Atlas scale speed motors - really slow to get moving

[Ed Kapuscinski]

I've had an amusing similar situation.

I've got two Atlas GP9s from the same run. I recently tore them completely down and cleaned them out.

One runs totally normal. The other is half as fast.

I think it's highly unlikely it's grease buildup (since I had cleaned them out) or the decoder settings (I loaded the same speed settings to both).

I haven't felt like digging into the one that's slow because it's disheartening to have a project you thought was done turn out to be a butthole like this.

But this thread might just get me to take it apart again and see WTF.

[peteski]

Few years ago there was a batch of defective Atlas motors.  The bearings were not seated properly and the armature was binding against them.  So the oco was running very slow and the motor would get hot rather fast.  But the problem would remain constant (the loco would not run faster after few minutes of running or come up to speed slowly).

It is easy to check whether that motor has the problem. Best to remove that motor from your loco, and using your fingers, gently spin the flywheel (thus spinning the armature).  You will immediately feel that there is extra resistance.  Better yet, have a good motor handy to compare how freely its flywheel/armature spins.

The fix I devised was to properly seat the bearing.  I documented this procedure on the forum. 
Here is the related thread:
https://www.therailwire.net/forum/index.php?topic=41287
And my fix:
https://www.therailwire.net/forum/index.php?topic=41287.msg515659#msg515659

So Ed, this could be the problem in your case.

[rrjim1]

I have a Extech DC regulated power supply, and a Pyle Digital Tachometer that I use to test these motors. The motor I received from Bart, started cold at 2.7 volts and .07 amps. I ran the motor for a few seconds and it would start at 1.8 volts and .04 amps. I am going to guess that one of the drive shafts had no play and was forcing the armature against the opposite bearing. I have seen this in a couple of locos and yes after running a few minutes they will speed up.  The loco usually get faster after running it for a couple hours depending on how bad the problem is.   

[peteski]

In my experience when a motor sits for some time there is some sort of buildup on the commutator or brushes. The starting voltage of such motor is higher, but after few seconds of running whatever is coating the commutator gets cleaned off, and for the rest of the session the motor works better (as expected).

 This occurs in motors with copper commutator and carbon brushes. It does not seem to happen to motors with precious metal commutator/brushes.

[peteski]

I ran the motor for a few seconds and it would start at 1.8 volts and .04 amps. I am going to guess that one of the drive shafts had no play and was forcing the armature against the opposite bearing.

This type of motor (sleeve bearings) should have some slight fore/aft play at the shaft.  Easily detectable when pulling/pushing the shaft by hand.  If there is no play, that is a problem.

[rrjim1]

Bart's motor was in perfect shape. To test for the problem that I suggest above take the loco half of the frame that holds the worm gears. Install the motor, and the drives shafts in the frame half. Now take a small screw driver and try to move the worm back and forth. There should be a little back and forth movement. If there isn't I usually press the flywheel on just enough to fix the problem. You can also remove the joint on the end of the shaft and shorten the shaft if there is enough room between it and the bearing next to the worm gear.   I'm only talking just enough to create a small back and forth movement.   

[peteski]

Bart's motor was in perfect shape. To test for the problem that I suggest above take the loco half of the frame that holds the worm gears. Install the motor, and the drives shafts in the frame half. Now take a small screw driver and try to move the worm back and forth. There should be a little back and forth movement. If there isn't I usually press the flywheel on just enough to fix the problem. You can also remove the joint on the end of the shaft and shorten the shaft if there is enough room between it and the bearing next to the worm gear.   I'm only talking just enough to create a small back and forth movement.

Hmm . . . in models where worms are not directly coupled to the motor shaft (they are coupled via some sort of universal or a hex-coupling), any play in the worm's shaft should not interfere or affect the play in the motor shaft. The couplings should have enough slop in them to accomplish that.  The entire reason for those couplings is to decouple the motor from the worms. The motor bearings should not be subjected to any longitudinal thrust. That thrust shroud only be at the worm bearings.  If pushing the worm shaft forward and backwards directly transfers that movement to the motor shaft, then the drive train is not assembled correctly.

