New to all this and currently using pre-owned locos. I'm thinking of buying a new loco - maybe Ivatt 2-6-0. Now I can see why, for accuracy, small motors would be desirable but how, honestly do they compare with old-style open frame in terms of power and reliability. Are they "better" or just different and downsized to fit? I like locos to have pulling power and traction and the heavy weight of the old motor and a metal body seems to work for me. I've not tried a new loco (I'm happy with dc) so wondering. I've heard the new motors are better at slow running???
In my opinion there is no contest in the regarding reliability. The older open frame motors only require regular servicing and replacement of wearing parts which can be carried out in a few minutes and will accept more abuse. Coreless motors require no servicing but require changing at regular periods when they fail, that if you can obtain a spare.
For me open frame motors win hands down, I have several bought pre-used in the early nineties that are still running.
Dodger
Another vote for open frame motors here. I have stuff in oo and N that is donkeys years old and still working because I can repair and service them.
I also have a newer loco that had to wait over a year for the motor to be available.
In addition, these sealed motors to not seem to last that long whereas I have some early 1980's open frame well used locos still on their original components.
I know a shop that has a working display who utilises old locos because the new ones will only last a couple of months of daily service before they pack up needing a new motor.
Elmo
It would be interesting to see how various locos compare for longevity. I'm happy with the coreless motors even though they don't run well with my feedback controller. Non of my coreless locos have done months of continuous running though. I may change my mind if I have problems. Probably my biggest concern is availability of spare motors; they should be easily available.
Is it clear which locos have coreless motors? We can be certain that all Dapol N gauge locos have traditional motors because we know that they were looking to find one for the Bullied Pacific. So far as I am aware the Farish Castle, Ivatt 2-6-0 and 64xx are coreless. Are there any others?
Quote from: Chris Morris on July 18, 2018, 07:05:54 AMI'm happy with the coreless motors even though they don't run well with my feedback controller.
The instructions from Farish specifically state to NOT use feedback controllers...
(In doing so you have probably shortened the motor life and invalidated the warranty... :thumbsdown:)
As others have said, old style traditional open frame motors - and also older can motors - at least have "user serviceable parts" eg. brushes and springs. I agree they can last for decades if not abused. I have locos made in the 60s and 70s still happily running on original motors and are still perfectly good enough for exhibition running.
Coreless motors are more efficient and draw less current, but as I understand it there are potential issues with them:
1) Because they don't have an iron cored armature they can't conduct away any heat build-up as well as a traditional motor. It is said that PWM controllers can induce such heat build up more readily than smooth DC.
2) Again because they don't have an iron armature, their Back-EMF response is different to a traditional motor. Hence if you use a feed-back controller it may not be tuned to the BEMF characteristics and may under- or over-compensate, resulting in jerky running.
3) They are often completely sealed with no option to replace brushes.
Of the points above, the heat build-up is probably more likely to cause reduction in motor life.
Remember that a feed-back controller is 99% likely to use PWM, but not all PWM controllers include feed-back circuitry.
Also remember that every DCC decoder I've ever heard of uses PWM for motor drive, and the majority seem to include feed-back although is it usually possible to switch it off. Also with more comprehensively specified decoders the PWM frequency and feed-back response can be tuned to better suit the motor characteristics. Most decoders use higher frequency PWM than a classic PWM controller.
I still use KPC PWM/feed-back controllers I've had since the 80s, and find they give no trouble at all nor do I notice any heat build up in locos, though my typical operating pattern is to run each train in a sequence rather than leave things belting round and round for many circuits. I did modify the controllers a long time ago to allow the feed-back to be switched off, and yes some more recent locos behave better without the feed-back. On balance I probably only use the feedback for 30% of the time, and that will be mostly with older models.
Quote from: ntpntpntp on July 18, 2018, 08:53:56 AM
As others have said, old style traditional open frame motors - and also older can motors - at least have "user serviceable parts" eg. brushes and springs. I agree they can last for decades if not abused. I have locos made in the 60s and 70s still happily running on original motors and are still perfectly good enough for exhibition running.
Coreless motors are more efficient and draw less current, but as I understand it there are potential issues with them:
1) Because they don't have an iron cored armature they can't conduct away any heat build-up as well as a traditional motor. It is said that PWM controllers can induce such heat build up more readily than smooth DC.
2) Again because they don't have an iron armature, their Back-EMF response is different to a traditional motor. Hence if you use a feed-back controller it may not be tuned to the BEMF characteristics and may under- or over-compensate, resulting in jerky running.
