Dynamic Balance Mugs guide

[Sam Morgan Moore]

I have read the primer and searched the forums

 

Is my understand of DB correct..

 

Simply

 

If you hang a brick from a rope it hangs vertical : perfect static balance. When one spins round fast enough the brick sits horizontally out during the fast spin due to the centrifugal forces created by that spin

 

The ulitimate example of 'out of dynamic balance'

 

Dynamic balance is creating a situation where centrifugal forces are in balance and the 'brick effect' wont happen

 

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If one had a rig with just 2 centres of mass - say camera and a weight

 

If the camera was 2kg and the weight 1kg then static balance with 'infinite' drop time would be acheived by putting the camera L cm from the Gimbal and the Weight 2*L cm from the gimbal

 

But if that rig was spun it would end up tilted absolutely horiztal ie the lens facing the floor or sky because the centrifugal forces would pull the rig into that position

 

Hence the need for a third centre of mass positioned in some way that the centrifugal forces can be equalised (while keeping static balance of course)

 

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The merlin is either designed where DB is hard to acheive because ther is no adustment of the wieghts in the horizontal plane OR designed so amazingly that the arms closes around a cicumference changing the ratio of the front and mildly rear masses making DB possible but not simple to grasp especially with the added confusion that not all of the cookbook settings includ a front weight, knowing of GB probably the latter...

Edited January 17, 2009 by Sam Morgan Moore

[Brian Freesh]

Ooh, science time!

 

As described, the brick example is flawed. The brick and string you mentioned are in perfect DB, assuming the string is parallel to a flat floor. However, if the string is your post, and the brick is either the camera or your counterweight, then yes, you're shooting sideways now, but with good DB. Of course, to shoot in that scenario you'd have to be constantly spinning to achieve the DB...

 

However, if the brick were dipping up and down as you went, there's your bad DB. But since you are constantly exerting your own forces, you can change how well that brick follows a perfect path.

 

So back to the Steadicam. You are correct with your example. If those were the weights and positions, then when spun the rig would lay horizontal. Again, perfect dynamic balance, but requiring the spinning to achieve. The gimbal is at the center of mass, so the camera won't have any place it wishes to rest. In theory it would balance perfectly horizontal without moving, but the second something changes, the inertia (centrifugal force doesn't exist, the effect that looks centrifugal force is created by inertia) will continue to pull even once the outside force has changed.

 

What you are trying to achieve though is perfect balance with the rig vertical. You don't necessarily need another weight in your example, you simply need to change the positions of the weights. All things being equal (the camera and weight being perfectly balanced shapes with their centers of mass in line with the post and each other) all you would need to do is move the gimbal towards the camera. How far is up to you and your drop time. You want the center of mass to be just below the gimbal, where you have your hand/fingers, not on the gimbal.

 

The problem then being that cameras are not perfectly balanced and have weird shapes offsetting them in all sorts of weird ways. That's when you need to start looking at how to offset things with additional weights.

 

I apologize though. I say all these things without ever having touched a merlin.

 

(and inertia combined with centripetal force is what causes that brick to go in that circle on the string. And also how we identify DB)

[Amando Crespo]

Well... First, I think, that post may be posted at "OPERATING...", But no problem.

You´ve search at the old forum post.... There are to many about it.

DB. are really, take a look: http://es.youtube.com/watch?v=D6GtkF3EofQ&...re=channel_page

But, please...SEARCH at the forum before post a question...."BE WATER MY FRIEND". <_< <_<

[RobinThwaites]

Hi Sam

 

We do a lot of work on DB at the workshop and playing with a bigger rig is visually easier than the Merlin HOWEVER is easily translated back down to the Merlin after.

 

One word of caution when you are playing, the spin only needs to be at the fasted you are likely to pan, if you spin the rig faster the inbalance may be masked.

 

Robin