Question: Small periodic jitter / shakes on the gimbal (visible in video)

Discussion in 'CineStar Showcase (Photo/Video)' started by Carsten Poulsen, Oct 2, 2012.

  1. Carsten Poulsen

    Carsten Poulsen New Member

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    Hi All,

    First of all, great and very useful forum here on freefly.

    Today I did my first test-video after installing the Radian controllers on my CineStar gimbal. I'm very pleased about the first results, flying with stock gain settings (roll: 70 Tilt:100). Much better video output now ;-)

    Link to the video :

    Anyway, playing back the recorded video - it seems that I have some very short but visible jitter / shock on the gimbal a couple of time pr. minute - did any of you recognizance this behavior. I saw some of the same behaviors (just worse) before the installation of the radian controllers. The CineStar 6 is flying MK electronic and with new XOAR 13 x 6,5 props (they were all in balance before installation). I have tried to analyze if this occurs eg. every time I decent - but cant find any logical pattern in this.

    You can see the behavior at 29 sec, 1.10 min, 3.19min

    Any feedback / ideas are very welcome....

    Perhaps further gain adjustments on the radian could help this out. (Did not find the time to do this yet)
     
  2. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I'm not able to view the video. I see a message that says: "Sorry. The creator of this video has not given you permission to embed it on this domain. This is a Vimeo Plus feature."

    Well, at least we know that their computers are sorry.... ;)

    Andy.
     
  3. Carsten Poulsen

    Carsten Poulsen New Member

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    Sorry Andy, It was my bad -- wrong setting on my Vimeo account!

    It is corrected now
     
  4. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Thanks, CPoulsen.
    I can see what I would describe as a slight "waggle" in the roll axis at 1:13 -- just like the roll axis twitched.
    I wasn't really able to see that kind of twitch at 0:29 or 3:19 -- which doesn't mean it's not happening. I'm viewing the video on an Apple 30" Cinema display. There is a lot of aircraft motion at 3:19 and it may be masking what you're seeing.

    Can you help narrow down what you're seeing -- is it indeed in the roll axis? Or are you seeing something else?

    Andy.
     
  5. Arthur Vieira

    Arthur Vieira Flight Squad

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    Try reducing the roll to 65 or 60, also how many O-Rings are you using on the vibrations dampers?
    I had this in my Tilt in the beginning of my Radian use. I've learned that, in my case, it was caused by a resonant vibration with a high Radian gain. Changing the Gain and also changing the O-Rings to more "hard" or stiff ones did the trick for me.
    Goog luck.
     
  6. Carsten Poulsen

    Carsten Poulsen New Member

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    Thanks Arthur - actually all O-Rings are mounted on each dampers - but they are the soft-ones from first Quadrocopter batch delivery, so I have already modified the construction so they don´t disappear out of their placements any more. Think it will be worth updating a.s.a.p.

    I have yesterday reduced the gain on roll from 70 to 60 so I´m just waiting for the rain to stop in Denmark.....

    I will post my results later....
     
  7. Rene Duijvelshoff

    Rene Duijvelshoff New Member

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    Did you solved your roll jitter by lower your roll Radian gain to 60? Or do you have another tip?
    I have exactly the same problem, only some jitter in the roll axis...
     
  8. Arthur Vieira

    Arthur Vieira Flight Squad

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    Rene, try lowering the gain (as it's the easiest thing to do) and double check that the camera is well balanced laterally, if it's a little heavy to on side the servo keeps fighting, also is the rool servo a FreeFly?
     
  9. Carsten Poulsen

    Carsten Poulsen New Member

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    @Rene - Yes, lowering the Gain solved it for me. I might adjust further with new O-rings on dampners - they are to soft.
     
  10. Rene Duijvelshoff

    Rene Duijvelshoff New Member

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    Ok, I will try it myself. I have balanced the camera (CX730) well, (It stays in every position) and I use a roll FreeFly servo indeed.

    It suprises me, that lower the gain gives less jitter: FreeFly advise to adjust the gain as high as possible, just before oscillating..
     
  11. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Think of oscillation that is about to happen as jitter -- on my system that's certainly the case -- the jitter is a pre-cursor to oscillation.
    What FF should perhaps say is adjust the gain as high as possible without jitter or oscillation. :)

    Andy.
     
  12. Rene Duijvelshoff

    Rene Duijvelshoff New Member

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    Andy, thanks for your reply.
    My roll gain starts to oscillate around 150. Even when I lower it to 100, there is no oscillation or what so ever, but still that little tiny nasty jitter in the roll axis so now and then....
     
  13. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Hmmm. Maybe that jitter isn't what I thought it was then -- if you see a single "jitter" (a jitt?), does it happen when you are changing the horizontal velocity of the copter? If so, that might be the vibration isolators stretching sideways and hitting the hub plate. In which case you might want to tray putting a thin cable tie in a horizontal loop around the O-rings in their mid-section so that it makes them more resistive to lateral deflection....

    If that doesn't cure the problem, please post a video from the payload camera (not FPV) of what you're seeing.

    I think the problem is that the word "jitter" is a somewhat ambiguous and I might have misconstrued what you meant.

    Andy.
     
  14. Rene Duijvelshoff

    Rene Duijvelshoff New Member

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    I have fixed the hub plate directly to the main frame and mounted the base plate for the camera on gel pads. There is no "high" frequency oscillation any more, but stil that tiny little roll vibration....

    Herewith a raw video. Roll vibration at 0:56 and 1:40-1:50

     
  15. Tim Joy

    Tim Joy Active Member

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    To me that looks like what you would get from the small general looseness in the axis from the belt stretching and/or servo gear backlash or flex of the parts, due to the high winds hitting it. Does it happen in calm air too?
     
  16. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Yeah....try pushing with your finger on the mid-point of the belt between the servo and the large pulley. The deflection should only be about 3mm. Anything more and it's too loose.

    Andy.
     
  17. Rene Duijvelshoff

    Rene Duijvelshoff New Member

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    I measured deflection, less than 3 mm. Wind was low during footage.
     
  18. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    For forum postings I need a "smiley" of an hourglass, meaning...."Hmmm. I'm thinking." :)

    It appears these "twitches" are either mechanical or electronic noise, but I'm not sure how we could gather data to show what it was....

    Initially we need to find something that changes the twitches that will give us a clue of their cause(s)....
    Joe? Arthur? Tabb? JohnC?

    Andy.
     
  19. Arthur Vieira

    Arthur Vieira Flight Squad

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    As Sherlock Holmes would say or something like it....
    - "Eliminating all things that are not the cause, whatever remains, as improbable it could be, must the reason."
    If you have MK electronics, try messing a little, very little!! with the Dynamic Stability and/or Gyro P/I. As we can't see the bird flying, maybe it's correcting it self a little too much and this could cause a resonance with the gimbal. WOW that's a really wild guess!!!!
    The other suggestion I would do is to add a second battery to the mainframe, increase the overall weight above the frame to change the Center of Gravity a little, just to shake things up.
    And btw, if possible, post a video with the camera's stabilizer off, so we can have a real look of the vibration. :)
    Anyway the footage looks very good, better than some of mine.
    Good luck.
     
    AerialVisioneering likes this.
  20. Rene Duijvelshoff

    Rene Duijvelshoff New Member

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    Dear Iguassu, thanks for your reply. A good point, I will take and upload a footage without stabilizer. Herwith my complete set-up:

    CS6, QC-3328, Maytech 50A opto ESC, APC 12X3.8, CS 2-axis gimbal, 2x Radian stabilizer, Lipo 5S 8000 mAh, DJI Wookong-M FC, Sony CX730
     

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