Atlas Motor Problem

[mmagliaro]

Just sent you a new PM with my address.

[davefoxx]

The motors are en route to @peteski and @mmagliaro.  You're looking at Friday deliveries.  Good luck, guys!

Thanks,
DFF

[peteski]

Oh goodie - another fun project is in the mail!   

[peteski]

Motor received in the mail today. Opened the package and took the motor to my workshop. Had it evaluated and fixed in about 30 seconds.  I'm not trying to brag here but since I just recently fixed 2 Atlas motors with a similar problem, my experience contributed to the quick fix.

So what I did?  I spun the armature (well, the flywheel) with my fingers and confirmed that it was really bound up and fairly difficult to turn. Not seized but stiff enough to cause serious problem.  Next, I pulled and pushed on the flywheel while holding the motor in my other hand. I was checking for front/aft play in the motor shaft.  There was none. The armature should have some play in it to spin freely, but in this motor it had no play at all.

Armed with my knowledge from fixing similar problem in the past I suspected that one of the bearings shifted inwards binding against the armature.  So I took a pair of cutters with thin jaws and inserted them between the motor frame and the flywheel. Then gently (but with some authority) I used them as a lever to push on the flywheel.  I heard a snap and the armature was now spinning freely.  It now had the expected amount of front/aft play.  I also dropped some oil in both bearings and the motor is now ready to be put back into action.

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The bottom line is that for some reason the bearing seems to shift inwards in some of these Atlas motors causing bind in the armature.  I don't really have an explanation.  But the motor is now fixed and I'll be mailing it back to Dave next week.  It is always good to have a spare. 

EDIT: I want to mention that the reason I used a pair of cutters as a lever (instead of let's say a screwdriver) is to exert even pressure on the flywheel from both sides, not to accidentally bend the motor shaft. I also made sure that the pressure points were in-line with the motor shaft.

While this was an obvious mechanical binding problem I did not take any voltage.current measurements before attempting the fix.
After repair, here are the measurements of the motor without a load:
Starting voltage is 1.7V and 32mA
At 12V the current consumption is 76mA
After the motor was running for several seconds it will keep on running at 1.27V (the lowest my power supply will go down to) and consume 30mA.

[davefoxx]

@peteski,

Thank you!  I'd love to know what causes that problem.  The good news is that I think that even I could manage that repair! 

I'll gladly pay for the return shipping.  Let me know if you use PayPal or want me to mail you a check.

DFF

[peteski]

@peteski,

Thank you!  I'd love to know what causes that problem.  The good news is that I think that even I could manage that repair! 

I'll gladly pay for the return shipping.  Let me know if you use PayPal or want me to mail you a check.

DFF

Yes, if you run into a similar problem (armature is binding with no front-to-aft play) then you should be able to pop the bearing out like I did.  As far as to why - I really don't have an answer.

Can you shed some light as to the history of the motor you set me?  Was it behaving normally for a while and then it developed the problem? Or was it a new (to you) loco which had the problem since the get-go?  The other 2 motors I had with this problem were new-old-stock Atlas locos bought from BLW.  So they came from the factory with the problem.  In that case the motor was not correctly assembled at the factory and probably never tested before being shipped.

Taking the motor apart and examining how the bearing is installed in the plastic holder might (or might not) shed some light on how the problem can occur, but is that really worth destroying a motor?

I do use Paypal and we can work the details out via a PM when I ship the motor back to you.

[Kisatchie]

Motor received in the mail today. Opened the package and took the motor to my workshop. Had it evaluated and fixed in about 30 seconds....

Hmm... it's a miracle!!!

[davefoxx]

That motor came out of a GP38 that I had for a long time.  It originally had no problem.  In fact, it was the pride of my C&O fleet and even made the trip to Lee's layout seven or eight years ago:



That said, it has been sidelined for several years, because I switched modeling eras and locale and built a new layout.  I don't know that if that has anything to do with it, although those NOS locomotives you bought from BLW also had significant shelf time.

DFF

[peteski]

So in both instances the models have been sitting idle for a while. Maybe the plastic in which the brass bearing insert sits swells with time (possibly from the lubricating oil used at the factory) and the bearing slides inwards eliminating the needed play?

