Hornby Ruston 48DS and feedback

[asjharrisParticipant]

Hello All,
I’ve managed to successfully convert my Hornby Ruston to EM but am finding it is a jerky runner on my Gaugemaster feedback controller, seems reasonable on pure DC, although not great. Other locos are absolutely fine.

The motor looks to me to be a poor quality thing and not coreless, but the jerky running seems to ape the feedback pulse to me. Is it actually a coreless motor does anyone know?

Thanks
Tony Harris

[asjharrisParticipant]

Here’s a shot of the conversion.

• This reply was modified 2 months, 1 week ago by asjharris.

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[Paul TomlinsonParticipant]

Tony, Hello. Hornby describe the motor as a “3-pole”, so not coreless (see the Tech Specs in the attached link). I assume you’re running with the match truck to aid pickup, and adjusted the wipers to cope with the increase in B2B?

As regards coreless motors, the smallest High Level do is a 1219, but Peter’s Spares have a good selection of smaller ones, if you feel inclined to replace it.

RT Models also do an etched chassis, and High Level do a 4WD drive.

https://uk.hornby.com/products/ruston-hornsby-48ds-0-4-0-200792-gower-princess-era-10-r30013

[asjharrisParticipant]

Paul, thank you for the link. I don’t want to replace with a coreless motor because I use DC feedback controllers and don’t want to put another chassis under it either, not sure why I should have to. Just disappointed that the mechanisms in these locos are so poor.

You can see in the second pic the pickups are working properly.

Thanks
Tony

[Stuart FirthParticipant]

Hi Tony, forgive me if you’ve already looked at this, but those wheels look very close to the brakes, closer than I could get away with – if they are metal is it possible there’s a slight short? Easily checked by turning out the lights. If they are plastic then could they be rubbing intermittently on the treads? Just some thoughts.

[asjharrisParticipant]

Thanks Stuart, good question. I think they are plastic. I think I have to rule out a physical problem because on a plain DC controller the loco runs ok, but on DC feedback it is jerky, but a consistent jerky, i.e. clearly a pattern can be seen in the jerkyness.

It’s not the controller as it works fine with other locos.

Cheers
Tony

• This reply was modified 2 months, 1 week ago by asjharris.

[Stuart FirthParticipant]

Fair enough – I too have had an issue with a motor ‘not liking’ feedback (Sorry Mr. Ridgway). This also is not a coreless motor, but one of the chunky 16mm square cans with a 6 pole armature that you can buy cheaply from ebay. On feedback it hunts and surges, but it’s great on pure DC and PWM controllers. I just give up and use a different controller with it. I have tried putting a grain of wheat bulb across the motor terminals, which can do the trick with coreless motors, but it didn’t improve. Might be worth a try with yours though.

[asjharrisParticipant]

Hello Stuart,
Thanks for the information, I tried the Ruston with a Medvend controller and it’s ok, I think these are PWM.

The idea of the grain of wheat bulb sounds interesting, not being an electronics expert, this does sound as if it is acting as some sort of resistor? Would fitting a resistor of some sort work? Is there any published information on this?

Cheers
Tony

• This reply was modified 2 months, 1 week ago by asjharris.
• This reply was modified 2 months, 1 week ago by asjharris.

[Stuart FirthParticipant]

I can’t remember the theory, am no electronics expert, no not at all, not by a long chalk, but will ask @Nick Ridgway to comment as he knows quite a bit about it I seem to recall.

[Nick RidgwayParticipant]

The resistance of a GOW bulb across the terminals is there to better match the motor and controller from the perspective of system dynamics and control system stability. Without it, a low-inertia motor will behave badly with feedback controllers.

Some decades ago I did some experiments with ECM Compspeed type A, a favourite of mine, with Portescap 1219, another favourite, connected to an oscilloscope. It revealed what was going on.

My write-up is available as a Manual sheet. If more explanation is needed I can up-rev it; please advise?

[Stuart FirthParticipant]

Manual Sheet 5.3.3. (6) – it was there all along !

[asjharrisParticipant]

Thank you Nick and Stuart, I also read something similar on RMweb last night, it does explain why I have got amazing running with my old iron motors on feedback. Funnily enough the same thread mentioned the EM gauge manual sheets on feedback, which I already have so will re-read.
Thank you everyone for your help so far….
Cheers
Tony

• This reply was modified 2 months ago by asjharris.

[Nick RidgwayParticipant]

If the feedback controller were to operate at 500Hz rather than being referenced to the mains at 50Hz, then there would be no problem with the smaller motor, as it could operate faster than the motor could change speed. However, not every modeller could cope with the sound of B above middle C coming out of models all day long.

Siemens experimented with variable frequency drive on DC traction in Germany recently. The variable frequency turned out to be the German national anthem… 😉

• This reply was modified 2 months ago by Nick Ridgway.

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