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Why a Backmounted Harnass works.....


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#1 RobVanGelder

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Posted 06 January 2004 - 05:41 AM

At the last Workshop I attended last year in Stockholm, led by Jerry Holway, who I greatly respect for his work and search for a better system, I was working met my own DSD harnass.

Of course, being a Tiffen workshop, Larry demonstrated the "new" Ultra harnass, which is basically an improved and more rigid IIIa vest, with new technology like ratchet buckles and such.
The main improvement to the vest was according to Larry that the chestplate was made bigger and the connections to the shoulderparts were rigid.
Also, he had put some extra straps on the waist-parts, to prevent them from sliding down during the work. There were some more minor changes that he made himself, as almost every operator will try to improve and fit his or her system to the body.

Larry and I had an interesting conversation about the use and reason for having an arm like the DSD has. He argued that weight doesn´t know how long the distance between the weight and the point of attack on the body is. Therefore, to have a very expensive carbon-fibre arm like that, was not needed. According to his theory we could mount the socketblock straight to the side of the Harnass, as this harnass is so rigid.
At that time I couldn´t come up with a proper explanation against it, his point of view seemed acceptable, but it kept lingering in my head.

Now I know that it isn´t like that at all. Shifting the point of attack on the body is essential for the distribution of all the forces.
To demonstrate it I was constantly trying to find an example of something everybody will understand and I think I found one.

Imagine a Firebrigade rescue-ladder-truck (is that the right word?), the one that helps people from high buildings

When it comes to the rescue, the driver wants to park it in such a way that it will not tip over when extended. That means he prefers to put the front of the car underneath the working area of the ladder.
This way, the whole mass and the distance from the base of the ladder to the front wheels will act as a counterweight and arm.
Now, imagine that you could shift the ladder-base sideways . It would immeadiately mean that you need support-legs that would reach out even further to the side. without it, it won´t tip over forward (the frontwheels still prevent that), but sideways for sure!
Now here is the big difference with the human body: we don´t have support-legs, which means we have to compensate that with bending our spine/hips to the opposite side(=leaning), or put enormous pressure on one foot (and hip), if possible.


Oh, regarding the Fire driver, I am aware that he always has to put out all the support legs, so his working area is everywhere. Safety procedure of course, I am only showing the theory here.

So why does the DSD harnass feel totally different than the frontmounted one?

I have made 2 sets of pictures with both harnasses and drawn some lines that will show the direction of the forces and were the counterweight and arms are.
I´m sure somebody with more theoretical knowledge will find some flaws in it, please correct me where I went wrong.

For sure it makes it clear why we experience less resistance or weight-change when moving the camera forward with DSD.
It also shows that with a FM harnass, the downward force from the point of attack is between the feet, under the body, while with a BM the same force is behind the feet and behind the body.
This means that you will tip over more easily with a FM than with a BM.
You have a smaller "foot-print" with a FM!
Harnasscompare IIIa+ forces
AND THIS ALSO EXPLAINS WHY YOU CAN RUN FASTER WITH A FM!!!
With a BM, you will have to overcome 4 points of resistance (e.g. the wheels of the firetruck), : heel-toe-heel-toe, over a certain distance.
While with the FM you have: toe-heel-toe (3 points) and at a shorter distance.

I hope my explanation is clear but please add to this discussion if you want.

Rob van Gelder, Amsterdam, Holland


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#2 RobVanGelder

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Posted 08 January 2004 - 04:45 PM

Sorry Jerry, for misspelling your name several times.

Rob van Gelder, Amsterdam, Holland
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#3 Jerry Holway

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Posted 19 January 2004 - 10:32 AM

Rob

Happy new year.

You got some of the physics right and some of it wrong, so I'd like to help clarify a few things...

Here's a clue: the firetruck has the ladder mounted on the "front!"

And I really like your pictures, because the weight (the rig) and you (the real resistance) are the same in both sets of pictures. Another big clue to what's going on.

What's wrong are your force diagrams. In both cases the rig wants to do nothing more than drop straight down. The arm transfers this force to your body via the vest, and you keep the rig up, and by leaning back, you keep from falling over.

All vests do two basic things. The first is to keep one end of the arm from dropping to the floor (holding up the weight). The second is enable our bodies to act like a lever above and below the attachment point so we can resist the downward force of the rig which is outside of our skeletal structure (like the firetruck example)

The DSD vest enables this leverage with a rigid back, the traditional vests do it with a rigid front and straps going around to the same point in the back. The DSD vest is slightly more efficient at this task than a very well designed traditional vest such as the newer Ultra vest or the PRO vest or others, and the rigid back of the DSD vest enables this leverage much much better than a poorly designed vest - and there are many of those out there.

