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Heljan GWR mogul - thoughts about improving slow running.


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I've had my mogul since the end of December and it hasn't been plain sailing; I had a few issues with the DCC, but that is now fine.   
I'm still not content with the slow running.   You could live with it if the loco was mainly used on trains that maintain a steady speed, but my layout is all about arrivals, shunting/running around the train and slow departures.
It doesn't stall and there is no interruption to the sound but it does have a noticeable random jerkiness which detracts from the sense of it being a heavy locomotive.  There is a stay alive in the Loksound decoder.   A number of people have suggested extra pickups, and I may well pursue this route.  One contributor who had fitted one axle's worth of pickups to the loco still found some judder.  Jon Fitness suggested enquiring whether spare parts designed for the Heljan prairie would do the job, as the chassis ought to be pretty similar.   It occurred to me that I could divert the wiring for the under-chassis loudspeaker for use with pickups on the loco itself, as I'm not using the chassis cavity for a speaker.  (My speaker is in the tender).   The point of this would be to avoid extra fiddly wiring and connectors between loco and tender.   
I noticed though, that occasionally the centre tender wheels are not rotating, as they are not dropping into slight dips in apparently level track.   The tender has no flex in its suspension so it must be riding (and picking up power) from just the outer four wheels.  Given that it is of a rigid design, I wonder if it's sometimes even reduced to three wheels firmly in contact with the track?
Adding extra loco pickups would certainly be easier than modifying the tender suspension to include some kind of compensation or springing.
I'm guessing that what happens when the loco jerks is that there is a momentary lack of power which slows/stops the motor and the gear driven by the motor shaft worm continues to turn.  When the motor restarts or picks up speed it then re-engages the worm causing a judder, because of the slop in the mesh between the worm and the gear.
I assume other people must have the same issue.   I'd be very interested to hear of successful strategies for improving this.
 

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33 minutes ago, 47606odin said:

Has it been properly run in and lubed? Things run better when a bit loose

I ran it  static, with the wheels suspended above the track in each direction for an hour when I got it.  I haven't added any extra lubrication.

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I’d be cautious about lubrication.  Insufficient will lead to disaster, eventually, too much can be a pita from day 1.

 

if it has an adequate keep alive, the jerkiness is not a pick-up issue.  Test keep alive by putting a piece of A4 paper on a suitable length of track, rubbing it down with your fingers so the edges of rails are creased.  Run you loco onto the paper at constant speed, if the KA is adequate, it’ll run most, if not all the way across your paper.  perhaps a bit less with sound.
 

if that doesn’t work, fix that first.  might be pickups, might be a wimpish capacitor.  Pickups need to pick up, continuously.  You need at least two wheels picking up  on each side as one might be on a dead spot, dead frog, mote of dirt, whatever.   Check pickups are connected to the decoder, the wipers & the wheels are clean, and the wheels touch the track.  Ensure the tender drawbar doesn’t hold the front wheels in the air, for example.

 

assuming pickups are ok, capacitor should have enough capacity to do the paper test, at least a couple of inches, ideally more.  Lots of places sell them.

 

If this doesn’t cure your issue, you’ve either got a poor connection from decoder to motor, dodgy motor or gearbox, or nadgered decoder.  Check connections with a multimeter, waggle wires & any plugs whilst you’re doing it.  You can test the motor gearbox by disconnecting the decoder wires and applying analog power directly to the motor terminals (never ever do this with any connections to the decoder or it’ll be toast).  You might want to run it in at low volts for an hour or two if it’s snicky.

 

if all else fails try a reset on the decoder, or swap decoders for a known good one.

 

hth

Simon

 

 

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Just an addition to what Simond has said; what about the free-running of the motion generally?  Sometimes on RTR stuff, part(s) of the motion (esp. crosshead, slide bars, etc.) may be mis-aligned, mis assembled, not glued or clipped into position properly, or very slightly bent (or not 'fettled') and causing a momentary mechanical contact that shouldn't normally happen.  This might be constant (in any location), or intermittent (e.g. only when negotiating a curve or perhaps only on LH ones).  This also might not show up (so much) whilst at speed (or being run-in at speed), but only at low speed when the effect is more pronounced or noticeable.

 

Just a thought anyway.

 

HTH

 

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  • 3 weeks later...
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@Stringfingerling sorry, only just found this thread.

My first 43xx (eventually returned for a replacement) was jerky at slow speed, but only running forwards. It ran nicely in reverse. This was due to a chewed up drive gear. The brass worm gear on the motor shaft couples to a straight cut plastic (nylon?) drive gear, so only the very edge of the drive gear is engaged, and it’s the opposite edge when running in the opposite direction. 
The replacement also ran a bit lumpy at first, but after four hours of running in on a rolling road it now runs sweetly in both directions.

I’m not sure how effective your running in would have been if the driving wheels were dangling free and under no load.

I’d suggest quite a bit more running in, on a rolling road if possible.

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10 hours ago, GWR57xx said:

@Stringfingerling sorry, only just found this thread.

My first 43xx (eventually returned for a replacement) was jerky at slow speed, but only running forwards. It ran nicely in reverse. This was due to a chewed up drive gear. The brass worm gear on the motor shaft couples to a straight cut plastic (nylon?) drive gear, so only the very edge of the drive gear is engaged, and it’s the opposite edge when running in the opposite direction. 
The replacement also ran a bit lumpy at first, but after four hours of running in on a rolling road it now runs sweetly in both directions.

I’m not sure how effective your running in would have been if the driving wheels were dangling free and under no load.

I’d suggest quite a bit more running in, on a rolling road if possible.

Glad to hear you've got one that works now :)   Mine has definitely improved with use.  I smoothed out the running surfaces of the slide bars as they seemed a bit rough and made sure the backs of the crosshead had no jaggy edges, as, to begin with, I was getting the occasional clash with the front crankpins.  I haven't even opened mine up to look at the gears, though I know what they look like from your and other people's photos.   Some of my problems were not really Heljan related but to do with decoder settings for the Loksound V5L.  I've got it much closer to the way I want now, though it's never going to be perfect.  Mine will run smoothly in both directions but there's something about the running when it is pulling a train that is not quite as silky smooth and consistent as I would like, but it's good enough.  The rolling road is a good idea I'm sure.

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