Film-Tech Forum ARCHIVE: Pre Alpha Potts Platter Motor?

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Posted by Steve Wilson (Member # 2411) on 05-12-2007, 04:18 PM:

I have, what I guess is the original Potts platter motors about 1983 models. I have 3 questions.

I aquired a couple of used back up motors and both of them have a very loud whining bearing type motor sound, the ones that I now have on my platter are near silent! Does this mean these motors are on the way out or how long will they typically last.

I also have a new motor to rebuild these units with Grainger 2M262.. I have noticed that some platter motors have a resistor across both ends of the switch and some do not. With the newer motors 2M262, do I or Do I not need these resestors across the switch.

And my third question. Does the Grainger 2M262 rebuild the orginal Potts motors as well as the newer Potts motors. Any problems with the newer motors being 2 stage motors.

Thanks

Steve Wilson
Holiday Drive In Theater

Posted by Monte L Fullmer (Member # 2797) on 05-12-2007, 06:14 PM:

Since I'm the one that threw the rebuild concept in the "tips" section on this topic, I'll help this one along some - in all of the 2M262 replacements that I've done (in as well as having a good stock of 1R236 brushes from Grainger in stock as well..), I've just maintained that when doing the motor switchout, you keep the same wiring configuration. (and you'll have to take off that front stage of that motor to make this all fit in..)

1- Bearing noise. Take your pick either disassembling the motor to clean and repack the bearings, pull them off and press on new ones, or just do a simple motor replacment.

2- I'd keep the same wiring configuration on the motor that you're having problems with.
You need the resistors to slow down the current rush so when the motor is switched between rewind and makeup/payout to keep the payout and rewind at a more stable rate since these motors are such high-torque motors....(Why you don't need the resistors on the MUT..it doesn't need that reduction where you need all the torque that motor can muster).

3- ON that question, I'm not sure, for the earliest one that I've done a 2M262 on was a BALCO platter - pre ALPHA platter..and it still worked okey.. Only way to find out is to actually disassemble one and see if the AMETEK/LAMB frame matches up with the one that youre disassembling and take it from there.

Later on, the diode was used to cut the current in half to reduce that payout torque with the Alpha platters came on board. Now, there's just that big 200w resistor mounted inthe tower to handle all of this for the AP-3 units.

Posted by Mark Gulbrandsen (Member # 72) on 05-12-2007, 08:25 PM:

The cheapest route is to get a new armature from either Graingers or a local Vacuum cleaner shop. The whole armature is about $16.00 list, brushes add another $8.00 and bearings add about 8 bucks to that. So for 32 buckaroos you get what amounts to a new motor. Be sure to run in the new brushes to seat them properly or the motor won't be able to develope full torque for quite a while...

Mark
Mark

Posted by Steve Guttag (Member # 268) on 05-12-2007, 09:32 PM:

Monte, you misunderstand the purpose of the resistor. It is there on the TAKE UP setting only. This will cause the elevator to go lower in order to compensate for the current restriction (higher voltage). Since the payout side will just have the variac voltage without the resistor it gives the payout circuit a speed advantage to prevent the system from wrapping, if all platters were timed using a common source (take up is most common but one could use the MUT as well. The motors and in particular the drive system is not what one would consider high-torque as compared say a Christie AW3 or a Xetron system (particularly the XNR system...they later added a series resistor to take the edge off the torque).

Steve

Posted by Dave Macaulay (Member # 813) on 05-12-2007, 10:23 PM:

Take the back cover off and check the commutator condition. If it's reasonably flat then new Grainger 1R236 brushes and bearings (R6ZZ?) will make it almost new again. If it's gnarly then someone probably let the brushes wear down to nothing which rapidly eats away the metal. That is a bad motor.
The commutator end bearing is a bugger to pull off, you can grind the jaws of a cheapo small 2-jaw puller to get a thin enough tooth to get under it though. You can leave the old bearings on the rotor and wash out the old grease then repack it if it feels smooth once you get the old goo out, if it's damaged then a new one is needed.
I've heard that the new 2M262 motors from Grainger are different from the old ones, everything is the same size and parts are interchangeable but the torque is different enough to cause trouble. I haven't had problems yet though.
I don't know about the resistor, I thought all the older platters with 3 pins used in the motor plugs have a resistor in the payout circuit.

