Glidecam 4000 - can you achieve dynamic balance?

[James Hooey]

Hi all,

Been checking these forums as well as HBS's forums with excellent discussion on several points of stabalizers. Thanks for these forums.

My question stems from what I have learned about stabalizer rigs from these forums. I own the Glidecam 4000/smooth shooter and have had some excellent results from it. As I spend more time on it however I also think of what is actually going on while shooting with it. I have recently begun to take note that many people are talking about static balance and dynamic balance and how either or both are useful for achieving certain results.

When balancing my rig I can achieve static balance quite easily and quickly. As outlined in the Glidecam manual, hanging your rig and making small adjustments to the sled position and working twoards a 2-3 second drop time is finicky but quite do-able. What I don't see outlined in the manual, or can figure out if it is even possible with this particular rig is how to achieve dynamic balance. With other rigs quite often the gimbal is movable, so setting it up on the center of gravity of the post and achieving complete horizontal balance with the camera facing all directions is achievable. The glidecam can't do this. It's a pressure fit gimbal so it cannot move along the main post.

So is it not possible to achieve dynamic balance from a Glidecam 4000? Is there an answer as simple as weight the bottom of the rig and sliding the post in/out until you could balance it horizontally on the gimbal?

As already mentioned I have some excellent results from this rig but am always looking to learn and develop more skills. In all my actual use with the 4000/smooth shooter it has been with generally static balance that I have it set up with. I do spin the rig front to back when balancing to try to achieve the most linear movement but it is never perfect.

I also understand about non-linear gimbals but I don't want to get into that right now until I can see if the rig can actually be properly dynamically balanced.....otherwise how would you ever know if your gimbal is actually non-linear?

Hope someone can shed some light on some/all of this and I appreciate the great communities available.

Regards,
James Hooey

[Jaron Berman]

It may be possible, but I don't have enough experience with that particular gimbal to know if it is centered on the post or not. Also note that there are VERY few instances where you want the rig to be balanced in all directions including drop. If indeed it's possible to dynamic balance, try this:

The position of the gimbal vertically on the post has little to nothing to do with dynamic balance. The length of the sled has a lot to do with it. There are diagrams and "dynamic balance primer"s on Steadicam's website, and while the methods of achieving it with a full rig are different than those with a T-rig are different, the forces in play are the same.

Technically, it should be easier to D-balance a glidecam style sled than a Pro-style sled, but in reality it's not. The problem you'll face is that your gimbal cannot move. This means that you must actually change the length of the sled or the weight at the bottom of the sled in order to get the drop time to be correct. Both of these variables affect D-balance.

My suggestion would be to take your camera and balance it on a broom handle or something similar LYING ON A TABLE. (NOT VERTICALLY!!!). Don't let go of it, just gently slide it back and forth till you find where it balances front to back. Mark that point. Do the same side-to-side. Mark that point. Now you know roughly where the center of gravity of the camera lies. When you mount the camera to the rig, screw the camera so that the point you marked lies about dead-center of the dovetail plate of the glidecam. When you put the camera on the rig, try and let your fore-aft balance mark fall about 3/4" behind an imaginary line running up the center of the post. If the side-side balance point is lined up dead center on the post, you should be in a pretty good place to start balancing the rig.

Extend the post to a length that you're comfortable with... probably about 2-3" of post showing. Do a quick check to see where you are on drop time. If it's too slow, add a little more weight to the base, or extend the post slightly. It'll probably work better if you leave the post and add weight, however. Important note: with this rig, add weight to the front weight slot and back weight slot EVENLY. This should make your life easier! Also line the stacks of weight up on the centers of their travel fore aft. This gives you more fudge room when balancing. The key to balancing a rig is to move from the "worst" balance up. Start with whatever is troubling you the most. Tweek your side-side balance so it's good. Then, feel for fore-aft balance. How does the rig hang? You want to make all your adjustments with the rear weight stack if possible. It should be pretty close already, but if the rig hangs with the camera tilted up, slide the rear weight stack forward in its slot until it counters the tilt and the rig hangs even. If the camera points down, do the opposite. Once you get it pretty balanced "statically" in this method, you should be very close to dynamic balance. Spin the rig GENTLY using 2 fingers just below the gimbal, so you don't push the rig in any direction, only spin it. If it spins pretty flat, you're about as close as can be with this type of rig. If it spins wildly, slide the rear weights one direction or another, lock them, adjust the top of the sled to rebalance static and spin again. It will either be better or worse. If it's better but not perfect, keep moving them in this direction. If worse, slide the weights back the other direction, just past where you started. Rebalance the top of the sled and you should be close.

