This is topic Bringing a motor up to speed in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.


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Posted by Cody Martin (Member # 2523) on 02-11-2005, 03:49 PM:
 
Hey,

I've been experimenting with my projector today. I got the reel arms set finally and they look good. I put some film on...threading up the 6000' reels and ran her. SNAP...right at the first roller. I tried a few times...always snap. It's not losing the loop or anything...it's like the motor is starting to fast. Is there an easy way to start a motor slower and work it up? Possibly a dimmer switch?

Thanks,
Cody
 

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Posted by Brad Miller (Member # 2) on 02-11-2005, 04:09 PM:
 
This is a major pain in the ass with reel to reel on anything larger than 2000' shipping reels.

First, you can use floating hub 6K reels with a 5 inch or larger hub. Often this is enough to solve the problem. Be warned, the clutch tension is very critical for this to work smoothly.

Next you can put a resistor inline with the motor's AC feed (or put one on the start winding).

Finally, I ended up using the resistor as well as making a tension arm to prevent the film from slacking during startup in my screening room. (Taking up on 24" split reels w/4 inch core.)

In an ideal world the projector motor would be 3 phase an on an inverter. Then you could set your ramp-up speed to whatever you desired.
 

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Posted by Dan Lyons (Member # 1454) on 02-11-2005, 05:55 PM:
 
I hope you're using junk film for all your testing and setup purposes.
You need to get everything set and running properly with 2ks, and get your scratch testing done before you even consider running a 6k.

What kind of equipment are you running?

You need a spring scale like this for setting the takeup. here
Get the Red one.
For a 6k reel, 14 Newtons on a 5" hub is good and won't cause any perf damage.

For the feed arm, you can set it much lower, below 8N.

If you set the tension properly, and run with floating hubs on your 6k reels, you shouldn't have a problem.
 

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Posted by Stephen Furley (Member # 1277) on 02-11-2005, 06:19 PM:
 
make sure you take up any slack film between the spools and the projector before pressing the start button. Havng the back tension on the feed spool set too low can also cause problems. Are you getting slack flm, which is then snatching? Most projectors can start 6k spools ok, large tower spools can be a problem though.

What projector are you using? I've run 6ks on 1950s Westar, recent Century, and various Philips/Kinotons, going back to early '60s
 

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Posted by Scott Norwood (Member # 30) on 02-11-2005, 06:37 PM:
 
If at all possible, try to get reels with 7" hubs. The 5" hubs are fine for 2000' reels, but I have a strong preference for 7" floating hubs when running 6000' reels. The 5" hubs are fine for feeding, but are less-than-ideal for use as takeups. If you can't get large-hub reels, put a few hundred feet of junk film around the hub of each reel and tape it there permanently (you may want to mark the edge of the reel so you can tell where the junk film begins in order to avoid missing changeovers).

You can set the tension without the spring scale, using old, brittle, junky trailers on acetate base stock. Basically, you want to use the largest reel you have and set the tension so that the film takes up evenly without breaking at startup or tearing perfs. With a 6000' reel, you won't get perfectly even tension throughout the reel (unless you have motor-driven takeups), but you want to make sure that the film winds fairly tightly out to the edge. If it winds loosely, the film will cinch when you rewind it. Be sure to test with 2000' reels (with both 4" and 5" hubs to make sure that you can take up easily onto those sizes, too. The whole process is a bit of trial and error and is far more critical when running the larger reels.

If you don't already have some junk film, you can order "picture sound fill" from an editing supply house (e.g. Christy's Editorial in Burbank, CA). This can usually be purchased quite cheaply.
 

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Posted by Gordon McLeod (Member # 33) on 02-11-2005, 07:12 PM:
 
Depending on the soundhead wire a 2 ohm 250watt resistor in serries with teh motor to slow down th start up
 

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Posted by Thomas King (Member # 2745) on 02-11-2005, 07:54 PM:
 
With some projectors, you can configure certain parameters like ramp-up speed. Our Vic5 ramps up very slowly.
 

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Posted by Gordon McLeod (Member # 33) on 02-11-2005, 10:21 PM:
 
most projectors running with 3 phase motors now run on invertors that allow programabel ramps not an option on older single phase motors
 

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Posted by Stan Gunn (Member # 554) on 02-11-2005, 10:40 PM:
 
Another way is to have a fly wheel fitted to the moter as in simplex and rca.

Regards
Stan.
 

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Posted by Monte L Fullmer (Member # 2797) on 02-12-2005, 02:24 AM:
 
True, this is where Simplex has it over with the slow ramp speed, esp when using the old SH-1000 soundheads when using 6k reels, with the absoluted needed floating hubs for takeup.

When doing this, just make sure that the tension is completely taught from lower holdback sprocket to reel when starting. Then when hitting the run switch, a practice that I did was to have my finger in the hole of the hub of the reel to make certain of the required taught, then when the motor took off, my finger would be assisting the rotation of the reel, thus preventing the inital slack that can happen when motor takes off and the takup belt and clutch having their delayed action before getting up to speed.

I had to do this many-a-times with MotioGraphs AA's with Mirrophonic 7400's soundheads - and we know how the Motiograph took off with their snap starts.

-Monte
 

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Posted by Cody Martin (Member # 2523) on 02-12-2005, 06:52 AM:
 
Hi,

The projector I'm using is a motiograph AA with sh-7500. I'll check about the hubs of the reels today. I may end up doing the resisor thing. I'll go back and do some more testing today. I've got her running with 2000 footers..but the 6000' are a killer.

Thanks again,
Cody
 

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Posted by Gordon McLeod (Member # 33) on 02-12-2005, 10:49 AM:
 
I have 1.5 ohm in serries with my motiographs to control them
 

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Posted by Monte L Fullmer (Member # 2797) on 02-12-2005, 02:16 PM:
 

quote: Cody Martin

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I've got her running with 2000 footers..but the 6000' are a killer.

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..worked at a Drive-In with this Motiograph setup using the 6k reels - just assisted the takeup reel to keep from busting the acetate on startup.

Never could figure out why Motiograph never put a big enough flywheel on the motor to have a more easier ramp speed.

Yep, Gord's got a pretty nifty MotioGraph setup at his house - see it in the picture's forum.

-Monte
 

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Posted by Frank Angel (Member # 248) on 02-15-2005, 11:15 PM:
 
I could never figure out why Kelmar just doesn't steal the spring loaded tension roller as is found on every plater system and incorporate it into their take-up arms. It's passive, it's simple and it would solve the problem quite elegantly.
 

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Posted by Brad Miller (Member # 2) on 02-16-2005, 01:46 AM:
 
Because that's not just a spring loaded roller. That arm (or elevator) is what is directlycontrolling the speed of the takeup. There is no "clutch" of sorts on a platter, hence why it has such precise takeup ability without varying tensions unlike running reel to reel with a conventional clutch.

(You've never ran a platter, have you? )
 

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Posted by Monte L Fullmer (Member # 2797) on 02-16-2005, 02:06 AM:
 
CHR AW3(r)'s with that rewind roller arm (which is spring loaded) makes a good accumuator roller for interlock systems when your tying two AW3's together for one print usage.

You just turn off that deck when using that arm for such.

Be nice if the Strong's "W", "yo-yo", etc. DID have some resistance to that assembly so when mistarts happen, that this device racing up doesn't bust up the leader before one has a chance to stop the "rewind" platter, especially with the platter situated at the "gear side" of the projector.

quote: Brad Miller

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unlike running reel to reel with a conventional clutch

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