3) They are often completely sealed with no option to replace brushes.
Of the points above, the heat build-up is probably more likely to cause reduction in motor life.
Remember that a feed-back controller is 99% likely to use PWM, but not all PWM controllers include feed-back circuitry.
Also remember that every DCC decoder I've ever heard of uses PWM for motor drive, and the majority seem to include feed-back although is it usually possible to switch it off. Also with more comprehensively specified decoders the PWM frequency and feed-back response can be tuned to better suit the motor characteristics. Most decoders use higher frequency PWM than a classic PWM controller.
I still use KPC PWM/feed-back controllers I've had since the 80s, and find they give no trouble at all nor do I notice any heat build up in locos, though my typical operating pattern is to run each train in a sequence rather than leave things belting round and round for many circuits. I did modify the controllers a long time ago to allow the feed-back to be switched off, and yes some more recent locos behave better without the feed-back. On balance I probably only use the feedback for 30% of the time, and that will be mostly with older models.
I also have a couple of non feedback controllers which I use with the coreless motor locos so I probably haven't either invalidated the warranty or shortened the motor life. My observation was merely that coreless motors don't run very well with feedback controllers.
I had an open frame motor on a Fleischmann tender drive burn out a couple of yeas ago I'd only had it since 1974,I have numerous other open frame motors still running of similar vintage. The only other burn out was a Minitrix class 27, that was due to using half wave power on an old H&M controller.
No problems here with coreless, lovely and smooth running especially at low speeds(on dcc). Note that Zimo decoders do have a specific setting for coreless motors, others may, but they usually say 'suitable' for coreless motors. This also applies to the (Zimo) one supplied by Bachmann, though you will not find any instructions for it about using the coreless motor feature on locos with coreless motors. The relevant CV's are not listed in the tiny instruction card. Can't remember them now, will look it up again if anyone's interested. I picked it up from the Zimo small decoders manual. Checked with Bach and they confirmed that the coreless setting should be used.
Regarding which are coreless, the Farish catalogue does say so for some. Those I know about are the Ivatt 2MT, N Class, Princess Coronation.
The open frame ones used by Dapol, in the A4's at least (I have 5) are awful. They may be user serviceable but about half of them seeem to be very poorly balanced and rattle the tender on the tracks, making the most awful noise. This can be improved by fitting a better decoder that the DCC23, by the way.
@Bramshot (http://www.ngaugeforum.co.uk/SMFN/index.php?action=profile;u=6700) - can you add/copy your advice on Zimo / coreless settings to the DCC section please
RoboMod
I'm not technically minded so cannot comment accordingly.
I do have two of the latest Farish Princess Coronations and they run superbly, and incredibly slow when wanted.
I use a four track Morley controller.
Wow! I hadn't expected to open such a can of worms. I had suspected that the new motors were smaller for scale purposes but didn't expect to hear they might have problems. On the one had if they were potentially so troubled you'd expect Bachmann to be handling a lot of returns. On the other, well I've often thought hi-tech can mean over-complex and unproven and with open frame, yes you can see issues and potentially fix them. I've some quite old stuff running fine and for my purposes, weight and traction are more important than pure scale.
Its strange the Dapol can motors as fitted to their early locos, 2005 vintage seem OK but there are few spares available. As regards to the Bachmann motor I had 2 failures in the 4CEP in three years and I've had to replace all of the motors in the Class 101 & 108 DMU's.
Discussions about 5 years ago suggested they had a life of about 100 hours, not very good in the scope motor life.
Interesting that Dapol change back to open frame motors for some of their later models.
Its a real can of worms and will never be resolved?
Dodger
Quote from: PLD on July 18, 2018, 07:54:14 AM
The instructions from Farish specifically state to NOT use feedback controllers...
(In doing so you have probably shortened the motor life and invalidated the warranty... :thumbsdown:)
Where is this stated?
I haven't seen any instructions regarding coreless motors from GF anywhere, so would be happy to see some.
Coreless perform much better than open frame motors and cost only a couple of dollars at trade prices, so in theory it would no great problem if they had to be replaced every few hundred hours rather than serviced.
Is there a source for official Farish replacement coreless motors and if not are there readily available alternatives out there on eBay?
Quote from: longbow on July 18, 2018, 10:17:48 PM
Coreless ... cost only a couple of dollars at trade prices, so in theory it would no great problem if they had to be replaced every few hundred hours rather than serviced.
Is there a source for official Farish replacement coreless motors and if not are there readily available alternatives out there on eBay?