As long as you don't change the length of the sled, the amount of weight at the bottom of the sled, or the positions of the weights at the bottom of the sled, you will remain in dynamic balance. If you always fly the same camera and accessories, mark the positions and numbers of weights you use on the bottom of your sled. Also mark the lower post section. This way, whenever you use the setup, you can set the entire lower sled to your marks, and once you adjust the x-y platform with your camera on it, it will all fall back into dynamic balance.

NOTE: EVERYTHING affects balance, including the position of your viewfinder AND screen on the top of the rig! Set it in one position and make sure when you're balancing and shooting it always stays in that position. Same goes for any accessory anywhere on the sled. If you're going to shoot with the screen in a certain position, balance with it in that position or you'll be off!

[James Hooey]

Jaron,

Thanks for the reply. I'm not sure how much of what you mention really answers the question on how/if you can 'dynamically' balance a camera on a Glidecam 4000. I may just not fully understand if what you mention is addressing static or dynamic balance. From what I have learned it is more that the camera will be completely balanced in all axis therefore spinning perfectly level. To achieve this I have read that with systems with a movable gimbal this is achieved by sliding the gimbal to the center of gravity of the post, hanging the rig horizontally and make adjustments to the sled and or weights until the camera will not tend to spin/fall in any orientation while in this horizontal position. This would then make sense that the camera and rig is balanced dynamically and will create perfect balance once the gimbal is moved to a desired drop time.

Last night I tried out a little scenario where I moved the post on the 4000 up until I was able to horizontally balance the camera. After that I was at a bit of a loss as to which adjustments would create certain results. The camera itself initially had tendencies to want to roll towards the viewfinder side (XHA1 with a WD-72 adapter) and after moving the sled around a bit I found a pretty good balance where the camera could sit in almost any position without spinning. However when I dropped the weights down again to about a 2 second drop time the rig was certainly not balanced statically to be level. That made me go back to the old method of balancing statically.

The best I could achieve was to use a very long drop time to balance the camera by. Upwards of 4 seconds. My reasoning was that if I can get it balanced statically with this long drop time where balance is so much more precise, then when I lowered the weights to my usual 2 second drop time it should be as close as achievable to both a good static and dynamic balance. My thinking is probably flawed in this respect as it is still not truely dynamically balanced but I will say that the results were fairly promising. This is little if any wobble when spinning and the static balance was still good.

Again I appreciate your reply Jaron and I will do some more work trying to follow your advice to see what results I can achieve.

The answer may still be out there however....can you truely dynamically balance a Glidecam 4000?

[Jaron Berman]

James -
Dynamic balance does not mean that the rig floats on a balanced point in all directions. Dynamic or "spin" balance means that the rig spins completely flat across the horizon. The reason this is a "big deal" has to do with the effort required to pan, most importantly whip-pan. For slow moves with little panning, dynamic balance is really not a big deal, and often times you can just do the shot in static balance. However, if you're whipping back and forth between characters, consider the delicate effort you hand would need to use in order to maintain a level horizon? If the rig pans competely flat, the difficult part of the whip pan is not maintaining horizon, it is only the start and stop of the move.

Dynamic and static balance are intertwined. You cannot dynamically balance a rig without it being in static. You can however static balance a rig without it being in dynamic balance. Confused yet? This will probably be a bit overhead, but read "dynamic balance primer."

