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Problem in AltHold mode: copter suddenly climbs

Posted by Sven Schmid on June 12, 2013 at 1:35pm

Hello,

my APM2.5 (ArduCopter V2.9.1b) showed a very strange behaviour when flying in AltHold mode. I have been flying in AltHold mode successfully for more than 30 flights - without any issues - so far. Then a couple of days ago my quad suddenly got out of control after being in AltHold mode for a few minutes. It climbed quickly (see plot below, after line number 7000). I tried to recover it by switching to STABILIZE and LOITER but I didn't suceed. Have a look at the logfile below:

 

3691030273?profile=original

The following graph shows the details of the incident:

3691030286?profile=original3691030217?profile=original

What you can see is that InavAlt and BaroAlt deviate from each other in that moment and AccCorrX shows a significant drop. AccCorrY and AccCorrZ stay close to 0. Can anybody tell me what kind of data AccCorrX represents? What is very surprising is that the ThrIN value stays constant while the copter rises quickly. I wouldn't have suspected to see that. What is the problem here? Can anybody give me a hint what went wrong?

Attached you can find the logfile of the flight. Thank you very much for your help in advance!

Cheers

Sven

2013-06-08 17-47 15.kmz

2013-06-08 17-47 15.log.gpx

2013-06-08 17-47 15.log

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Replies

  • T3
    Richard Boyhan June 12, 2013 at 7:48pm
    General rule 2, when in trouble switch to stabilize mode and fly manually. Loiter uses altitude hold as it bases. If altitude hold messes up switching to loiter won't help. General rule 1, learn to fly really well in stabilize mode. You'll be glad you did!
  • Jan June 12, 2013 at 1:59pm

    Sven,

    I had a quick look to your logs.
    Could it be related to your throttle going out of the deadband (more than 60%)?

    What I saw is that around 6430 your throttle slightly increases from 567 to 604, around 6800 it goes to 635 this is also when the quad starts to climb slowly.
    It is just a thought of course.

    Cheers

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