Posted by Tristan Lane (Member # 1169) on 05-13-2007, 12:21 AM:

Dave,

You're correct on the newer 2M262 motors being a bit different on torque. This isn't much of an issue with DMC or SCDC platters, but can cause major timing issues on AP3 and alpha/potts style platters.

If I had to do a retrofit on an alpha or AP3, I would change all three motors at once. Then I would be left with two good motors that I'd clean up and use for the next repairs. For future reference it's easy to determine which motors are replaced due to the motor housing not being painted.

Posted by Monte L Fullmer (Member # 2797) on 05-13-2007, 12:41 AM:

Thx Steve to guide me in the right direction on this topic on the resistor usage - will remember this from now on.

Tristian (thx for your clearing up the torque issue with the new 2M262 motors) In this torque difference, what did AMETEK do to cause this-change the amount of wraps in the field to the change or something else?

But, it's good to know that if a changout in using the 2M262 motor, one must change out the other two to get things to balance again.

On the same topic, a small theatre in Boise did buy a new motor from STRONG ($$$$) and they are having the same problem - rewind is okey, but the payout is sluggish..and the motor sleeve is the large 1/2" variety...Thus, STRONG got these same motors as well for their customers.

--Monte

Posted by Mark Gulbrandsen (Member # 72) on 05-13-2007, 09:51 AM:

Guys: You're are all lost in platter motor land! If you were on one of those reality shows called "Platter Island" you'd all be booted off! Please read the following.....

quote: Dave Macaulay
I've heard that the new 2M262 motors from Grainger are different from the old ones, everything is the same size and parts are interchangeable but the torque is different enough to cause trouble. I haven't had problems yet though.

The new motors are lower torque and this was delt with in a tech bulletin from Strong a while back but they've removed it from their site... along with alot of other useful tech bullitens. There may be a need to change the diameter of the screw on sleeve in order to get the new motors to time properly with the old motors. If memory serves me there are now three sizes of screw on drive sleeves!! The sleeves are available from Strong. I've had to do this with both new motors and rebuilt motors so I am pretty sure the change is in the armature. If anyone needs armatures, brushes, bearings, or different diameter sleeves we stock them all by the gazoodles.

I reccomend the use of rubber sealed bearings in rebuilding all platter motors. This helps keep the carbon dust out of the bearing and usually results in much longer bearing/motor life.

quote: Dave Macaulay
you can grind the jaws of a cheapo small 2-jaw puller to get a thin enough tooth to get under it though.

There is a tool available that called a bearing seperator that goes right in under that commutator side bearing and works in conjunction with a normal gear puller. This is the prefered way to remove a bearing when tight clearance is involved. There are different sizes of them for different size bearings. I also use a large one to pull the lower drive gear from the DP-70 verticle Shaft.
Bearing Seperator

quote: Tristan Lane
If I had to do a retrofit on an alpha or AP3, I would change all three motors at once.

No need to change all three motors.... just change the drive sleeve diameter that unscrews from the armature shaft to bring timming in range. They work perfectly then.

I've been through this ******* torque problem so many times I can't tell you! A simple change of the sleeve fixed every one of them.

quote: Steve Guttag
(particularly the XNR system...they later added a series resistor to take the edge off the torque).

Steve,
Have you had any of those resistors melt the vitrious coating right off of them? I've seen quite a few do that... that takes some huge amount of heat to do. The new board version 198 or what ever it is I'm told is supposed to take care of thet problem.

Mark

Posted by Steve Guttag (Member # 268) on 05-13-2007, 11:38 AM:

On the bearing separator...it is the preferred way of removing a bearing, always...it holds the bearing in the right spot...be careful to adjust it properly or you will be also cutting into the shaft you are trying to get the bearing off of.

As to the resistor...Oddly enough...I re-engineered it without realizing Xetron had done the change. We had a site that after the poly thing happened started throwing prints that were over 2-hours towards the end of the show...the problem was...the platter would jerk on/off on payout as the anular ring of film was nearing near end...it just deformed and moved.