( http://jerryholway.com/manuals.shtml)

While it does not mention glide-cam style rigs at all, the physics are the same, and if you reread my earlier response, you can see how I tried to apply these principals to your rig. Can the glidecam be d-balanced? Absolutely. How hard is it? I'm not sure. With a system like the glidecam, you can add and subtract weight to the foot of the sled, meaning that eventually, you CAN do it.

The first thing you need to do, however, is lose the notion that dynamic or static balance have anything to do with the rig sitting neutrally in all directions. The only time where you may ever balance a rig that even approaches an infinite drop time is in a vehicle mount that is intended to accelerate extremely hard. With a neutral drop, you aren't subjected to the pendulum forces that would otherwise rip the rig out of your hand or bump the shot. This very particular circumstance is balancing with an extremely slow drop time, or "neutrally," NOT dynamically balancing.

The problem you ran into when trying to rebalance your rig was that you changed one of the only things that can affect dynamic balance - sled length. This is a major limitation of the glidecam rig - the fixed gimbal. On a standard rig, you set up the sled so the length makes you happy, and adjust your gimbal to set your drop time. Glidecam, you have to kind of tinker a bit to get a combination of drop time and sled length that together make you happy. Not a huge deal, just understand that any time you change the length of your sled, you aren't just throwing it out of static balance, you're also starting from scratch in terms of dynamic balance.

The moral of the story is: I don't know where you read about dynamic balance before, but it was incorrect. One of the two guys on earth who discovered what it is and why it matters is Jerry Holway, so follow that link above to his website and read his dynamic balance primer as gospel. It's a difficult thing to understand without someone explaining it to you in person and demonstrating on a rig, but the article is certainly better than most of what's out there touching on the subject.

[Pascal Jolink]

Actually Dynamic Balance on a 4000 is pretty simple.

Assuming that the gimbal is perfectly centered (XYZ allignment):

Place the center of gravity of the camera directly above the center line of the post (the CG's on the bottom are on the same plane)

Use an equal amount of washers at an equal distance form the post (Example: 3 washers on both sides at 3" from the post)

Balance by adjusting the camera fore-aft side-side, three second droptime and you're done

[edit]

The length of the post on a 4000 sled doesn't influence dynamic balance because the weights on the bottom are on the same horizontal plane. On any other rig it would throw off dynamic balance

[Mikko Wilson]

Pascal is of course dead on.


Let me add a few points of clarification (or confusion)...

*These apply to all Steadicam like stabilizers with 3 (or more) notable masses.*


These are the only things that have an effect on DB:
- The mass of each of the lower wights.
- The "radius" (distance out from the center of rotation [the post]) of each lower weight.
- The "distance" down from the CAMERA (not gimbal) of each lower weight.
- The "radius" of the camera from the center of rotation.

That's it, you can forget about all the other elements for DB - The Mass of the camera and it's height above the gimble, both have NO EFFECT on Dynamic Balance. They ONLY affect drop time - which has nothing to do with DB. (so adding accessories to your camera doesn't effect DB, except you may need to adjust it's position to bring it back into static balance.



The rule of thumb is: You dynamically balance the sled [= Dynamic Equilibrium], then statically balance with the camera [= Dynamic Balance], then adjust drop time with the gimble's position [= Personal preferance for the amount of downwards pull.].

In practicality you get the drop time about right first so that you can properly observe the other stages of the balancing, then fine tune the drop time at the end as normal.




The position of the gimbal on the post has *no* effect on Dynamic Balance. If you sled had anti-gravity and didn't need a gimbal at all, "DB" would still work the exact same way.

What the gimble's position does affect is drop time, and that affects "how hard" the sled pulls down to vertical .. and therefore how noticeable DB is .. not it's amount, just how noticeable it is - just like how much the sled wants to pendulum when you accelerate.


The system of holding the sled horizontal and adjusting the components so that it doesn't roll either way is WRONG. That only balances out the radius and mass of each weight - but it doesn't help with the distance of the weights from the camera, so it can't be used to define DB (in fact, normally you WON'T get DB with this method.)


