Optimum Height(s) for Steadicam
 

Im considering a DIY balance rig project. The question I have is about the optimum length of the main tube. Obviously, a short tube lets you get lower shots without flipping the rig. A longer tube gives more stability.

I could also build the length to be configurable as short and long.

Thoughts?

A longer tube is often not as stable, particularly if it forces the gimbal further away from the lens.

To understand the gimbal position issue, grab a pencil. Hold it between thumb and finger of your left hand, and wiggle the bottom of the pencil with your right hand. When you hold the pencil in in the middle, the eraser moves a lot. But if you hold it up close toward the eraser, the eraser moves much less. So having the gimbal closer to the lens decreases the effect of sled movement at the lens.

But since the weight has to be balanced at the gimbal, a longer tube will tend to move the gimbal away from the lens.

Also, a simple vertical tube doesn't increase stability in the pan axis at all. You'll need some type of crossbar with weights at the end for that. Check out the CMR Blackbird as an example. There's a good picture about 2/3 down the article here:
NAB2009 Stabilizer Wrap-Up at DVInfo.net

For best results:
1) Make the length of the tube configurable.
2) Make sure the gimbal can slide up and down the tube.
3) Add some type of cross-bar at the bottom to increase stability in the pan axis.

Good point about keeping the gimbal relatively high, and to make the position adjustable. I could make the telescope, but from what minimum to what maximum?

The sled would be for a 5D Mark II. I'm considering a carbon fiber main tube (and possibly the cross bar), which can be costly, so it's important to get the main tube right the first time. I plan to make it as light as possible, so I can handhold it for short periods before I get a vest. But I also want good angular momentum for stability.

Charles Papert posted a photo a while ago with a 5D2 on a sled that looked to be six feet tall (!) Some sleds look to be only a bit over two feet tall. Any guidance on specific lengths would be helpful.

Interestingly, I have been doing the same sort of testing using different arrangements and configurations. One was an all metal pipe arrangement with a spread at the bottom, to promote stability. It seems to me that the longer the tube, the more I had to contend with a pendulum affect.

Most recently I have gone a bit different direction. This is what I am currently doing, with bits and pieces from my scrap pile to come up with a prototype:

YouTube - Testing Design of DIY Hand Held Steady Cam Prototype

I would probably add something to let me point camera up and down, as I wanted.

Jon:

Not sure about my 6' long rig (don't have one of those)! Was it this picture? Maybe the stand being right behind it made it look confusing--the center post is probably around 2' long.

The length of the post is less critical to angular stability than the overall mass of the system. A long carbon fiber post with just a few pounds on top (bare 5D, for instance) and a little bit of counterweight will be more squirrely than a short post with more weight. For handholding, it's better to go with less weight, of course. I'd recommend perhaps an 18" post; if you can make it telescope, maybe 14" to 20". These numbers are somewhat off the top of my head however!

What will be helpful since you are considering making it work both handheld and body-mounted is to build in the possibility of adding more weight top and bottom, particularly with the inertia-building design of the Pilot (weight placed at the outside corners). An outboard monitor would be a good add-on later along with a battery. I'd run cables inside the post while you are in the design phase also; there will be low-cost focus systems on the market very soon and you will definitely want one with your rig, which means running power to the receiver on top (smart money would be on getting a 12v adaptor for your camera and powering that from the sled also).

The pendulum affect has more to do with the drop time, not the length of the post. If you have a 3-second drop time, I don't think it matters what the post length is for the pendulum effect.

If you haven't already, watch the Pilot video.
YouTube - Steadicam Pilot - How to demonstration
Even though you will be building your own stabilizer, the baisc conecpts are shown very well here, so it's 9 minutes well spent.

As a point of reference, the Steadicam Pilot carbon fiber vertical post extends from 18" to 31", and the lower metal cross-bar is 14".

I believe carbon fiber is particularly good for the vertical post, since you get better inertia when more of the weight is at the ends and less is in the middle.

Charles,

Yes, that's the photo. And, yes, I was confused. :)

I plan to have a monitor at the bottom, and am definitely looking forward to a low cost focus controller.

So, the full range is 14" (Charles) to 31" (Dave). That gives me a good idea of what to strive for. To keep from needing three sections, I'll need to keep the ratio less than 2:1 with around 5-inches of overlap. I could do something like 14-23, 16-27, 17-29, or 18-31.

It looks like 18-31 is the place to start. I can always cut it shorter, but cutting it longer is tough.

Thanks!