Cinestar HL / MOVI MR - Shooting long lens

Discussion in 'Cinestar 8' started by Justin A Zattelman, Sep 17, 2015.

  1. Justin A Zattelman

    Justin A Zattelman New Member

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    Hi guys,

    See attached for our latest custom Cinestar HL build.

    We have been flying our Black Magic 4K production camera and testing both of our f4 17-40mm and f1.8 85mm Canon lenses on it.

    Setup:
    You can see in the picture of the MOVI (on the left side of the image) a black custom power/ signal cable which runs from the back of the MOVI and run along each axis all the way to the tilt axis of the camera. The wires are terminated by XT30 connections so I can change cameras easily and or other modules. There are three silicon wires one to control the camera, an regulated 4S power cable to power the camera and a regulated 12V cable for the SDI to HDMI module and pull focus. It's a neat solution because the wires don't get caught in flight as the MOVI moves around and I can install different cameras quickly by simply unplugging all the wires connected to the tilt axis. The custom wire cable doesn't seem to affect the balance of the MOVI because I have carefully introduced a "relief" half loop near the tilt axis which enables the axis to move freefly and the custom cable just moves around it.

    Long Lens Experimentation
    We have been experimenting with longer lenses and are not satisfied with the results so far. Using the 17-40mm lens (and setting to 40mm) you would expect pretty perfect stabilisation in the air (We get almost perfect results using handheld with the 85mm lens on the ground).

    I have removed the leg extensions of the MOVI thinking that the prop wash was causing vibrations to the legs. It did indeed lead to better stabilisation however still not good enough for commercial work, even in light wind (5-10 knots) conditions. See a video link on youtube:




    The Alta uses different legs on the MOVI because they were getting in the way of the prop wash and generating vibrations. Just wandering if anyone has any information which may be able to help us.

    Vibration Isolation
    We use the blue vibration isolators and typically have been testing in 16deg celcius / 60 deg fahrenheit temperatures.

    Movi settings
    After a quick autotune the settings come up as:
    Pan stiffness: 101
    Roll Stiffness: 59

    Tilt Stiffness: 37

    The Gyro filter and Output filter are both 3. (Should we be changing these numbers?)

    In the video using the 40mm lens our settings were:
    Pan stiffness: 215
    Roll Stiffness: 62

    Tilt Stiffness: 57

    Any less on the tilt was causing larger movement in the tilt axis.

    Thanks guys for any information you may have!

     

    Attached Files:

  2. Steve Maller

    Steve Maller UAV Grief Counselor

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    I took a quick look at your photos, and this jumped out at me. There's one cable that's pulled kind of taught. Is that an illusion or is it really that tight? If it is, it's likely going to affect your tilt axis on the MōVI.

    Screen-Shot-2015-09-17-at-6.44.02-PM.jpg
     
  3. Justin A Zattelman

    Justin A Zattelman New Member

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    Thanks Steve, I had a quick look and it seems to be an illusion. There is plenty of slack in the HDMI cable to allow the tilt axis to move smoothly. I just find it strange that in hand held mode I can shake the MOVI quite violently and not replicate the instability found and flying...
     
  4. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Justin:
    So, from what you say, it would seem like there might be a lot of vibration coming down from the the Cinestar into the MoVI. Do you happen to have a GoPro (or equivalent) that you can hard mount on to one of the Cinestar's booms and can get some footage from it -- that would give us a clue whether the Cinestar is indeed vibrating badly.

    Have you balanced the props and the motors? I'm not suggesting that you should have done -- just looking for possible causes of vibration in the Cinestar frameset.

    Andy.
     
  5. Justin A Zattelman

    Justin A Zattelman New Member

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    I don't think it's vibration from the Cinestar because I've mounted a GoPro to one of the arms previously and the footage was almost perfect. No noticeable vibration....

    I really do think something strange is occurring with the standard MOVI legs. I have seen it in the forum where people have noticed the vibration more when they attach wheels to the legs. Could be caused by the prop wash?
     
  6. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Hmm. The only way to test that theory, Justin, would be to remove the legs and have a helper do a hand launch and then, at the end of the flight a hand catch. This is NOT the safest of things to do, but it would certainly prove whether the legs are the problem.

    Andy.
     
  7. Justin A Zattelman

    Justin A Zattelman New Member

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    Hi guys,

    So have gone a little further and taken video of the MOVi during flight by attaching my GoPro camera to one of the arms, just underneath the motor. I attached tufts of wool/ string to the MOVi at different points to see what the wind flow was doing during hovering and movement at different velocities. I did make a note that the footage appears to be a little smoother when the DJI A2 flight controller is in Attitude mode, not GPS. Still the footage is not perfect....

    I was hoping to check whether the MOVI legs were inline with the propeller thrust, perhaps causing vibrations.

    Can you guys see anything unusual going on? It does look like there is a slight vibration in the MOVi sometimes but it doesn't appear to be too noticeable in the video.

    Enjoy,

     
  8. Martin Osborne

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    Did you ever solve this problem? And if so, how?
     
  9. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Good experiment. I don't see anything unusual -- the lateral wind flow over the legs seems proportional to the lateral motion of the copter as you would expect -- and there doesn't seem to be much turbulence on the MōVI when hovering.

    It'll be interested to see if any of the folks at FF have any additional comments.
    Andy

    Forensic Software & sUAV / Drone Analyst : Photographer : Videographer : Pilot (Portland, Oregon, USA): Trees=2, Ground=1, Props=11. :(
    The Ground Is The Limit™
    ---------- Forensic Drone Analyst : Forensic sUAV Analyst : Forensic Unmanned Aircraft Analyst : Forensic Drone Expert
     

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