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Author Topic: Projector speed issues Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 02-08-2004 05:32 PM                     Most good machines Were equipped with Synchronus motors right from the factory. Almost all new machines are also equipped this way today. The use of a digital tachometer(not very expensive either)is a good way to ascertain that your projector speed is correct. Mark @ CLACO  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 02-08-2004 05:53 PM                     Mark the Vic 4 would be about 40 years old now at the newest as I beleive it was around 64 that they quit making them at that time no northamerican manufacturer was selling theatrical machines with sync motor except for studio/preview room aplications  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 02-08-2004 06:05 PM                       10-Roger that, Mark. Since Bevan has been desigining new equipment, I just figured...  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 02-08-2004 08:20 PM                     The Century JJ has always come equipped standard with a sync motor as has the DP-70 and DP-75. All Vic 8's that I have seen also had sync motors but most of them were imported with 3 phase. Sync was also an option on any Century back then and many around Chicago had that option. Mark  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 02-08-2004 08:45 PM                     Bzzzzt....I deal with a pair of DP-75s that most certainly run nowhere near 24fps eventhough they are for the USA market. They have Async motors...start up way too fast and run rather briskly. These machines are circa 1992. I'll check at the Uptown but I think those motors are Async and they are JJs with the double poly-V pullies (24 and 30 fps). Sync motors for American machines didn't become normal until the the mid '80s. Interlocking I'm sure is what drove it too. A word of caution for those with 3-phase motors and controllers...they are not always accurate either. We recently ran across a Reliance controller that displayed the wrong frequency. We used a strobe to confirm the correct frequency and added in a scaling factor. Even with that, we were able to have the controller read out in fps with 3 sig. figs. Steve  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 02-08-2004 10:46 PM                     Steve, I have only seen FP-20's with async motors..that was common on them. Even the FP-16's out here are all sync. I recently overhauled a motor in one of them. The projectors at the Uptown are not actual JJ's they are Converted 3 strip Cinerama heads, only somewhat similar to a JJ. That is most likely why they do not have sync motors on them. The original JJ manual we have shows a sync motor as the drive motor with no other motors listed. All the JJ's I've ever encountered in the states were Sync driven and some were timming belt, some were poly V. Agreed on the possibility three phase motors being off speed as Jeff finally discovered on his. A hand held optical tach can be used to check speed while a show is running measuring the pulses of light, or by changing to the generator probe and taking it off a shaft center such as the shutter shaft or intermittent cam shaft. JJ's and DP-70's are usually dead on speed. Mark @ CLACO  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 02-09-2004 05:29 AM                        Assuming that one isn't interested in interlocking, two-strip 3D, dubbers, variable speed, etc., what's the advantage of using a sync motor? How much closer would the speed be to an actual 24fps and would anyone really notice the difference?  |  IP: Logged Dick Vaughan Phenomenal Film Handler Posts: 1032 From: Bradford, West Yorkshire, UK Registered: Jul 2000 posted 02-09-2004 05:46 AM                        Tim said quote: Here's the easiest way. Print this out, and tape it to one of the sprockets (4 and 8 frame sprockets). Look at it under a florescent light, and adjust the speed til the pattern appears stationary... then you're at 24.00 fps (180 or 360 rpm shaft speed, actually). This of course won't work in Europe with our much maligned (by North Americans )50Hz system.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 02-09-2004 07:45 AM                     "How much closer would the speed be to an actual 24fps and would anyone really notice the difference?" No one would probably notice the difference except perhaps someone with musical abilities. They most likeky would notice the pitch being off on a machine without a sync motor. A movie running time with a sync motor is of course as advertised and music is perfectly on pitch and so on. There is generally alot lower wow(the diference is measurable too!) as the speed is very constant through the equipment, not affected by power surges and variations, sync motors are only affected by frequqncy shifts, something that rarely happens today except up north of the border with the Hydro companies. Electrical interlocking has nothing to do with this issue as the selsyn or electronic drive is actually driving the second machine to exactly the speed of the first machine( if its set up properly). On 3D projection the shutters must also open and close at the same time or severe headaches may result. Mark @ CLACO  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 02-09-2004 08:43 AM                     the disadvantages of sync motors is the run much hotter for there give HP. And they require a permenant magnet in the pole peices to prevent slip and as such do have a shorter lifespan  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 02-09-2004 09:25 AM                     Properly designed and loaded sync motors don't run all that much hotter than async counterparts do after 5 or 6 hours of run time. There is no magnet in the pole