Coreless motors and worm gearboxes.

sam.makins
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Coreless motors and worm gearboxes.

Postby sam.makins » Fri Dec 08, 2017 5:13 pm

Hi all,

I've been told that you shouldn't mount a worm gearbox directly on to a coreless motor because they're not designed to cope with the end thrust created by a worm.

Does anyone know if there's any truth in this?

I'm attracted to the idea of using coreless motors for their smoothness and lack of cogging at low speed but would like to use Chris Gibbons beautiful gearboxes because they're readily available and the range is so adaptable to suit different locos.

Sam

nigelcliffe
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Re: Coreless motors and worm gearboxes.

Postby nigelcliffe » Fri Dec 08, 2017 5:21 pm

sam.makins wrote:Hi all,

I've been told that you shouldn't mount a worm gearbox directly on to a coreless motor because they're not designed to cope with the end thrust created by a worm.

Does anyone know if there's any truth in this?


Depends on the motor and the amount of end-thrust you're going to get. Doesn't matter if its a cored or coreless motor design.

Where did this story come from ? Some coreless motors don't have suitable bearings for end-thrusts. So, put that motor in a hulking great big mainline loco which is half-full of lead, attach a dozen coaches, and the worm pushes the end out of the motor. And thus you have a story which does the rounds.

Can you use worms directly onto small coreless motors ? Yes, because otherwise my 2mm locos will instantly stop working (they're still working a decade or more after some were built).

So, it depends on the motor, and the loads you're subjecting it to. Any motor will be a lot happier if you've put something in between the motor and worm to take out the end thrust, but depends if you can squeeze in suitable bearings and a small drive clutch, or come up with an arrangement where the motor is free to move along its thrust axis, and some bearings stop the worm from moving too far.


- Nigel

sam.makins
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Re: Coreless motors and worm gearboxes.

Postby sam.makins » Fri Dec 08, 2017 6:24 pm

Nigel,

Thanks for that comprehensive reply.

The story came from my dad but not sure where he got it from!

The motor in question is a Maxon 16x26 going into a LNWR 2-4-2. According to the datasheet the maximum permissable dynamic axial load is 0.8N but I've got no idea how much thrust a worm can produce in a 4mm loco! I don't think I can fit a drive clutch in unfortunately.

I think I might just try it and hope for the best!

Sam

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grovenor-2685
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Re: Coreless motors and worm gearboxes.

Postby grovenor-2685 » Fri Dec 08, 2017 6:46 pm

Where did this story come from ?

That was the "state of knowledge" when coreless motors came into modelling with the introduction of the Portescap and micro-metalsmiths gearbox systems. I recollect reading it many times, I'm sure a read of magazines from that era will soon bring up examples. No doubt things have changed in the 40 odd years since but it is certainly a good idea to check the spec of the motor you are using.
If you can spare 10mm then you should be able to fit Chris Gibbons tenderiser parts with a short universal.
Regards

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steamraiser
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Re: Coreless motors and worm gearboxes.

Postby steamraiser » Fri Dec 08, 2017 8:34 pm

I believe some HL gearboxes are designed so that the motor need not be part of the main construction but can be mounted separately, linked by an intermediate drive shaft.

It might be worth your while to ring Chris Gibbons (HL) direct and discuss what you would like to do.
He is quite helpful.

Gordon A

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grovenor-2685
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Re: Coreless motors and worm gearboxes.

Postby grovenor-2685 » Fri Dec 08, 2017 9:27 pm

steamraiser wrote:I believe some HL gearboxes are designed so that the motor need not be part of the main construction but can be mounted separately, linked by an intermediate drive shaft.
Gordon A

That's the 'tenderiser' I mentioned.
Regards

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steamraiser
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Re: Coreless motors and worm gearboxes.

Postby steamraiser » Sat Dec 09, 2017 12:40 am

I understand the tenderisder to be the gear box that has an out put shaft lower than the input / motor shaft.

What I was referring to was the final drive gear boxes that have an additional etch for a bearing in place of the motor.

Gordon A

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Paul Townsend
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Re: Coreless motors and worm gearboxes.

Postby Paul Townsend » Sat Dec 09, 2017 7:54 am

sam.makins wrote:Nigel,

Thanks for that comprehensive reply.

The story came from my dad but not sure where he got it from!

The motor in question is a Maxon 16x26 going into a LNWR 2-4-2. According to the datasheet the maximum permissable dynamic axial load is 0.8N but I've got no idea how much thrust a worm can produce in a 4mm loco! I don't think I can fit a drive clutch in unfortunately.

I think I might just try it and hope for the best!

Sam


I used to design professional small servos with mostly Escap coreless motors.
The full Escap catalogue that I used to have gave longtitudinal thrust specifications.
I may later find that cat, but recall the figure was very small.
So the rumour your Dad heard was valid.

Nigel gets away with it by choice of motor and careful build of gearing aided by lower drive power and thrust required in 2mm.

In 4mm or larger scales with Escap coreless motors you MUST either use bevel gears as the late lamented Portescap drives did or decouple the thrust of the worm from the motor. It is not too difficult to arrange with a decent gearbox to add a thrust bearing or use tender drive via cardan shaft etc
It may be that Maxon coreless have more tolerance to thrust but I doubt it and don't have the full specs to hand....yet.....said catalogues are buried due to house move and may take some unearthing.

nigelcliffe
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Re: Coreless motors and worm gearboxes.