But therein lies the problem - the ready availability of spares at sensible prices if their longevity isn't great. Plus not all modellers are confident in performing open heart surgery on their models and would want to send them in to be serviced which all adds to the expense.
I recently had to get a replacement motor for a Liliput N gauge FLIRT EMU (another Bachmann brand these days). In the end I bought two from Liliput Austria, having read quite a few reports on german forums of these particular motors failing. Cost me 40 Euros for the pair so not cheap.
Coreless is the way forward - Bachmann won't go back.
They are totally smooth (no iron core means not cogging between 'poles'). They draw virtually no current (10mA compared to 100mA plus for older open frames). They are tiny diameter (7mm diameter x16mm long) as compared the 8mm diameter armature on an old Farish open frame (so much larger once magnet, poles included).
In terms of failures, I've only seen one, but don't know the cause. I've seen far more in older Farish can motors, or Dapol open frames. In terms of spares, I have 10, bought a while back on ebay for about a fiver - not sure if they are exactly the same, but the one I've used fit perfectly and performed identically.
I don't see that folks should assume longevity is small when there are no reported failures due to the number of hours run. I don't think there's anything to worry about for most people's use, and so long as the common sense precautions are taken (no PWM, electric track cleaners, feedback - though Feedback shouldn't generally be used on N anyway).
Cheers,
Alan
The one that was dead, I tore down:
(https://farm8.staticflickr.com/7782/26938619121_459197ef2a_b.jpg)
(https://farm8.staticflickr.com/7633/26938618831_d6620e105e_b.jpg)
(https://farm8.staticflickr.com/7583/26912679222_c7b60748bd_b.jpg)
Looking at the photo again I recall the failure - it was one coil detached from the solder pads - it hadn't overheated and may well have just been from manufacturing.
Cheers,
Alan
There is no similar warning on the coreless steam locos that I have, the closest it says is not to run a non dcc loco on a dcc supply as analogue 0.
It has always been the case that coreless motors should not be used with low frequency DC feedback controllers. Their higher efficiency and lower current draw means they over-react to feedback pulses, hence the 'jittery' performance they give on such controller types. This effect has also become common with more 'ordinary' iron-rotor motors as their designs have become more efficient in recent times. As a result, and combined with the smaller size and current draw of N/2mm size motors the normal advice is not to use feedback control with N.
In respect of DCC decoders they now use higher frequency with some having, additionally, added adjustments to motor control parameters that can be enabled, to ensure they run quite okay.
Izzy
It has been an established fact for a long time that feedback controllers are detrimental to N gauge motors.
I run DC, and have had problems with said controllers. I use quite simple transistorised controllers (one of which is homemade) off a 12VDC supply with no problems.
Poor performance. No real damage. But they made noises that suggested that there could be if I kept using feedback controllers.
Quote from: Dr Al on July 19, 2018, 12:03:23 AM
(https://farm8.staticflickr.com/7633/26938618831_d6620e105e_b.jpg)
(https://farm8.staticflickr.com/7583/26912679222_c7b60748bd_b.jpg)
Looking at the photo again I recall the failure - it was one coil detached from the solder pads - it hadn't overheated and may well have just been from manufacturing.
Cheers,
Alan
Dr Al, was it also missing a commutator segment, or did that come off during tear Down?
Quote from: Lindi on July 19, 2018, 09:49:11 AM
Quote from: Bealman on July 19, 2018, 09:45:38 AM
It has been an established fact for a long time that feedback controllers are detrimental to N gauge motors.
Fact? Any evidence to support this or is it just that it has been said enough times that it is taken as 'fact'
Indeed. As is often the case people confuse the terms "Feedback" and PWM".
Agreed that PWM is not always kind to motors and can cause heat build up. Low frequency PWM makes motors growl at low duty cycle.
As I wrote earlier, Feedback controllers are pretty much all based on PWM designs as it's an easy technology to control electronically and/or programmatically (that's why decoders use PWM) and it provides the "space" in the duty cycle to sense the Back-EMF generated by the motor. Not all PWM controllers include feedback circuitry.
Feedback is simply the application of a negative control loop in the controller itself, causing the controller to adjust the PWM duty cycle in an attempt to maintain constant speed based on Back-EMF measurements. Feedback won't in itself damage the motor, it cannot cause the controller to drive beyond its maximum output voltage and 100% PWM duty cycle (ie. full speed). However, because it's an automatic process there is the chance the controller could try and push a struggling or stalled motor too hard without the user noticing, it would be the same as someone turning up to full speed to try and get a struggling train up a gradient.
