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Author Topic: Christe 50Hz Projector Running too fast Eric J. Cantrell Film Handler Posts: 3 From: North Hollywood, CA, United States Registered: Jun 2004 posted 07-02-2004 07:12 PM                     I have a Christie GPS35 projector with a 220v 50Hz motor running the film for a ride-film attraction in Aqaba, Jordan, but the projector does not run the film through at a true 24 frames per second. In fact, we are running about 0.75% too fast. For regular cinema applications where the sound is coming from the optical track of the film, this is not a big problem, but we are running our sound off of a digital hard disk recorder, which is synchronized to timecode that is printed in the optical sound track. Because of this unusual situation, we have a bit of a "drift" between the visuals and the audio. This becomes quite annoying when the people on screen appear to talk but the audio doesn't happen until a few seconds later. The single phase synchronous motor locks to the frequency of the power, but our power's frequency has a tendancy to fluctuate lower and higher than 50hz. Does anyone have any idea how I can slow the projector down and stabilize it to a true 24 frames per second?  |  IP: Logged Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 07-02-2004 07:36 PM                  Eric, welcome to Film-Tech. I'm a bit confused at what seems to be contradictory statements in your post. quote: Eric J. Cantrell ...we are running our sound off of a digital hard disk recorder, which is synchronized to timecode that is printed in the optical sound track. If it is really synchronized, it would NOT drift unless the speed variance was outside the capture ratio and tracking ability of the synchronizer. The 0.75% increase you mention should be well within any system and should be able to track OK. I would make sure the system was really designed as you say and verify that it is working properly. From what you say, it sounds like it is not. quote: Eric J. Cantrell The single phase synchronous motor locks to the frequency of the power, but our power's frequency has a tendancy to fluctuate lower and higher than 50hz. Since it's a sync motor, the projector speed is following the line frequency and thus the projector speed will vary as the line frequency varies. I would suggest you power the projector motor from a Variable Frequency AC motor drive. Doing so will provide a stable frequency to the motor independent of what the AC line is doing. >>> Phil  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-02-2004 07:57 PM                     I pretty much agree with Phil. There are several ways to do this and keep it in sync but you may also have to calculate and program a proper offset into your T.C. genny, if you can, in order to allow the projector to reach speed and sound to come up in sync. I think what you are seeing is the difference in projector speed divided by the absolute accuracy of the H.D. player plus the inability of the H.D. player to properly chase the time code(if it even can) which has gone way out of range. You end up being several seconds off, or perhaps as much as 60 to 80 frames. The solid state drive systems that both Baldor and Reliance market are crystal refrenced and are also capable of feedback type correction for even greater accuracy if needed.... they are also very inexpensive for the smallest size 1/4 hp motor you would need to drive a P35. With unpredictable power frequency this is your only inexpensive road to accurate speed. You may also want to look closely at the DTS XD-10 playback system. It is inexpensive to purchase, reliable, and inexpensive to have your digital masters encoded to as many as 8 channels of full range APTX encoded DTS audio. When combined with the latest DTS time code generator its flexibility is unbeatable and then the icing on the cake is the ability to have compression free lossless audio playback if you so desire. But to really take advantage of the lossless playback your master and originals should have been recorded at 24/96!! If you so require we would be happy to assist you in custom mounting a Baldor motor to a P35GP. We have motors, controllers and a P-35GP in stock to do the testing with. We commonly use the Baldors to replace bad motors on Phillips DP-70's as they are less expensive than rebuilding the original motor and offer other benefits that far outweigh the older motors. Mark @ CLACO CLACO Equipment And Service 1212 South State St. Salt Lake City, UT 84111 801-355-1250  |  IP: Logged Eric J. Cantrell Film Handler Posts: 3 From: North Hollywood, CA, United States Registered: Jun 2004 posted 07-02-2004 08:28 PM                     To clarify, Yes, I did say we were synchronizing the sound to the timecode on the film. That is the theory. What we are actually doing now is using the timecode to trigger our show controller (which is listening for a particular timecode frame). When the Show Controller hears the trigger frame, it starts the Hard Disk Recorder playing. I have set up the HD Recorder to play at a varispeed of +0.75% so we are relatively "in sync" though we are freewheeling. The reason we cannot follow and chase the timecode completely is the timecode has blips in it that confuse the HD recorder. When these blips happen and it is chasing the timecode, it will either drop audio and come in again a half second later (if it is in Jam Continuous mode) or will pitch shift to attempt to catch up (if it is in LTC-Chase mode). Either of these "solutions" on the part of the HD recorder make the difference worse. The solution employed at the moment is "working" but I don't feel like it is an ideal solution. The reason we are not using DTS is because we are doing a special spatial surround sound system with 16 discrete channels...and the Producer/Director wants to mix the sound in the auditorium and we don't have time to take it back and have DTS discs made and then get them back to Jordan and test it just for the Director to make a change and do the whole thing over again. You mentioned a Motor Speed Drive. Try to find one for single phase. Good luck. The only one I found was an "Industry first" called the "Eagle Drive." I bought one. It blew up. The Eagle Drive is not meant for capacitor-start motors and cannot handle the switching over from the start windings to the run windings. I came up with a solution that involved time delay