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Topic: Speed Problem on Elmo St-1200
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Steve Klare
Film Guy
Posts: 7016
From: Long Island, NY, USA
Registered: Jun 2003
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posted October 23, 2010 06:00 AM
I'm not saying that the addditional drag of the flywheel would be huge, just a little bit more, and maybe just enough to push the thing over the edge.
Basically this machine depends on friction, and I'm thinking of the friction between the rollers and shutter wheel in particular. There are two kinds of friction: static and kinetic. Static is when you step on your brakes and the tires are still rolling on the pavement. Kinetic is when you panic and step too hard on the pedal and go into a skid. This is bad because kinetic is always less frictional force than static and you won't stop as fast (-there is the steering thing too, but that's beside the point here.)
The idea was that Adam may be putting his ST-1200 into a "skid" going forward and that last bit of drag that pushed him over the edge could be the extra drag of starting the flywheel going from a dead stop.
-So now the roller is slipping on the shutter wheel and the machine is slow because of it.
I've noticed the problem more after a switch from 18 to 24 FPS so maybe Dino is right an the roller isn't seating consistently and it takes a couple of seconds in reverse to wedge it in place. I've noticed some slop in the rocker mechanism, so maybe it's not certain how much pressure there is between the roller and the shutter wheel.
It could be a combination of his idea and my idea.
Roy, I don't understand what a camtank is. Please explain: waterproof teflon grease is ready when you are! Once again: every last bit of drag may count.
I'm looking forward to literally getting mine "up to speed": these are great machines and there 's a lot I can do with it once it's right.
[ October 23, 2010, 07:05 AM: Message edited by: Steve Klare ]
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All I ask is a wide screen and a projector to light her by...
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Roy Neil
Expert Film Handler
Posts: 203
From: Menlo Park, CA
Registered: Sep 2007
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posted March 30, 2011 03:56 PM
Sorry for not seeing this more soonerererer ...
The camtank is the thingy that houses the cam, which the arm rides and which causes the pulldown claw to move down, in, up, and out - hows that for a technical description ? ![[Smile]](smile.gif)
Remove the back of the projector, look at where the shutter attaches in the center. The shutter is attached to the cam, it is what causes the cam to turn. If you get a flashlight and look in there, you can probably make out a piece of foam rubber jammed in there which is meant to act as a 'lubricant reservoir'. Typically these are bone dry, and I use some teflon based grease ( just a tad ! ) to re-lubricate the cam, and any excess is sucked up into the foam rubber so now it has a little in the 'reservoir'.
To properly work on this area of the projector it really needs to be removed ... which is not trivial. I started to type steps and I realized its too complicated to type out here.
The slow down on these projectors can come from too much tension on the shutter wheel. The rubber wheels are designed to 'just touch' the shutter, not bear down against it with great force - too much force and it causes the mechanism to bind and slow down.
I have one machine that is kind of like my own personal pet project, it has been a huge restoration effort and still is not 100% - although - it works well enough for me to use and as such has become my primary machine of late. I noticed that until the machine is 'warmed-up' the film will run slowly, even though everything is in top condition. After it runs for about 2~5 minutes, there is no speed problem - until the machine is powered down for more than 2 hours, at which time it reappears. Since the problem only exists for 2~5 minutes it makes diagnosing the issue very difficult, as you must now wait 2 hours to re-examine, or, test a solution. After a year ... I have finally determined that it is the motor itself. I would warm up the machine by putting it in forward for 2~5 minutes, however, I have learned that only the motor needs to be activated, not the mechanics. I was under the impression that the mechanics itself were 'stiff' however it appears the motor itself will not achieve full torque until warmed up.
The take-up mechanism is another source for temporary speed problems. This is designed to 'slip' and if there is too much friction it can cause the machine to 'bog' until the clutch slips more freely. Do not put lubricant on the cork pad in the clutch ! it needs to be dry - if anything use a very small amount of teflon powder, do not use grease or oil !
Sorry for the lengthy and hasty post, Im short on time but I wanted to post a reply
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