What does the ball bearing at end of worm shaft do?

Revok

Revok

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Recently I had to replace the axle cogs on my LGB 'Casey' loco. After a couple of false starts I got the correct cogs and fitted them successfully. The loco ran fine for about an hour doing simple loops round the track. I left it running, and when I came back it had stopped. The PSU (a piko 1.5A controller) had tripped. So I reset the psu, and the loco started to move forward, but in a very jerky way. Then the psu tripped again. But here's the thing. It would run in reverse with no problem at all. Occasionally it would run forward, but not for long before this stutter jerky would happen. Go back to reverse and it was fine.

I put the loco onto my test bench upside down so the wheels could turn freely and attached a variable psu. Runs fine both forward and back, drawing about 0.3A at 6v, and up to about 0.5 A at 15v, which I think would be about right. Used my fingers to apply a bit more load to the motor, and the current draw increased bit not by much, certainly nowhere near enough to trip the piko controller. I couldn't see anything wrong at all.

I removed all the motion rods in case it was something to do with quartering, but still on the track I was having problems going forward, but never in reverse. There were times when it would seem ok for 30 mins or so, then stutter and psu trip. Always fine in reverse. Frustratingly I could never replicate the issue on my test bench though.

So, to cut to the chase. I had read about ball bearings on some motors at the end of the worm shaft. With nothing to lose, I thought I'd try simulating that with a shim of plasticard wedged into place. To my surprise, the loco worked fine after that. Used it all day, for long stretches pulling a couple of wagons. Same next day, so feeling quietly confident the proplem is resolved, and all I need to do is get a ball bearing.

But I don't understand why! Can someone make any sense of this?
 
A worm will try to 'walk' to one end of any slack in the motor mounting or shaft..
The ball takes up the slack in one direction.

If things move, the gear-train can bind. - It always happens under load, and nearly always, you are not able to simulate it, with the loco off the track.

If you are really lucky.. The ball bearing will be lurking in the grease, or stuck to the motor casing (magnet).. If you are unlucky, the ball bearing will be inside the motor. - Don't ask!
 
Probably to stop the shaft floating and keep things in mesh?
 
Right. Because the worm exerts a force on the wheel, the wheel necessarily exerts a force on the worm. If the worm is only supported by the motor shaft, all that force is taken by the motor bearings. In practice the motor bearings cope with some forces better than others - they aren't usually designed for much pushing and pulling along the axis of the shaft. An extra constraint on the worm shaft, such as this ball, either directly takes some load off the motor bearings - or just stops them being pulled into a position where they don't work as well.
 
I thought LGB only used balls at the ends of the motor shafts on early models and were deemed unnecessary if the motor was replaced by a later version. Did any versions of "Casey" have these balls?
 
Neil Robinson said:
I thought LGB only used balls at the ends of the motor shafts on early models and were deemed unnecessary if the motor was replaced by a later version. Did any versions of "Casey" have these balls?
Click to expand...
Does anyone know the diameter of the balls?
Regards,
Paul.
 
Neil Robinson said:
I thought LGB only used balls at the ends of the motor shafts on early models and were deemed unnecessary if the motor was replaced by a later version. Did any versions of "Casey" have these balls?
Click to expand...

FWIW, my Casey is apparently a 'Toytrain' version if that adds any useful info.

To be honest I have no idea if it should or shouldn't have balls. I bought it as a beat up wreck dead cheap, so I couldn't say for sure if there was ever a ball in place, or whether I lost it. But absolutely without a doubt since I wedged a small piece of plastic to reduce the shaft movement I have had several days of trouble free playing.

Now if *I* had balls, I'd remove the shim and see if the fault re-occurs!
 
Neil is correct on only early units. The ball is the thrust bearing for the motor, the heck with the gears, it keeps the commutator from moving too far and the brushes centered, if it moves too much one way, I believe the brushes hit the end of the commutator segments where the windings are soldered on. Too much the other way and sort of goes off the end of the commutator. Either way bad for brushes, and can damage commutator.
 
Revok said:
FWIW, my Casey is apparently a 'Toytrain' version if that adds any useful info.
Click to expand...

The service diagram doesn't show any motor balls and I'm sure they were only fitted to the larger "Stainz" type motors and then not after about 1980 if not sooner.
 
Lateral thinking.. - A few thoughts..

Could the collar be missing / misplaced on the motor? - If it has one for alignment.

Could the thread be stripped in the 'block, so the top (or bottom) are not seating as they should be?

Are the various metal strips inside the 'block seated correctly / in the correct place?
 
To cover some of the points / comments so far.

The motor seems to sit perfectly in its housing. Each end of the shaft align with slot, and are not proud or sunken in any way. With the axles removed the motor spins when power applied, and even at 20v and running fast it all seems to be in line, there is no sign of a 'wobble' anywhere. It just 'feels' right if you know what I mean. Everything slots positively into place.

One of the 4 threads on the block, while not stripped entirely, doesn't tighten fully... but it does grip. I use the tissue paper trick to give the screw something to bite on, and it feel pretty much ok. I kinda discounted this as a source of problem, because its been that way since I got it last year, and this issue is only since last week when I replaced the gears. But a good suggestion, and I really should have mentioned that in my description of the fault.
 
Oh my, balls.....:rofl:
 
Paul2727 said:
I ordered a bag today.
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:eek:

A bag! - I hope it is a small one?

I *think* I have had three loco's pass my way, that had / needed the ball-bearing.

I did not know about them the first-time, and the motor locked-up after I had replaced gears etc. .. .. .. ..
Eventually, I realised the motor was jamming.. Took it apart.. .. Guess where I found the ball-bearing! :rolleyes:

Since then, if an old loco/block, the first thing I check.. ? Is there a ball-bearing, buried in the grease ? :nerd:
 
The Chloe and Olmana still use a motor needing the ball bearing. This is a thrust limiter in that the motor does NOT have a thrust bushing. Motor armature will slid bhack and forth (hint hint).
Only the old motors needed this and they had the red and black brush holders and onlly on short shaft and long shaft motors. AND ALL CHLOE motors to this date!!
 
Neil Robinson said:
The service diagram doesn't show any motor balls and I'm sure they were only fitted to the larger "Stainz" type motors and then not after about 1980 if not sooner.
Click to expand...
I have suspicion they were also used in the feldbahn locos. Or, is it my imagination?:wasntme:
 
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