Occasional Issue w/ GPS Hold – Pendulum Oscillation

Discussion in 'Cinestar 6' started by Josh Wilson, Aug 24, 2013.

  1. Josh Wilson

    Josh Wilson Member

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    GPS hold has worked very well for me. The position fix stays dead on, even during windy conditions.

    However, sometimes the ship will begin to Oscillate on the horizontal axis at times. The wobble will get worse and worse until I switch off the GPS hold. The oscillation resembles a plate that wobbles on a table top with increasing severity. The camera is clearly acting like a pendulum and the GPS hold feature needs to be fine-tuned.

    Aside from checking the balance of the camera on the gimbal, can anyone suggest what setting in the GPS MKTools Parameters to adjust?

    Here are the GPS Settings…
    [​IMG]

    [​IMG]
     
  2. Gary Haynes

    Gary Haynes Administrator
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    Josh what are you flying and what all up weight? I found a gain of 85% was better for me than 100%. Also when were you were flying and got the wandering? Did you check the GPS storm data at n3kl.org? You can see the chart at the bottom of my weather station homepage at home.comcast.net/~999kg. Level 1-2 should be rock solid, be careful at level 3 and 4 and above GPS may be totally unusable.
     
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  3. Josh Wilson

    Josh Wilson Member

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    Thanks for the quick reply Gary. I'm carrying only a 6,200 mAh battery and CX760 so the weight is nothing extreme. I have yet to actually weight the setup.

    I don't have any wandering. It stays in one place even when it starts doing the washbowl effect.

    I did just check the gimbal placement and camera placement and found that I was able to make some adjustments. Now, when I fire up the radians and start rocking the ship with my hands it seems more neutral. Before, when I started rocking it with my hands, I could feel the gimbal fight with the balance of the ship. Sooo maybe it's all good now, without even making any changes in MKtools.

    I will test and let you know the results. If not, then I will test out a change with the GPS gain.
     
  4. Dave King

    Dave King Well-Known Member

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    Josh

    I've experienced that at times as well in windy conditions. All your settings look good except the GPS gain which Gary as mentioned already. You can also upgrade to 2.0 software which has some GPS improvements.
     
  5. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    The phenomenon the copter may have been experiencing is called "toilet bowling," Josh.
    As Gary says, reduce the GPS gain to 85%.
    There was a coronal mass ejection last Tuesday when a comet dove into the sun, but it looks like the Kp Index never made it above 4 (the Earth dodged an bullet!)

    Had you calibrated the compass?

    Google searches that might be relevant:
    copter toilet bowling
    mikrokopter toilet bowling

    Hope this helps
    Andy.
     
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  6. Josh Wilson

    Josh Wilson Member

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    Excellent information Dave and Andy.

    Yes, the compass was calibrated prior to the flight so that was probably not the culprit.

    I will reduce the GPS gain to 85% as well. Easy enough!
     
  7. Jason Smoker

    Jason Smoker Active Member

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    Josh also have you updated your firmware lately?

    If you did you gps pid settings need to changed too. I have played with these a little seems to help.
     
  8. Adam Paugh

    Adam Paugh Distributor

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    Hello Josh,

    Here is a simple test: Take off in manual and fly to 5meters or so. Face nose of kopter to north and activate GPS hold, note behavior. Disengage GPS and yaw 90 degrees to face nose to east and activate GPS hold, note behavior. Do this for each of the four cardinal directions. During period of high solar activity position hold in S/SE/SW may behave differently then N/NE/NW.

    Report with your findings.

    Greetings,
    Adam
     
  9. Dave King

    Dave King Well-Known Member

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    Adam

    That's a great little test. Have you guys at QC found the new GPS PID settings that MK uses for the new firmware good for our heavier copters? Are you finding you need to tweak them?
     
  10. Steve Maller

    Steve Maller UAV Grief Counselor

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    Dave, are those "new" numbers posted anywhere? I'd like to compare them to what I'm using.
    After the ACC 2.2 and firmware upgrades, I'm experiencing a little bit of toilet-bowling (even in calm air) that I never saw before except in very high winds. Not severe, but definitely not ideal. Thanks!
     