With coreless motors (and other high-efficiency types) it is the controller over-compensating due to lack of Back-EMF which causes the jittery performance. For example I see it with Kato motors especially in their earlier models without flywheels, and this was the original reason I modified my controllers to make the feedback circuit switchable. Long before I had any models with coreless motors.
Quote from: Bramshot on July 19, 2018, 10:20:23 AM
Dr Al, was it also missing a commutator segment, or did that come off during tear Down?
No. None of the segments are missing.
Regards,
Alan
Thanks for that.
I understand the jargon, but all I know is there was a huge hum from a loco when stopped, which to me suggests a heating up of the coil.
Oh, I thought the lower photo showed the commutator on the end of the shaft and the top segment looked missing. Must be an illusion!
Quote from: Bealman on July 19, 2018, 10:35:07 AM
.. there was a huge hum from a loco when stopped, which to me suggests a heating up of the coil.
Had the loco stalled, or was the controller not fully turned off? Dodgy controller if it didn't totally cut power when the knob was turned off. I agree if there was a hum with no movement then yes all you're doing is heating the motor, but you wouldn't leave it like that. Almost as bad as when you put an un-chipped loco on a DCC track.
You're right.
When I switched the thing to neutral, the hum stopped.
Still don't trust them, though! :thumbsup:
I made this bit of video today. It shows how the Dapol 45xx can be tamed with a feedback controller while the coreless motored Farish 2MT is fine with a non feedback controller ( a Gaugemaster W) but noisy and rough when using feedback. Hopefully this illustrates that it is not good to use a feedback controller with a coreless motor but feedback controllers have their place with older cruder mechanisms. Whilst the 45xx is not a really old mechanism it is renowned for being very poor at slow running. The feedback controller, a very old H&M Walkabout, is good for this loco.
Bear in mind the 45xx's can motor is very vulnerable to overheating if driven hard by feedback (e.g. it derails or suchlike) - the commutator will disintegrate if it gets too warm from excess driven current (and that level is not very high - something like 200mA). It's nowhere near as robust as some of the much older Farish for example which will only exhibit failure at 400mA+ (albeit this is usually a coil burn out).
Cheers,
Alan
For a DC controller I've yet to find a better design than one I found in an electronics magazine some years ago; I've not seen a commercial controller using the same principle. I've made a few modifications to the original circuit, at the time I did show it to the Tech man at Farish near Poole (that dates it!) his opinion was that it would not harm Poole Farish motors, I've used it ever since with no problems, slow running control is superb, 5 minutes to cover 12", it even tames Dapol M7s.
When using simple controllers the motors used in many model locos are reluctant to start until the voltage rises above a certain level, but once started this voltage is enough to cause them to leap away in most unprototypical fashion.
This circuit uses a narrow pulse, (about 3ms mark, 12V, 27ms space, 0volts) that is just sufficient to make trhe motor start to turn, to increase speed the pulse is "mixed" with a DC level; as the speed control is increased the DC level is increased so at low speed the mark remains at 12V but the space rises to say 3v, this will increasethe average current and the motor speed rises, as the control is increased so the space voltage increases, further increasing the average current, until with control at full the motor is getting a full 12 V.
The circuit uses transistors, diodes and a CMOS chip, it also has a good overload protection circuit.
The full circuit and full description is at
https://www.dropbox.com/s/xm6r72p27iqbqox/controller.pdf?dl=0 (https://www.dropbox.com/s/xm6r72p27iqbqox/controller.pdf?dl=0)
Quote from: Dorsetmike on July 19, 2018, 05:35:29 PM
For a DC controller I've yet to find a better design than one I found in an electronics magazine some years ago; I've not seen a commercial controller using the same principle. I've made a few modifications to the original circuit, at the time I did show it to the Tech man at Farish near Poole (that dates it!) his opinion was that it would not harm Poole Farish motors, I've used it ever since with no problems, slow running control is superb, 5 minutes to cover 12", it even tames Dapol M7s.
When using simple controllers the motors used in many model locos are reluctant to start until the voltage rises above a certain level, but once started this voltage is enough to cause them to leap away in most unprototypical fashion.
This circuit uses a narrow pulse, (about 3ms mark, 12V, 27ms space, 0volts) that is just sufficient to make trhe motor start to turn, to increase speed the pulse is "mixed" with a DC level; as the speed control is increased the DC level is increased so at low speed the mark remains at 12V but the space rises to say 3v, this will increasethe average current and the motor speed rises, as the control is increased so the space voltage increases, further increasing the average current, until with control at full the motor is getting a full 12 V.
