Vibrating in Position Hold

Discussion in 'ALTA' started by Stefan Helborg, Dec 29, 2015.

  1. Stefan Helborg

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    Hi

    First flight with camera and gimbal under my ALTA :)

    Apart from a lot of wind, it flew fine in Manual mode. As soon as I set it into Position Hold, it began slowly to vibrate. I could se it on the arms, witch began vibrating slightly up and down. I could see it in the light indicators but also hear it.

    When I turn it back to Manual mode again, and the vibration stops. I then mounted the black dampers, and I imagine that it helped a little bit. But the vibrations are still there.

    M-15 with BMPC 4K = a total of about 13.3 kg.

    Anyone have an idea for what it can be?
     
  2. Even Sigstad

    Even Sigstad New Member

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    Tune down vertical stifness and hold strength under height dynamics, and also tune down horizontal stifness and hold strenght under the position parameters. Tune it down step by step, testfly and repeat until you don't have any vibrations. Hope that helps!
     
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  3. ausweger daniel

    ausweger daniel New Member

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    i had the same issue on a x8 with wookong. in gps mode the arms began to shake up and down like hell when i changed to atti- or manual mode it stoped. i had to decrease the gains, especially the vertical and attitude gains.
     
  4. ausweger daniel

    ausweger daniel New Member

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    even was faster ;-)
     
  5. Stefan Helborg

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    Ok thanks I will try that. How far down have you set your settings on those?
     
  6. Even Sigstad

    Even Sigstad New Member

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    Don't remember all my settings but do know that my vertical stiffness is set as low as 5 when flying with M10 and Red.
     
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  7. Stefan Helborg

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    It helped a lot. However, I have only tried in virtually no wind, but the vibrations are completely gone now.

    However, I have experienced a few times that ALTA has started in "position hold" slowly to make small circles ... then I flew a little, then it stoped. It comes and goes a little. Any idea why it does it? Have I turned down for Hold strenght too much? think I've put it at 60
     
  8. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    What you are describing is called "toilet bowling" (the flying in small circles). It could well be caused by changing the Position Tuning : Hold Gain Strength. I can also be a sign of the signals from the GPS satellites "twinkling" during a solar storm. Do you check the solar weather before you fly? The specific thing to look for is the Kp Index (the planetary measure of proton influx). See such sites as n3kl.org (look at the lower center image for the Kp Index.).

    Andy.
     
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  9. Stefan Helborg

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    Yes the Kp index was actually at 4 (yellow) when I flew. Mabye thats why it made the toilet bowling :)
     
  10. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Stefan: Yup....that could be part of the explanation -- especially bearing in mind that the Kp Index is an overall planetary index. There is nothing to say that the effect on the GPS satellites that your ALTA was receiving were not more severely affected by the proton flux.

    I would try adjusting the Position Tuning : Hold Gain Strength when the Kp Index is back down to 1 or 2 -- then you can really see what that adjustment is doing without having to worry about whether the GPS is working correctly.

    Andy.
     
  11. Stefan Helborg

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    Today I tested again this toilet bowling. Kp index was 2, and it was completely calm.

    It still made toilet bowl. It starts with very small scale, which then become bigger and bigger. It also means that when I will fly sideways, then it starts slowly to fly obliquely forward.

    I've tested both Horizontal stiffness and Hold strenght of 25-40-60-75-86 and do not think there was much difference.
     
  12. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Stefan:
    OK. That seems to eliminate the Kp Index, doesn't it.

    What you might want to consider doing is: (and the following has been edited to correct my mistakes!)

    PHASE 1 TESTING
    1. Save your ALTA's current settings to a file.
    2. Reset all of the ALTA's parameters back to their factory settings.
    3. Suspend the ALTA from the center of the handle and make sure it balances with all the booms horizontal. The gimbal and camera must be powered off -- you will need to use some Velcro to stop the M15 flopping around and shifting the center of gravity during the balancing.
    4. While you have the ALTA suspended, power up the M15 and camera and do an autotune of the M15. Once you've done that power off the M15 and camera and replace the Velcro to hold the M15 steady.
    5. Go to the test flight location and recalibrate the compass with the M15 and camera mounted but powered off (you'll probably need an assistant with the M15 and camera you're using).
    6. Test fly but with the gimbal and camera powered off -- again with Velcro to stop the M15 flopping around and shifting the center of gravity during flight.
    PHASE 2 TESTING
    If the ALTA still toilet bowls, then you probably don't need to do this phase -- you've already got your answer.
    1. Power up the M15 and camera.
    2. Recalibrate the compass (yeah, it's a pain, I know but the electrical currents flowing when the M15 and camera are powered up may be affecting the magnetometers on the ALTA).
    3. Test fly.
    If you still see toilet bowling then I suspect it's time to email to support@freeflysystems.com.
    My suggestions are based on the complex interactions between all the adjustments and the physical mechanics of the ALTA and the gimbal. So the above is trying to eliminate the gimbal and camera as the possible source of the problem by just having them on the aircraft as inert weight.
    Andy.
     
  13. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    On my posting above, change "might need to use Velcro" to "WILL need to use Velcro!" Sorry.

    Andy
     
  14. Stefan Helborg

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    Hi Andy

    Thank you for super fast reply. I can also mount the battery tray with the weight, so it corresponds to the gimbal and camera ...! Wouldn't that be preferable?

    When you're talking about autotune the ALTA, I can only remember that I can autotune the gimbals stiffness settings.

    Is it autotune the compas or what do you mean?
     
  15. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Stefan:
    I suspect that a single monolithic mass is not a good proxy for the M15 and camera. It might weigh the same, but its center of gravity would probably be in a different place with respect to the Toad in the Hole.

    I realize in my haste to reply I mixed up two separate concepts.
    Let me edit my post above and try again! :) (After another cup of coffee!)

    EDIT: OK, I think the caffeine kicked in enough for me to be able to enunciate what I was trying to suggest. See Message #12 above, please.

    Andy
     
  16. Stefan Helborg

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    Thank you for your detailed posts. I will try the proposed as soon as I have time for it and will return with the results..
     
  17. Stefan Helborg

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    Do you want to calibrate the compass while the gimbal and camera is turned on?
    Then gimbal well fight like crazy when you turn around the ALTA...!
     
  18. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Yeah. I realize that. But you only need to flip it over twice (once in each orientation)
    The problem is that without the MōVI powered on, you will be calibrating the ALTA in a less-than-realistic magnetic environment. I'm not quite sure what FF recommends, though. This is just what I do.

    Andy.
     
  19. Benjamin Kenobi

    Benjamin Kenobi New Member

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    Hey guys,

    I had toilet bowling at first, I simply re-calibrated the compass (without the payload) and all good. I think the M5/M15 has enough separation on the ALTA to not have a huge magnetic effect.
     
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  20. Stefan Helborg

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    I re-calibrated the compass without the payload, and it seems that it helped a lot. I think it still have a little toilet bowling, but it is aceteble now.
     

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