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adjusting Master arm


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#1 kes

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Posted 21 March 2004 - 03:01 PM

Please forgive me for taking the liberty and approach you with such a basic question. I need a little advise and so I thought I might get some solutions from operators who had some experience with the Master arm. I am new to steadicam - bought a Master six months ago and ever since then practice hard daily. I practice the steadicam for six months with a much heavier wight than one operate in TV productions, the field I am aiming at - Like they say "hard in training easy in fight". However today for the first time I tried practicing with a lighter set up, same wight as I will probably operate normally - My setting was a bare Betacam Digital without a batterie ( I am going to work with a Triax ) and without mounting any transmitters/receivers ( I pull my own focus and zoom ) + the heavy A/B ProPack to power my sled and my Master CRT green monitor. Sound quite nice and light setting , the only problem I had was when I was trying to adjust my forearm arm section, the section that is close to the sled - even after turning the adjustment knob all the way left the forearm section still rises. Is there any way I can make my forearm section falls a little bit and than lifting that 'little bit' when operating - just the way I did for the last six months. I just do not want to add unnecessary wight to force this arm section to fall. Having said all that I also think to replace my CRT to LCD monitor and my heavy ProPack to a Dionic bateries which gives me even a lighter setting - Than what will I do.
Please give me your comments.
Kes
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#2 Brad Grimmett

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Posted 21 March 2004 - 06:45 PM

Sounds strange to me. This setup is more than enough weight for your arm. All I can think is that maybe you have a problem with your arm. Maybe some blown bearings? If something is binding this could be causing it I think. If you can't figure it out call Robert Luna and maybe he can help you.
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#3 kes

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Posted 22 March 2004 - 03:20 AM

Thanks Brad. I just had a close look at my arm and it all seems fine to me although I might admit I do not have experience in fixing arms and like I said it may only looks ok. Theoretically I should be able to turn the adjusment knob more to the left as I see a bit more room to the screw I could play with, may be there is other adjustments I can do and which I am not aware of. By the way who is Robert Luna and how can I contact him.
Kes
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#4 charlesneufeld

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Posted 22 March 2004 - 11:43 AM

Hi Kes,

I'm know there are others here that could tell ya the history of Mr. Luna... I personally do not know his history, but I think he worked for CP (please correct me if this is wrong) But I think it boils down to that he is the man when it comes to arms :)

Robert Luna 323-938-5659

I too will be calling him soon.

Hope this helps

Charles
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#5 WillArnot

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Posted 22 March 2004 - 09:33 PM

There is another coarse adjustment to the Master arm. You need a long (>8") allen wrench with a ball end. To understand the coarse adjustment picture an 'S' curve, like the exposure curve of film... where you can bias the tension of the arm to allow for full, medium, or light strength. Or easier perhaps, if you always had 100 lbs of bricks in the trunk of your car, your suspension will always be taxed and the car not as responsive. Ultimately this shortens the life of the springs. That's why it's advisable to back off the red knobs all the way if you can, if anticipate not using the arm for a while.

If you look at the front end of both arm sections (nearest the camera, and nearest the elbow for the lower section) where the start of the spring / cable assembly starts there is I believe a 1/4" allen key bolt right at the head of the spring. This bolt is roughly 2"-4" long, and is how the tension is ultimately released by a PROFESSIONAL TECHNICIAN when taking your arm apart.

I am far from a professional arm technician, and this is not an adjustment you want to tinker with often and certainly not in the field. It was explained to me that by releasing some of that Pre-set/coarse tension, you essentially give a little life back to the spring b/c it is not being set at it's absolutely maximum all the time.

I released about 3/4 inch of bolt (maybe 10 turns on the allen) and could easily still fly full 35mm set up, Panavision Primos, with say 3 motors, and a Kino ballast & kino tube on mattbox. I found that this release in the coarse tension gave the arm a little more feel and touch. It definately made a difference, especially when lighter loads were concerned.

But beware. As you will see, when turning the allen key you have to hold the spring so that the cables don't twist. This is quite easy when you are releasing the tension, b/c the spring naturally wants to contract (get shorter). The issue is if you want to add FULL power back to the arm it is very difficult to hold the spring while you screw the bolt back in, to make the spring come back to the bolt head. The bolt doesn't actually move, the spring travels up and down the bolt. I think the thing to use is a strap wrench to wrap around the head of the spring.

