Problem with Motor in Intermountain F unit.

[skytop35]

I noticed one of my F units in a 4 unit set was running significantly slower in one direction vs the reverse direction. The top speed is extremely slow in forward, it's better in reverse but still slower than my other F's in the set. Exhausting all decoder and drive-train problems, I pulled the motor and applied a 9 volt battery and got the same results. I guess I need to replace the motor. I probably need to contact Intermountain to see about buying a replacement. Just wondering if anyone has experienced this and had another solution or used another motor (Kato or Atlas) as a replacement?

[narrowminded]

I assume you tried oiling the bearings.  If not, give it a try.  

This is some background to that suggestion that may be useful to some.  While it is entirely possible that the motor is shot it may just be the bearing has caked debris in it that acts like a wedge in one direction.  I've experienced this doing extensive testing on coreless motors in my small power chassis.  In fact, with proper max voltage and appropriate gearing, therefore comfortably within the motor's rated amp draw, pulse power or straight DC, it has surfaced as the most likely source of a motor problem.  In these conditions the brushes last thousands of hours while the shaft bushings may require oiling in several hundred hours.  That's still about 3 weeks straight, 24 hours a day, and at any speed from full to just creeping.  I was expecting brushes to be the weakest link but that hasn't proven to be so and actually, much to my surprise.

I'm suspicious it's not just wear or external debris finding its way into them but maybe the porosity of sintered bronze bearings holding some extremely fine debris from the manufacturing process.  The oil impregnation step performed on less than clean parts and/ or with dirty oil.  Of course, it could also just be debris from wear and perfectly normal but I'm not convinced of that yet with such low bearing loads.  I'm trying to chase down a couple of theories but it's hard to prove each test and extremely time consuming performing them.  The service life in the tests performed is comfortably in the window of acceptable but I still want it to be the best it can be.  Still putzing with that.

[skytop35]

I assume you tried oiling the bearings.  If not, give it a try.  

This is some background to that suggestion that may be useful to some.  While it is entirely possible that the motor is shot it may just be the bearing has caked debris in it that acts like a wedge in one direction.  I've experienced this doing extensive testing on coreless motors in my small power chassis.  In fact, with proper max voltage and appropriate gearing, therefore comfortably within the motor's rated amp draw, pulse power or straight DC, it has surfaced as the most likely source of a motor problem.  In these conditions the brushes last thousands of hours while the shaft bushings may require oiling in several hundred hours.  That's still about 3 weeks straight, 24 hours a day, and at any speed from full to just creeping.  I was expecting brushes to be the weakest link but that hasn't proven to be so and actually, much to my surprise.

I'm suspicious it's not just wear or external debris finding its way into them but maybe the porosity of sintered bronze bearings holding some extremely fine debris from the manufacturing process.  The oil impregnation step performed on less than clean parts and/ or with dirty oil.  Of course, it could also just be debris from wear and perfectly normal but I'm not convinced of that yet with such low bearing loads.  I'm trying to chase down a couple of theories but it's hard to prove each test and extremely time consuming performing them.  The service life in the tests performed is comfortably in the window of acceptable but I still want it to be the best it can be.  Still putzing with that.

I did notice some debris around the bearings but did not have time to clean and oil before I had to leave for work this morning. Will do that tonight and report back.

[mmagliaro]

Once you've done that...
Measure the current draw and look at the commutator slots.  If they have loaded up with carbon, the motor will slow
down, run hotter, and draw more current.

[peteski]

Once you've done that...
Measure the current draw and look at the commutator slots.  If they have loaded up with carbon, the motor will slow
down, run hotter, and draw more current.

But only in one direction?  That should affect it equally in both direction. I am leaning more towards a mechanical problem/bind.  The trucks have fore/aft play in them. The bind might be in the area of the worm area.

[peteski]

But only in one direction?  That should affect it equally in both direction. I am leaning more towards a mechanical problem/bind.  The trucks have fore/aft play in them. The bind might be in the area of the worm area.

Can't edit posts!  Dammit!
Since bill has more than one model, he can for example start swapping parts between a good model and this one. For example put on "good" trucks and see how it runs. If no fix, istall the original trucks and just swap worms., The motor would be next and last.  At that point we should have a handle on what is the problem.

[Doug G.]

He said he already pulled the motor and got the same results, though. I'm assuming he means the motor, itself, goes slower in one direction than the other. Also, it doesn't appear to go in either direction normally. I would check the commutator/slots/brushes, too. Remove the brushes and see if they're OK. Springs, too.

Doug

[Doug G.]

Another possibility, of course, is a broken winding or desoldered/broken commutator connection at the commutator. If it's a five poler and only one winding is open, it will still usually start on its own every time but will run slower. If more than one winding is open, the motor will usually not start on its own every time and will run very poorly.

Doug

[skytop35]

Yes, I took the motor completely out of the unit to test it. No decoder or gears to worry about. The motor spins slower in one direction when I swap the wire leads from the battery.

[peteski]

Yes, I took the motor completely out of the unit to test it. No decoder or gears to worry about. The motor spins slower in one direction when I swap the wire leads from the battery.

I missed that obvious part.    Well then we know what the problem is. But I'm still puzzled why it acts that way. Any problems with the winding being open or shorted) should IMO affect both directions of rotation.  The only other thing that to me would cause this type of a problem would be if the commutator rotated slightly (to change the angle of the brushes relative to the wingdings. But I just don't think  that the commutator could shift on its own.

Is this a new set of locos?   If not, when did the problem start?

[skytop35]

This is an old set. Not sure when it started since it always runs in a four unit set and could have been dragged along for who knows how long. I was prepping and cleaning locos for Trainfest when I noticed it last night.

[Doug G.]

Although it is possible for the commutator to rotate on the shaft. I think it's less likely with the newer motors of today than it as in the early N days. I have seen it fairly often in the Rivarossi can motor.

A broken winding should, theoretically affect the motor the same in either direction. Brushes jamming in one direction but not the other could do it. That's why I always check them first with odd symptoms.

Doug

[mmagliaro]

Peteski, good point about the behavior not being uniform in both directions.
I would still look for carbon build up, but since you mentioned this, that made me also suspect something else.
The brushes. 

When brushes get worn, and the springs get extended and relaxed, all sorts of weird things happen.  I chunk can break off a corner, a crack can develop in them, or they can wear unevenly.  Any of these things can make the motor run faster in one direction than another.

I'd still double down on cleaning the slots, but I'll hedge my bet somewhat and add "check the brushes."

[peteski]

If Bill is willing, I volunteer to do analysis of that motor (yeah, like I need another project).  I also suspect that Max might also be willing offer his analytical services.  Right Max?  Stuff like this really piques my curiosity. And I'm a very curious person.  I have feeling that Max like me.

[mmagliaro]

Doug,
I didn't see your remark about brushes before I posted, honest!  (I didn't want it to look like I ignored you and then
said, "Yeah!  Yeah!  That's the ticket!  It could be the brushes! "    )

As for volunteering,  sure.  Bill, it's up to you.  We can flip a coin, or you can do whatever you wish.  If you want me to
look at your motor for you, I'd be happy to.  But do understand, that there may be nothing that can be done.
There may just be something mysterious wrong with it that cannot be fixed.

As for a replacement, I once bought a replacement AC-12 motor from IM to experiment with.  I just called them up and ordered it.  It was not too expensive as I recall - less than $20.   It took a few weeks to show up, but they did send it.