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Author Topic: brittle prints break at startup - argh! Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 11-24-2008 12:01 PM                        Let me start by saying that I have an unusual setup for my screening room. It's a changeover setup, with these bases: The takeup mechanism is a standard Kelmar clutch, driven by the soundhead. The takeup path runs under the first black roller and over the top of the big white roller at the back. The projector motors lack the usual flywheels (why?) and also lack start capacitors. They come up to speed rather quickly (I thread at "9"). Normally, all is well, but old, brittle prints sometimes break at startup (fortunately, it has only happened on leaders). The film makes it through the projector and soundhead without difficulty and then breaks after the first (black) takeup roller. No amount of adjusting takeup tension (yes, I have the spring scale thing) seems to help this. I am wondering if there is perhaps some issue with the severe angles in the takeup path. I am using standard fixed-hub 2000' Goldberg reels (5" hub). My current plan is to install start capacitors (standard Century slow-start kits) this weekend and clean the grease off the the takeup belts (one of them tends to slip a bit). Do I need to get inverter drives with programmable ramp-up? Is anyone using an electronic constant-tension takeup system and, if so, is it worth the upgrade? I've never had this issue elsewhere, but, again, my own setup is unusual. I don't damage/tear/stretch perfs with normal acetate or polyester prints.  |  IP: Logged Bob Koch Expert Film Handler Posts: 183 From: williams ca Registered: Nov 2001 posted 11-24-2008 12:41 PM                     Years ago, when economics precluded a proper solution and I was stuck with RCA 1040 soundheads[no flywheel] I used a couple of conical heater elements in series with the ac line[yes you heard right] in order to eliminte that "wrench" at the start. The projector mechanism must be free, no high spots on the intermittent, for this to work as it reduces the torque somewhat.I wouldnt dare do this with the booth personnel used today.Used a 2 ohm 200 watt resistor later on Motiograph 7500`s As this is your screen room in which ,I assume you are the "operator" maybe it would work.  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 11-24-2008 12:50 PM                       Scott, the slow-start kit should help, but I'm guessing that black roller's shaft isn't precisely perpendicular to the pedestal frame, so one side of the film is getting tugged on harder than the other. Can you just go straight down to the takeup reel, and bypass those rollers entirely, when running composite prints?  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 11-24-2008 01:44 PM                     Wow. This brings back memories when running a full Motiograph booth! We know that the Mirrorphonic 7400 soundheads were chain driven and the motor had no flywheel to allow ramp up speed, thus the unit would take off suddenly. With the film wrapped around the takeup reel, if you didn't have things snug an tight, you'd snap the film in a heartbeat when the machine would take off. Thus, it was common practice, when we would hit the motor switch, is to have our hand holding that takeup reel to keep the film tight, to actually spin the reel as the motor took off. This prevented any film breakage from sudden the sudden takeoff that the Mirrorphonic heads were known for. Thus Scott - get your finger on the takeup reel when you hit the motor switch .. to keep the film tight on the reel as you turn it when the projector takes off - which looks like you got a Century setup there, which ramps up pretty quick in itself. If you had a good ol SH-1000 (4 star) head, you wouldn't be sending this note... -Monte  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 11-24-2008 01:45 PM                     Scott, It looks like a Century soundhead there. FIRST get the flywheels...it will help with both starts and stops...not to mention, smooth out the whole operation. On the start capacitor....do you have Async or Sync motors? If they are Async...then a suitable high-wattage resistor (about 40-Ohm, as I recall) will really knock the kick out of the start up and allow it to run nice. However, if you have sync motors...I'm much more in favor of actually switching out to inverter controlled. You can get inverters that are of decent quality for just a couple of hundred and you can set the ramp ups/downs anyway you want. You also get a variable speed machine when you are done too. Steve  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 11-24-2008 03:28 PM                        Thanks, all. These are async Westinghouse motors, 1725 RPM. Soundheads are Century MTR3-67 (same as MR-3). I'm going to order the flywheels and install the slow-start kits and see what happens. If anyone has any more ideas, let me know.  |  IP: Logged Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 11-24-2008 04:00 PM                  Scott, (If I were you...(and I'm NOT!) HA! ) I would invest in 3-phase motors and variable freq drive controllers for your home projectors. (Ask Steve for recommendations...he's helped me alot to get on the right track!) I bet by the time you get done futzing with all the flywheels and slo-starts and the associated crap, there will not be much $ difference. In the long run, it's well worth it for the gentle film handling of the controlled ramps and accuracy of that system!  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 11-24-2008 04:27 PM                     Plus with motor drives if the movie is boring you can run them faster  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 11-24-2008 05:08 PM                     I think Andy Margolin made those as custom bases many years ago.. his bases were typically teamed up with Century machines. Mark  |  IP: Logged Jack Ondracek Film God Posts: 2348 From: Port Orchard, WA, USA Registered: Oct 2002 posted 11-24-2008 05:18 PM                        Scott, the film looks slack as it goes onto the reel. Is that the way it is when you start the projector, or did you just thread that up for the picture? In the Motiograph booths I ran, we usually had little trouble, as long as we manually turned the spindle key clockwise to snug up that slack after threading.  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 11-24-2008 07:39 PM                     Scott, definitely go the route of 3 phase motors with inverters. You will be extremely happy you did down the road as they are well worth it. I also added a dancer arm to my setup, but that is because I am often getting a 24" split reel with a 4" core up to speed on takeup. The arm takes out any bounce and can be made out of just about anything with a spring.  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 11-24-2008 08:58 PM                        3-phase motors would require having 3-phase power, correct? If so, that idea is out. I do like the idea of having variable speed but, as a practical matter, it would not be all that useful. I'm more concerned about print condition, since I regularly run old film, some of which has been stored poorly and has dried out. Jack--the picture is old and was probably taken before I inched the film forward. It isn't normally that way.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 11-24-2008 09:00 PM                     Just be careful WHICH variable drive motors you use... some I've tested (8 brands so far), particuluarly Baldors and Reliance, suffer from bad speed drift. The speed drift is also induced by the load you are driving as things like temperature and other factors cause the load itself to change. You will not get closed loop speed performance unless you spend some pretty big bucks but you can get adaquate performance by selecting the right drive and motor. My favorite motors so far are the Mitsubishi brushless motor series... Mitsubishi Brushless DC Servo expensive but worth it! A 2KW motor is about equivelent to a 1/4hp AC motor. Mark  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 11-24-2008 09:58 PM                     I have done many cinemecanica and prevost installs with 3 phase motors running on either the Baldor or the Gavasi inverters from single phase with zero issues An Assync motor will hunt for speed depending on all the variables Mark mentioned even worse for single phase soft start I always put a 2ohm 200 watt resistor in line with them to rob them of some starting torque  |  IP: Logged Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 11-25-2008 01:26 AM                  quote: Scott Norwood 3-phase motors would require having 3-phase power, correct? Using an inverter will allow the 120vac single-phase supply power to be converted to 208/230 volt 3-phase for the motor.  |  IP: Logged

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