relays that allow the motor to run to get up inertia, thus switching over to the run windings, then changing the power source to the Eagle Drive. With this idea in place, I bought another Eagle Drive. The system worked for two weeks and blew up. Now the supplier will not sell me another one because I have proven twice that it will not work. I think we'll just have to live with it being a little fast and the cuts not being exactly where we intended them, but rather a few frames off. The varispeed option has made it possible to keep the mouths and voices relatively close together. If you have any more suggestions, I am willing to give them a try (provided I haven't already tried it ). Thanks for the quick replys. Eric J. Cantrell  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-02-2004 09:28 PM                     Actually if your player could chase the T.C. it would probably hold sync just fine. Your setup definately won't be able to hold sync for very long. However, a DTS player would generally work fine in this situation with just your 50 hz motor. Baldor makes a 1/4 hp three phase motor and single phase 120/240 volt solid state drive which runs about 500 bucks for the pair. The Baldor stuff is pretty indestructable and it has overcurrent sensing on each phase that shuts it down if the current drawn per phase exceeds a user preset amount. If you blew one up I'd be amazed . Thats about as cheap a solution you'll probably find. Reliance also makes a single phase unit but I think the smallest they make is around 1/2 hp. Another route I've used for exact speed and syncing to video subtitles is a crystal oscillator driving a 500 watt 2 ohm capable power amp in turn driving the motor. This is also a very reliable method but is only as good as the 50 hz oscillator is stable. Its also alot bulkier method than the Baldor solution and really not any less expensive. I would have probably gone the DTS player route at the begginning of the project. DTS likes these sorts of projects and supports them very well. Mark @ CLACO  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 07-03-2004 03:23 PM                     Just to clarify, Mark, when you say, "Baldor makes a 1/4 hp three phase motor and single phase 120/240 volt solid state drive," you mean a drive with single-phase input, not single-phase output. Right? --jhawk  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 07-03-2004 09:05 PM                     Well if the projector isn't running at speed the pitch will be off Best method is to use a shaftencoder and drive the player direc tly off it the Akai DigiDubbers will do that nicely  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-03-2004 09:42 PM                     The original statement..... "Baldor makes a 1/4 hp three phase motor and single phase 120/240 volt solid state drive" Yes, Its a three phase motor but there is a 120/240 volt AC single phase input to the solid state drive unit. The drive unit generates the necessary three phase to drive the motor. Mark  |  IP: Logged David Favel Jedi Master Film Handler Posts: 764 From: Ashburton, New Zealand Registered: Feb 2002 posted 07-04-2004 05:24 AM                     If the film is running at 25 fps the sound will be at most a semi tone out, most people will not notice.  |  IP: Logged Dave Macaulay Film God Posts: 2321 From: Toronto, Canada Registered: Apr 2001 posted 07-04-2004 08:43 AM                     From your explanation I would say you are trying to either make your hardware do something it wasn't made to do, or your timecode is defective. Timecode on film is not commonly used in post production. A shaft encoder on the projector with a timecode converter is the usual way. DTS has a lot of tricks built in to deal with time code weirdness; studio recorders expect and require near-perfect timecode and don't deal well with dropouts or incongruities. Once you get a final mix and commit to a DTS disc you should be fine but until then you will have plenty of problems with your setup as I picture it from your description. A frequency drive will give you speed stability but you won't find one for the standard motor - a 3-phase motor and frequency drive is the easiest way to get stable speed from an unstable power source.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-04-2004 10:28 AM                     Dave, While I prefer the vari speed drive systems he could also use a high power 2 ohm capable power amp driven by a TCXO time base with sine wave output divided down to 50 hz to directly drive the existing motor. I've done this with 29.97 derived from black burst to drive a sync motor in post once. It works very reliably. However I doubt there is any cost savings over the frequency drive. My case was a sudden need to sync at 29.97 for a front projection TV commercial shoot. Mark @ CLACO  |  IP: Logged Eric J. Cantrell Film Handler Posts: 3 From: North Hollywood, CA, United States Registered: Jun 2004 posted 07-04-2004 01:49 PM                     Okay, tell me more about the shaft encoder that converts to timecode. Maybe that's a more viable option.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-04-2004 03:35 PM                     Actually thats alot more expensive "fix" than the frequency drive motor system! A decent wemm made optical shaft encoder will run you at least the price of the entire frequency drive system alone, $500.00. At additional cost you will need to adapt the shaft encoder to the P35 with a mounting plate, proper pulley reduction and belt. Then you need a time code generator that will generate T.C. from a shaft encoder. Not all T.C. gennys can do that. Figure about 1K for a decent genny that can. Now, back to the drive motor system....... Mark @ CLACO  |  IP: Logged Richard Fowler Film God Posts: 2392 From: Ft. Lauderdale, FL, USA Registered: Jun 2001 posted 07-04-2004 03:53 PM                     Look at the optical encoder kit supplied by JSK Engineering. Pricey but becoming more common for interlock and control use of hard drives and other components. Mounts easily on the projector using a DTS type of bracket. www.jskengineering.com  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 07-04-2004 04:10 PM                     Many of the digidubbers such as the akai that is gaining a lot of popularity in many post houses will directly accept the biphase of a shaftencoder  |  IP: Logged

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