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» Film-Tech Forum ARCHIVE   » Operations   » Film Handlers' Forum   » Basic question about interlocking (Page 1)

 
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Author Topic: Basic question about interlocking
David Stambaugh
Film God

Posts: 4021
From: Eugene, Oregon
Registered: Jan 2002

- posted 08-07-2002 09:24 PM      Profile for David Stambaugh   Author's Homepage   Email David Stambaugh   Send New Private Message       Edit/Delete Post 
One thing I've never really understood is how 2 or more interlocked projectors can pull film through at basically EXACTLY the same rate. I understand synchronous motors. But with gears, pulleys, and belts, how can you know for sure that one projector isn't running slightly faster or slower than the other? I realize there's an accumulator loop, but doesn't that only allow for a couple feet of "error"? If you're running a 10,000 foot movie interlocked, and one projector ends up pulling 2 more feet of film through it than the other projector over the film's running time (compensated for by the accumulator), that's only 0.02% difference in speed (if my calculation is right). Is the answer as simple as something like adjustable motor speed controls so you can get them exactly the same? Or is the 24fps speed really that precise across different projectors?


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Steve Kraus
Film God

Posts: 4094
From: Chicago, IL, USA
Registered: May 2000

- posted 08-07-2002 09:51 PM      Profile for Steve Kraus     Send New Private Message       Edit/Delete Post 
Yes, the speed really is that precise. Don't forget that we are talking about timing (toothed) belts and gears & shafts. So unless a timing belt jumps a tooth or there is a stripped gear somewhere (both of which would be causing problems quite apart from interlock operation) the speeds will match exactly. The fact that the medium is sprocket driven is important too--one turn of a sprocket advances so much film, regardless of tiny variations caused by shrinkage or expansion. If it were, say, mag tape being driven by a rubber pinch roller you'd have to have a control track with pulses and some sort of a servo feedback loop to control the speed which would be much more difficult. Film makes it so easy.

The accumulator is really just to compensate for varation at startup as the machines come up to speed as there may be a difference from one to another. Once up to speed and locked synchronously to the power line the contents of the accumulator will not change.

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Bobby Henderson
"Ask me about Trajan."

Posts: 10973
From: Lawton, OK, USA
Registered: Apr 2001

- posted 08-07-2002 10:17 PM      Profile for Bobby Henderson   Email Bobby Henderson   Send New Private Message       Edit/Delete Post 
Interlocking is a pretty simple thing. But it is a practice many theaters do not do very often at all. In the 8 1/2 years the Carmike 8 has been in operation here in Lawton, I think they have interlocked films only 3 times (with two occaisions happening just last year). The idea works, but it has to be carefully tested before running a release print through it.

And then you have the added task of burning an extra set of DTS CD-ROMs since only one set comes with a print.

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Michael Schaffer
"Where is the
Boardwalk Hotel?"

Posts: 4143
From: Boston, MA
Registered: Apr 2002

- posted 08-07-2002 10:35 PM      Profile for Michael Schaffer   Author's Homepage   Email Michael Schaffer   Send New Private Message       Edit/Delete Post 
Steve is right. At the prevoius theater I worked for, we interlocked (Kinoton FP30D) all the time, and the machines ran very accurately, with the exception of slightly different startup times. The Pennywise matrix which comes as the standard automation with Kinoton projectors ONLY sends motor start/stop signals over the serial bus with which the projectors (or rather the matrices) have to be connected to make interlocking possible.
Once we had a faulty matrix which failed to send a motor stop signal to the 2nd (master) projector, when the first (slave) stopped playing for no apparent reason, so the master kept pulling the film. The result was an incredible mess and a lot of damage on the two projectors.
Michael

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Brad Miller
Administrator

Posts: 17775
From: Plano, TX (36.2 miles NW of Rockwall)
Registered: May 99

- posted 08-07-2002 10:52 PM      Profile for Brad Miller   Author's Homepage   Email Brad Miller       Edit/Delete Post 
Did someone say interlocking?

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Darryl Spicer
Film God

Posts: 3250
From: Lexington, KY, USA
Registered: Dec 2000

- posted 08-07-2002 11:02 PM      Profile for Darryl Spicer     Send New Private Message       Edit/Delete Post 
>>The accumulator is really just to compensate for varation at startup as the machines come up to speed as there may be a difference from one to another. Once up to speed and locked synchronously to the power line the contents of the accumulator will not change.<<

It is also to maintain tension on falesafes.


There is one problem with it and I encountered it at one of our theaters here. We were trying to interlock four machines. Three machines at this location ran fine but the lead payout machine in the line was feeding the film slightly faster than the other machines. So after a few minutes it would shut down and we would have to rush and shut down the other three. Well, it turns out after a little investigating that the lead payout machine had its motor changed out at some point. THe motor was only like maybe a year old or so. Everything was correct and matched but the newer motor was pulling just a bit faster. So I guess if you are still interlocking and you have to change a motor out on one of those machines. I would switch out a motor from another machine and put the new one on the other machine or invest in two new motors and replace both of them on the interlock machines.


