Atlas Motor Problem

[davefoxx]

Has anyone else had a problem with Atlas motors becoming slower, to the point where the locomotive will only go approximately 25% of full speed, even with the throttle cranked up to 100%?  I've had this happen a couple of times over the past several years and swapped the motors out to fix it.

This week, I finally got around to dealing with a slow U23B.  I just happened to have a B23-7 lying around for a project that never got off the ground, so I swapped the motors.  This confirmed that the motor is the problem, because, until I speed match the U23B, it's a jackrabbit now!  None of the other driveline was swapped (they wouldn't have fit), nor did I even lube the driveline.  The motor is the only variable here.

What causes this and can it be fixed?  I have no less than three locomotives in my fleet that have no motors due to swaps and at least three bad motors.

Thanks,
DFF

[narrowminded]

Did you try a drop of oil at each motor shaft?  Those are bronze bushings and they can get "dry" leading to tight running.  You might be able to get a sense if that's the problem by spinning the shaft, especially if you have a known good one to compare it to.  If bad enough you may be able to feel the difference.

[mmagliaro]

There are three obvious things that could be happening. 

1. Either the bearings are getting so dry that they are causing a lot of friction and slowing the motor down,
2. or there is a short in the armature windings.  Either way, you would likely have a motor that gets very hot when it runs.
A dry bearing usually squeals like mad when things get this bad.
Can you run a motor on your workbench, with a milliammeter hooked up in line to measure the current?  That will be the first, most important, thing to check.

After you measure the current, try putting *one* drop of light oil on each shaft bearing, and see if the motor speeds up and/or the current drops.  If that does not help, it's probably the armature and there ain't much you can do except replace the motor.

3. Or .... do these motors hook into the drivetrain with a ball, cup, U-joint thing pressed onto the motor shaft?   (I don't keep track of all the nuances of these diesel drivetrains.  I know some have a flywheel with a machined recess for the shaft drive, some have a plastic fitting).  When you replaced the motors, did they come with those plastic fittings already installed?  It's possible that those fittings were slipping on the motor shaft, and that the motor itself wasn't bad at all.

[davefoxx]

Did you try a drop of oil at each motor shaft?  Those are bronze bushings and they can get "dry" leading to tight running.  You might be able to get a sense if that's the problem by spinning the shaft, especially if you have a known good one to compare it to.  If bad enough you may be able to feel the difference.

Yes, I did apply a drop of oil at each end of the motor shaft a while back when I first started experiencing problems.  I cannot feel a difference between the bad motor and a good motor when spinning the motor by hand.

Thanks,
DFF

[davefoxx]

There are three obvious things that could be happening. 

1. Either the bearings are getting so dry that they are causing a lot of friction and slowing the motor down,
2. or there is a short in the armature windings.  Either way, you would likely have a motor that gets very hot when it runs.
A dry bearing usually squeals like mad when things get this bad.
Can you run a motor on your workbench, with a milliammeter hooked up in line to measure the current?  That will be the first, most important, thing to check.

After you measure the current, try putting *one* drop of light oil on each shaft bearing, and see if the motor speeds up and/or the current drops.  If that does not help, it's probably the armature and there ain't much you can do except replace the motor.

3. Or .... do these motors hook into the drivetrain with a ball, cup, U-joint thing pressed onto the motor shaft?   (I don't keep track of all the nuances of these diesel drivetrains.  I know some have a flywheel with a machined recess for the shaft drive, some have a plastic fitting).  When you replaced the motors, did they come with those plastic fittings already installed?  It's possible that those fittings were slipping on the motor shaft, and that the motor itself wasn't bad at all.

I don't believe the affected motors have the ball cup.  I know for a fact that the one I was working on with the U23B has the hex shaped hole in the flywheel, and the driveline is not slipping.  As I stated in my previous post, I did try oiling the bearings a while back when I first tried to deal with the problem.  The motor was not making any squealing noises at all, and I never noticed that the motor got hot, either.

I'll try to measure with a multimeter.  I've got one but don't really know how to use it.  I may ask for some guidance when I get the opportunity to get some time at the workbench.

Thanks,
DFF

[Jim Costello]

Check your motor commutators for carbon buildup. Sometimes a soft carbon brush will leave deposits in these gaps causing motors to slow down.
A careful clean up with a very fine pin or in a ultrasonic cleaner also works

Jim

[mu26aeh]

I don't believe the affected motors have the ball cup.  I know for a fact that the one I was working on with the U23B has the hex shaped hole in the flywheel, and the driveline is not slipping.  As I stated in my previous post, I did try oiling the bearings a while back when I first tried to deal with the problem.  The motor was not making any squealing noises at all, and I never noticed that the motor got hot, either.

I'll try to measure with a multimeter.  I've got one but don't really know how to use it.  I may ask for some guidance when I get the opportunity to get some time at the workbench.

Thanks,
DFF

I'm with you there Dave on the multimeter.  Asked similar question in the DCC section about uses for them while installing decoders. 

[peteski]

I have eperienced hardened grease in many Atlas (and other brand models). The grease and oil gets stiky to the point that it impedes the movement of the mechanism.  Cleanig the entire mechanism and fresh lube job takes care of the problem.  Since the motor has to work harder that will show up as increased current draw.

Fouled up commutator can also affect the motor speed.  If the bowdered brush carbon gets in between commutator segments, that will alos cause increased current draw.


If the u-joints were cracked and slipping on the motor or worm shafts then you should be able to hear the motor racing at high speed while the loco barely moves.

Just recently friend bought couple of locos from BLW (new old stock). Both were really poor runners (High starting speed and they seemed to really labor) and the motor would get really hot!  The problem was that the armature wasn't spinning freely because the motor shaft had no longitudinal play between the bearings.  I had to re-seat the bearings to increase the play. Once that was done, the loco started running fine.

[wazzou]

Yeah, count me in the camp of uninformed multi-meter users.  I have two of them but both had documentation that assumes you already know what you're doing.

[tehachapifan]

I have an Athearn FP45 that runs slower than slow, but very smooth. While always on the slow side, I swear it used to run a little faster than it does now.

[peteski]

Yeah, count me in the camp of uninformed multi-meter users.  I have two of them but both had documentation that assumes you already know what you're doing.

Recently this type of inquiry was answered in https://www.therailwire.net/forum/index.php?topic=41253.msg513738#msg513738

You will be interested in measuring DC current consumed by the locomotive as it runs - but without a reference (another identical or similar model running well) it is not all that useful.

[MK]

Dave, it happened to me once with an Atlas RS-11.  It would run very slow, like only 50% at full throttle.  So I took it apart and found nothing out of the ordinary.  I also noticed that it felt warm, say 100F, but not hot to the touch.  I tried "fixing" it but eventually gave up and returned it to the store where I bought it from and got another one.  That one ran like a fine time piece.  Unfortunately I never went back to that store (I was consulting in a different state and the gig was done) to see if they found out what was wrong.  The guy said he would open it up and take a look and the store had some really good technical people.

[Ed Kapuscinski]

I have a friend with some inside knowledge on these things. He said it's likely a defective motor that's slowly eating itself, and the only fix is to replace it.

[chicken45]

"obligatory lubrication joke"

[peteski]

I have no less than three locomotives in my fleet that have no motors due to swaps and at least three bad motors.

Thanks,
DFF

Dave,
if you were willing to send me one of those bad motors I could give it a postmortem as I'm curious as to what is wrong.   Of course with the number of projects I have sitting on my workbench it will take me a while to get to it.   But it would be good to find out what happened.