The method of starting with the camera's CG 3/4" behind the center of the post is only valid for larger scale Steadicams - the Steadicam Master & Ultra systems to be precise. This distance can vary greatly based on the scale of all the components on the sled .. which of course is very different between the Glidecam 4000 and the Steadicam Ultra. It's only really a "quick estimation" of a good place to start with the larger rigs.


- Mikko

[Jaron Berman]

ah, thanks mikko. SO used to doing things a certain way... forgot about the simplicity of the T-bar stabilizer.

the one thing I would add is that you should be absolutely sure that the foot of the sled is EXACTLY in line with the top, or it'll be awfully tough to d-bal.

[Charles Papert]

You guys are ALL wrong!

no no no, I'm just goofing. Lots of good info here, although it might be a bit heady for those with smaller handheld rigs.

It is indeed true that a T-shaped sled is the easiest to dynamic balance, by centering all the masses (easy to understand because it is a symmetrical shape). Once you have a raised monitor, the dynamic balance becomes more complicated. I believe somewhere in Jerry's treatise he has the diagrams that show what happens if the monitor is on the same horizontal plane as the batteries, then if it is up on the same plane as the camera (just as a theoretical example) and what must occur with the camera and battery masses to balance these, so it is simply a matter of splitting the difference to place the monitor somewhere in between (hence the 3/4" behind-the-post concept).

This all said, I would not be at all surprised that a Glidecam mounted with a perfectly symmetrical weight on top and equally spaced washers front and rear of the lower section will still not spin entirely flat due to the typical non-linearity of the gimbals, as I often hear.

[James Hooey]

Holy zonkers! I am blown away by the great responses to what I thought was a question I relatively understood. Everyone has been very helpful.

I'm still doing my homework on all this and getting a feel for things but here's a few things I hope I have gotten out of this so far.

Finding the COG of my camera is the starting point, and aligning that with the center of my vertical post is critical. This may be the only step I had never fully considered. I say that because I had set up the camera on the plate such that it was generally pretty centered already and thought that through adjustment of its front/back left/right adjustments that this was naturally finding the cameras center of balance already.

Post/weight lenght won't affect my Glidecam assuming I am usiing equal weights front and back (which I currently am) because they are on the same horizontal plane to each other. If this statement is correct then I also wonder if adding a monitor to the weight base will start to change that.

Set my post lenght for a working drop time (say 2 seconds)

Move the bottom weights, in particular the rear weight (why the rear weight btw?) in or out from the post will achieve dynamic balance. But in essence if they are equal distance from the post then it is already dynamically balanced.

Moving the sled is finding the static balance of the rig. In this situation if my listening skills are working it shouldn't have to move much as I have already aligned my cameras center of gravity to the post?? Just a few tweaks to fine tune the balance.

Recheck drop time and it should be done and spin level.

Having wrote this from bed at 2 am may not entirely help my thinking but I will catch up with this thread later in the day.

Once again thanks to everyone in helping me understand this.

James Hooey

[Jaron Berman]

My comment about moving the rear weight, as Mikko pointed out, doesn't really affect your particular rig right now. If you move one stack closer to the post, move the other stack the same distance. If you add a monitor to the base, its center of gravity will surely be different than the stack of weights, so in that case you'll probably need to follow more of the "big rig" style of d-balance.

Looking at the rig, I'd say that your best bet would be to put the weight stacks all the way out in their slots. I'd measure the distances from the post, just to make sure the slots themselves are the same length. Then I'd try and make sure the foot of the sled is pointing in exactly the same direction as the stage on top. THEN I'd put the camera on, and if it balances statically...... it SHOULD be in dynamic balance. But as Charles mentioned, the gimbals aren't famous for being linear.

If you get it balanced nicely, but feel you need a little less inertia when panning, you could move both stacks inwards toward the post. Not sure how much it'll affect things, but again - it SHOULD. Make sure that if you do this, you don't touch the top stage to rebalance. Move one stack where you want it, then carefully move the other stack until the rig balances. If you do this, it will remain in dynamic balance (if it was before).