Motor mystery: "crank starting" a Kato motor

[Hedron]

I have the motor from an older N Kato/Atlas U25B (truck mounted Rapidos). I have it out of the chassis.

The armature won't start spinning until you give it flip with a finger (or a little twist of the flywheel), no matter how much or little current you give it. Once you do that, it hums along fine until you cut the current. But, once you cut it, you have to flip it again to get it going again.

As a bare motor, though, it seems to have plenty of speed. When I do have it in the chassis and on the track, and I get it running with the flick, it tends to run slow, which is not expected give these older motors that tended to have an exuberant top speed.

Here's what I have done:

* Thorough rinsing of the innards using QD contact cleaner, then let it dry for several hours. There was some oil in the motor itself.
* Pulled the brushes. They are slightly worn, but look more than long enough to do their job. I cleaned the "cups" to make sure the springs are moving freely.
* While the brushes were pulled, I cleaned the commutator with acetone on a microbrush. The grooves look clear.

So, I'm out of ideas of what to try here. Is it possible that the motor is done for?

[tehachapifan]

Could maybe be a bad motor pole, although my experience is it would be more of an intermittent problem based on the position of the bad pole.

[u18b]

Yep.   Classic description of damaged motor pole.
 

[Hedron]

Now that you say that, I do notice some of the copper winding out of place, just one or two strands that want to stray from the armature stack....

[peteski]

Yes, either open wire in one of the pole wingdings, or the wires from the pole winding disconnected from the commutator segment(s).

I had one just like the later one I described.  You don't  have to flick it to start it - just keep the power applied, then slowly turn the motor shaft. At some point, it will start running (once it goes past the dead spot).  While it is running, the inertial will keep it going past the dead spot.

Here is a closeup photo.


In Kato motors the wires are not soldered to the commutator. The commutator's tab is simply folded over the wire passing through, and crimped tight. That crimp is supposed to pierce through the enamel insulation to electrically connect the wire with the commutator segment.  But in my motor, the crimp was not made tight enough to pierce the enamel.  To fix it, I gently scraped the enamel off the wire at the arrow and soldered it to the commutator segment. That fixed the motor.

[randgust]

The classic definition of a 'burned out motor' is when the windings overheat and actually separate, usually somewhere where you can't see it.

But if you CAN see it, like Peteski says, there's at least some potential to repair it.   And the connection with the commutator plates is the most likely point of failure.

I did this several times with old Rivarossi Yugo motors, figuring they were expendable anyway.

The problem with virtually all Atlas motors has become that it's hit and miss on motor replacement and every new version tweaks 'something' with  non-unique part numbers.

You're already into original vs slow speed.....
Slow speed:  https://shop.atlasrr.com/p-1625-n-u25b-motor-flywheel-assemb-scale-speed.aspx    (note the preorder, I guess that means out)
Original:  https://shop.atlasrr.com/p-3025-n-u25b-motor-assembly.aspx  (that looks promising)
Japan:  (Kato??)  https://shop.atlasrr.com/p-2998-n-u25b-motor-japan.aspx

And classics are not the same motor as the original Kato atlas builds, but might fit.

Knowing that you can still get a Kato motor should give you courage on attempting a fix of what you have.   But as you can see, you're going to have to drive the original flywheels out and then remount them on a new motor, which may be more difficult than reconnecting an armature wire.

Oh, and doing a search on the Atlas website reminded me of why the parts resale guy on Ebay that you all despise has a purpose, actually.   That photo of the "Kato" motor is so poor you can't tell what the devil it is, really, and it's not clearly identified.   I've bought enough wrong parts off the Atlas website already that I've come to realize the value on just properly identifying and photographing parts is worth.

[peteski]

There were 2 versions of Kato GM-5 motor.  The one on the right is the older one, and on the left is the current production motor.

[mmagliaro]

Note, you said "plenty of speed" , but in the loco, it runs slow.
It's impossible to tell with your eye how fast that motor is really spinning on its own.  But with your eye, you're not going to tell the difference between 6000 and 12000 RPM.   I bet with an optical RPM reader,
you'd find that it is spinning much slower than a good motor, because it has a dead armature coil (bad "pole").

If you're lucky, the break is at the tab on the commutator, like Peteski was showing, and you could put a dot of flux there, scrape a little insulation, and hit it with a soldering iron to fix it.  If you are unlucky, there is a break in the wire somewhere else.

Can you post a photo of the actual motor?  I have a stash of Atlas/Kato motors and I might be able to help you out here.  Post the photo and send me a PM.

[Hedron]

I am pretty sure this is the motor labeled "japan" on the Atlas site. The flywheels have nylon cores and can be removed from the axle of the motor easily, which is probably why the flywheels aren't included with the assembly as sold.
Peering in, I can't say any pads on the commutator missing their wires. There seems to be one with a free end loose in that area, but with no empty pad to match. There's another wire, as mentioned above, with a free end between one of the grooves in the stack. I can't get good pictures in there with the iPhone. I'll have to break out my real camera to get better pics, if anyone wants a look.

[mmagliaro]

Just about any modern era Atlas motor that has that classic body shape ( the metal frame with the slightly smaller plastic brush holder end) will work.  (Excluding, of course, things like the motor from Shay, or the Kato FEF etc  I mean all the bead-and-butter diesel motors that look like the one you've got there)

Being that it's the older straight-wound type with the fast armature, I would probably just buy a newer-era Atlas motor and transfer over the brush holders and flywheels.  It will probably work better.

[peteski]

Yes, it is a current-production Kato motor. The easiest and most painless way to fix the problem is to buy a new motor from Kato.  They should have them in stock.

[mmagliaro]

Ironically, this exact problem just cropped up in one of my Rivarossi motor rebuilds I did for somebody.  Ran great,
mailed it out, and they had this exact problem - wouldn't run unless they spun it first.  They mailed it back to me,
I took it apart, and it was obvious there was a broken coil wire near the nose end (opposite the commutator).

[Nato]

    I have a first gen KATO UP E-8 that for several years will not start with out taking the body off and spinning the armature . It then runs nicely , normally and will mate with other units from the same batch even running at a slow speed, however when stopped after use it needs a restart. I have not done anything to these early 8's because I have a lot of newer ones either converted to DCC or factory converted with sound otherwise I would have converted as the UP body on it was super detailed and given the later era paint scheme by myself. Nate Goodman. (Nato). Salt Lake ,Utah.   

[mmagliaro]

Nate:
If the motor really does run the same speed as other similar ones, it sounds like either a dirty commutator
or possibly a stuck or chipped brush.  Either one causes spotty contact between the brushes and commutator,
Once you get it spinning, the brush wiggles around a little to a spot where it makes decent contact on the comm, and
they clean each other off a little as it runs.   But once it stops for a while, you're back to square 1.

Are you able to remove the brushes to check them and the springs, and then clean the commutator slots and surfaces? 
This is should be a first-try fix on any motor that acts like this.

As a related  aside... some of you will recall regular dumps of Atlas/Kato motors that were appearing on eBay (and actually still do)
for only a couple of bucks.  I bought a few batches of them, and several would not start on their own until I cleaned the commutators
with alcohol.  I recall reading another person's account of that same behavior with those motors.  It was almost as if there
was some sort of invisible clear coat on the commutator.  But once I cleaned the comm with alcohol, the motors ran great.

[Maletrain]

Max, Any reason to clean the commutators with alcohol instead of something like an electrical contact cleaner?