can result in the kind of thing you got, and that issue is being worked on. But there have been other crashes, mine included, which weren't a GPS issue either as the copter was flying AWAY from where the GPS was telling it it needed to be.


  • Anyone any ideas?

  • I have also just found the Mission Planner telemetry log, though I can't glean any more information from it.  Here it is in case it helps anyone else.  You can see where I switched to stabilize just after 17:50 by plotting throttle against chan3_raw.  The APM stuck the throttle up to 100% and I slammed my rc throttle stick to zero in a mad panic.

    2013-09-22 17-47-06.tlog

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