Dynamic Balance

[Eric Fletcher S.O.C.]

Okay let me amend my post to say that I dynamic balance in the morning and then tweek as time permits during the day. Having said that Production have never waited for me to balance

[Brad Grimmett]

I find that production almost always plans to wait for steadicam to set up at the beginning of the day. So normally there is time to do a dynamic balance at least once. I rarely do it more than once, or feel that I need to. After doing it once I just tweak when necessary.

[Kareem La Vaullee]

Every time you change a mag, change a Lens or a filter, move your gimbal, adjust your rig for a shot, the rig will be out of dynamic balance.

 

Hi Erwin,

 

If your Sled is in Dynamic Balance and you change a Lens or a filter or do anything on the camera and then you do the usual static balance, even with moving the gimbal up or down the center post, then you will still be in Dynamic Balance.

 

The only way to loose Dynamic Balance is to move a component below the gimbal, in other terms : move, add or subtract weight on the lower part of the Sled.

 

In the morning I do an absolutely perfect Dynamic Balance and after if something is changed on the camera it's never a problem, do your static balance, do your drop time, and you will see that you are still in Dynamic Balance, check it by yourself.

 

I just have to make sure that nothing will move down there during the day, like the angle of my PRO Monitor, that's one of the good things in the Ultra's design : as it was built with Dynamic Balance in mind, the Monitor turns around it's Center of Gravity, with any other sled or monitor combination if you change your monitor viewing angle you will instantly be out of Dynamic Balance.

 

So the extra minutes taken to do the Dynamic Balance in the morning are even more worthing it

 

Thanks to Jerry Holway who did such an excellent work in learning us the art of Dynamic Balance.

 

In fact after I finally understood how to get in Dynamic Balance I discovered that my usual sled setting wasn't very far from it, not perfectly there, but not too far.

 

On the net you can see operators' pictures with sleds so far away from Dynamic Balance it's unbelievable

 

Now the next step is to try to get the extra time to do the Dynamic Balance when you go to Low Mode...

 

And one other thing : in order to make sure that your sled is in perfect Dynamic Balance you have to spin test it fast, really fast, not a gentle slow Pan, it's just like testing the Dynamic Balance of an Helicopter's Rotor in the Factory.

 

A few days ago I was at a Camera Rental Facility helping a friend to do his prep, he wasn't able to Dynamic Balance my Flyer, in something like 3 minutes I showed him how to do it and did a perfect Dynamic Balance, the camera on the Sled was a small HDV thing in a cage with my Antlers on top of it.

I did an extremely fast spin test and the center post was turning perfectly vertical (and with the Antlers above turning super fast and super flat it looks even cooler), a guy there was watching us, he was also trying to Dynamic Balance a Clipper he had to work with on a shooting the day after, he was actually unsuccessfully trying for hours... (ok, I helped him also)

 

It is just a matter of knowing what your are doing and then you will get what you want a lot more easily

 

A Dynamic Balance Primer

 

Cheers,

 

K.

[Marc Abernathy]

kareem,

 

nice post.

 

i still feel like i dont have DB (Dynamic Balance) in 100%.. more like 80%. i also spin slow. my problem with trying to spin fast is i usually muck it up with my hand, throwing off the spin.

 

Kareem or anyone who wishes to contribute to this post,

 

what "hand gesture" do you use to spin your Rig fast? do you just grip it and twist or something more subtle?

 

static balance is a no brainer for me but i could brush up more on my spin test...

[chris fawcett]

Marc,

 

You should use your normal grip; the one you use for pans/whip pans. That is the one that is best trained to control the rig. If you are still unsure, you can spin the post and correct its precessing with subtle finger movements until it seems to be spinning fine, then let go and see what happens.

 

Read Jerry Holway's post at http://www.steadicamforum.com/forums/index...577entry14577

 

It's a reliable method of getting DB without too much headache.

 

Best of luck,

 

Chris

[Marc Abernathy]

thx chris,

 

ive read just about everything published that jerry has written and know the above information well. i will try your suggestion re: correct as i spin and see how that works...

[Lohengrin Zapiain]

I use Jerry's system to balance my sled, I rarely shoot if I?m not happy with my DB but I?ve found that anticipation is the key to succes.

 

Always DB with a filter or 2 if you are shooting exteriors. That depends pretty much on the film stock and on the DP. Whenever you are shooting with a set of lenses find out if they are the same weight; I?ve been shooting with Zeiss Ultra primes for a while (somehow) and I?ve found that I can switch between the 16mm, 20mm, 24mm, 32mm and 50mm (god forgive me to shooting with an 85MM) without any change of weight. If I have to go to a 10mm (much heavier) I let know the DP that it would take me 5 minutes to do it. You have to educate the DP and the Director, I don?t mean to make them wait but let them know about the times you usually use to balance your sled and what changes you can do immediately without having the production waiting for you. In my short career I have follow this rules and they have never waited for me. Usually if you say you need 5 minutes the DOP will find something to do with this time so it doesn?t look like they are waiting for you but more important: THE FIRST STEP FOR GOOD OPERATING IS GOOD BALANCE.

