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Balancing Problems

Dynamic Balance Static Balance Balance Ultra 2C

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#1 Steven Magrath

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Posted 12 June 2013 - 06:31 AM

Hi Guys,

 

I work as a 1st with the same Operator and we've noticed a problem has developed in obtaining a Dynamic Balance, would love to know if anyone has experienced or heard of this before, and open for all suggestions to fix.

 

After a buy the book setup is complete, achieving good monitor position, drop time and Static Balance we then proceed to spin and/or drop the camera side on to test for dynamic balance. Once the Dynamic balance has been achieved, the camera will always rest in tilting up position. So we Re-Static Balance the camera which in turn always creates a monitor(fore) heavy Dynamic Balance. No matter what combination of battery in, monitor out, camera forward or back, drop time, etc.. you can only obtain a good Static balance with a monitor(fore) heavy dynamic balance OR a good Dynamic balance with the camera resting in a tilted up position.  Interestingly the tilted position seems to be fairly consistent without putting an inclinometer on it. Also we have tuned the gimbal to take this out of the equation.

 

Thanks Steve


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#2 Victor Lazaro

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Posted 12 June 2013 - 09:59 AM

Is your goal balanced? When on the stand, try balancing the sled while facing left, then spin it facing right. Does it keep the balance?
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#3 Jerry Holway

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Posted 12 June 2013 - 10:01 AM

Read the dynamic balance primer, but skip the math and go directly to page 12.

 

Your monitor is raised up somewhat with the Ultra2 so the "side drop test" is useless.

 

Start with the camera c.g. about at the back of the gimbal sized post (about 19mm or 3/4ths of an inch) and you will be close to dynamic balance when you are in static balance.

 

A small adjustment - moving the battery forwards or back, a few mm at a time, and re-balancing with the camera for static balance, will get you in dynamic balance quickly.

 

http://www.steadicam...namicPrimer.pdf

 

Jerry


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#4 Bryant Swanstrom

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Posted 12 June 2013 - 10:48 AM

The last time this happened to me it was because the ac had zip tied the micro force and it was wiggling around while doing the balance so it was different every time until I noticed and then switched it to velcro.

 

I know it seems obvious but it wasn't to me at first since I wasn't there for the first couple days of the shoot.


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#5 Alan Rencher

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Posted 12 June 2013 - 12:49 PM

Is your gimbal out of balance?


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#6 Steven Magrath

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Posted 12 June 2013 - 02:21 PM

Hey guys,  Thanks for the speedy replies, 

 

Victor: I believe the goal is balanced, but will check again today. Thanks

 

Jerry: Page 12 you say... Just before I threw up this post I printed out page 12!!!! : ), but read the primer several times last night trying to get my head around the maths too, Im about to head into work and follow it step by step. Great work, nice website! Thanks

 

Bryant: I too instantly figured that whilst testing the drop time after the initial static balance that leads and accessories may have shifted causing my problem, (I am using a RED!!!!!) subsequently I de-rig all cables and Velcro items from the camera and started again and the problem still occured.   Thanks

 

Alan: Our gimbal was slightly out, but we have corrected in pre for the current film we're working on. Thanks

 

Im about to head off to work, and will check the goal/gimbal and rig the camera without leads and then walk through a balance whilst reading page 12. Will let you know how I go.

 

Thanks again

Steven


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#7 PeterAbraham

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Posted 12 June 2013 - 05:47 PM

You may want to have the gimbal looked at by Tiffen to insure that the precision adjust bolts you are turning using the Blue Whale are not slowly turning back out of true after you are centering it up.

In theory the Whale can be used and the gimbal will be just fine. But if you keep doing very subtle adjustments to center the gimbal and then it goes out, it needs to be looked at.

To be very specific here: When you center the gimbal using the Blue Whale and get it to hold center long enough to spin balance- and it does spin balance flat and true, at what point does it go out of center again? Right away? After use? After rugged vehicle mount type use? Just wondering.

Best,

Peter Abraham, S.O.C.
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#8 Steven Magrath

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Posted 24 June 2013 - 05:48 AM

Hi Guys,

 

Sorry for the EXTREMELY late reply. Post Productions in 4days, so I'll let you know how I go. (more controlled test e.g. no wind, or rushing AD's ;)

 

QUICK QUESTION:

Having a preston MDR mounted under the front of the junction box/electronics, does this affect how far back the camera cg. should be from the post? Does this make sense?  (I plan on taking some pictures in post, maybe a video or two)

 

Thanks

Steve


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#9 Jerry Holway

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Posted 24 June 2013 - 07:38 AM

Steve- 

Every mass has an effect on static and dynamic balance; how much depends on how large the mass is and its position.

 

In practice, we only move the monitor, batteries, and camera (with all accessories, film, tape, cards, whatever attached). And we lenghten or shorten the sled. So those are the things we adjust to achieve both static and dynamic balance.

 

When sled are designed, we use the formulas to be sure we can manipulate the masses to achieve static and dynamic balance over a wide range of choices.

 

In the field, just fix the length and monitor position, put the camera close to the final position, and move the battery and camera for dynamic balance. Whatever else is in the sled (including the mass of the sled itself) will just take care of itself.


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#10 PeterAbraham

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Posted 25 June 2013 - 05:37 PM

Exactamundo. Some experimenting NOT in an on-set situation will make your eyes and brain wrap around this. You add a motor, you take away a motor. You use a short end instead of a full 400', etc. The variables shouldn't freak you out- it isn't that there are not literally thousands ( millions? ) of combinations of masses to be added and taken away. It's just that with a bit of exploration you will see how ALL masses affect a rig that can be rapidly put into dynamic balance.

 

Once that makes sense, you can set your rig up in the morning and during the workflow of the day, make the subtle adjustments needed to keep it spinning flat.


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#11 Steven Magrath

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Posted 09 July 2013 - 11:45 PM

Hi guys.

 

Post done and controlled test's carried out.

 

The Conclusion:

The Gimbal 

 

After centring the gimbal this time we believed the precision adjust bolts were not tight enough to hold the calibration the last time we used the blue whale. (the manual mentions not to over tighten them, but i think we were a bit to generous and left them too loose) If the problem develops again we will most likely have Tiffen look at the gimbal, but so far so good.

 

Off to a different film set tomorrow for a full day of Steadi, (on Alexa : D ) 

 

Thanks for all the comments and suggestions!!

Steven


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