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Dynamic balance - side to side


Michael Wilson
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Trying to dynamic balance my rig with a fairly light weight f55 yesterday. When I would do a spin test the rig would dip to the left. Usually it needs to be adjusted forwards or backwards. Only thing I can think of is the ab battery on my Marshall is not centered. But I've balanced before w this monitor. I have the mk-v 1.5" gimbal. I can static balance 360 degrees. But when I spin it, it eventually starts dipping to the side.

 

Thoughts?

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Do you have a telescoping post? There's a chance the top and bottom stages aren't aligned dead center. Or even a camera slightly twisted on the dovetail (more apparent with longer payloads). Or if your monitor bracket rotates off center on the post. I check all the possible off center items first when that happens.

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The camera can be twisted and/or tilted (as in Mike's pix), but the monitor and battery c.g.'s must be on a line that runs through the center of the post, or put another way, the 3 c.g.'s (monitor, battery, camera and accessories c.g.'s) must form a plane that is coincident with the vertical axis of the gimbal... or more simply, you cannot easily correct for dynamic balance if the c.g.'s are off center side to side.

 

If you can, remove the monitor and check where its c.g. is; same for the battery.

 

Jerry

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We talked about the Zephyr "Mickey" method over here:

 

http://www.steadicamforum.com/index.php?showtopic=17941&hl=mickey

 

Works like a charm, you just need a 1/4x20 bolt, a nut, and a bearing with 1/4" ID. I think it ran me $5 at McMaster Carr...

 

Seriously this method gets you 95% of the way there in no time... and the adjustments are intuitive while you're doing it. No trial and error. You quickly learn that 1 mm adjustment on one of the rods makes a big difference.

 

My 2 cents :)

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To be clear, the Mickey is a complete waste of time when the monitor c.g. is raised up from the battery c.g. – as it is in many sleds.

 

If the monitor is raised up on your sled, the sled needs to be front heavy without the camera, and the Mickey can't help you at all.

 

If this seems wrong to you, you could do the math, or you could just spin balance your rig (however you get there), then remove the camera, and it will be clear.

 

On the other hand, if the monitor c.g. is not raised up, then the camera c.g. will be directly over the center post, and you don't really need a Mickey to balance your sled in a separate step - you've got a lovely gimbal to do that already.

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To be clear, the Mickey is a complete waste of time when the monitor c.g. is raised up from the battery c.g. – as it is in many sleds.

Actually Jerry if you'd think before you post you'd realize the the Mickey works with every sled configuration, maybe it's too outside of your limited (Tiffen only) experience

 

This thread is about side to side balance...

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To be clear, the Mickey is a complete waste of time when the monitor c.g. is raised up from the battery c.g. – as it is in many sleds.

 

If the monitor is raised up on your sled, the sled needs to be front heavy without the camera, and the Mickey can't help you at all.

 

If this seems wrong to you, you could do the math, or you could just spin balance your rig (however you get there), then remove the camera, and it will be clear.

 

On the other hand, if the monitor c.g. is not raised up, then the camera c.g. will be directly over the center post, and you don't really need a Mickey to balance your sled in a separate step - you've got a lovely gimbal to do that already.

Thanks Jerry,

 

As always you're level of understanding of all things steadicam is a valuable insight and resource. Please don't stop coming here on account of the rudeness (I could go on but I'd like to keep this forum a respectful and courteous place).

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The effects of the centrifugal force applied to the post will be different the higher or lower its applied. Hence a non coplanar monitor will balance great on the mickey and not be in dynamic balance.

 

This is what Jerry is saying and it seems entirely correct to me. Eric, if you dispute this howabout doing so with some science.

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