Roll Under-correction

Discussion in 'Radian' started by Matt White, Jun 6, 2013.

  1. Matt White

    Matt White New Member

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    Radian on a 3-axis cinestar gimbal, latest 1.03 firmware. Savox on pitch, FF servos on pan and roll. Camera balanced without belts on.

    We've had quite a bit of roll trouble with our Radian, most of which we've managed to address by addressing mechanical issues. Here's what we've done so far:

    We determined that the main pan wheel had worked itself a little loose, so the 3-axis was slightly looser than it would be only on isolators. We tightened every bolt, and that's no longer an issue.

    We swapped the red o-rings out with blue.

    We also found that the savox servo that we did have on the roll was allowing some play, and determined that some of the gears in the servo must be a bit worn. So we swapped that out with a new FF servo, which is much tighter and doesn't seem loose at all.

    Finally, we determined that the camera wasn't vertically balanced on the roll axis. It was balanced in the center, but wouldn't remain at any orientation when left there. We raised the camera to ensure that, belts-off, it will remain in any roll orientation.

    This has pretty much eliminated all of the high-frequency twitching that we had been experiencing, at least at gain levels that should be possible. We've gotten it up to 140 now, any higher than that and we begin to see some high-frequency jitters. Actually, in reviewing the following video I still see a little bit of oscillation, so it might still be too high.

    So whats the problem?
    It seems like the Radian is consistently slow to compensate for roll movement, especially with sudden direction changes. So if the heli is in any kind of wind that requires it to make rapid adjustments, we see a lot of under-compensation that manifests itself as a bit of a shake around the direction change. See the following video, from about 0:18 to 1:00 (we turned off the Radian @ 1:00). The Radian was running in non-slew mode, so no camera operator was involved. There was a fair amount of wind, probably between 10 and 15mph.



    Tilt and pan are pretty much perfect, it's just the roll that we're stumped on. It's almost there, but unfortunately it's so close that the smallest deviation really sticks out. We can probably eliminate this with stabilization in Final Cut, but it seems like we should be able to get it more locked in on the Radian. If I increase the gain to try to get the Radian more sensitive we start to get high frequency oscillations, but if we lower it the roll under-correction gets worse.

    Any thoughts would be greatly appreciated!
     
  2. Gary Haynes

    Gary Haynes Administrator
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    Have you tried a test flight sequence of

    1. Fly a pattern with the Radians off.
    2. Fly the same pattern with the Radians on.
    3. Fly the same pattern with only the tilt servo running.
    4. Fly the same pattern with only the roll servo running.

    It is a process of elimination. You haven't mentioned what camera/weight you are carrying? Also screen shots of your Radian configuration would help. Some folks have gone to black o-rings or double star plates with heavier setups.

    When you do the tests do them while flying forward since sitting in the disturbed air of a hover is the worst situation for any copter, micro or full sized Jetranger.
     
  3. Philip Ellerbroek

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    Your description and problem is common, particularly with any heavier dslr like the Canon 5d. The roll servo is not strong or quick enough to handle the weight. This is only heightened by a pulley system which causes even more delay. This, people are looking for direct drive brushless enhancements to combat this issue. This has been posted by several users to no avail, including myself. Only fix is excessive post stabilization.

    Phil
     
  4. Matt White

    Matt White New Member

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    Gary-

    Thanks for the response!

    We've done 1 and 2, that's how we verified that we had mostly eliminated the oscillation... Prior to that there was a pronounced high-freq shake when the radians were on, and none with them off.

    We'll give 3 and 4 a try, though. I'll try doing it in cleaner air as well.

    Camera is a Panny HDC-TM900 HD cam. Pretty light, only 1lb or so.
     
  5. Matt White

    Matt White New Member

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    Thanks for the info, Phillip... It helps to know others are experiencing similar issues, I was hoping there was something I was missing, especially since stabilization does so well on pitch. But of course it's more difficult to see issues on pitch anyway, so it's probably just less obvious.

     

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