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3A Arm type


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#1 Fabian Meller

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Posted 18 December 2011 - 01:37 PM

Hey guys!

I recently got my first big rig - It's an older Sachtler Artemis - It's fairly okay except the arm is a bit clumsy, though. Anyway, it's a good way for me to start out..

I'm not sure, but the Artemis arm is a 3A arm type, right?

Now I'm wondering about how to adjust the arm. I've heard that it's supposed to adjust the 4 screws pretty much the same. (I'm working with lighter cameras too, what forces me to relax the springs - Certainly it becomes less "iso-elastic" then.

Yet, playing around with it I found it better to have the lower bones (regarding only one arm section!) tighter/ the upper ones more relaxed. This makes it feel easier for me to boom it up and down, even with lighter loads.
But now I'm concerned about the mechanics. Could this adjustment be any bad for the arm/springs?

One more thing - What grease would you recommend for this arm if squeaking occurs? And also where to grease??

Thank You in advance!
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#2 Eric Fletcher S.O.C.

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Posted 18 December 2011 - 02:05 PM

First off let's clear something up. Any Cinema Products Arm produced before the Masters Seres Arm is NOT Iso-Elastic (Which honestly is just a code word for friction)

So what that means is that no matter how you adjust a 3A or earlier arm you will not increase or decrease anything BUT lifting power.

You should always adjust the arm equally in order to keep the springs centered so that they don't mechanically foul on the bones. In the past we had been told that we equally adjust the springs so that you would risk breaking a spring due to over stretching, springs don't work that way, they will always self equalize. Also you should adjust the front and rear sections to lift in unison you don't want the rear following the front, you will see it in your booming.

As for lubrication use a lite weight machine oil. Altough I'd be interested in trying some "Frog lube" on it
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#3 Fabian Meller

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Posted 18 December 2011 - 02:41 PM

Thank You Eric! I actually know about the term iso-elastic.

What I wanted to describe with it is just the effort that is needed to boom up. As the springs are tightened (due to a heavier load) it definitely gets easier to boom!! So thats what I meant with "iso-elastic"

I think I'm good with the machine oil... Maybe if I can find one, I'll give the frog lube a try some time
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#4 Eric Fletcher S.O.C.

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Posted 18 December 2011 - 02:50 PM

What I wanted to describe with it is just the effort that is needed to boom up. As the springs are tightened (due to a heavier load) it definitely gets easier to boom!! So thats what I meant with "iso-elastic"


Yet Iso-elastic according to Tiffen means that the arm stays where you put it and the force/lift curve remains linear or close to linear over the boom range

What you are describing is a simple increase of lift, the 3A arm will still require a force delta of 5+ pounds at the ends of travel
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#5 Fabian Meller

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Posted 18 December 2011 - 03:00 PM

Oh I see! Thanks for clarifying!
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#6 Jerry Holway

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Posted 19 December 2011 - 09:14 AM

Geez, Eric-

Your definition of iso-elastic is not right at all.

It is not about friction at all, but the relative effort required to raise or lower an arm from its float point. Less effort, more iso.

Put another way, an iso-elastic arm is less reactive to vertical changes - it takes less effort to control as one goes up and down, as the arm does not seek its float point strongly.

The friction in the original master series arms - which were iso-elastic - caused the arms to be sticky, not a good thing. Later Master Series arms, after the bearings and other parts were upgraded, were much less frictional.

IIIa type arms were and are more iso-elastic IF working at or near their maximum, and less iso-elastic when lifting less weight. They change their performance as the load changes.

The original arms were all iso-elastic because they all worked at or near their maximum - the load range was very small.

The Pro arm is iso-elastic, in part because one changes the springs and number of them and this keeps the springs working at or near their maximum.

When you say "according to Tiffen" you should check your facts..... test a IIIa arm, etc.

Jerry
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#7 Eric Fletcher S.O.C.

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Posted 25 December 2011 - 02:30 AM

Geez, Eric-

Your definition of iso-elastic is not right at all.

It is not about friction at all, but the relative effort required to raise or lower an arm from its float point. Less effort, more iso.

Put another way, an iso-elastic arm is less reactive to vertical changes - it takes less effort to control as one goes up and down, as the arm does not seek its float point strongly.

The friction in the original master series arms - which were iso-elastic - caused the arms to be sticky, not a good thing. Later Master Series arms, after the bearings and other parts were upgraded, were much less frictional.