  11. Gary Haynes

    Gary Haynes Administrator
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    Steve, from the Wiki

    http://www.mikrokopter.de/ucwiki/en/Firmware-2.00
    GPS parameters


    • The GPS parameters were slightly changed and the algorithms have been improved.
    • GPS parameters are changesd (P = 90 -> 100, I = 90 -> 90, D = 90 -> 120, A = 40)
    • If PH leads to oscillate, should maybe reduce GPS-ACC (the compass should work well of course as in all previous versions)
    • You will probably notice that the MK brakes differently after changing the pH position.
    • The GPS algorithms now run slightly faster with 40Hz.
     
  12. Dave King

    Dave King Well-Known Member

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    This is why I went back to 90j. I just don't have to tweak.
     
  13. Steve Maller

    Steve Maller UAV Grief Counselor

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    Well, I finally worked up the courage to try the hack of assigning a value to a POTI so that I could adjust things in flight.
    Here's what I did...
    1. connected up my Xbee
    2. launched MKtool on my laptop
    3. configured one of my Graupner mx20 CTRLs to xmit on channel 12
    4. configured POTI 8 to be Channel 12
    5. assigned the value of GPS Gain to POTI 8
    6. switched the info screen on MKtool's main screen to #4 where it shows the GPS Gain
    7. rotated the designated Graupner mx20 dial and verified that the GPS gain was changing (here I should mention that the granularity of that dial is not very good, so each 'tick' on the dial represented a change of 4-6 in the value of the GPS Gain)
    8. set the GPS Gain to 86 with the dial
    9. launched the copter, climbed to 8-10 meters or so, then engaged AH and PH
    10. after allowing the copter to "settle down", I slowly increased the gain from 86->92->98->103 and waited a moment at each increment. i confirmed the settings on my laptop in MKtool (Xbee is cool!).
    11. as per Adam's suggestion above, i also repeated this at each cardinal direction.
    12. turned off AH and PH and landed.
    13. replaced the setting for GPS Gain to 90 instead of POTI 8 (don't forget this!)
    What I found was that the copter gradually settled down with very little drift at a setting of 90, so that's what I'm going with. :)
     
  14. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Thanks for the information Steve! Good to know some actual data.
    Andy.
     
  15. Steve Maller

    Steve Maller UAV Grief Counselor

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    I'm still trying to figure out how to hack the mx20's dials to be more like a volume control where I could define min and max and it would scale smoothly between them. They seem to be hard-wired as balance controls, which only sort of works with values in the 128+/-N range when you start monkeying with min/max values, although that doesn't even work very well.

    All I want is a setting where I could say the min value is 4 and the max value is 10. But the UI seems to be all about +/- percentages, which doesn't map well to that usage. Or maybe my 3rd grade math has finally failed me.
     
  16. Josh Wilson

    Josh Wilson Member

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    Great news. I have been flying almost every day and the GPS hold has been working perfectly at 85% gain. Had one day with moderate winds up to 15 mph gusts and still held steady. I'm sure the better balance of the gimbal w/ camera did not hurt either. Thanks again for everyone's suggestions!
     
  17. Gary McCready

    Gary McCready Active Member

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    Thanks for this info guys! My GPS hold has also been a bit off since the last update. I even asked Quadrocopter for their MKTool file settings for the CS6 and tried that, but it was even worse.
     
  18. Steve Maller

    Steve Maller UAV Grief Counselor

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    I recently tried an experiment and lowered the "Compass Effect" to zero, and my position hold is spot on again. Ever since I upgraded to the new ACC hardware and the 2.0 firmware, my position hold has been plagued by some toilet bowling. Not serious, but enough that it's quite disconcerting. But ever since lowering the gain and removing the compass effect, it's great again.
     
  19. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Steve: I've been seeing reports along those lines. My understanding was the Compass Effect controlled the degree to which the compass fed into the yaw control/stabilization....but it seems as though with the latest firmware it's causing toilet bowling....

    Andy.
     
  20. Steve Maller

    Steve Maller UAV Grief Counselor

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