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Topic: Synchronizing 2 projectors

Warren Smyth
Expert Film Handler

Posts: 158
From: Auckland ,New Zealand
Registered: Aug 2003

posted 09-05-2016 11:22 PM

If you are serious about using 35mm which is an expensive medium, then selsyn motors are an option. They must be coupled for accurate sync with sprocketed belts to the drive pulleys on the projectors. Keep in mind that these are not drive motors but simply hold sync when electrically coupled to other selsyn motors of the same type.

I was involved in running a three strip presentation in a theatre in the early nineteen seventies. We had three 35mm projectors plus a separate mag sound reproducer to reproduce multi channel sound. All equipment was fitted with selsyns with sprocketed timing belts locking the mechanisms, induction drive motors and selsyns together.

It all worked beautifully with frame accuracy without any problems during hundreds of screenings. We noticed that the drive motors heated after a few minutes probably because they were hunting slightly against the selsyns so we switched the selsyns off after the equipment was up to speed. The induction drive motors and constant line frequency did their job and held everything in sync perfectly.

For anyone who is interested in the production, there is an account in an interview with the executive producer.

http://www.in70mm.com/news/2009/new_zealand/index.htm
Alternatively an internet search of 3 strip This is New Zealand with my name should find it

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