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This topic comprises 3 pages: 1 2 3
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Author
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Topic: Running 3-D without selsyn motors
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Jeff Joseph
Expert Film Handler
![](http://www.film-tech.com/ubbmembers/511.jpg)
Posts: 131
From: Palmdale, CA, USA
Registered: Jun 2000
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posted 04-15-2004 08:33 PM
I'm now running 3-D without selsyn motors... and it works great! I'm posting this so that others know there is a way to do this... and to see if I'm missing something and doing something wrong.
We have 2 V-4's; been running 3-D with selsyn motors, no problem. One motor burned out. Replaced it. Turned out the new motor was faster than the old motor, so had to replace both motors. Now I have 2 new synchronous motors. But we're running them non-synchronous and using the selsyns, no problem.
But now I notice that we're running a little fast, so we switch the motors to synchronous and add some speed controllers. Tweek the controllers so I'm running 24fps... and now I can't use the selsyns. Why? Both speed controllers have to be exactly the same speed... and they're not. Even if both displays say, for example, 57.8, one might be 57.81 and the other one might be 57.82. No way to make them perfectly the same. So the selsyns have to work way too hard and they heat up.
So I call Chapin at Boston Light and Sound. He suggests we run both projectors off one controller (after making sure the controller can indeed handle the current of 2 motors). We install a relay/switch, so when running 2-D, each projector works off one controller. We switch to 3-D, now both projectors work off one controller.
We still have a start switch that turns on both projectors at the exact same moment. So: We set the phase at the same point on both projectors. Then push "start".... both projectors start to run... they stay in sync as they are both seeing the same exact frequency.
And, of course, this would work even if we were not using a speed controller. Both projectors would see the 60 Hz and stay in sync that way.
So: It works. I've run a feature film in double system interlock and it stayed in perfect sync. But it just feels wrong somehow not having the selsyns on.
Am I missing something?
Thanks,
Jeff
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Jeff Joseph
Expert Film Handler
![](http://www.film-tech.com/ubbmembers/511.jpg)
Posts: 131
From: Palmdale, CA, USA
Registered: Jun 2000
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posted 04-16-2004 12:29 AM
So most theatres have sync motors nowadays, correct?
At least in those theatres (and that have 2 projectors and can run 6000' loads...and have a silver screen)... all you need to set up for 3-D is a switch to start both projectors at the same time....no need to install selsyns...maybe a few more theatres will set up for double system 3-D.... well, one can hope.
Just as an FYI, as far as I know, there are only 5 theatres in the entire USA currently set up for interlock 3-D:
Castro, San Francisco Music Box, Chicago Film Forum, NYC Lafayette, Suffern NY Charles Theatre, Baltimore
Jeff
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