pieces of either the Master, GE, or the Leeson motor Strong uses today. In fact the Leeson runs VERY cool after hours on screen. Older sync motors like the Bodines, and many European motors run hot enough to bake Mrs. Fields cookies on. The FP-16 sync motor is a good example of a HOT running motor. Mark @ CLACO  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 02-09-2004 10:03 AM                        I CAN print that strobe out, but why would I want to? It's easy to figure out the speed of your projector by timing a known length of film, but THEN what? It's a lot harder figuring out how to change the speed of an errant machine than it is to determine if it is going fast or slow....at least not without spending lots of cash (like installing synchronous motors). But then last time I queried "who could tell if a projector is a little off a fps or two," everyone jumped on it and said lots of people could tell, that the audio would sound very odd. But then, don't they run ALL American films on European TV at 25fps? No one gripes about the audio sounding too fast or that the pitch is off, do they? Anyway, as I said, that strobe printed out fine for me. Great. Just what I need, something else become anal about -- my machines running too fast or to slow. Frank  |  IP: Logged Daryl C. W. O'Shea Film God Posts: 3977 From: Midland Ontario Canada (where Panavision & IMAX lenses come from) Registered: Jun 2002 posted 02-09-2004 12:49 PM                        quote: A movie running time with a sync motor is of course as advertised and music is perfectly on pitch and so on. I've found that's the exception to the rule. Most sync motor I've seen, running on inverters, are still a little fast, albeit at a constant speed. quote: sync motors are only affected by frequency shifts, something that rarely happens today except up north of the border with the Hydro companies. Say what? Surely you must be referring to the folks way up north, running their iglo off of a generator.  |  IP: Logged Adam Martin I'm not even gonna point out the irony. Posts: 3686 From: Dallas, TX Registered: Nov 2000 posted 02-09-2004 01:17 PM                     quote: On 3D projection the shutters must also open and close at the same time or severe headaches may result. The Imax GT projector alternates images on the screen for both polarized and electronic 3D. While the left image is on screen, the right image is behind the flicker shutter and/or goggle shutter and vice versa. Headaches are caused by misaligned images or out-of-sync filmstrips.  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 02-09-2004 01:32 PM                     My, we've come somewhat far afield from the original question. Why we care Frank asks why you'd want to do this ("It's easy to figure out the speed...but THEN what?"). The whole point here is that Jeff has adjustable speed but no calibrated readout to indicate what the real speed is. It's easy for him to vary the speed and he wants to get it as good as he can. That's totally the right thing for him to do. 25fps versus 24fps 25fps is clearly distinguishable from 24fps. It's enough to be annoying, but not enough to be catastrophic. But it unequivocably wrong. 24.1fps isn't in the same boat. It's off by a very small amount, and it is within acceptable tollerances for most people. It's worth distinguishing two cases: whether you can hear the difference if you A/B comparing them, and whether you can hear the difference in an absolute way, if you walk in off the street. 25fps falls in the latter category: the film will sound wrong. 24.1fps, for most people, falls in the former category: you can tell the difference but you probably wouldn't notice on your own. sync vs. async There seems to be confusion about sync motors. The important characteristic of sync motors is that they run at their fixed speed independant of load. But async motors are fine as long as their load is within a particular rated range. So either one ought ot be perfectly satisfactory. And either one only is as good as the input frequency and the gearing. Having a sync motor won't save you if the frequency changes a lot where you are. You'll have problems with both sync and async. I suppose you could probably find a motor controller that you could modify to feed with a good local oscillator (or maybe find some off the shelf), but it's hard to imagine that really being important for anyone. frequency stability of the grid However, it is not true that frequency change only happens in igloo/generator land. While power companies do strive to hit around 60.0 Hz (and probably no more significant figures), that is an average number over the course of a day. Within that time, frequency will drop during heavy load periods and will be artificially increased during low load periods to make up for it. I think you can expect to see variations of +- 0.1Hz within the course of a day in a major metropolitan area. eye patterns Tim is right about the eye patternss, though (for some reason I keep forgetting that option). They're a cool way to address this and I had forgotten about them. They are only as good as your line AC frequency, but that means they should be good to 0.2%, which is 0.05fps. (Can we agree to reserve the term "strobe" for the actual use of a stroboscope and use some other term for the patterns?). I think the best choice might be to produce a PDF file with the eye patterns for popular speeds and sprocket sizes, with one page for 50Hz and one page for 60Hz. It could be in the manuals section. I will summarize If there's any interest, drop me an e-mail with your sprocket sizes, tooth-counts, and rpms, and I will summarize here and produce such a thing. --jhawk [ 02-09-2004, 02:49 PM: Message edited by: John Hawkinson ]  |  IP: Logged

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