Film-Tech Forum ARCHIVE: Shape of intermittent cam.

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Topic: Shape of intermittent cam.

Brian Tristam Williams
Film Handler

Posts: 93
From: Johannesburg, South Africa
Registered: Apr 2002

posted 07-02-2002 01:18 PM

Tim Reed, I tried to e-mail you on this, but your address is not made public.

I saw the animation in the 'Videos' section, and I want to build a larger-than-life working model of this. Someone I know, who's a bit of a mechanical engineer, says that this shape will never work. I've researched this, and I see that there are several ways of creating an intermittent motion. Is the animation merely a fanciful example, or is that the shape of most real intermittents?

If this model will work, could you send me a 3D object file of it, Tim? The engineering shop needs it on disk to build me one.

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"One man can make a difference."

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Josh Jones
Redhat

Posts: 1207
From: Plano, TX
Registered: Apr 2000

posted 07-02-2002 01:58 PM

That is really what they look like. I'll post a pic of what a brenkert movement looks like.

*Pic here*

As you can see, the "starwheel" does indeed posses a star shape.

Josh

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Brian Tristam Williams
Film Handler

Posts: 93
From: Johannesburg, South Africa
Registered: Apr 2002

posted 07-02-2002 02:26 PM

Well I didn't see your pic (unless your asterisks represented the starwheel).

Anyhow, I wasn't questioning the star-wheel, but rather the cam that engages it - I've seen different shapes for this.

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Paul Cassidy
Jedi Master Film Handler

Posts: 549
From: Auckland, New Zealand
Registered: Aug 2001

posted 07-02-2002 02:46 PM

Pehaps the easy way to do this is to get old movement to see how it works , but it has been working for over 100 years so I don't know how your engineer friend can't figure out the workings of it , it is soooo simple but clever with very close working tolerances.

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A KIWI eats,roots & Leaves.

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Josh Jones
Redhat

Posts: 1207
From: Plano, TX
Registered: Apr 2000

posted 07-02-2002 03:05 PM

Had to rip a movement apart to show how it works

Josh

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Brian Tristam Williams
Film Handler

Posts: 93
From: Johannesburg, South Africa
Registered: Apr 2002

posted 07-02-2002 03:28 PM

You did that just for me, Josh?

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Paul Cassidy
Jedi Master Film Handler

Posts: 549
From: Auckland, New Zealand
Registered: Aug 2001

posted 07-02-2002 03:43 PM

Great work Josh .

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A KIWI eats,roots & Leaves.

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Gerard S. Cohen
Jedi Master Film Handler

Posts: 975
From: Forest Hills, NY, USA
Registered: Sep 2001

posted 07-02-2002 04:09 PM

Brian,
You probably know the "star" is also called a "Geneva movement" or "Maltese Cross."
However, an alternative, non-cross intermittant was invented by J. Powers and used on his projectors, although they could be ordered with a conventional cross, pin & cam movement if desired. The Powers
proprietary movement had several pins and cams in place of a cross,
but its use did not become popular. I don't think it was used on non-Powers projectors, but those who used it claimed it worked fine and was smooth and quiet.
Gerard

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Jon Miller
Jedi Master Film Handler

Posts: 973
From: San Diego, CA, USA
Registered: Sep 1999

posted 07-02-2002 11:15 PM

Josh,

Thats one impressive intermittent! Is that beast really from a Brenkert? I can't imagine a monster like that being used in an ordinary 35mm machine.

(I've never got up close and personal, so to speak, with a Brenkert.)

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Josh Jones
Redhat

Posts: 1207
From: Plano, TX
Registered: Apr 2000

posted 07-02-2002 11:42 PM

yes that is really from a brenkert. the star is about 1.5-2.5 inches in diameter, close to the size of a PRO-35 stargear. I was bored today so I took one apart and then put it back together

The second picture shows the cycle the movement goes through during pull-down. all these parts are machined to 1/10,000th of an inch!! Now THAT is precision.

Josh

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Josh Jones
Redhat

Posts: 1207
From: Plano, TX
Registered: Apr 2000

posted 07-02-2002 11:48 PM

John, I see your a simplex man

the simplex machines have smaller stars and cams(xl's), the century's even smaller(at least on the earlier machines, like a C or CC).

Josh

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Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 07-02-2002 11:53 PM

John, if you think the star in a Brenkert is big, check out a Ballentyne star!

Oops....Josh already said that.

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German Marin
Expert Film Handler

Posts: 227
From: Verbania (VB), Italy
Registered: Jul 2001

posted 07-03-2002 02:41 AM

I don't know where is this Maltesse cross and which is its function, but I got this picture from my boss.

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Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 07-03-2002 04:40 AM

German, where is the sprocket?

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 07-03-2002 08:52 AM

Check out the new Kodak "Quickermittent" design, that slightly modifies the 4-slot starwheel and cam to produce a faster pulldown (56 degrees cam rotation instead of 90 degrees), greatly increasing efficiency of illumination:

"Design Improvements for Motion Picture Film Projectors"
C.L.DuMont, A.F.Kurtz, B.D.Silverstein, D.H.Kirkpatrick
SMPTE Journal, November 2001, pp 785-791.

The paper is also published in the June 2002 issue of BKSTS Cinema Technology (Volume 15, Number 2).

Prototype starwheels and cams were retrofitted into Century, Simplex and Christie intermittents.

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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: +1 585 477 5325 Cell: +1 585 781 4036 Fax: +1 585 722 7243
e-mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

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