Mickey????

[Thomas English]

Point taken Eric.

 

Considering my theoretical twin J-box sled that Spin Dynamically balances perfectly (2 x 5kg Jboxs both out the front. One at the bottom of the sled and one at the top). Well it wouldn't be in Static balance upright. For it to Statically balance upright the top J box would have to point forward and the bottom backwards (or visa versa). This would then be in Static balance, in spin balance and in "Eric" balance.

 

Basically to be in dynamic balance it doesn't necessarilly matter what direction the weight is going but how far it is away from the sled. The reason why Mickeys and "Erics" can be quite successful at Dynamic Spin balance is because our alignment is entirely either forward or backwards.

 

Sorry I had to thrash that out to myself.

 

OK then.... In that case could it be that some peoples sleds are more side heavy? Are people that are failing to Dynamically balance their sleds using an Eric or a Mickey; are they making sure they test the sled both on its side (with the camera parallel to the ground)and on its side but with the camera pointing at the sky?

 

I think I officially give up otherwise and will leave this thread gracefully.

[Eric Fletcher S.O.C.]

OK then.... In that case could it be that some peoples sleds are more side heavy? Are people that are failing to Dynamically balance their sleds using an Eric or a Mickey; are they making sure they test the sled both on its side (with the camera parallel to the ground)and on its side but with the camera pointing at the sky?

 

I think I officially give up otherwise and will leave this thread gracefully.

 

 

Why do people makes this so damn over complex, contrary to what has been taught in the past there is no black magic.

 

As long as the rig hangs level your side to side is balanced, agreed?

 

As long as the rig has zero tilt your are fore aft balanced, agreed?

 

The 90degree drop test will then answer the question of, is the above the gimbal mass exerting the same rotational acceleration as the below the gimbal mass.

 

That's it. That's "Dynamic balance"

 

As long as the AGM is chanced out by the BGM the rig will spin flat everytime

[Jerry Holway]

All-

 

The methods in the book and in the Primer are correct, and they work for all rigs in any configuration.

 

The math and the explanations are "complex" because I did not want to leave out a crucial step or concept. I also wanted to explain it in several different ways, as different operators may find one way of learning better or easier than another.

 

I've demonstrated the "simple" way (see page 12 of the Pirmer!) and several alternate ways of achieving dynamic balance 100's of times, publicly, with my peers watching, at workshops and tradeshows, with all sorts of sleds. It's a well vetted technique - over 22 years of doing it time and time again. I also demo the reasons why it works, and what to do if one changes the sled length, monitor radius, monitor weight, battery weight, tilt-head angle, etc. It's neither magic or rig specific. I design new rigs big and small) using the same math, and they can all be balanced. So what is going on here?

 

Eric's balancing method - which Ted Churchill pioneered as afar as I know (at least pre-1982) - is a quick way to get a rig into a fine state of static balance - which is necessarily part of dynamic balance - it's the last step before spinning the rig.

 

If one has found dynamic balance once for a "standard" set up, then of course all one would do when using that set up is statically balance, and Eric's method works for this purpose. I even use it sometimes as the final step in dynamic balancing. But it is not the only step, as testing and demonstrations have proved over and over again.

 

Most of the time, after placing the camera c.g. close to what experience has shown to be the right spot relative to the centerpost, I will statically balance the rig and - no surprise - it is in dynamic balance just as Eric's rig drops into dynamic balance, and that's all I do. But that's knowing where the camera should go. Put the camera in the wrong spot and it won't work.

 

There are many combinations of placing masses that make perfectly statically balanced sleds - but there is only one combination that is also dynamically balanced. All methods that work all the time with any rig necessarily involve spin balancing.

 

Jerry

[Robert Starling SOC]

I'm way far from being an expert on theoretical "dynamic anything" but I've learned both methods. What I have found though is that the alternate "Churchill/Alternate method" takes about 1/10th the time or less and is working just as well for me. No matter how you spin it (no pun intended), less time for the same results equals more time on other work / pleasure IMHO.

 

As long as I get the results I need I don't care what name it is called or who developed it. The only math I want to know on set is how it relates to focus, remaining film, lunch and over time!

 

Robert

[Jerry Holway]

 

You can achieve the same results by setting a 3 or 4 second drop time and then bringing the rig up 90 degrees like you would for a drop test and then panning it 90 degrees so that the monitor and battery rack are level and then doing a drop test. If the rig rolls to the monitor you need to either shorten the monitor arm or lengthen the battery moment. The rebalance the camera to get the rig to hang flat (Battery's back so camera forward) if the rig rolls to the batteries they need to be shortened up or the monitor arm lengthened and the camera moved back to level it.

 

Do this until the rig does not roll/pan when dropped and you will be in dynamic balance (Jerry will tell you that you're not but the rig does spin flat and that is the definition of Dynamic balance) I've been doing it this way for years and have never had an issue, the folks I've converted over to this method also like it over the spin method.

 

All-

 

I wish Eric had been more clear in the above explanation, it might have saved a lot of writing.

 

I hate confusion, and I want to know the why and wherefore of a technique, not just the results. What's in the book is correct: the math is correct, and the methods are correct.

 

But Eric's method is another way of getting all the masses in the right place, and may be quicker for some. But he's left out some steps (I asked for an explanation of those steps; I don't need a "shoot-out.").

 

Eric speaks of two tests in the above quote- the sideways drop for spin, and then a second "rebalance the camera" which should be "re-balance the sled - either camera or battery or monitor - and side drop test again and again until it drops flat.

 

The side drop test substitutes, in part, for spin balancing, i.e., it is a test for the rotational forces.

 

I'll say this again, because this is the opposite of what I had said before, i.e., I now believe I was wrong about it. Later, I will try for a needlessly complex (and perhaps mathematical) explanation for it, just for the nerds who hate BS and voodoo as much as I do. The side drop test works as part of a method of achieving dynamic balance.

 

(BTW the Mickey is another animal and does not work except in one case).

 

So, if one first places the camera nearly at the right place to start, and choose the monitor position, length of sled, etc. (as we would do for either method, I assume), and one statically balances the rig vertical, and one then does the side drop test, rebalances for vertical, re-side drop test, rebalance for vertical, etc., as Eric states, one will get to dynamic balance, and perhaps get there faster than "spin balancing." Spin balancing is of course, the last real test of spinning balance, because it takes into account all the forces acting on the rig. (One could be off on one of the two tests, and not know it).

 

Hope this helps.

 

For those that want to try Eric's method and understand what's going on, try balancing the rig first with the camera forward of the centerpost. Go through the steps, each time sliding the camera back (do not move the monitor, just the camera back and the batteries forward) until the two tests don't require any more adjustment. Spin balance between the tests, just for fun.

 

Jerry

[RonBaldwin]

There's gonna be a shootout all right! Loser buys booze. I am stuck out of town, I'm pretty bummed that I'll miss the spin-off of the century! Should have it at Jumbos, the pole might prove useful for balancing as a true vertical reference.