The circuit uses transistors, diodes and a CMOS chip, it also has a good overload protection circuit.
The full circuit and full description is at
https://www.dropbox.com/s/xm6r72p27iqbqox/controller.pdf?dl=0 (https://www.dropbox.com/s/xm6r72p27iqbqox/controller.pdf?dl=0)
Interesting concept Mike - essentially a straight mix of pure DC and pulsing.
Where's the soldering iron.... :-)
Cheers,
Alan
Quote from: Dr Al on July 19, 2018, 04:44:06 PM
Bear in mind the 45xx's can motor is very vulnerable to overheating if driven hard by feedback (e.g. it derails or suchlike) - the commutator will disintegrate if it gets too warm from excess driven current (and that level is not very high - something like 200mA). It's nowhere near as robust as some of the much older Farish for example which will only exhibit failure at 400mA+ (albeit this is usually a coil burn out).
Cheers,
Alan
My little 45xx (as shown in the video) has coped with many days at exhibitions using the feedback controller and runs the same as it always has. She still has quite a turn of speed too...
Quote from: Chris Morris on July 19, 2018, 04:32:39 PM
I made this bit of video today. It shows how the Dapol 45xx can be tamed with a feedback controller while the coreless motored Farish 2MT is fine with a non feedback controller ( a Gaugemaster W) but noisy and rough when using feedback.
It would be interesting to try the 45xx (and indeed the 2MT) on a PWM controller without feedback, to see if the pulsed power is enough to overcome the stickiness without actually needing to adjust the output rapidly via feedback.
Actually I think I've got a 45xx somewhere (was never very impressed with it), I'll dig it out and try it on my KPC with and without feedback.
Quote from: Chris Morris on July 19, 2018, 05:57:14 PM
My little 45xx (as shown in the video) has coped with many days at exhibitions using the feedback controller and runs the same as it always has. She still has quite a turn of speed too...
Wow! Much more impressive than mine on my Kato controller.
Can you tell me which model it is for comparison please, mine's 2S-014-002.
Quote from: ten0G on July 19, 2018, 06:37:35 PM
Quote from: Chris Morris on July 19, 2018, 05:57:14 PM
My little 45xx (as shown in the video) has coped with many days at exhibitions using the feedback controller and runs the same as it always has. She still has quite a turn of speed too...
Wow! Much more impressive than mine on my Kato controller.
Can you tell me which model it is for comparison please, mine's 2S-014-002.
I think the model number is ND-035. You model number suggests it is a later one which may have been geared more sensibly; the gearing was certainly well wrong on the early editions like mine.
Quote from: Chris Morris on July 20, 2018, 07:39:53 AM
I think the model number is ND-035. You model number suggests it is a later one which may have been geared more sensibly; the gearing was certainly well wrong on the early editions like mine.
They are all mechanically identical. Any difference will come from the magnetisation of the motor, and the wheelsets (quartering and wheel slippage on the axles is common on these).
Having said that on the ones I've seen there's little difference between batches in terms of performance.
Cheers,
Alan
Lots to think about for a newbie, quite happy with dc. I'm using a simple Gaugemaster Combi at the moment and all my stuff is open frame and pre-owned. Other than the odd rogue loco with issues I have pretty fair running even with an old clunker with brass gears. Interested to try a new loco, which I'd rarely run continuously for 10 -15 minutes anyway. Hopefully if a new loco ran ok during it's warranty period it should continue to do so?
Quote from: Old Crow on July 20, 2018, 04:05:07 PM
Interested to try a new loco, which I'd rarely run continuously for 10 -15 minutes anyway. Hopefully if a new loco ran ok during it's warranty period it should continue to do so?
I think you are massively overanalysing this - these motors have been around in locos for a good few years with virtually no reported failures.
So just buy the loco you fancy, and run it.
Cheers,
Alan
Quote from: Dr Al on July 20, 2018, 04:26:08 PM
Quote from: Old Crow on July 20, 2018, 04:05:07 PM
Interested to try a new loco, which I'd rarely run continuously for 10 -15 minutes anyway. Hopefully if a new loco ran ok during it's warranty period it should continue to do so?
I think you are massively overanalysing this - these motors have been around in locos for a good few years with virtually no reported failures.
So just buy the loco you fancy, and run it.
Cheers,
Alan
Agreed. The Gaugemaster should be fine for all.
