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Author Topic: Running 3-D without selsyn motors Jeff Joseph Expert Film Handler Posts: 131 From: Palmdale, CA, USA Registered: Jun 2000 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  |  IP: Logged Floyd Justin Newton Jedi Master Film Handler Posts: 559 From: Phoenix, Arizona, USA Registered: Jun 2002 posted 04-15-2004 08:56 PM                     Jeff-- What are you missing? You're doing something correctly. Why worry? It's working! fjn Local 294 Ret.  |  IP: Logged Richard Fowler Film God Posts: 2392 From: Ft. Lauderdale, FL, USA Registered: Jun 2001 posted 04-15-2004 08:57 PM                     No, not missing anything. Selsyn control can be brutal at start up with normal motors, less so with sync motors in their effort to lock in. You have identical sync motors on machines with the same load factors and film passage so the motor "slippage" should be nil under the crystal frequency control of the invertor control....with a normal sync motor with four poles it should have 5 reference points to phase to per film frame.....dissimilar machines would probably be another story.  |  IP: Logged Andrew Lee Film Handler Posts: 99 From: Oakville, Ontario, Canada Registered: Jun 2002 posted 04-15-2004 11:29 PM                     Jeff, I know that feeling your talking about. Just run with it for the time being. Take a close look at the credits at the very end of your presentation. If they jive.....you're on the way.  |  IP: Logged Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 04-16-2004 12:16 AM                    Eh...a really big timing belt..er...make that a roller chain between machines. SH-1000's would be great for this. 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. Perhaps. But I'd wager there would be a greater chance that the two motors would come up to synchronous speed slightly differently. Remember you'd be throwing them suddenly on 60Hz and they'd not be in sync at first, just trying really hard to get there. With an inverter drive ramping them up from zero they are under full control from the moment you hit start and never given a brief moment to do their own thing.  |  IP: Logged Jeff Joseph Expert Film Handler Posts: 131 From: Palmdale, CA, USA Registered: Jun 2000 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  |  IP: Logged Pete Naples Phenomenal Film Handler Posts: 1565 From: Dunfermline, Scotland Registered: Feb 2001 posted 04-16-2004 02:52 AM                     How well does it work, as surely your two projectors are raked and toe'd in to achieve alignment? I've installed 2 projector 3D system in the past, these were custom built Balantyne Pro35's with micrometer adjustable lens mounts, which means that the optical centres of both machines were pointing flat and perpendicular to the sheet, the picture alignment being achieve by shifting the lens off axis. Hence nop keystone distortion and hence the 3D works very very well. Those mechs also have stepper motor drive, via Strongs SV automation, synch'd to SMPTE timcode. The accuracy of synchronisation over a days of showing the same film 4 times and hour is truly astonishing.  |  IP: Logged Bill Carter Expert Film Handler Posts: 162 From: Minneapolis, Minnesota Registered: Sep 1999 posted 04-16-2004 04:17 AM                     Add the Oak Street Cinema in Minneapolis to your list of interlock and silver screen equipped theaters. They've run the new dual prints of both Kiss Me Kate and House of Wax within the last year or so.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 04-16-2004 07:38 AM                     Jeff, Steve is correct...just having sync motors is not sufficient for reliable 3-D operation...the absolutely need to be controlled by the same controller, not hit with a 60Hz line frequency and hope the motor and loading are exact enough to bring them up to speed frame-for-frame. Are your sync motors 3-phase? That is how the motor controller can really ramp both up at the same time. It is true that once up to speed, ordinary sync motors driven off of the same line frequency will run turn-for-turn. Anyone that has done interlock know this...they also know that upon start up, film accumulators move a little bit too. As to your 2-strip 3-D list... The AFI Theatre at the Kennedy Center in Washington DC is capable and has run many performances. They use the selsyn method. The AFI/Silver theatre in Silver Spring, MD is a bit more impressive in its ability...in the Historic theatre, they have four projectors. Each pair of projectors can run together and each pair can changeover to the other. The only thing they lack is the silver screen. So they are 3-D ready but not completely done. The National Archives II in Greenbelt, MD has two systems that are also 3-D capable. The systems were set up for side-by-side viewing of two different prints of the same title but they too are only a silver screen away from 3-D capability. Steve  |  IP: Logged Carl Martin Phenomenal Film Handler Posts: 1424 From: Oakland, CA, USA Registered: Feb 2002 posted 04-16-2004 08:02 AM                        the castro theater replaced their silver screen (with non-silver) to get more even illumination, so they're not quite there anymore. a few years ago the stanford theater in palo alto was showing 3-d. don't know if they're still capable. quote: The AFI/Silver theatre in Silver Spring, MD ... The only thing they lack is the silver screen. too tired to think of punchline. carl  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 04-16-2004 08:14 AM                        Steve--could Williamsburg do 3D now, assuming that they put in a silver screen? I would hope that at least the Kinotons in the screening room would be capable.  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 04-16-2004 08:45 AM                        Doesn't optimal 3D viewing also require that the two shutters be in phase also? --- i.e., that they open and close at exactly the same time.  |  IP: Logged Mitchell Dvoskin Phenomenal Film Handler Posts: 1869 From: West Milford, NJ, USA Registered: Jan 2001 posted 04-16-2004 10:58 AM                     Yes, both shutters must be in phase. This is usually done by spinning the motor by hand on each projector prior to threading.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 04-16-2004 12:19 PM                     At the AFI - Kennedy Center we have marked the motor flywheels in quadrents to allow for the shutters to also be in sync with each other. As to Williamsburg, no...they are not 3-D capable. The screen isn't a Silver (heck they are only using 700-watts as it is) and the projectors do not have the necessary 3-D interlock electronics to allow them to track with one another. Steve  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 04-16-2004 12:55 PM                     The best method is to use a servo controled motor on each projector with a shaftencoder telling the drive its position and the shutters will stay in sync A sync motor by itself can be hit and miss due to sync speed is reached after the run up and that will vary depending on the load of the machine Also your VIc4's would like a slow ramp up to full speed to protect the gear train and without servo interlock a slow start would through the sync off  |  IP: Logged

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