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Vibrations and jello - solved!

Discussion in 'Pro/Adv Discussion' started by Vertigo, Jun 18, 2016.

  1. Vertigo

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    Ive partially rebuilt a crashed Phantom3 advanced I recently bought. Ive replaced 2 motors that spun a little rougher and Ive temporarily straightened the gimbal yaw arm which was bent badly (new one is on its way).

    It works now, but Im having quite a bit of jello. Just looking at the phantom flying, it doesnt surprise me. The phantom seems nervous in the air, as if with too high PIDs. There is a slight vibration in the frame that seems too low frequency for prop inbalance, on the order of 10hz. Really, as if too high P factor. The gimbal and the landing gear shake a lot more. Its difficult to capture on video, but Ive tried by recording this with my mobius at 60FPS (be sure to watch in 60FPS):



    And no, it doesnt hover that badly, Im flying it to capture different angles and movement. In reality its worse than it looks here. I can best see it on video around 21 seconds and 1m32, but its still difficult. And I realize Im flying low, but 3-4 meter up, its the same, I just cant capture it on video there. There was some wind when I did this, but it also happens with no wind at all.

    This is with brand new props. I did not balance them yet, because I cant with my prop balancer. Again, I have a phantom prop balancing rod on order. But it would surprise me brand new original props would be so badly out of balance to cause this. Also with the first pair of props, which admittedly are slightly worn, its about the same.

    I did all the obvious things, like recalibrating IMU, gimbal etc.. Any other idea's ? If you hover your Phantom 3 in front of you, do you see the gimbal and landing legs shake at all, or anything like mine?
     
  2. Vertigo

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    I solved it at last. Things I had tried that didnt work

    - New props and trying to balance the props on a Dubro Truspin. But the DJI props balanced perfectly anyway.

    - Ive replaced all 4 motors based on bad advice/judgment. 2 actually needed replacement because they had bad bearings. The other 2, I changed because when I ran one prop at the time @idle with the phantom tied down, oscillations would occur on those motors that shook the entire quad. This however, proves nothing. If your quad isnt 100% level (and it never will be), one motor will speed up a little even when "idle", and this can cause enough wind and turbulence to hit a resonance frequency and the thing will shake. Even with perfect motors and balanced props.

    - Replaced gimbal dampeners. Tried with and without drop pins

    - tweaking settings like gains etc

    What finally did it was replacing the gimbal yaw arm. I had it on order and planned to replace it since the beginning, but it only arrived today and I never thought it would actually do the trick because the one on my phantom looked fine after bending it back. When the new one came in, and I could compare them side by side, I had even less hope it would solve anything as I could barely see any difference in geometry:
    [​IMG]
    [​IMG]

    (perspective lies, the difference is even smaller in reality).

    But I just did a short 2 minute testflight in windy conditions, and there was no hint of jello. I wouldnt have bet a penny on this after seeing the two arms, but there it is.
     

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  3. DPD

    DPD

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    The gimbal dampeners in the video looks to be a little bit snug, I see u are using just to drop which is correct. What I do notice in the video is they do look like they're being squeezed instead of actually hanging from the gimbal. For some reason IMO they look a little bit snug or a little bit too tight being squeezed causing the vibration. I could be wrong, but it's worth looking and checking again because you did work on the gimbal, something May be a little too snug causing them to be pushed up and not doing their job properly I would check again. Hope this helps...


    Sent from my iPad using PhantomPilots mobile app
     
  4. Vertigo

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    No, I had already tried without drop pins too, it made no difference. I think I tried just about any conceivable solution until the gimbal arm arrived.
     
  5. DPD

    DPD

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    Good luck with it. Hope it all works out...
     
  6. Reed L

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    ^ +1
    And it looks like the right front lower camera mount is tweaked a bit. It's definitely not sitting straight. I never saw a shot during the video where the right side didn't look crunched a bit. Glad you got it fixed but check the lower plate, it should be perfectly straight and flat

    Untitledddfhg.jpg
     
  7. Vertigo

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    both plates are flat as a razor. Maybe the fisheye lens is making it look different.
     
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  8. Gixxer55

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    Hi Vertigo, I have had my p3p for a few months now, flies great and its easy for me as I am a Goblin pilot,570. I just started to notice at hover as you say, a vibration in the legs and gimbal. looks just like your video. I have the newest firmware for radio and bird. I'm gonna try new blades. no crashes at all. any other suggestions? I noticed that when I jam the collective up and she takes off all is good. seems to be only at hover. thanks
     
  9. Reed L

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    Check the balance of your props, this seems to be a normal cause. Also check the rubber pads that hold the camera, replace them if they feel stiff.