[Steveruger45]

Hmm . . . in models where worms are not directly coupled to the motor shaft (they are coupled via some sort of universal or a hex-coupling), any play in the worm's shaft should not interfere or affect the play in the motor shaft. The couplings should have enough slop in them to accomplish that.  The entire reason for those couplings is to decouple the motor from the worms. The motor bearings should not be subjected to any longitudinal thrust. That thrust shroud only be at the worm bearings.  If pushing the worm shaft forward and backwards directly transfers that movement to the motor shaft, then the drive train is not assembled correctly.

Yes.  There should be some movement of the worms between the bearings but none of that movement should be allowed to cause a bind on the motor. Most motors I have come across do have some axial movement on their own and that should be taken into account to prevent the motor binding on the drive train too.   If it runs good forward and slower in reverse or vice versa that’s a good indicator of binding due to axial bind.
Often I have found that the motor cradle looks good but isn’t and can cause a bind or noise in the drive train.  I’m a bit OCD on getting locos to run smooth and quiet.

[Bart1701]

I am positively amazed at the knowledge of the people on this site and very thankful for everyone’s help and thoughts! I wish I knew as much as you all do about electrical motors and all of the variables that can impact their performance. I know that I learned a lot from this post. In fact, I had to find a diagram of a motor to make sure that I was clear about every one of the parts were that people were referring to!

Seems that you like to run your models rather fast (not that there is anything wrong with that). 

While I MAY be able to run my locomotives with Kato motors around the layout like a slot car, trust me that I do not. I ran one of my locomotives at what I consider an average speed for my layout and based on the time it took to make a single lap, it was running around 35-40 smph.

But I 'm still puzzled by the statement you made in your initial post: "Even if I crank up the throttle to around 50 when I start the engine, it still takes forever to get up to speed. I have a smaller layout, with about 30 feet of mainline track, and it may take 2 laps around the layout before it gets up to speed.".

That is not how any motor behaves (slwo or fast speed) (unless there is some other problem with the mechanism, like thickened grease).  If you set the speed to 50, the  model will leap to that speed within a second or two, without any slow momentum like you described.  It would  not take 60 feet of travel. But again, the motors have been replaced, and the important thing is that you are pleased with the result.

As far as my original comment about cranking my throttle up to a value of 50 and it taking almost 2 laps for the locomotive to get up to speed, that is definitely what I had observed. I had checked the acceleration momentum and unless I read the wrong CV or did something else wrong, it was set to a 0 value. But, it sure seemed like the locomotive was trying to pull a heavy boat anchor around the layout!

I wish I could repeat this again, but this locomotive now has the Kato motor in it and it performs much better.

I checked out 2 other Atlas locomotives with scale speed motors and they behave as Peteski expected. If I crank the throttle up to a value of 50, it only takes a second or two for them to get up to speed.

Why my one locomotive behaved so differently is going to be one of those mysteries we’ll probably never be able to solve now!

My best guess is that there must have been something else that was out of whack that the disassembly/reassembly of the locomotive and the installation of the Kato motor with the Atlas flywheels on it must have corrected.

On another note, I have been tweaking CV2 on all of my locomotives to get them to start moving when my throttle is moved to a value of 1. This has made a vast improvement in the locomotives.

Thanks,
Bart

[rrjim1]

Why my one locomotive behaved so differently is going to be one of those mysteries we’ll probably never be able to solve now!

Bart

When I received your motor the first thing I did was measure the flywheels distance from the motor. One was not pressed on far enough. I corrected that problem when I pressed the flywheels on the Kato motor that I sent to you. That's why your loco runs so much better with the Kato motor. Jim

[Steveruger45]

When I received your motor the first thing I did was measure the flywheels distance from the motor. One was not pressed on far enough. I corrected that problem when I pressed the flywheels on the Kato motor that I sent to you. That's why your loco runs so much better with the Kato motor. Jim

Thanks for that @rrjim1.  That sort of confirms what I was thinking that there was some sort of bind. I’ve had the same issue on occasions too, but have nearly always managed to correct it by adjusting the worm universal and on very rare occasions had to adjust one or both of the flywheels.