I'm looking for an advice what should be tuned differently in my otherwise very nicely flying copter. It's very stable, vibrations are well within recommended limits - when recording video with GoPro there is no jello at all. However when I switch from stabilize mode to AltHold and fly with just a bit more dynamics sooner or later the copter shoots up. I mean the throttle is out of sudden set to maximum value and copter ascends rapidly. The only reliable way how to prevent it from flying to completely insane height is to switch back to Stabilize and descend manually.

Any ideas what should I change here?

My setup:

TBS Discovery w/metal arms 250mm

2830 motors

10x3.8 carbon props

APM 2.5.2

FW: 3.1 RC6

External compass

3691079627?profile=original

log.graph.althold.shoots.up.png

copter.pids.png

basic.pids.png

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          • Developer

            What you see in the logs is the filtered version.

            Don't quote me here but I think we are going from the 8g setting to the 16g setting. That give you some idea how strong the high frequency vibration can be. And remember it is clipping before it goes through the filter so we didn't realise how high the peeks really were.

            • Leonard,

              Is there a dev mailing list where this is being discussed in more details?

              Thanks

              --Alex

              • Developer

                I think there is something on drones discuss, but I haven't had a look.

  • @Jakub - I'm wondering if you were able to solve your problem at all? Was it the vibrations?

    I have the same problem on a large wooden hex with 15" props. It is rock solid at hover with nil vibrations but if I move relatively fast in Alt Hold it will suddenly shoot up into the sky. My logs look just like yours and it requires switching quickly into stabilize mode in order to control it. I also noticed the same problem (spontaneously shooting upwards) during an auto mission, especially when the hex was moving into a 5-10mph wind. The hex would suddenly shoot up ~5-10m but would settle back down to the proper altitude, yet forward progress was slow since it kept bobbing along. Downwind was fine. I was thinking it might be something with the baro and aerodynamics creating a high pressure situation (???).  Anyway, I'd like to hear what you may have found out.

    Thanks,

    Carl

  • Developer

    Hi Jakub,

    I think this is a pretty clear case of vibrations that happen when you start flying quickly that cause the IMU to get messed up. Your vertical rate goes negative and the copter climbs rapidly. This is also backed up with your INAV log.

    If you added a IMU log you would see your vibration get bad as this happens but they will probably look fine at hover. I had a copter that did this too.

  • Hi Jakub, My quad was experienced same phenomenon as yours today and result a crash. My quad shoots up suddenly in Loiter mode after I move a lot in Loiter mode. My story is that I am using clone Qu4D frame with APM2.6 and AC 3.01 and flew in X-frame perfectly with more than 30 flights without single incident of shooting up. Alt-hold and Loiter is perfect, so that vibration is not a problem with my set up. I changed to V-frame today and try to test whether there is improvement and shoot up happened in my third flight today.

    After I saw the quad went up quickly, my first thought is that it went into failsafe mode, but the quad only 20m away from my transmitter. I went home and read the log and find that no RTL was trigger. I am quite sure the problem is not related to THR-MID, vibration and barometer affected by light. It just randomly happened. Of course I am also not sure whether the problem is related to V-frame. It is worth for you to try to set up your quad in X-frame type (I assume you are using V-frame type with TBS frame) and see the problem still persist or not.

    3692891030?profile=original

    2013-12-01 17-38 3.log

  • After adjusting THR_MID to 405 as suggested by Tom, I flew the copter again. It seemed that it's slightly more difficult to get it to that state. But after few attempts it was there again. Especially at the times 2:55 and 4:20 in the video from last flight it's clearly visible. Also attaching the logs for reference.

    Log visualisation detail of the event at 4:20 from video:

    3692888098?profile=original

    Full flight as seen from the ground camera. Check time around 4:20 for clearly visible example of copter shooting up.

    http://youtu.be/jUtBe2wMNsQ

    Failsafes from the radio are unlikely. I use FrsKy modules, D8R-IIplus in the craft. And the distance is very small. I can fly easily much further on without any glitches.

  • Did you use logs to calibrate your THR_MID value as shown in Randy's AC3.0 maiden flight video?

This reply was deleted.

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