Film-Tech Forum ARCHIVE: AP-3 Setup

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Posted by Paul Stevens (Member # 4016) on 12-03-2006, 07:37 PM:

Has anyone ever adjusted the position of there platter motors to achieve a specific torque or applied film tension with the dancer in the center locked position, rather than the speed adjust called for in the manual. This seems more advantages in achieving a uniform film tension from each platter in rewind mode. Further, this allows a more optimum positioning of dancer to provide a bit more electrical power to the platter in playout mode. In effect, this makes the reaction of the playout platter more robust.
[sleep]

Any comments would be welcome.

Paul Stevens

[ 12-04-2006, 01:37 AM: Message edited by: Paul Stevens ]

Posted by Richard May (Member # 2627) on 12-03-2006, 08:31 PM:

I thought the film tension was determined by the weight of the yo yo

Posted by Dave Macaulay (Member # 813) on 12-03-2006, 09:31 PM:

You're not adjusting the tension with the motor position. The motor adjustment allows balancing the differences between supposedly identical motors.
The weight of the dancer unit sets the rewind tension.
The platter's payout deck will get really stupid if you don't match the speeds properly. When the platters are timed to the same approximate speed, the rewind deck will run at some speed slightly slower than the free turning speed (as seen during timing) because of the drag from the film tension. When the payout deck is "behind" and the control asks for full speed, since the payour deck motor is powered from the rewind variac it will run a bit faster (since there's no tension holding it back) than the rewind platter and "catch up".
If you've timed the payout deck to run faster than the rewind deck the payout will oscillate and maybe even throw a print. If the payout deck is timed too slow then it will not be able to "catch up" so it has to brain wrap instead.

Posted by Monte L Fullmer (Member # 2797) on 12-03-2006, 11:53 PM:

yea..basically, one puts a tab of masking tape on the end of each three decks.

Put the dancer in the locked position and tape up the return roller so all three decks are spinning. Find the fastest deck by counting the tape tabs rotation per minute and adjust the other two decks to this fastest deck by either raising or lowering the motors by loosening the motor mount bolts. (ya, kinda sucks doing adjustments this way...)

And,,this is the same procedure on BALCO and earlier Alpha A-3 platters...

..tons easier doing this when using a Christie Platter Tachometer..

Does your AP-3 setup uses microswitches or phase controls on the brains.?

-Monte

Posted by Paul Stevens (Member # 4016) on 12-04-2006, 12:11 PM:

Thanks again for the responses.

I agree that there should be a speed balance between platters, and by the way thanks for correcting me on the word "dancer." What I was really trying to accomplish by slowing all three platters down mechanically slightly, was to cause the dancer to react by lowering itself slightly to compensate. By doing so, the variable buss voltage supplied by the variac will rise incrementally. The added voltage will permit a more robust response from the controller governed platter during playout. The sluggishness I have observed from platters in playout during normal projector operation contrasts sharply with the response observed when the dancer is in the locked position for testing.

What I am suggesting is that over time the speed calibrations performed earlier may have error'ed towards achieving parity at the faster speeds rather than slower over all. In addition, because the intended voltage drop provided by the 2 ohm resister for the speed controller during playout may have inadvertently, by virtue of the higher dancer position, just barely provides enough voltage in playout to keep up. Sorry for the run on sentence.

I acknowledge my ignorance but am I nuts as well?

Paul Stevens [sleep]

Oh yes! The brains use phase controls.

Posted by Monte L Fullmer (Member # 2797) on 12-04-2006, 11:44 PM:

Hmm...Phase Controls... could be your problem with lagging since the LED could be getting on the dim side not allowing the full current to run on payout.

Yes, I love phase controls to death, but all of my 32 STRONG A(P)-3 units are microswitched based.brains and are tons more reliable than dying phase control units..only have to replace microswitches once a year, to almost once every other year..

..and are tons cheaper than the phase control unit that has to be replaced when these things go bad..

Also, failed to ask - do you have just one AP-3 setup, or are you in a complex with more that one STRONG platter setup to compare operations with..?

good luck on this venture.. - Monte

Posted by Paul Stevens (Member # 4016) on 12-10-2006, 12:41 PM:

Well after the great advise from everyone and finding the time to measure some actual data points, I was able to synthesize a fairly useful set of procedures to get AP-3 to behave properly.

Once each variac is cleaned up,(important), brushes and contactors replaced as needed the device can produce fairly linear voltage control with constant current. After a rough mechanical setup as called for in the manual, I locked the elevator, (dancer), in the center position. The following produced outstanding results:

1. Slightly loosen the cap screw holding the control arm and with a digital voltmeter, adjust shaft hub to produce 37 VAC. You can be a several tenths plus or minus, but I selected 37 volts as a uniform set point for all my platter systems. Re-tighten the cap screw making sure to hold the hub and swing arm in place with your opposite thumb and forefinger. Re-check the voltage and tweek as needed. Close up the box.

2. With the elevator (dancer) still in the locked position, I clocked each platter in free run one at a time with a stopwatch, (caster switch closed). I adjusted each platter/motor combination to 40 RPM exactly. Remember as the manual calls for, make sure a loaded platter has time to speed up to overcome its mass before starting your count. If you have an actual tachometer that even better.

That's it! Providing that there are no defective micro switches, sticky rollers or defective brains, it all came together and worked perfectly in each operating mode. Film tension was also gentle but firm on the return path from the projector after threading to standby. No snaps.

Thanks again for all the advice.

Paul Stevens

Posted by Louis Bornwasser (Member # 3063) on 12-11-2006, 08:55 AM:

Paul: thanks for the details. I just adjust the takeup (by means of the variac arm) to very slowly creep when in the bottom dancer hole. I think we are on the same page. Louis

Posted by Mark Gulbrandsen (Member # 72) on 12-11-2006, 10:02 AM:

Interestingly on a call last week I had one deck in which all the rivits that secure the extensions to the center spider had loosened up. I've never seen that happen before. Re-riviting it with 18- 3/16" steel pop rivits took care of the problem but it takes a while to do this.
Mark

Posted by Richard Fowler (Member # 893) on 12-11-2006, 12:26 PM:

I've seen the "loose" rivets on disk problem in theatres where they move the prints by swapping disks with the print [Roll Eyes]