The point of attachment does not matter. At all. Here's a clue: Think about all the work and expense to make the DSD socket block/arm attachment point rigid from the side of the vest all the way to the back. All the strength of that carbon fiber part keeps the attachment point fixed relative to the shell. The arm is actually attached to the SIDE of the shell.

Another consequence of the DSD vest - and one that many operators like - is that the vest places almost all the weight carrying capacity on your hips. Traditional vests spread this out more, with the upper torso sharing some of the load.

A downside of this part of the DSD vest design is that there is very little side to side torque resistance compared to a traditional design, which is why the DSD vest must be fit so carefully and so tight on the operator's hips. See the posts last year on "a strange event" (sorry no link) for another consequence of this.

Hope this helps a little more...

Jerry
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#4 Mitch Gross

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Posted 19 January 2004 - 01:41 PM

Jerry spells the differences out very clearly. I'd like to add that the big difference in a backmounted design putting the weight on the hips means that the single largest and strongest bone assembly in your body is taking the load. On a frontmounted vest the spine is compressed and the ribcage partially restricted. The backmount uses a large bone assembly while the frontmount uses a collection of many bones and muscles. That's part of the reason why frontmount users tend to fatigue more at the end of the day compared to backmount. That pressure on and exertion by various chest and back muscles essentially does not exist (at least to the same degree) in the backmount design. And yes, that's why it must be fitted very well, otherwise your back will be doing vastly more exertion.
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#5 JamieSilverstein

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Posted 20 January 2004 - 05:34 AM

So if both Mitch and Jerry are right, then its not the point of attack , but the over use by an FM vest on your shoulders (many injuries reported to date concerning shoulders and fm vests, and back, I need not report on that part of the body to any of us here). The hips bearing the brunt of the weight allow us as operators to use our brains for more operating and less survival. In other words, a back mounted vest is more energy efficient...........
The only question I have concerning point of attack is if your back begins to tilt forward as is the case after a long day in an FM vest, aren't you effectivly bringing your center of gravity foward and placing more and more stress on your lower back. Additionally, in a non rigid vest, if the vest twists as you work, say in low mode, doesn't that also place different stress on the body at different points?
Finally, the design of the BM vest, provides for a "hinge effect in the back, pushing the vest into your back as you walk, rather than pushing the vest away from you as is the case with an FM vest. If the vest pushes into you rather than away from you, doesn't that affect the where the weight affects you? So maybe its not about where the Center of Gravity exists on a vest, if all equal, but how that CG affects you in a rigid vs non rigid vest.
For my body, and career the back mounted system has made a tremendous difference, all of which has been explained.
The bottom line, regardless of the science, is that there is a notable difference between the two systems. I personally prefer the Back Mounted to the front.
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#6 Larry McConkey

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Posted 20 January 2004 - 08:27 AM

If you get tired and stop balancing the Steadicam (let it pull you over) you are certainly going to see problems with your operating with either system. The difference I see and feel with the back mount pushing into my back is that it helps to support my lower back which has to do more of that balancing effort with a FM. This balancing effort is now being shared with my glutes that are better suited to it. Also, and this was quite noticeable from the beginning of my use of the DSD, because it is pushing into my back, rather than the FM which pulls away from my chest, there is remarkably less side to side shifting as I move the Steadicam from side to side. It is like a better designed ski boot that allows for more control with less discomfort if it fits right... and again the fit is all important as Jerry mentioned. Too long, too short, too wide or narrow, too deep or shallow and the DSD will not do its magic.
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#7 Alec Jarnagin SOC

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Posted 20 January 2004 - 11:23 AM

Very interesting. As I've stated before, I've never been as uncomfortable in a vest, as I have been will an ill-fitting DSD. Recently, I tried Jamie's, which offered me my closest fitting yet - close enough to finally appreciate the merits of the system first hand (although with lots of the "tingle" in the leg, as it was still a little too big and pushing down too much).

