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3/4" behind the CG on SC Pilot?!


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#1 Jay Ryde

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Posted 18 June 2009 - 11:14 AM

Ive changed my Camera .. Having spoken to many a SC operator and read the SC Op Guide (Grey book), 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.

I've tried balancing with the cams CG more or less directly over the Sled vertical, and it balances perfectly! Managed to get the dynamic balance more or less acceptable! Just unsure why the book says ITS VERY IMPORTANT TO HAVE THE CG 3/4" BEHIND when in fact on my gear, it looks like it cant be done?!

Your thoughts would be appreciated thanks...

Edited by Jay Ryde, 18 June 2009 - 11:22 AM.

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#2 Jay Ryde

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Posted 18 June 2009 - 11:32 AM

I forgot to post the pic:

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#3 Tom Wills

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Posted 18 June 2009 - 11:49 AM

Ive changed my Camera .. Having spoken to many a SC operator and read the SC Op Guide (Grey book), I cannot see how one could balance a Panasonic HMC151 with its CG 3/4" behind the sled post. ... Just unsure why the book says ITS VERY IMPORTANT TO HAVE THE CG 3/4" BEHIND when in fact on my gear, it looks like it cant be done?!

Your thoughts would be appreciated thanks...


Jay,

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.

Hope that helps, and maybe Jerry himself can pop in here and give you some truly pro advice.
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#4 Jerry Holway

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Posted 18 June 2009 - 12:21 PM

Jay-

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.

Hope this helps.

Jerry
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#5 Jay Ryde

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Posted 18 June 2009 - 03:35 PM

Jay-

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.

Hope this helps.

Jerry



Many thanks Tom and Jerry (sorry, no pun intended!), what you both have said makes perfect sense. Jerry, the Pilots Monitor and battery can move back and forth independently, but for some reason SteadiCam have not given enough flex for the monitor to extend further out (maybe they had good reason for this??)

The picture you see above shows the monitor at its furthest point possible from the sled's vertical. I am managing to get a relatively good balance dynamically.. I was just a little confused with what I thought was a hard-and-fast rule over the postion of the cam's CG!

Overall I am very impressed with this rig and it's quality, as well as the help and support I've received from users such as yourselves.

Again, many thanks to both of you.
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#6 Iain Baird

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Posted 18 June 2009 - 03:43 PM

Is it possible to unwind the cable on the monitor post to move it farther from center? I seems to me that should add the few inches you need to fully extend.
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#7 Dave Gish

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Posted 18 June 2009 - 11:06 PM

Is it possible to unwind the cable on the monitor post to move it farther from center? I seems to me that should add the few inches you need to fully extend.

Yes, this is definitely possible, as shown in the picture below:

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.

The Pilot has the ability to move the whole lower crossbar forward or aft using the hex screw in the middle. I've had a lot of luck achieving DB on the Pilot by leaving the monitor & battery out as far they will go (for more inertia), and then tweaking the lower crossbar forward/aft together with dialing the stage forward/aft to compensate with static balance. I've always been able to get DB fairly quickly this way.

Also, by keeping the monitor & battery always out as far as they will go, this makes it really easy to reproduce, since you don't have to move the lower crossbar to pack up the Pilot. In other words, I can reproduce the weight distribution on the bottom within seconds on unpacking, so DB is usually just a quick check to be sure it's still in.

One note: With Sony cameras, the only way I've been able to achieve DB is to move the camera one hole back on the stage plate, which means the tripod adapter plate hangs off the back a little. Doesn't hurt anything, but it looks a little weird. This has been true for the EX1, EX3, and V1U, and it doesn't seem to matter what accessories I'm flying.
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Edited by Dave Gish, 18 June 2009 - 11:11 PM.

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#8 Jay Ryde

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Posted 19 June 2009 - 07:12 AM

Thanks again all of you, I've managed much better now and appear to have a faster set-up time.

I managed move the cable as you described.. Iv'e put it through the centre of the monitor bracket. It was pretty obvious really and feel silly I didnt think of unwiding it.. DUH!

Posted Image Posted Image

I've rebalanced my rig moving the Monitor and Battery to its outer-most position. DB is now much quicker to acquire. However, in my case, I found that I had to put the MErlin weights at the bottom to stop the cam from waivering arounf during forward motion.

:)

Posted Image

SteadiCam: Pilot/ 5.8" Mon./IDX Power
Camera: PANASONIC HMC151E AVCCAM
Mic: RODE NTG-2
Trainers (Footwear): UMBRO!
Bank Account: Empty!

Edited by Jay Ryde, 19 June 2009 - 07:16 AM.

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