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Charles King
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I read a post on the Steadicam forum and thought it was something I had to add to here on HBS. I thought it was interesting to know this as I thought otherwise but this explaination makes perfect sense. So here goes. For all who have tried getting DB with a smaller rig will find this discussion very useful.
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"...I cannot see how one could balance a Panasonic HMC151 with its CG 3/4" behind the sled post. I've tried every conceivable way but by doing so, just pushes the balance wayyyyy off well over 60 degrees... One could never use the fine tuners for that degree of off-balance or move horizontal post (bit that holds the battery and monitor) to offset it." by Jay Ryde
1st response:
"...While I don't have the experience of many on this forum, I think I can give you some information on how this works. Dynamic balance, in the simplest situation, has a monitor and battery on the same horizontal plane, and the camera directly above the post. Pretty simple really. Once the monitor begins being raised above the battery though, as it is on almost all rigs, the camera must move back to compensate, and the batteries must move in. I remember someone, I believe it was Jerry Holway, describing a circle that all 3 masses sit on. As you move the monitor up, The camera must move back, and the monitor must move in - the whole circle spins clockwise to keep it in balance. It made a lot of sense for me, maybe it'll help for you too.
So, with regards to how far behind the post your CG should be - on big rigs, where the monitor can be many inches above the batteries, the starting point is 3/4". On a smaller rig like yours though, the monitor and battery weigh much less, and aren't very far apart in terms of what plane they lie on, so something less behind the post would make more sense. The true test is whether the rig spins flat or not, and if it does, then you've got DB... " By Tom Wills
2nd Response:
"Tom has it right; the 3/4 inch is only a starting place for "big" rigs with the monitor raised up quite a bit - percentage wise - from the battery's c.g. to the camera's c.g. - aka the sled length.
It's more than 3/4 inch if the camera is lighter and/or the monitor is higher, less if the camera is heavier and/or the monitor is lower - again, it's just one starting point for big rigs before the spin testing begins. There are some other starting points mentioned in the Steadicam Operator's Handbook, BTW.
With any rig with the monitor not raised much, (like the Pilot) the c.g. of any camera is going to be very close to the centerline of the main post.
With the Pilot, I'd start with the camera c.g. directly over the center post, knowing that it has to move back very little for perfect dynamic balance. Try to get the monitor as close to the final position and balance with the battery.
You are somewhat limited in not being able to independently move the battery vs. the monitor, so you might try (with the set up you have shown), moving the monitor forward to balance as you move the camera back - and do it in small increments, say 1/8th of an inch or so at a time.
Spin and test; is it better or worse? Do not spin the rig very fast; try normal panning speeds.
Also remember if you trim for headroom, you take the sled out of purely vertical static balance, and therefore out of dynamic balance as well." By Jerry Holiway
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