Postby nigelcliffe » Sat Dec 09, 2017 8:37 am

sam.makins wrote:
I don't think I can fit a drive clutch in unfortunately.



A simple and small clutch is as follows:

Put a flat on the motor shaft, filing/grinding until the diameter, so it has a D profile at its end.
Put a flat on the worm shaft, with a similar D.
Fit a collar around the worm shaft (cylinder of metal) with adhesive, this leaves a D-shaped hole into which the motor can drive. That collar can be one of the worm thrust bearings.

A slightly posher version uses a flat (screw driver appearance) into a slot.

All that's now required is to support the motor so it stays aligned with the gearbox. With many Maxon/Faulhaber style motors, they have a standard screw nose which could fit around the clutch described above.


- Nigel

Clive Impey
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Re: Coreless motors and worm gearboxes.

Postby Clive Impey » Sat Dec 09, 2017 12:06 pm

Sam,

On Page 25 of Scalefour News 205 there is a photo of a GWR 633 class tank. The loco has a Portescap motor driving a dog clutch on a High Level gearbox. I am sure the builder would help you if you were to contact him.

Clive

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grovenor-2685
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Re: Coreless motors and worm gearboxes.

Postby grovenor-2685 » Sat Dec 09, 2017 12:23 pm

steamraiser wrote:I understand the tenderisder to be the gear box that has an out put shaft lower than the input / motor shaft.

What I was referring to was the final drive gear boxes that have an additional etch for a bearing in place of the motor.

Gordon A

You may be right Gordon, I thought the additional etch was part of the tenderiser, its that extra etch I was suggesting to use.
Better check the website to pick the right names :)
Regards

Alan Turner
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Re: Coreless motors and worm gearboxes.

Postby Alan Turner » Sat Dec 09, 2017 1:06 pm

grovenor-2685 wrote:
steamraiser wrote:I understand the tenderisder to be the gear box that has an out put shaft lower than the input / motor shaft.

What I was referring to was the final drive gear boxes that have an additional etch for a bearing in place of the motor.

Gordon A

You may be right Gordon, I thought the additional etch was part of the tenderiser, its that extra etch I was suggesting to use.
Better check the website to pick the right names :)
Regards


Well if there such gear boxes it is certainly not clear from the HL web site.

regards

Alan

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steamraiser
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Re: Coreless motors and worm gearboxes.

Postby steamraiser » Sat Dec 09, 2017 3:58 pm

That's why in my post I said it would be worth ringing Chris and discussing requirements, just in case I was dreaming.
(Shame posts on each thread are not automatically numbered as on RMW for reference).

Gordon A

sam.makins
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Re: Coreless motors and worm gearboxes.

Postby sam.makins » Sat Dec 09, 2017 6:28 pm

Thanks for you help and advice so far gents.

Keith, Gordon & Alan, most of the high level gearboxes (possibly all) do include facility for remote drive using a pair of bearings mounted fore and aft of the box to carry the worm.

Nigel, thanks for your suggestions, the simple drive clutch you've described should be relatively easy to set up providing I've got enough room to spare. I may have to use a smaller motor and save the big Maxon for a tender loco.

Paul, thanks, I'll look at options to decouple the worm from the motor etc.

Clive, I'd spotted the 633 Class in the latest S4 news, that's what set me thinking again as it shows coreless drive on a high level box can be done in a small tank loco. I've emailed Pete Sutherland to ask how he did it but not sure if I've found a good address for him.

Sam

Clive Impey
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Re: Coreless motors and worm gearboxes.

Postby Clive Impey » Fri Dec 15, 2017 3:52 pm

Sam

In Scalefour News number 139 there is an article by Peter Sutherland describing the fitting of coreless motors to High Level gearboxes. Also in S4News 149 Graham Seed has an article on fitting Maxon motors to High Level boxes.

Clive.

sam.makins
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Re: Coreless motors and worm gearboxes.

Postby sam.makins » Sat Dec 16, 2017 9:47 pm

Hi Clive,

Thanks very much, I'll have a look at those.

Sam

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Horsetan
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Re: Coreless motors and worm gearboxes.

Postby Horsetan » Mon Jan 01, 2018 4:39 pm

Paul Townsend wrote:....In 4mm or larger scales with Escap coreless motors you MUST either use bevel gears as the late lamented Portescap drives did or decouple the thrust of the worm from the motor. It is not too difficult to arrange with a decent gearbox to add a thrust bearing or use tender drive via cardan shaft etc
It may be that Maxon coreless have more tolerance to thrust but I doubt it and don't have the full specs to hand....yet....


I note that the European HO people have had a lively industry offering remotoring kits based around Faulhaber and Maxon coreless for years. All of these seem to have direct worm drive, especially for the tender-driven engines (of which there are many).

Examples here - not particularly elegant solutions, but they seem to be the in-thing.

I still prefer reversible geartrains. :thumb
That would be an ecumenical matter.

sam.makins
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Re: Coreless motors and worm gearboxes.

Postby sam.makins » Wed Jan 03, 2018 11:07 pm

Hi Horsetan,

I'd found that site the other day and noticed their use of worms myself. I'm going to try and contact them to see if they use / supply motors specced with more robust bearings than normal.

I too prefer reversible drives but want to use high level or similar boxes for their ease of construction and ready availability.

Sam


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