IIIa type arms were and are more iso-elastic IF working at or near their maximum, and less iso-elastic when lifting less weight. They change their performance as the load changes.

The original arms were all iso-elastic because they all worked at or near their maximum - the load range was very small.

The Pro arm is iso-elastic, in part because one changes the springs and number of them and this keeps the springs working at or near their maximum.

When you say "according to Tiffen" you should check your facts..... test a IIIa arm, etc.

Jerry



Jerry

First off, unless you are talking about Mathematical economics there is no such word as Iso-elastic other than the one that was made up when the Masters arm was introduced (Google is you friend if you'd like to double check this, I linked it   Right here)  Since we now agree that it's a made up word let's address your reply.

In the second line of your post you state that Iso-elastic "is not about friction at all, but the relative effort required to raise or lower an arm from its float point"  then in the third line you state "Put another way, an iso-elastic arm is less reactive to vertical changes". In the real world where there are real definitions that's called Friction.  In Auto Racing (Where I happen to do suspension engineering and guess what, the cars are held up with springs) any time "the arm does not seek its float point strongly." (Lets replace Arm with Car) I'd tell the lads to start checking spring alignment to minimize side load on the dampers, and to check with all the suspension heims because we have a friction problem. (I'd also have them check anti dive and anti squat to make sure we aren't locking out the suspension but that's another matter I'll address later) See when a car doesn't return to it's ride height setting (Float point) it's damn near impossible to set it up in a predictable manner and that's a bad thing. Anti-Dive/Squat lockup brings to mind the behavior of the both the Masters series arm and the G series arm when the front and rear section don't track and you get lockup, you don't know when it's going to happen but it does.  

If you really want to use a real word for the behavior of the Master and G-Series arms it would be "Digressive". Digressive suspension (Face it all these arms are IS Suspension nothing more) is one that isn't reactive to vertical load at low speed, In car terms that would be less than 3"/second of suspension movement in the steadicam world that would be a slow walk but IS reactive in high speed (Greater than 4"/Second or any sort of booming/running) This would explain why you see your footsteps in those arms at a slow walk.

The Pro arm and the 3A arm are "Progressive" Arms. They have a force curve that at the natural float point requires very little force to move and stays that way for a good part of their travel then stiffens up at the ends to prevent you from riding the bump stops. This in an arm is a very natural feel since it gives you feedback on the arms travel

You're assessment of how the PRO arm operates is incorrect, you do not need to run the springs at their maximum or even near it to get the arm to function correctly, You should test it and check your facts

As for my testing of a 3A arm?  Well, I owned one, I also owned a model 1 arm (Actually figured out and modified both of those arms to provide a force curve that only had a 2lbs delta over it's entire boom range) Then after trying the masters arm I bought a PRO arm. Over the years I've used masters arms and G-Series arms as recently as two weeks ago, so yes Jerry I know what I'm talking about.

If you's like to discuss this any further I'm happy to.
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#8 Janice Arthur

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Posted 25 December 2011 - 10:34 AM

I think a cage match is due!!

Some kind of engineering duel !!

I'd buy a ticket to that one.

Arms/dynamic balance etc

Neither would convince the other to change his mind
but it would be fun to watch ( and learn ).

JA
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#9 Jerry Holway

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Posted 25 December 2011 - 10:54 AM

Eric-

As I've always said, both on the forum and in print and in workshops, "iso-elastic" is a marketing term, coined by CP to describe an arm that takes less effort to boom up or down from the float point, or, to describe it another way, an arm less reactive to vertical changes. A flatter force curve, to use your language. Sharper or flatter force curves can be affected by geometry and choice of spring length and type within a given geometry in a car or desk lamp or arm or garage door, etc.

The PRO arm, I also always said, is iso-elastic in part because the springs are working close to their ideal (it's why you have 8 springs in combinations to be iso at all loads). The MS and Geo arms achieve the trick differently, the G- arms, in part, with a single, low aspect ration spring.

If you independently choose to re-define iso-elastic, what more can I say? We can not have a coherent conversation.

Friction and going over centers clearly affect how arms behave, but they are not what the term iso-elastic describes. I am weary of repeating this all in threads on this forum...

BTW, since you do not own a G-series arm, you should know that they do not go over centers and lock up without warning, as you claim.

You adjust the iso to the max or less for each load, and the max is defined by the arm not going over centers and locking up.....