[mmagliaro]

My test subject also arrived today.  This one ran, you will recall, but to slowly. 
What I saw on the bench was that it didn't draw excessive current, and it seemed to run at a full 12v without
getting hot (about 80 mA spinning free, which seems perfectly reasonable for this motor).

But I noticed that the speed consistency was lousy.  It would speed up and slow down, and at start-up, it usually wouldn't start until I got it up to about 7v, which is pretty awful.  These ought to start at around 3.5-4 v or even less.

I have fully disassembled the motor (flywheels pressed off, case apart, armature out, and it's obvious what the problem is.  The commutator slots are all completely filled up with carbon.   And I mean filled, all the way across the length of the slot, and all the way to the top.  I will clean them out, put it back together, and report back.

Photos will follow later.

How many miles did this motor have on it?  Usually this kind of commutator clogging results from lots of age or driving the motor too hard.

[davefoxx]

I don't know, Max.  It's been out of its donor for a long time, so I can't verify what locomotive it even came out of, meaning I am uncertain of its life.  I will say that it's likely that it has a lot of hours on it.  A concern that has occurred to me is that I widen the backspacing of most wheelsets in my fleet to allow them to run through Atlas Code 55 turnouts smoothly. As we all know, many locomotives come from the factory with their wheel backspacing too narrow.  I'm wondering if this could have put too much stress on the motor.  While the trucks are not exactly free rolling when this is done, they're certainly not bound up.  But, is this too much for a small motor to handle over years of running?  I don't know.

Thanks,
DFF

[peteski]

Even if the low friction trucks are a bit tighter (due to the wheel gauge adjustment), like you say, they still will roll fairly freely. They still roll much more free than for example stock Arnold or Bachmann trucks with wheel-back electrical pickups and inside-bearings.  I don't think that your modifications would cause appreciable load on the motor. I think a long train being pulled by the loco would be more of a factor as far as motor wear is concerned.

I also updated my post with some electrical measurements (to compare my motor to Max's).

[mmagliaro]

Well, after cleaning the comm slots and putting it back together, this motor does not start and run at anywhere near the low voltages Peteski is getting.  They are so different that I'm seriously wondering if they are really identical motors.  It starts at about 5v.  After it starts, it will run down to about 3v.

I have 3-4 other gray-case scale-speed motors here, all brand new, and they behave about the same as this one.

What follows are photos of what I did.  Now that it's back together, it does 14,800 rpm at 12v.   I foolishly did not measure it before I took it apart, so I don't know if it's faster.

It runs consistently now, no more up and down in the speed and no more sputtering,
so I don't think there's any more I can do with it.  Dave, I'll mail it back to you and you can see if performs any better for you in an engine.








Okay, I'm not gonna lie.  I am posting this one just so you can see that I really did get that basket of parts back together into a working motor!  LOL.

[peteski]

Max,
Does your motor's shaft have enough play forward/aft? It does look just like the one I have (including the numbered poles and blue stuff for balancing the armature.  Actually I was surprised how smooth mine runs and at such low voltage. It is better than Kato's equivalent motors. But I think the smoothness is due to the skew armature in the Atlas motors.

Too bad yours still isn't apart - I would have been interested in how the bearings are mounted in the motor's body.

[mmagliaro]

Max,
Does your motor's shaft have enough play forward/aft? It does look just like the one I have (including the numbered poles and blue stuff for balancing the armature.  Actually I was surprised how smooth mine runs and at such low voltage. It is better than Kato's equivalent motors. But I think the smoothness is due to the skew armature in the Atlas motors.

Too bad yours still isn't apart - I would have been interested in how the bearings are mounted in the motor's body.

The armature does not feel tight and there is definitely some play fore and aft to it, not at all like it's bound.
I have other Atlas skew wound motors here, and none of them can get moving at a voltage that low.  Starting up around 4.5 or higher is the way they all are.   That Walthers 3-pole 0-8-0 switcher motor is one that can really start up from a standstill under 2v.  Very nice.