But I never had to do this (add the tension back). I think the only scenario I can imagine is if you might fly BL 4's. Thank god I haven't had to do that in about 7 yrs!!

But again, check w/ Rob Luna. He is the one who indeed headed up the arm dept. @ CP for many years.

Good luck,

Will
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#6 kes

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Posted 23 March 2004 - 12:06 PM

Many thanks Will. My brother has just spoke with Mr. Luna and also with Robin at Optex and they told him to do exactely what you said. Hopefully that should help.
Kes
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#7 pbalsdon

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Posted 24 March 2004 - 03:41 PM

The Master Film Series arms where rated with a minimum camera weight of 20lbs, the tv series arms a minimum of 15lbs but a max of only 35lbs. The only difference physically between the two is the process described by Will in his post. CP seemed reluctant to tell people about this, maybe they thought film ops would go for the cheaper TV rigs if they new how easy the adjustment was. I discovered this by experience when my arm went down and another op lent me his Broadcast arm which wouldn't support a BL's weight, to his surprise and mine. The engineer working on my arm discovered the difference.
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#8 Jerry Holway

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Posted 29 March 2004 - 05:43 PM

A few thoughts on the MS/Ultra arm:

I think it's highly unlikely that relaxing the springs when the arm is not in use will have any effect on spring life.

In the unloaded (or up) position, the springs are barely loaded; hardly stretched, especially compared to the maximum stretch, or down position.

If an extension spring does not "take a set" from OVER extension, then it will perform near constantly for ever. (Try over-extending a small and cheap extension spring from a pen. When it is over-stretched, it will instantly fail to perform.)

In normal use, the arms we use can't overstretch the springs- because the stretch is limited by the geometry of the arms and not by the load - unless, of course, something goes terribly wrong.

Other factors that affect spring life are shock loading, rapid recycling, and high temperatures, none of which are encountered in normal Steadicam operating.

"De-tuning" a Master Series/Ultra arm will affect how it behaves. Theoretically, it works "best" at the maximum spring tension, just as Model I, II, or III type arms also work best at their maximum spring tensions. Relaxing or detuning any of these arms takes it out of the "ideal" and makes for a more centered and harder ride.

With older arms and lighter-than-maximum weight cameras, it takes a lot more effort from the operator to boom all the way up or all the way down, and more damping to keep the camera exactly at one height as one walks along, steps off a curb, etc.

What Will suggests with the Master/Ultra arm, however, is a slight de-tuning that has very little effect on that arm's "ideal" performance with only a slight loss in ultimate lift capacity.

It can be really useful to "de tune" the section of the arm closest to your body, as this section has widely varying loads depending on the angle of the second section, and it also lifts more or less depending on the angle of your body. Making this section more "centered" by detuning will help to keep it from locking up or down. (Better posture will have a similar effect...).

AGAIN the WARNING: if you de-tune, be sure the wires to the springs don't get crossed, otherwise it's an expensive mess.

Last note: in adjusting the MS/Ultra arms, adjust the forearm (closest to gimbal) section first so that it carries the load both above and below horizontal. Then adjust the other section so that it follows or tracks the forearm section as you boom all the way up and down. As a test: once you get it right, lean back or worse, forward, and see what happens as you boom up and down.

Jerry
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#9 WillArnot

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Posted 29 March 2004 - 08:57 PM

These are great tips from Jerry. It actually took me a couple of yrs of operating to truly understand the finesse that a Master arm is capable of. However, this did take alot of 'arm lock-ups', sometimes at very in-opportune moments, to really make me aware that this arm needs constant attention. Every Panavision Primo lens change warrants a tweak of the knobs. This arm needs to be tuned exactly to bring out it's full potential.

Experiment...be aware of how each section booms. Like Jerry pointed out adjust the front section then the back section as a 'slave' to the front. Be aware of your posture and how that affects the angles, and boom action.
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#10 PeterAbraham

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Posted 26 July 2004 - 10:17 PM

When I got my MS arm in 1996, I was so befuddled as to exactly how to fine-tune it, that I got some help from G.B. on the matter. It took a few weeks at least to find out just where the best spots were for any given camera- and more than a few weeks to stop hauling the darned thing up so hard.......and allowing it to do its amazingly graceful work.

Great arm, just great. Felt like............ my Flyer arm.

:D

Peter Abraham
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