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Barry Martin
Expert Film Handler

Posts: 203
From: Newington, CT USA
Registered: Jul 2002

- posted 08-07-2002 11:14 PM      Profile for Barry Martin   Author's Homepage   Email Barry Martin   Send New Private Message       Edit/Delete Post 
I have never experienced any lost accumulation when running interlocks on the Strong Simplexes at my theater. Interlocks are rare, but we probably do at least 10 days of interlocking a year. Mostly the big releases like Star Wars, Spider-man, and Perfect Storm (big here in MA because of the location). They have all run pretty smoothly, but I have experienced a little delay when starting the projectors if only for a half a second. I just don't like the idea of running film over 100 feet of open booth space and across the hall requiring walking "through" the film in order to get to the other side of the booth.

------------------
"The greatest thing you will ever learn, is just love and be loved in return."

Barry C. Martin
IATSE Local 182

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Darryl Spicer
Film God

Posts: 3250
From: Lexington, KY, USA
Registered: Dec 2000

- posted 08-07-2002 11:19 PM      Profile for Darryl Spicer     Send New Private Message       Edit/Delete Post 
The projectors at that location are simplex 1050's. Since that motor was newer I guess it was just running just slightly faster than the others.


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Steve Kraus
Film God

Posts: 4094
From: Chicago, IL, USA
Registered: May 2000

- posted 08-07-2002 11:53 PM      Profile for Steve Kraus     Send New Private Message       Edit/Delete Post 
New or old shouldn't matter on a sync motor unless it is somehow defective and not locking up. A machine problem creating a greater load than the motor can drive could cause non-sync operation but in your case you're saying it's faster not slower. If the motor was running noticably hotter than normal for its type it may be that the start switch is not disconnecting the start winding. Not sure if that would make it go faster but I suppose it's possible. I presume it wasn't so blatant like a 50 Hz motor being run on 60 Hz. Sure that they are all sync motors?


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Darryl Spicer
Film God

Posts: 3250
From: Lexington, KY, USA
Registered: Dec 2000

- posted 08-08-2002 12:54 AM      Profile for Darryl Spicer     Send New Private Message       Edit/Delete Post 
Actually, this projector was the first projector in the series that was being fed first. The motor on it was newer so that would mean that it was running correctly. The other three projectors have older motors probably 10 years old. Now they could be slowing down just a tad. Yes they are all the correct motors.

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Gracia L. Babbidge
Jedi Master Film Handler

Posts: 709
From: Bowdoin, Maine
Registered: Aug 2000

- posted 08-08-2002 01:54 AM      Profile for Gracia L. Babbidge   Author's Homepage   Email Gracia L. Babbidge   Send New Private Message       Edit/Delete Post 
I've not had any serious troubles with my interlock setup. The machines in my interlock setup face in opposite directions (thus are almost back-to-back), one is a Christie P35C, the other is a Century JJ2, its quite an interesting rig to watch in action.

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Alex Grasic
Film Handler

Posts: 90
From: Toronto, ON, Canada
Registered: Jul 2002

- posted 08-08-2002 02:57 AM      Profile for Alex Grasic   Email Alex Grasic   Send New Private Message       Edit/Delete Post 
I work at a fairly new theatre (only open for 8 months) and there has not been any setup made for any interlocks. Despite this, I'm always intriguied in the operation of an interlock and because of this, I want to try it at some point in the VERY near future. I have the capability of EASILY interlocking 9 although interlocking all 18 would be really an interesting experience!!

What would be the simplest course of action that I would have to start with to setup my booth for interlocks (even if it's just two machines). The easiest two I could see it happening with would be my #3 and #7 projectors which are almost back to back and have the payout and rewind on the same side as the opposite projector (if that makes sense to you...or would a diagram help more??...I knew it's crude but better than nothing)

Any advice would be appreciated!!


|----------|
| || proj #3 |
|----------|

/----\
/plater\
\ /
\----/ /----\
/plater\
\ /
\----/

|----------|
| proj #7 | ||
|----------|

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Frank Angel
Film God

Posts: 5305
From: Brooklyn NY USA
Registered: Dec 1999

- posted 08-08-2002 03:06 AM      Profile for Frank Angel   Author's Homepage   Email Frank Angel   Send New Private Message       Edit/Delete Post 
All the interlocks I have seen in operation (someone else's operation, not mine, thank you) have been with synchronous motors. They actually interlocked 4 projectors together -- Gracia said it is an interesting rig to watch -- I thought it was downright scary! But my question is about selsyn motors. I know you can use them to interlock two projectors, but is there any way to get them to interlock more than two like you can with synchronous motors? Can you buss the control voltage across more than two motors?

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Brad Miller
Administrator

Posts: 17775
From: Plano, TX (36.2 miles NW of Rockwall)
Registered: May 99

- posted 08-08-2002 03:20 AM      Profile for Brad Miller   Author's Homepage   Email Brad Miller       Edit/Delete Post 
Frank,

Scary, eh? May I direct you to the "videos" page of this website. Once you're there, you will find what you are looking for.


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Peter Kerchinsky
Master Film Handler

Posts: 326
From: Seattle, WA, USA
Registered: Jan 2002

- posted 08-08-2002 04:53 AM      Profile for Peter Kerchinsky   Email Peter Kerchinsky   Send New Private Message       Edit/Delete Post 
What about 3-panel Cinerama.
The "interlock", which I assume were sylsen motors were not only tied in with 3 projectors, but also the sound dubber.
It's been a while since I've seen it, but it works.
I've run interlock in two Seattle theatres and have never had a problem with it.
With all the prints they're producing these days and the fact bookers want to scatter showtimes, interlock may be a thing of the past.


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