X8 with Pixhawk, 3.2 flip in AltHold

Hello Gentleman,

Long time lurker around here, but found all my answers in your informative posts. Well, util recently that is.

We have a strange problem with one of our multis, an X8 with Pixhawk running 3.2.

When originally built, we did not have the GPS yet, so we flew it without, in stabilize/althold only. Everything went fine.

When the GPS units arrived, (NEO M8N) we went ahead and mount it, done the usual settings/mag calibration.

To our surprise, a few minutes into the flight, after switched to althold, the copter just flips into the ground. This is not good. Looking at the logs, we can clearly see the mag2 values went nuts.

Thinking there might be something wrong with the new mag and to eliminate this question, we went ahead and changed it to the second GPS unit and redone all the calibration. The first flight went fine, so we thought that was the root of the problem, but what do you know, on the second flight, the same flip happened.

I am attaching both logs, maybe someone could figure this out.




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  • Hello Stuart, 

    Looks like your advice was the winner, we had 3 good flights today, after switching to a BEC to power the Pixhawk. The voltage is now 5.2 +/- 0.05 through the whole flight.

    I was puzzled by the mag2 readings, but I guess that must be a consequence of the high voltage, not the cause of the flip.

    Thanks again Stuart, you've been really helpful, I appreciate that.


    • Cool, I hope it continues.

      Yeah it is strange, could be due to current peaking due to the esc output rises...but it doesn;t appear in the curr- current log, maybe the data is false due to excessive Vcc...I don't know.

      Hope your flights remain good though :)

  • Hi, neither of those logs show a flip. But pitch and roll don't seem to follow desired pitch and roll very well

    • Thanks for looking, I think the log is not complete since the battery got ejected on the way down.

      Apart from the pitch and roll not following perfectly, although in the air the copter is flying good, the only thing out of the ordinary I find in 63.bin, mag2 seems to go haywire.

      Also at the same time, the rcout ch1-8 go up like the mag2.


      • It does seem to end at altitude of 2m or so, was that the height you observed?

        I din't believe compass should affect pitch roll at all, just heading. did it yaw?

        Looks more like a power issue to me. You Vcc is very high at 5.6V, and it goes up to 5.7 at the end of 63.bin.

        how many flights have you had prior to using alt hold...I suspect its a coincidence that it happened in alt hold.

        I ran the automatic analysis on both files, but it didn't detect a brown out....but that may be because the altitude is below its test threshold.

        What are you using to power the flight controller?

        • That was the altitude when it happened the first time. The copter flew perfect in both stab and althold for at least 4 flights prior to adding the GPS+mag. That was my understanding as well, mag not affecting the pitch/roll and I'm not saying it is, but that was the only thing out of the ordinary I could find myself.

          I noticed the vcc a little high, it is powered by a pixhawk power module.

          Oh, the battery disconnected mid flip.

          Thank you!

          • i believe mag 2 when you have an external compass is for the internal onboard compass.  Mag 1 (external) looks to be unaffected.

            In 65 I can only see motor 1 rise and the other fall to 0, that would make it flip! as you say though in 63 they all rise. I guess not for long as it would have climbed like crazy.

            OK if it was mid flip points more towards a power issue then to me unless for some odd reason your log sample rates are very slow. I would expect a few samples of data prior to spinning enough to eject a battery. Are you sure the gps/compass cable isn't causing a intermittent short or something? I have been involved in helping someone who had power glitches casued by a bad telemetry cable, in that case the cable woule connect/disconnect and the Rob Lefebvre said the capacitors in the telem radio charging could drag the Vcc down.

            How long were these flights? The logs don't have a huge number of samples and its not showing time when I look at the logs like it does with my own logs.


            • You know what, you might be on to something here, I noticed both the gps and i2c plugs seemed not seated properly, whell not actually the plugs but the little pins inside. After the first happening (63 log) we changed the gps and made sure every pin is all the way inserted. 

              It flew fine once, in all modes, including loiter, thats why no 64 log. But again in 65 it happened.

              63 lasted less than a minute, in 65 I'm not sure, I have to ask my friend who flew.

              Thanks again Stuart for taking the time to look into this.

        • OK I am not a pixhawk user but just read that 5.7 is the max for pixhawk


          I am not sure what happens if 5.7 is exceeded.

          Might be a red herring.

          did the battery fly out on the fround or in the air...there is no sign in pitch and roll occured that could make the battery fly out..

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