Anyway, I did find myself wondering why not attach the socket block to the front? The long, expensive carbon fiber arm just moves the socket block to the front. Bare with me for a moment here, guys. It seems to me, that the biggest difference in design is the shape and rigidity of said design, not the attachment point. Your entire back is enclosed with a rigid piece, and your entire waist is enclosed with a rigid structure as well. By moving the socket block to the front, you should yield the same results, but with a much slimmer profile - at least in theory. As said before, with a traditional front mounted vest, you are attaching to a front plate that pulls forward, placing stress on your lower back (and other parts). This is in part because there is no material of any substantial nature covering your lower back. This is why the famed "jumper" straps make such a large difference (if you are using a front mounted vest without these, I highly recommend adding them). Imagine taking a traditional front mounted vest and wearing it backwards (obviously, don't try this), yet you were somehow able to still attach the arm to your front side. Now you'd find the larger portion of the vest pushing into your back. It is the same with a DSD. The DSD offers lumbar support that pushes into your lower back. If the arm is attached to the front of the vest, it will still cause that lumbar to push into your lower back, as the entire vest is very rigid. The addition of a carbon fiber arm is simply connecting your socket block to your back via a rigid arm. If the socket block were mounted to the front of the vest, it would still be connected to your back via a rigid carbon fiber shell.

I'm not sure if I'm explaining this right, but in a nutshell you have two large masses. You and the rig. The distance between these two masses is all that really matters. Right?
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#8 Mitch Gross

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Posted 20 January 2004 - 05:47 PM

Alec, I thin you are essentially correct except that it would result in a much more massive front section of the vest. So much more massive that it could become constricting. Think of it this way--the backmount design is essentially a ring that rests on your hips with shoulder straps that keep it firmly in place along your spine. The front part of the ring (which are where the straps are in the DSD design) would have to become rigid and far more massive in order to support the socket block. I suppose you could get into the vest by simply slipping it over your head, but that would be cumbersome and the vest would weigh considerably more even when constructed of carbon fiber.

Of the beauties of the backmount design is that it presses against the spine in such a way as to help support and mesh with the spine. It becomes an extension of the spine, molding to it and offering additional support. Frontmount vests COMPRESS the spine, putting so much strain into the lower and central back. We all know the feeling of those muscles exerting themselves down there. Frontmount vests in general use more muscles along with bones for support compared to backmount vests. This brings on strain and fatigue. And compressing the spine is never a good thing.

There's a lot of room for that spine to move, ya know. Astonauts and cosmonauts who've spent considerable time in space stations routinely grow an inch or two as the lack of gravity uncompresses the discs in their spines. When they return to Earth after long trips some cannot walk for considerable periods.
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#9 Larry McConkey

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Posted 20 January 2004 - 10:36 PM

Another real trick that the DSD accomplishes is to make the transition from the rigid part of the system - the back plate - to the soft tissues of the Operators' body. There has to be some allowance for the body to move around some especially to allow for comfort. This is done with the DSD by transitioning from the rigid back through stiff but much more flexible side panels made of leather. This means the front of the vest should remain pliable, not rigid, so that is why the separate rigid DSD arm coming from the rigid back plate around towards the front is so important. You could engineer a longer DSD arm to get all the way to the front, but you have added a lot of weight and probably lost some important rigidity. Early models that I tested had a small amount of flex and this resulted in terrible vibrations to the image very noticeable with longer lenses whenever I took a step. Walter beefed up the design until it was rigid enough to stop this.

Larry
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#10 Erwin Landau

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Posted 21 January 2004 - 02:44 AM

I had tried the DSD vest 6 times over the periode of 3 years. I found it very uncomfortable the first 5 times due to the fact that it moved to much and I was able to stick my fist between the shell and my spine.
As I have scoliosis and a shorter left leg, that resultet in a very painful experience... (In the past I had avoided such problems due to the years of power lifting and Bodybuilding which actually made the Front Mounted Vest, feel very well) All that changed when I tried the latest version with the Air bladder. It made a huge difference after Walter had found the right shell size plus the right amount of padding including the inflated bladder which convinced me to write the check...
The fitting is key.

Alec, I guess that it would be possible to hard mount the Socket Block to the side of the shell.... but that would also eliminate the possibility for the conveniante quick adjustment in heights that the Carbon fiber Arm delivers. In the past I was able to raise the Arm of the Vest by undoing the knob with the right hand while holding the rig in the left, without having to go back, dock and pull out a longer arm post... It's quite unorthodox but it leaves the DP, on Music Videos, while screeming that he always has to wait for Steadicam, quickly speechless and without a valid complaint... Comes in handy.

