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:







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





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!