 

Anyway they will respect your times if they see that you know what you are doing. I do a lot of projects as A cam/Steadi where we shoot between 5 and 8 pages a day and I always have time to DB my sled.

[Jerry Holway]

To clarify:

 

Changing lenses and filters or even cameras (+/- any weight) will have ZERO effect on dynamic balance IF IF IF the overall length of the rig, i.e., the distance from the camera c.g. to the battery c.g., does not change AND you don't move the monitor, change accessories below the camera, etc. Just re-balance statically and you are good to go.

 

Minor changes in the the overall length (like adding an obie light above the camera c.g., adding focus motors higher than the camera c.g, or a radical tilt with the tilt head, etc.) may shift the dynamic balance ever so slightly... sometimes making it better!!

 

The shorter the overall length of the rig, the more sensitive the rig will be to changes in the overall length, as any change is a bigger percentage of the overall length.

 

Jerry

[Lohengrin Zapiain]

Hi Jerry,

 

I agree that with a minor change on the weight on the top stage you can re-balance statically and then you are ready to go but sometimes when changing lenses I even have to make my sled (an Ultra) longer to get a proper drop time and then start from zero.

 

I have never tried to ad a filter and then check the DB but I will definitely do that. As I mentioned before I use your method and I find it very quick, once you get to know your sled and the longer you have being working with the same camera the faster you get

[Thomas English]

I think maybe I am too lazy with DB. At home with Rob s weight cage I dynamically balanced every possible setup on the bottom of my sled. So I know if I am using pag lockon s my monitor needs to be out at notch 3. If I use 2 batteries my back battery neeeds to be 3cm from its furthest extension. Then on the day I simply statically balanced knowing the data in my head vis a vis the bottom of my sled to be in DB.

 

Is this too lazy... seems to work and I never have a problem whith whips.

[Dan Coplan]

If this has been mentioned previously, my apologies. I searched the archives ahead of time but didn't find anything.

 

I'm not a physicist (I got a 'D' in high school) and I haven't been spinning rigs as long as most people here so I may be off the mark, but it all makes sense to me:

 

We're trying to balance the weight on top evenly with the weight on the bottom. If the weight on the bottom is already balanced to itself, all that's required is to place the camera on top at it's center of gravity. My theory then is to set the balance of the sled without the camera on top. Put the rig on the balancing peg and move the batteries and monitor up, down, all around until the sled is perfectly level. Then all you have to do is plop the camera on top and tweak the fore/aft and side-to-side until level once more.

 

No more spinning and trying to remember which way the lower stage components need to move.

 

Am I making sense? Am I repeating what everyone already knows?

 

Dan

[Afton Grant]

Whatup, DC?

 

The thing is, rotational (dynamic) balance is much different than static balance. A lot of new physics come into play when things are spun. What seems to make sense at sight, all of a sudden doesn't work out anymore.

 

Read through Jerry Holway's Dynamic Balance Primer. It's probably the best explanation of the mathematics and theories on the subject.

 

http://www.steadicam.com/techIInfoDynamicPrimer.html

 

Peace!

Afton

[Dan Coplan]

I have read through the primer and I understand the concepts (this reply is not snotty like it sounds). I don't know if my theory is right, but if it is, then my method is far simpler than throwing the whole rig together and then going through a series of spins, adjustments, spins, etc.

 

By balancing just the lower elements leaving the top stage free of equipment and self-centered at the top of the post, you're setting the center of gravity to be in line with the post. Spinning it in this configuration should maintain dynamic balance. All that's left is to add the camera (with accessories) and adjusting that. No adjustment of the bottom elements should be necessary, drop time notwithstanding, but that's another issue.

 

Again, I don't know that I'm right on this, but it sounds awfully good. Any dynamic balance experts/physics majors out there care to comment?

 

Dan

[RobVanGelder]

Dan, i think it is difficult to find that balance - unloaded. Basically because the bottom part keeps functioning as a pendulum, so it will always find its most downward position.

Even if you put the gimbal all the way down, so you move to point around which it turns towards the masses, it will be still out of balance. Tiny differences, that already have a big influence on the dynamic balance, will not be noticed due to the relatively big masses down there.

 

So while you might get closer to dynamic balance, you cannot really be sure.

Now you could balance as Bearbel does with the Mickey-tool. It will get you close. This way you balance the rig on it's side and it does provide a reasonable balance for the for and aft of the components. In this situation you change the centerpoint where everything revolves around (normally through the vertical center of the gimbal and in the center of gravity there as well) into a scale-like system, but with the turning point between the masses of the lower section and the vertical through the post, which is now in a 90 degrees angle to that same post. (do I make myself clear?)

 

You-ll get closer like this, but might find in the end that new accessories that are off-center (like Hard-disc recorders, etc. might influence it again.

[Jerry Holway]

I have read through the primer and I understand the concepts (this reply is not snotty like it sounds). I don't know if my theory is right, but if it is, then my method is far simpler than throwing the whole rig together and then going through a series of spins, adjustments, spins, etc.

Dan

Dan, I encourage you to read the primer again. The idea you have is, alas, simply wrong. Many, many of us for years thought along the same lines (you are not alone in this).

 

The empirical methods discussed in the Primer are the easiest and fastest way to get dynamic balance.

 

Jerry