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Author Topic: brittle prints break at startup - argh! Robert Minichino Master Film Handler Posts: 350 From: Haskell, NJ, USA Registered: Dec 2005 posted 11-25-2008 08:32 AM                        Mark, Hitachi has an encoder feedback module for their SJ300 VFD. That should give better speed regulation than a sync motor without feedback and be significantly cheaper than a DC servo system.  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 11-25-2008 11:17 AM                        How do you do changeovers with a long ramp-up speed?  |  IP: Logged Robert Minichino Master Film Handler Posts: 350 From: Haskell, NJ, USA Registered: Dec 2005 posted 11-25-2008 12:30 PM                        You just thread up later (lower number) on the leader on the incoming projector. The longer ramp times also tend to be more predictable, so you can make your changeovers more repeatable.  |  IP: Logged Tony Bandiera Jr Film God Posts: 3067 From: Moreland Idaho Registered: Apr 2004 posted 11-25-2008 02:40 PM                     Robert's right...the ramp times are very predictable and make for easy changeovers. I have a relatively short ramp time on my machines at UC Irvine, and I thread up 12 frames past "8" on the Academy leader..my changeovers will hit the first or second frame of the incoming reel. quote: Phil Hill Using an inverter will allow the 120vac single-phase supply power to be converted to 208/230 volt 3-phase for the motor. Yep, the coot's absolutely correct. Many brands of inverters will accept 120vac single phase and give you the three phase out. I have used ABB and Woods E-Trac inverters with no speed regulation issues. I have also used Danfoss, a quality inverter but very touchy on setup (I call 'em Damn-Fussy). Another thing to remember when dealing with inverters, regardless of brand: READ the manual throughly!! And be sure to set the "PWM Frequency" (the basic frequency of the output, most are set at 4,000 or 8,000 from the factory) to the setting that produces the least amount of whine and noise.  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 11-25-2008 07:09 PM                        quote: Robert Minichino You just thread up later (lower number) on the leader on the incoming projector. You mean later -- on a higher number, no?  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 11-25-2008 07:49 PM                       Lower number, Frank. The projector is taking longer to come up to speed.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 11-25-2008 09:33 PM                     I tend to target 2.75-3.00 second ramp ups. Most operators are comfortable with them and you don't have flutter issues with the sound on changeover. I've been happy with both TB Woods and Lenze inverters. I've also had very good luck and perfect speed (checked with strobe) on Bodine Inverter rated motors. I've used other brands of inverters and other motors and have had less than accurate results...normally being the inverter's fault...it said 60Hz but as it turns out (verified on an O'scope) it wasn't. For most industrial applications...the speed variance isn't significant...for film, in my opinion, there is the correct speed and the rest is incorrect. It affects not only motion but the pitch of the sound (and over 2-hours, the actual running time).  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 11-26-2008 04:22 AM                     I'll have to look at the ramp-up time on my inverters in my screening room, as I specifically did a number of tests to find out just how slow I could have it start without sacrificing a drop from SRD to analog at the changeovers. I do not recall what that number was off the top of my head though.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 11-26-2008 07:06 AM                     Brad, I seem to recall you telling me that 5-seconds was the ramp up time that just barely made it, sound wise. Steve  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 11-26-2008 09:18 AM                     I set up our Baldor and Gavazzi invertors on the vic8's and vic 5's as a 4 sec up ramp and 2 sec down ramp  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 11-26-2008 11:05 AM                     On ramp downs (and I normally ramp down, not coast)...I tend towards 5 seconds or so from 24fps.  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 09-30-2009 09:29 PM                        Bump. As an update, I finally got around to installing the flywheels (which involved rerouting the takeup belts) and they made a world of difference in smoothing out the startup of the machines. Everything is now as gentle as can be, with no "bounce" in the takeup at all. The slow-start kits are next weekend's project, but I am now questioning whether they are necessary at this point. Three-phase motors with inverters would have been nice, but also would have been cost-prohibitive, especially since I don't absolutely need variable-speed operation.  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 10-02-2009 03:28 AM                        I taken it you were having snapping problems with you older acetate prints, yes? Perhaps adding a length of poly leader right at the start of the count down so that the initial tug will be on poly and not the acetate would be the poor man's solution, although it sounds like the flywheel addition pretty much solved your problem fairly well. Nice to hear that you had a successful outcome without too much headache....love when that happens!  |  IP: Logged Robert Throop Master Film Handler Posts: 412 From: Vernon, NY USA Registered: Jun 99 posted 10-02-2009 01:00 PM                     quote: Monte L Fullmer We know that the Mirrorphonic 7400 soundheads were chain driven . Monte, I think you mean the Motiograph SH 7500 soundheads. The Erpi TA7400 was an entirely different beast. These were also called Mirrophonic. Bob  |  IP: Logged Bruce Hansen Jedi Master Film Handler Posts: 847 From: Stone Mountain, GA, USA Registered: Dec 1999 posted 10-02-2009 07:27 PM                     Would using a plastic reel for take-up help it keep up, since it would be lighter? Could you put a spring on one of the rollers?  |  IP: Logged

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