G arms also boom higher and lower than other arms; part of the geometry is prevent that from happening.... other arms prevent the going over centers and locking up by restricting the vertical travel. The old CP ProVid arm was so prone to going over centers that the arm travel was severely restricted.... MS arms were closer to the edge; if you were in bad form and leaned back (operating in the guitar hero or tower of pisa posture), the arm locked up, just as most arms do when you go into the rest position.

I'm pretty deep into designing the G-arms; but not as deeply as others, but I m very clearly and deeply involved in using and adjusting these arms, and know how they work and why. I've even parsed the patents....

Peace

Jerry
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#10 JobScholtze

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Posted 25 December 2011 - 06:05 PM

Not to get to much involved, but i have a question.
I own a G50 and a Pro arm. ( sold my G70 6 month ago )
I find it WAY easyer to boom up and down AND keep the arm in a higher position or lower then a G50. Why is that? It should be the other way around is it?
Or is there something wrong with the G50. Yes i tryd the ride in all positions, but it keeps feeling stiff.

Thx
Job
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#11 Eric Fletcher S.O.C.

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Posted 25 December 2011 - 07:54 PM

I own a G50 and a Pro arm. ( sold my G70 6 month ago )
I find it WAY easyer to boom up and down AND keep the arm in a higher position or lower then a G50. Why is that? It should be the other way around is it?
Or is there something wrong with the G50. Yes i tryd the ride in all positions, but it keeps feeling stiff.


That's Digressive vs Linear, it's also friction. Bet you see your footsteps with the G50
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#12 Brian Freesh

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Posted 26 December 2011 - 12:24 AM

I may be mistaken, but I think Job is saying the G50 more strongly seeks a float point than the Pro arm. Which does seem odd to me.

I'm somewhat of a tech geek, though hardly as knowledgeable as either Eric or Jerry, so I find these discussions very interesting. Ultimately though, all I care about is if the arm is doing what it is supposed to do. It's like the dynamic balance technical debates. I do not and never have cared if I can spin the sled flat for multiple 360 degree pans, certainly not super fast. I'll never do that on a shoot. I just care that I can make a flat pan when it counts. With the arm, I want it to hold the rig and negate as much of my movement as possible.

I have a master arm that stays at whatever level it's at when I let go. I have a flyer arm that seeks the balanced float point. I prefer the flyer arm's behavior by miles. I struggled initially with the master arm, and when I have used G50s and G70s, because it doesn't negate as much of my vertical movement as the pro or Flyer arm. If I step up, the arm steps up with me, so i have to compensate with my boom hand. I've become accustomed to this and am very good even at very slow speeds, but I don't feel I should have to. It seems to me that the Masters and G series arms partly defeat their own purpose. I've no idea or care if this has anything to do with iso-elasticity or friction anymore, I just wish it worked better. I shouldn't have to fight the system.

I'm fine with the master arm being what it is, I prefer it to it's predecessors. However, i wish the G series arms performed better. I like them just fine except for that one issue, which to me is quite a big deal. It may not be to others. If I needed an arm with a 50lb weight max I would be stoked with a G50. But if I need to replace my master arm with what is currently available, the extra cost of a pro arm vs a G70 is more than worth it.

As usual with these rigs, it comes down to preference. I know plenty of people who prefer the master arms and/or G-series over the Pro arm. I know many more who prefer the pro arm. They're all good arms over all. I care how they perform, not how the physics work. :P

my $.02
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#13 RonBaldwin

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Posted 26 December 2011 - 04:17 AM

It's all about the lube...Tiffen doesn't use Lisagav!
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#14 JobScholtze

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Posted 26 December 2011 - 05:03 AM

Bet you see your footsteps with the G50

Yes, very much. Hence the pro, wich dasnt have that problem
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#15 Jerry Holway

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Posted 26 December 2011 - 09:38 AM

Anyone interested in trying out a new arm should get themselves to the Tiffen factory or a workshop or trade show.

Both the G-50 and G-70 have been improved and have new designations, the G-50x and the G-70x.

Both have extremely low friction due to new bearings and more iso capability, i.e., the potential for a flatter response curve.

BTW, all the G series arm's response curves can be flat or steep (user controllable) and also have a non-flat section near each end of boom travel.

The G-70x has some additional geometry tricks that make it a joy to use....

But, as it is ultimately about user preference, I suggest users try the new arms and compare them to any other arm out there.

Jerry
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