One of my coreless motors in a Princess Coronation just developed a fault. It runs erratically at very low speed, so that when starting a loco, it gives all the symptoms you might expect from a loco with jamming mechanism, muck in gears and so on. Starts then stops, whizzes away, stops. After checking the mechanism for binding, I removed the motor and ran it with the worm disengaged, and the motor itself exhibited the same behaviour with no load. I suspected the decoder at first, as this loco had recently been converted to sound, but after testing with a spare Dapol A4 motor, it seems the decoder is fine. So I have a replacement motor on order. @Dr Al (http://www.ngaugeforum.co.uk/SMFN/index.php?action=profile;u=263), can you tell me if the motors are supplied by Bachmann with the worm fitted, or do I have to take the worm from the existing motor? If so, how is it removed / replaced?
I'd check the motor on DC - DCC is a pain for diagnosing problems.
In terms of Bachmann - I'd presume they'll come with a worm. Mine didn't, but weren't bought from Bachmann, so a worm puller was needed to switch over the worm from the old motor.
Cheers,
Alan
Quote from: Dr Al on August 03, 2018, 01:25:40 PM
In terms of Bachmann - I'd presume they'll come with a worm. Mine didn't, but weren't bought from Bachmann, so a worm puller was needed to switch over the worm from the old motor.
Where do you get yours from? £19 from Bachmann, but I didn't find any alternative source on line.
Hoping it comes with the worm as I do not have a puller!
Quote from: Bramshot on August 03, 2018, 05:20:49 PM
Hoping it comes with the worm as I do not have a puller!
A very useful tool for the box!
https://www.ebay.co.uk/itm/Walkera-W010-Gear-Pinion-Puller-Remover-Tools-Set-For-Rc-Motor-Pinion-Parts-Y5Y3/282751336226?epid=1169032754&hash=item41d54aff22:g:K9kAAOSw43haHJzS (https://www.ebay.co.uk/itm/Walkera-W010-Gear-Pinion-Puller-Remover-Tools-Set-For-Rc-Motor-Pinion-Parts-Y5Y3/282751336226?epid=1169032754&hash=item41d54aff22:g:K9kAAOSw43haHJzS)
I have ordered one!
Quote from: Bramshot on August 03, 2018, 05:20:49 PM
Where do you get yours from? £19 from Bachmann, but I didn't find any alternative source on line.
There were some on eBay a year or more ago - nothing identical currently or for a while - but they were 10 for about £15 delivered IIRC.
Cheers,
Alan
I know you are well up with the DCC decoder settings to use for coreless ( I presume the sound install settings motor control was checked - I have found they sometimes use basic settings I wouldn't if they are tuned for particular loco make/motor installs - since they aren't usually scale specific), but one issue I have had, which might just be the problem here, is that the motor leads can break/fracture internally, and give this kind of on/off power supply. Not easy to replace since they are wired into the end casing, which aren't meant to be removed.
It's just a thought,
Izzy
Yes, it is also a Zimo sound decoder, and I had set the coreless settings in it. It ran happily for several hours with the new decoder, then was shelved to make way for a different era. When brought back, it ran ok on day one, but the fault appeared on day two at startup. I had been fiddling with CVs so assumed at first that I had mucked something up, but the problem persisted after reset, for which I needed some assistance from You Choos, as it doesn't appear to reset using POM and I had to use the programming track. However, the fault persisted and I have today replaced the motor with a new one (thanks Bachmann for a two day turn around) and the replacement thankfully did have a worm fitted. Fault cleared.
I had noticed that the wire insulation was frayed to expose the conductors where it enters the motor end cap. This was a loco where the torque restraint was not engaging properly in the mounting bracket, and the wires were doing the restraining, so maybe it fatigued then.
Pity the loco was just out of warranty, though they may not have accepted it after sound had been fitted.
I only noticed the longish delivery on the puller I ordered aftre having ordered it ( a month or so estimated), so I am glad the replacement had a worm already fitted!
Update
Well the puller arrived, it works after a fashion, except the pushing pin isn't long enough to push the shaft right through the worm. It needed a tapping with a small screwdriver shaft to get it right off.
Just to see if it would work, using the busted motor, I tried replacing the worm, just by tapping it on again, with the none-drive end of the motor resting on a table. It worked, did not have to tap too hard and the bearing seems no worse for wear afterwards. So there must be something internal for the shaft to press up against.
So there is hope, if you can find a cheap replacement motor.
I guess Dr Al must already have done something similar?