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Old October 30th, 2006, 09:35 AM   #1
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Troubleshooting jerky motion

After building a dolly using the best wheels and bearings I could lay my hands on, I still find the motion to be somewhat jerky. This is not an issue in wide shots, but I find it objectionable on close-ups.

In the attached clip, the camera operator was standing on the dolly, which was of the eight-perpendicular-wheel, PVC-rail type. The dolly grip tried pushing it and pulling it, but either way there were sections where he felt resistance. What could be the cause? Here is a list of my suspects:
  • Unevenness in the level of the (hardwood) floor.
  • Poor connection of the track segments.
  • Stratches on and caving of the PVC pipes.
  • Imperfections in the mounting of the wheels (so they do not make perfect contact with the track).
Note that the camera is moving slightly even when the dolly is stationary. I presume this is due to the camera operator, who was getting ready to pull focus. Could the mere fact that the operator is standing rather than sitting be a significant source of shake?
Attached Files
File Type: zip dolly.zip (1.29 MB, 167 views)
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Old October 31st, 2006, 05:56 PM   #2
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Quote:
Originally Posted by Emre Safak
After building a dolly using the best wheels and bearings I could lay my hands on, I still find the motion to be somewhat jerky. This is not an issue in wide shots, but I find it objectionable on close-ups.

In the attached clip, the camera operator was standing on the dolly, which was of the eight-perpendicular-wheel, PVC-rail type. The dolly grip tried pushing it and pulling it, but either way there were sections where he felt resistance. What could be the cause? Here is a list of my suspects:
  • Unevenness in the level of the (hardwood) floor.
  • Poor connection of the track segments.
  • Stratches on and caving of the PVC pipes.
  • Imperfections in the mounting of the wheels (so they do not make perfect contact with the track).
Note that the camera is moving slightly even when the dolly is stationary. I presume this is due to the camera operator, who was getting ready to pull focus. Could the mere fact that the operator is standing rather than sitting be a significant source of shake?

Did you use spacers between the bearings? If you didn't, it will not work right. Check each wheel for smooth turning.

Mike
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Old November 10th, 2006, 01:45 PM   #3
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Emre, my experience with dollies is limited to what we used for two years in film school, but maybe it can help. First off, I'd totally check what Mike is suggesting and make sure your wheels are rolling smoothly.

I watched your footage, and one thing that comes to mind is that in my limited knowledge opinion, the physics of using a dolly are a lot like using a camera and fluid head. For small, smooth, incremental movement, you're going to fair better with a heavy camera and strong, smooth resistance. This is also true of a dolly. A heavier dolly allows the grip to more easily anticipate the amount of energy needed to move the dolly slowly and smoothly. It also sounds like another issue is that a lot of the weight is high (the operator is standing) and since the dolly is light, its a bit like trying to pull the rug from out under the operators feet. This wouldn't be an issue if a heavy dolly on solid track was being used. That's what we had in school (it normally took 4 students to lift the dolly on the track) and when I went to NAB I noticed the lighter more portable dolly systems we sort of "hyper-sensitive" in comparision. Those are just my thoughts, I don't know how well they relate to the issues your having. Nice DOF by the way in your footage.
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Old November 11th, 2006, 09:15 AM   #4
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Cal, I think you are right on. My dolly grip and I decided to just weigh the thing down as much as possible. In addition I lubricated the track but he disagrees with me on that. What do you think?
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Old August 26th, 2007, 06:37 PM   #5
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having the extra weight of a sitting cameraman can help.
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Old August 27th, 2007, 05:41 AM   #6
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Thanks, Chris. The project is over and I learned that the best practice is to weigh it down with inanimate objects.
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