Thursday, August 7, 2014

On Glidecams : Dynamic Balance and Why You Need It!


So remember how I got a glidecam, and thought I had it balanced pretty well after a couple days?  Well it turns out I only had it very well statically balanced, but when you bring dynamic balance into the equation it wasn't doing so well.   So here's what I learned after copious amounts of online tutorial videos and reading on the subject.    Also, that video above is a quick look at my first two weeks of collecting footage on my glidecam flying my gopro,  I know it's nothing special, but thanks for watching anyways!



So static and dynamic balance, lets differentiate the two for you first;

Static : when something is stationary it is static, your glidecam may be balanced straight up and down when your standing still, but get moving and something else may happen,

Dynamic : when your camera is moving in any number of directions, at a range of speeds, (vectors) it should remain balanced as it was in static, provided you manage your inertia.

I watched almost every youtube video by anyone who said they could set up a glidecam, truth is, they all somewhat know what they are talking about, and few seem to really know exactly what they're talking about, and I only had my 'eureka' moment after I saw some formulae on paper written in the 1990s explaining dynamic balance, written apparently by the camera man who 'discovered it'.

What you need for dynamic balance:

1. A camera with its centre of gravity located directly over the post/gimbal system
2. A perfectly calibrated gimbal
3. A perfectly balanced weight system underneath to match the top.

1. When you watch a video on youtube of someone balancing a glidecam, they are really only completing the first step, of getting the camera above the column/post.  I did this, and under the guidance of YouTube, I thought I was finished, when I knew - by my footage - that I wasn't.   Everything I learned in high school physics told me dynamic balance is possible, and I should be achieving it.

First bogus rule that is commonly propagated through YouTube videos : balance your camera in your shooting position.  This is wrong, when you have dynamic balance, the column of your glidecam system should be perfectly vertical at 0, 90, 180 and 270 degrees of rotation to the handle.   Though you may develop a 'shooting position' from practice holding it and having a preference, your shooting position should have no affect on the balance of the system as a whole.

2. A perfectly calibrated gimbal. It actually took a few days to locate the equipment I needed to calibrate the gimbal, being a #10 Torx (star) key to loosen the gimbal plate up top.   You also need a #9 ( or #10 I forget :P  )  hex key as well.   Truthfully, I want to make my own video of gimbal calibration to answer the questions left out of the Glidecam one from a few years ago on YouTube.  Nitsan TV on YouTube also had the only other mention of the gimbal, but also scared me a little while talking about it.  Yes you can ruin your gimbal performance as much as you can fix it.

3. I finished these two steps, and I was still baffled why I didn't have dynamic balance.  I should have been able to spin the glidecam system and have the gimbal remain stationary and the camera spin level, provided I didn't add any unbalanced lateral forces in my spin.  Though, I could tell when I spun the system after the first two steps, it was much closer than before, but it was still visibly not perfect.

--Disclaimer Here--
The system I am using right now is super basic and lightweight and so my solution is a little more basic than most.  If you have a monitor on your sled on the bottom, or audio capture - I no longer know how to help you any further. 

If you have a system that is involving glidecam, and a camera on top, strictly, then you can do as I've done.  But long and short of it is, I was balancing my glidecam with the washer-weights (I'll call them) located at different distances from centre column. Which is easy to do, since one 'slot' for weights is longer than the other to make space for the monitor mounting hole.  In any case, the formula showed using plain math that you can't achieve a balanced centrifugal force when your weights are not even, that is equal amounts, and equal distances from the axis of rotation. "equation is unsolvable" was all I had to read, and that was it. Sure enough, get the tape measure out, make sure the weights are equidistant to the centre, and then rebalance the camera on the top 'cheese plate' ever so slightly and we are in business.  Also, your sled weights on the bottom need to be in perfect alignment to the camera cheese plate on top, which is a direct argument with one of the more prominent how to set up your glidecam vids, but that's cool.

The name of the paper containing the formula is "Dynamic Balance Primer" by Jerry Holway and should be readily found as a PDF through google search.  It speaks about different models, but its the foundations of the math that is important.

So when you add a monitor or audio devices to your sled post, you bring that totally equal weight distribution out of balance, and so, I didn't read any further about how to correct that - will cross that bridge when I get there.

So…

a nice ultra-dry post for you, likely only useful for those experiencing the same problem, but regardless, I hope it helps all of you budding glidecam'ers like myself out there who had nothing but questions once you unboxed your glidecam!

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