Mitch... I had tried other Backmounted Vests in the past that where virtually turned around Frontmounted ones which were very painful experiences... The shell/foam combo makes the difference, you can't just stick the chest spar into your back and expect to get the same results...
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#11 Larry McConkey

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Posted 21 January 2004 - 09:06 AM

When I went to Walter's shop to be fitted several years ago, he and Daniel showed me several prototypes they had gone through including one that was rigid along the sides and mounted the socket block directly to it. They found it unacceptable and went to the separate arm design. Again, I think it all has to do with allowing the harness to be flexible were it can be (along the sides and front) and rigid where it must be (in the back). Walter continues to develop the design and I am sure it will become lighter, smaller, more comfortable and more flexible in the future, because he doesn't know how to stop improving a design if he thinks it can be improved!!

Larry
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#12 Alec Jarnagin SOC

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Posted 21 January 2004 - 06:00 PM

Larry

Not at all surprised to hear that Walter has explored that avenue. While I have only met him once, he is obviously a very thorough man (fyi, it was in NYC a number of years back, when he first came to demo the vest - he had just come from showing you on the set of... don't remember, oh well). My point was as much academic as anything - it seems many are convinced this vest works because the arm attaches to the back. While I am no physicist (that would be my father - he has a PhD in the subject), it seemed to me that ultimately it boils down to your mass and the rigs mass and the relation between the two. The key to the vest is its rigidity.

Practically speaking, I am finally giving serious thought to purchasing a DSD/Klassen vest this year (which is it now? - another thing that worries me), but I'm just trying to make sure I understand it as well as possible. I'm still very nervous about spending $9000 and ending up with a tingle in my leg, as this is a problem I do not have at the moment. Is the general consensus, once you have a proper fit, this is not an issue?

Erwin, yes, the ability to slide the arm up and down to alter lens height is a very nice thing. Also, I'm very eager to try a vest with an air bladder, as none of the ones I've used have had this feature. As I mentioned, Jamie's almost fit. I suspect if it had had an air bladder, it would have done the trick. It seems like a very good feature.
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#13 Larry McConkey

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Posted 21 January 2004 - 10:00 PM

I have never had this tingling either, so I don't really know what it is from. The only problems I ever had were the result of sitting while wearing a front mount vest that was adjusted long enough that the bottom cut into my legs just below the waist. I learned never to do that again!

One thing you can be sure of with Walter is absolute customer satisfaction, whatever it takes! It may take some doing to get you fit correctly, but he will not rest easy until it happens. That is certainly the story I have heard from others as well as from my own experience. If you can possibly do it, a trip to his shop for fitting is well worth it, but otherwise certainly talk to him on the phone and get guidance for how to measure yourself carefully.

Again, in terms of the design, I think what is at the heart of the design is the rigid, form-fitting (especially with the air bladder) back piece that attaches rigidly to the Steadicam arm (in this case via the Harness "Arm" coming from the back piece) and the back piece is connected firmly to the body with a flexible, and with proper foam pieces, comfortable harness that gives you control without pain.

I toyed for a while with the idea of attaching the front section of my Ultra vest to the back piece of the DSD Harness. I had Walter build in attachments to connect the two. I reasoned that this could give my the back support, and also give me back the control I get from using a FM by manipulating my stomach muscles, and thereby get some of the best of both worlds, without the external arm getting in my way. I never went so far as to try operating with this hybrid because the DSD design ultimately worked so well, as is. I just had to use my FM today, however, because of clearance problems in a tight hallway. It was much, much harder than working with the BM and I was very glad to go back! It made me think I should look again at my hybrid idea for these situations...

Larry
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#14 Mitch Gross

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Posted 22 January 2004 - 12:37 AM

Alec, I think you're entirely correct that the key to the backmount design is the way it fits rigidly and distributes the weight to the body, not the fact that the arm mounts from the back. Frankly the arm mount could be on the sides, swing up over top or rise up between you legs for all it matters, because the static weight still comes from the center of gravity point and not the contact point of the arm mount to the vest. I think the backmount at it simplest has the arm mount come from the back because that's where there's already the most material for solid mounting. It's economy of design.

Larry, I have a little trouble imagining what the advantages would be of your hybrid concept. Would you be giving up a little lack-of-fatigue in the stomach muscles for increased control?
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#15 ericoh

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Posted 23 January 2004 - 12:49 AM

Walter continues to develop the design and I am sure it will become lighter, smaller, more comfortable and more flexible in the future, because he doesn't know how to stop improving a design if he thinks it can be improved!!

Larry

Walter has recently developed a slightly lighter harness with the same features of the "deluxe". Slightly cheaper than the deluxe Klassen Vest from what I understand.

I'm test flying it this weekend on a music video...
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