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-   -   S.F dynamic balance issues (https://www.dvinfo.net/forum/additional-camera-support-topics/40550-s-f-dynamic-balance-issues.html)

John DeLuca March 5th, 2005 12:36 PM

S.F dynamic balance issues
 
Im having trouble getting the Dynamic Balance just right with a PD-170wME-66(on shock mount) and two NP-1 batteries on the steadicam flyer. Its about 90+% perfect spin, but the front of the camera dips down a bit. Whip pans have about 5 or more% wobble. Unlike the ultra the tiffen steadi stand actually prevents a whole D.B spin because of the LCD monitor.

With the help of the steadicam forum, I downloaded the ultras D.B manual. Is the C.G supposed to be .75 inches behind the center line of the post on the flyer? Does that measurement cross over considering the smaller post girth of the flyer? Does the D.B have to be 100% perfect, or can it be close and be ok? Is the PDs odd c.g preventing a perfect spin?


John

Charles Papert March 6th, 2005 10:07 AM

John:

I'm sure you've already tried this, but extending the batteries further back and sliding the camera forward should help with a nose-heavy rig. If you are out of adjustment with the batteries, try taping a small weight to them as a test procedure, or possibly folding the monitor closer to the post.

Not sure about the .75" statistic on the Flyer--I've always gotten lost in the Holway/Brown theory of dynamic balance myself, preferring to believe in the spin balance and a certain amount of trial and error rather than measuring distances of each component of the rig and plugging them into spreadsheets etc.

That's a bone about the dock preventing a continuous spin, hadn't realized that. Can you spin it 360 on the arm? (think so, according to the brochure pic). It's a bummer to have to wear it for this procedure but at least you can get through more than a partial spin.

I'm not sure of your experience level since you referenced the Ultra, so please forgive me if this is already something you know: you have to make sure that you get a clean spin that does not have a bias from the beginning, i.e. your hand doesn't introduce an off-axis attitude. That's why it is so important to have an unobstructed 360 degrees so you can check out multiple rotations. I prefer to do a slow spin these days, it's easier to see the precession (tendency to dip in one direction or another) than when the rig is colorfully whipping around like a banshee. Generally a clean spin will start the rig level, then it will find its own rotation if it is not in dynamic balance. A couple of spins with similar results will confirm the issue and eliminate the possibility of operator influence.

Let me know how this progresses.

Mikko Wilson March 6th, 2005 12:34 PM

Not sure how much the ME-66 weighs, but that shouldnt' matter too much with DB anyway.

The Flyer should DB nicely though.
One thing to try might be to take one of your batteries (the bottom one of course...) of the rig and see what you can do then. :-)

Don't forget the monitor arm bends in TWO places...

Good luck!

- Mikko Wilson

John DeLuca March 6th, 2005 08:52 PM

Charles and Mikko,

I appreciate the advice. Still in the(hair pulling) testing phase.

Tilting the lcd by the allen bolt near the post does allow clearance(just barely), but at the cost of a decent viewing angle. Even with a two second drop time, leveled with duel axis bubble levels, and the C.G slightly behind the center post, it still goes into a wobble :-( For some reason I can get a good D.B, but only when the rig is VERY bottom heavy(about a half second drop time) I can see why everyone raves about the workshops now.

I definitely have alot of respect for professional operators now. I cant imagine the stress you guys have when the whole set is watching, and the pressure is on.

On the upside, I have gotten very good shots with a 90%+ D.B spin/two second drop time. Almost perfect. I've only had the flyer a couple weeks, and I would recommend it to anyone.

BTW- Does tiffen sell thicker padding for the vest? The shoulder straps arnt adjustable. I could always have my tailor make me one(in black instead of grey), it velcros out.

John

Mikko Wilson March 7th, 2005 03:58 AM

Haha, just be sure to keep track fo those allen bolts when adjusting them.. dont' forget one of them will also drop the sled off the post (Supprize!)

I have some bad news, a very bottom heavy sled isnt' in any more DB than a more neutral one. it's just harder for it to swing of verticle. - the position of the gimble on the post actually has NO effect on DB what so ever. :-P

The best way of adjusting to DB is by makign the sled as neutral as possible.. (think 4.. 5 sec drop time) then when you get it close with that, then set it back to yoru 2-3secs.. and it will be much flatter.

Also, don't forget that it could also be that you (!) are introducing wobble to the spin. - infact this is very often the cause [practice practice practice] - try spiing it the other direction, and switching hands. - if the error is consistent than it's prolly not you. - another trick is as you spin it (with just your top 2 fingers of course) then lightly slide your fingers down the gimble a little as you let go.. you will be able to feel if you spun it straight.

Don't feel too restricted by the 'textbook' correct position for the camera, as that varies gratly between rigs, and also on the configuration of the rigs. - Experiment! (just check that stage locking pin and monitor clearance before you do ;-) )

And as you quite correctly point out.. you've only had the rig a couple of weeks. You will get better with time as you hone in those finer points.


Not sure if Tiffen makes extra foam. Though if they (or anyone who makes accessories) are listening, it would be a nice idea.
They do also make a 'compact' vest that is designed for the shorter operator. - If the regular vest seems big on you, then maybe switching it for a compact one might be an idea.

If you realy want something special, Peter Abraham has been modifying/making vests for some time now.


- Mikko

John DeLuca March 8th, 2005 05:00 PM

Update:


Success! ......I finally got a few good continuous spins after days of testing. The trick was dumping the second battery, and placing the battery mount closer to the C.G. The rig feels very "planted" now, and easy to control. Operating is actaully alot of fun :-)

Thanks agian for everyones advice.

John

Terry Thompson March 8th, 2005 11:49 PM

Is there an easy way to remember which way to adjust the camera / battery for front or back heaviness? Some kind of jingle or saying would be helpful. There are so many things to learn and remember about steadycams (generic term) that the dynamic balance adjustment kind of escapes me.

By the way Charles P., I've been working of some of the things you mentioned and thanks again.

Tery

Charles Papert March 9th, 2005 01:00 AM

Oh boy, dynamic balance...

I could go on and on about this one, but you'll have to wait for the video, it's pretty visual. Here's a simple rule of thumb: do exactly the opposite adjustment you would do with a static balance. In other words, if the camera nose dips forward when spinning, logic dictates that you should slide it back, but instead, slide it forward. Then compensate with the sled.

Terry Thompson March 9th, 2005 07:21 PM

Oh boy...the video. Now that is what I'm waiting for.

FYI Charles, I have found that when someone is doing something of value (like your video), some else is also doing the exact same thing. For instance, while I have been working on my Indicam system for use with the Glidecam 2000 / 4000, there were others doing the same thing as you can see on the web. Mine isn't the first available even though I velieve I started working on it first. I do think it will be the best for value, features, and operation.

The moral of the story: Please get working on that video so I can buy it and include it with my system. Great moral huh? I knew you'ld like it.

Tery


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