Unsteady alt-hold

My quad has problems with alt-hold.  It flies fine in stab but once I switch it over it begins to lurch a lot.  It fails to hold altitude too, sometimes it rises and sometimes it drops.

I have altitude Kp set to channel 6 and it is allowed to vary between 0.5 and 3.  This setting does not seem to make much difference as the copter has similar symptoms over the entire range.

I'm not sure if my gains are too high or too low.  I was thinking about setting throttle accel Ki to zero and adjusting either throttle accel Kp or throttle rate Kp using ch6.  I don't want to make it go unstable though.

The other settings that I want to fiddle with are INAV_TC_Z and THR_MID.  What is the difference between THR_MID and TRIM_THROTTLE?

My board has a problem with logging so I am unable to collect/post a log.

Any suggestions?

Here is the video:

http://youtu.be/gHWLuRwdiYs

These are my current settings.  I have also tried the default settings to no avail.3691104117?profile=original

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Replies

  • I've been experiencing almost exactly the same problem with a brand new - fresh out of the box - 3DRobotics IRIS. I checked and there were no problems with vibrations. All other drone functions seem to work fine. 3DR replaced the Pixhawk in my IRIS, but alt hold was still unstable.

    For example if the drone was set to loiter indefinitely at 20m then the actual altitude would fluctuate from say 4m to 25m. The altitude fluctuations occurred in time periods of say 5-10 seconds.

    Eventually I found that reverting from ArduCopter V3.1.2 (e2ed3dd1) to ArduCopter V3.1.1 (681dafcf) has completely resolved the issue for me. I've let 3DR know, and suspect a firmware bug. Hope this helps!

  • Lower vibrations in your system.

    Protect barometer.

    Check Throttle MID

    Try Settings:

    1. Throttle Accel P 0.5-0.6

    2. Throttle Accel I 1.0-1.2

    2. Throttle Accel D 0.002-0.004

    3. Throttle Rate 4.0-5.0

    5. Altitude Hold P 1.05-1.1

    Refine in small increments.

  • Once I put my APM 2.5 under a black dome and shaded the pressure sensor the AH performance improved dramatically. I know that using foam to cover it is a common solution, but if you can get a frame with an opaque dome, even better.

  • What board do you have ?

    • 2.5.2 HK clone

      • How are you finding the clone? Have you used the 3DR version before? If so, how do you find the clone in comparison?

        • Well considering that I blew my 3.3v reg which turned out to be a great intro to surface mount soldering for me and I am having my fair share of tuning problems, my experience hasn't been too great.

          But with that said I know some of my problems are my own fault. I also don't know what my experience would have been with a genuine board. It may very well have been identical.

          I do know that genuine boards get much better support. I waited almost one month for shipping. That was painful. I didn't return my damaged board because the round trip shipping times and hassle would have been too high. I had a lot of firsts with this project. I learned how to use eagle cad, I looked through a bunch of data sheets, I expanded my soldering skills, and i now have a very good understanding of the hardware. In my opinion all of that would not have been worth the cost savings for the average consumer. Then again the average consumer buys naza. I like digging into things and in the end I have a working board so I am happy with the way things worked out.

          Then there are the ethical, economical, and philosophical considerations to ponder about genuine vs clone...

          Hopefully this helps your decision one way or the other.
          • Thanks for sharing your experience with the clone. I have the genuine 3DR product on my quadcopter. I was just curious to see what your thoughts were - I know people have jumped to conclusions here before about the clone...

            I see the positive here for me is learning. The clone makes you work but it is a good learning experience by the sound of it.

            Thanks again! 

  • Here is something obvious, but did you cover your barometer with a small piece of cotton or foam?  It is very sensitive to wind and also light.

    • Yeah, I taped a cotton ball to it with a bunch of masking tape to guard from prop wash.
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