I ended up putting in a resistor to de-torque the motor (sized based on load...so no excessive heat) and also used TWO adjustable rings on the payout side so as to be able to set the payout so it had a "barely faster than take up" and a "somewhat faster than take-up" speed. Somewhere I made notes on how to calibrate it if someone came in after me. They never threw another print.

SPECO really got this sort of speed thing right on their platter (LP270). The payout has three speeds. OFF, Relative to Take UP, Full-speed. The platter deck is heavy and acts like a flywheel. As such, after start up it is pretty stable (it is a bit too slow on start up but once it catches up, it is stable for the rest of the show and never needs retiming unless abused or the payout module has some failure).

I think Mark is right on the number of shafts now...it is somewhere around 3. Then there is the diode in/out thing so one can get motors similar but their torque curves seem different anyway...you will get the speeds similar for some point during hte show but the will not necessarily match at another part. It is one reason I still use the Take Up Elevator to calibrate two decks to each other...I want them loaded similarly.

Steve

Posted by Mark Gulbrandsen (Member # 72) on 05-13-2007, 11:54 AM:

I;m not sure what causes the resistors to melt down on the older drive boards... if its the motor or some failure on the board that causes it. I think they areon the 5th version of that drive board for the Neutronic platter. The latest version was engineered by Noel Makisoc(sorry if I spelled it wrong Noel!) and it too had problems at first but now seems to work just fine. It still has the big WW resistor on it.

Mark

Posted by Steve Guttag (Member # 268) on 05-13-2007, 10:34 PM:

I was referring to the XNR platter, not the Neutronic...the XNR used raw components...no PCBs. It also used two microswitches on the centerfeed. A bearing pushed one off or the other one on.

Posted by Tristan Lane (Member # 1169) on 05-13-2007, 10:53 PM:

Mark,

I'm well aware of the tech bulletin from Strong in regards to the shaft sleeves. But in the platters that I've replaced with the grainger motors, I've always ended up with the new motors being much slower than the other two existing motors on the platter tree. The different diameter sleeves still did not increase startup torque to a level that would provide reliable timing between platters.

Perhaps I misread the bulletin.

I believe that there is an electrical difference between the motors that strong uses, and the motors sold by Grainger. Who knows.... maybe I missed something. But If I missed it, so did many other techs in the field who encountered the same problem. I'd be interested in seeing the bulletin you are referring to. I've questioned a couple of strong representatives about this, and they admitted that the motors were different. They also encouraged me to purchase the motors directly from them...

Posted by Monte L Fullmer (Member # 2797) on 05-14-2007, 02:53 AM:

Yes Mark, I also know of the need to switch to the 1/2" sleeve from the 5/16" sleeve when doing the motor changeout, for I've ordered a good bunch of those larger sleeves, but somehow doing this with these new motors just doesn't do the help much even with the larger sleeves - still on the slow side and wraps on payout.

(Why I made that comment above of a $tock motor from STRONG that has that larger sleeve installed, still was on the slow side for payout for this one small cinema in our area...)

Posted by Mark Gulbrandsen (Member # 72) on 05-14-2007, 08:13 AM:

I have not had the problem both of you mention... and on well over 50 motor rebuilds. You might consider putting smaller sleeves on both the other older motors to slow em down. We probably do 150+ of those motor rebuilds a year!!

We only use a new Grainger motor if the windings are shot... Instead of using the Grainger motor all the time you may want to consider just rebuilding them yourself, it is about half the price and you end up with better bearings.

Mark

Posted by Dave Macaulay (Member # 813) on 05-14-2007, 01:14 PM:

I know about bearing separators. I just don't think it's cost effective, I haven't found a cheap "oriental" one and $50.00 to be gentle on a bearing I'm throwing away doesn't make sense to me. Grinding the jaws of a $5.00 puller works just fine!

Posted by Tristan Lane (Member # 1169) on 05-14-2007, 07:06 PM:

Cheap and crappy bearing separator

If you can't find a cheap tool at harbor freight, I'd be suprised if you'd find it anywhere else.

Their screw drivers are the ultimate in crappyness, right along the lines of "task force" tools.