Discussions

Vibe Xok Ybad IMU problem

Posted by Gerhard Laubscher on May 15, 2016 at 1:36am

Hi Group, 

(Quad Tarot 650S, Motor-4114, Prop 15.5

PixHawk FC FW333, Batt 6S, Atun Success, MP 1.3.37)

I have had this problem where plotting the Vibes Graph in MP I find that the X-axis appears ok,

whilst the Y-axis is 'way' diff to X.

I have inspected the rig to check for bad mechanics, all seems good.

Used diff sets of props of which I correct the balance, imho

I am not experienced enough to eval the problem, I hope that within the community to find info

to assist resolving the perceived problem.

I have attached the bin file here for review as well as the various pics and Atun params.

When plotting the Des/Att Pitch & Roll, it appears to me the Att P&R follows the Des P&R

closely? Although I observe in Att P&R what appears to be a continuous ~sinus-curve as it

tracks the Des P&R.  Not sure is this is normal or acceptable?

The craft flies 'ok', however, since this is actually the first time for me in the uav tech,

I admit I am not experienced enough to evaluate the craft's 'practical' in the air

flight dynamics and performance.  Although, in STBLZ mode it is quite 'agail' and 'responsive'.

In AltH and PosH it 'appears' to be good, as I understand it. 

I am though concerned about the Vibes, I don't believe it is correct and may bite me on the 'bum' in the future if not sorted.

Lastly, note that I am not an experienced pilot at all.

I appreciate any feedback or pointers to help me resolve this, if possible.

Thank you for your time.

Regards,

Gerhard

Cape Town, South Africa

3691297686?profile=original3691297441?profile=original3691297629?profile=original3691297695?profile=original

2016-05-13 16-28-40.bin

J1023.rar

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Replies

  • Vesselin Goranov May 16, 2016 at 4:44am

    Hi,

    You do have too much Y vibrations, look at the graph.
     The controller do need good damping before any other tests.

    3702242186?profile=original

    regards!

    • Gerhard Laubscher > Vesselin Goranov May 16, 2016 at 5:36am

      Hi Vesselin,

      Thank you for your reply.

      I understand that the Y-axis is bad.

      Besides mech and the mounting of the FC, could there be any other reason why the Y-ax is

      so much way-out, compared to the X-ax.  From my limited understanding, the X-ax looks 'ok'

      particularly if viewed with the 333 vibe option?  Further, it appears that both IMU(1) and 2 exhibit

      the same plotted params? Thus my conclusion that it is not a case of that IMU(1) is 'faulty',  that

      the error lies then within the mechanics of the craft or indeed the FC mounting,

      and not electronics, as in the FC itself ?

      Historicallly, I had good 'Vibe' plots prior to this, hence my concern.

       I did not modify or change the mounting of the FC.

      Could a 'bad' autoTune result in what I have now?

      Are there any other params that you can see, with your insight, in the .bin file

      that could result in the Y-axis being 'off' or any other config/result issues in general?

      What other mechanical issues, besides FC mounting, may result in this bad Y-ax vibration, typically?

      Is it possible  to record/plot individual motor vibrations?

         If so, then how do one do it?

      In the mean time I will inspect and attempt to re-mount the FC

      btw - in order for me to understand which is X/Y axis on my craft,

      can you please advise from the pasted picture, hereunder, is the correct Axis orientation? 

       I am of the opinion that is  A?  Am I right to say X=Roll('Left-Right')  and Y=Pitch('Fwd,Bwd')

      Thank you for your valued feedback and education in this most interesting technology.

      Gerhard

      3702632738?profile=original

      • Derek > Gerhard Laubscher May 16, 2016 at 3:50pm

        Check for wires that might vibrate against the flight controller. Check for anything that can have side to side (y axis) movement, but not forward/back. Perhaps an antenna, gps pole? I had a similar problem and ended up being a torroid ring that was vibrating against a tube.

      • Vesselin Goranov > Gerhard Laubscher May 16, 2016 at 5:53am

        Hi,

        Here is link that may help: http://ardupilot.org/copter/docs/common-vibration-damping.html

        The sensors orientations are there.

        3702744687?profile=original So standard (0 = No rotation) X is front/back, and Y is left/right direction.

        Too aggressive PIDs can cause more vibrations, but in this particular case the damping is not working in Y direction, it is constant, not depending of the movements.

        If you send some pictures of the controller installation, will be easier to help you.

        Regards

        PS In most non-symmetrical frames the autotune is not working well, so I can suggest manual tune, starting from the default params.

        Vibration Damping — Copter documentation
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