Jitter on tilt when conrtrolling with Spektrum

Discussion in 'Radian' started by Thijm, Oct 9, 2012.

  1. Thijm

    Thijm Member

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    Hi,
    I have some jitter on the tilt axes when controlling it with the Spektrum dx8.
    Gain is set to 100 and i do not have jitter when i moving the mount/copter
    Is the gain setting only for stabilization or also relevant to tx control?

    Thnx for the help
    Tfcm
     
  2. Thijm

    Thijm Member

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    Lowering the gain to 75 and 95 (tilt-roll) solved the jitter while moving the stick controls
    IMG_0421.jpg IMG_0422.jpg
     
  3. kjetil tønnesen

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    too higth gain can be the reasen for jitter,try to adjuse the gain abit

    what servoes do you have on the gimble?
     
  4. Thijm

    Thijm Member

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    Org FF, the new type.
    I find it a bit strange that you have to lower gain to stop jitter when you control the tx sticks, while stabilization moves without!
     
  5. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    As I understand it, the gain is purely for the stabilization feedback loop -- but you may find that if you command slew motion with the transmitter, you move an otherwise "stable" system into instability and it starts to oscillate. So kjetil is correct, back the gain off a percentage point or two until that stops.

    Also, what I've seen done (and done myself), is to deliberately tap the gimbal with my hand to see if it starts to oscillate. It should have a very "dead" response, rather than obviously exhibiting what is technically called "damped harmonic oscillation." :)

    Andy.
     
  6. Thijm

    Thijm Member

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    Right. this makes sense. when moving the mount/copter the camera is sort of stationary!

    Deliberately tap the gimbal did not show any oscillation on any of the axes. I think the epic tilt bar upgrade added some more play in the system and that i have to deal with lower gain's

    Thnx for the explanation
     
  7. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I'm using the Epic tilt bars and I didn't see any more play -- have you checked the tightness of the tilt belt? If you push with a finger on the midpoint between the small and large pulley, I see a deflection of about 2-3mm. Also check that the grub screw on the large pulley is tight on the shaft -- I've seen play if that works loose.

    Andy.
     
  8. Thijm

    Thijm Member

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    The belts are all ok and tight. added xtra screw in the large pulley and drilled holes in the shaft to prevent it from slipping.
    On the tilt bar shaft side i sanded the carbon inserts so that they have more grip.
    Can you tell what would be normal gains when mounting a Epic?

    Thijm
     
  9. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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  10. Thijm

    Thijm Member

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    Hmm. indeed a bit higher. But i do not know what the numbers represent
    I measured the play on the cam plate and it's 1mm. So that seems ok.
    going to test system in air. Maybe then i can get some higher gains.
     
  11. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    The gain is just an arbitrary percentage, as far as I know -- more from the "adjust up until it oscillates, and then down until it don't." :)
    JohnC is this correct? Or is it a carefully computed number in megagruntz per kilohertz?

    Andy.
     
  12. John Cunningham

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    The gain does affect the slewing stability as it all gets lumped together when it goes through the PID loop for the gimbal control. You will notice that the slew rate relative to the ground for the Radian remains constant. By that I mean if you pitch nose up while slewing nose down, it will drive faster so that the camera rate relative to the ground is constant.

    The % is arbitrary now. It did mean something - but I changed it to put the final values somewhere around the 100% mark which is more logical to people who don't care if it means anything specific internally.

    Having said all that, a notchy slew can be a result of the mount not being balanced properly for the camera.

    And I also use the tap test : give the mount a sharp tap and see if it oscillates.
     
  13. Thijm

    Thijm Member

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    Thnx. Tested the Scarlet today. Cam is 100% balanced. We had to fit longer boom arms on the roll axes to get the Epic or Scarlet in perfect balance and have full tilt down
    I still can see a little jitter but i do not see that in the video. so 75 on tilt is the max.
    The tap test only gave some oscillations when the gains are set above 150.
    Overall very happy with the system. Horizon and tilt are working fine. We do not make fast movements, so lower gains do not appear a big problem.

    Tfcm
     
  14. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    How much does the Scarlet weigh? Just curious to learn what battery configuration and flight time you got with the Scarlet?
    Glad to hear that jitter is not a problem.

    Thanks
    Andy
     
  15. Thijm

    Thijm Member

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    You meant gain i guess :)

    Scarlet without lens 2.5kg. Epic without lens 3kg (Prod versions are a little lighter 200gr)
    Total weight of the copter (3.4kg Cam) is around 10.6Kg. Flight time with 2x 6s 5800 are 7min with 30sec left to land.
     
  16. Josh Lambeth

    Josh Lambeth Well-Known Member

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    What motors, escs, and FC are you using? Don't mean to thread Jacko just curious.

    Josh
     
  17. Thijm

    Thijm Member

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  18. Howard Dapp

    Howard Dapp Active Member

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    A couple of questions..are you using Hekules II or have you gotten a set of the new Herkules III? Which lens do you have mounted on the Epic in your photo? Also, your motors appear to be 830kv? Wow those things must scream on 6s!
     
  19. Thijm

    Thijm Member

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    Herkules is type 2.
    Lens is a simple zeiss 16mm compact prime only for testing. The problem with these are that they do not give a clear image round the edges with 5k.
    The Tigers perform reasonably well, considering the flight time and that they are already more then a year old. At the time they where a good choice. Still looking for a good replacement but not decided yet.
    5s would be better, but i bought 6s with a motor upgrade in mind
     
  20. Howard Dapp

    Howard Dapp Active Member

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    Thanks!

    We're seriously considering the Kopterworx KW10 motor (600kv) running 6s and 14x8 props. In my brain this is a good setup.
     

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