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Hi, despite much reading and internet searching I am still completely unsure as to what combination of gears I need and how to order them from their descriptions on the 2mm web-site. I'm more a pictures sort of learner and there aren't as many as I find comfortable; particularly when trying to match ratios etc to the shop offerings, so please excuse my ignorance!

In particular I'm after a set of gears from a tender mounted motor to a gear box on the large single driver of a Midland Spinner. I think I'm looking for a high gear ratio to get some form of slow running. And I know that there may not be much in the way of pulling power with a single driver so a tender drive might be the answer eventually. I've done this in N Gauge by driving the tender with a Dapol Terrier chassis and I'd like to make a 2mm version too!

Any thoughts?

Cheers

Simon

post-7598-0-92566500-1483189932_thumb.jpg

 

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You work out the gear ratios by dividing the number of teeth on the following gear by the number on the driving gear. E.g.an 18t gear at the motor end onto a 36t gear gives 2:1 as does a 14t to a 28t. The same 18t gear to a 27t gives 1.5:1 and so on. You then multiply that by the worm ratio (the number of teeth on the worm wheel) to get the overall ratio. Any intermediate (lay) gears don't make any difference other than reversing the direction of rotation.

Jim

Edited by Caley Jim
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Simon, see the 2mm finescale chassis thread nearby. Lots of discussion on the pros and cons of tender drives.

 

Are you scratch building the chassis? Either one of the two worksheets combined with an subsequent further reduction of 1.5-2 to 1 should be ample. Use the meshing centre table in the yearbook to draw out a possible gearchain.

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Whilst we're on the subject of gears, can anybody recommend a beginners guide please? Jim's explanation is helpful but like Simon I find this sort of stuff easier with pictures!

 

Thanks,

 

David V.

 

If you are a 2mm Association member, and the Handbook is still available to download from the website, you could do worse than the chapter on loco construction. It has some examples of various gear arrangements for different chassis that are a good starting point to working out the best set up for your own project. Often it is more a case of what will fit in the space available than what is the best arrangement.

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Suggest the 2mm book list on the shop pages; they are under Shop-1 for historic reasons.

 

P-103 covers chassis design and includes some sections on gears.

P-106 is pretty much all loco superstructure and detailing elements.

P-109 is the magazine backnumbers (eg. gear theory articles in the 1990's by Brownlee and Oversloot), plus a few out-of-print booklets which will have information in them (eg. "build an 0-6-0".

 

 

 

- Nigel

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A couple of points to remember when choosing gear ratios is that the diameter of the final gear on the driven axle must be less than that of the driving wheel itself (unless your planning on never running the loco through a turnout).  I recall a Groves Trophy entrant which ran perfectly smoothly on plain track andthen leapt in the air when it came to a turnout.  The owner's excuse was that hi test track didn't have any turnouts on it!

 

The second point is that if you are having a reduction between the worm wheel and the axle, you must make sure that there will be clearance between the wormwheel and the muff on the axle.  I.e. the centres of the secondary gears must be =>wormwheel radius+muff radius.

 

Jim

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In one of the early MRJs, Allan Sibley wrote about powering a 4mm kit for a Midland Spinner using an RG4 motor/gearbox combo to drive the trailing axle rather than the driving wheel.

 

Now we can't get a 2mm equivalent of an RG4 but it should certainly be possible to do something similar by bringing the drive forwards and then back onto the trailing axle with a 2 stage spur stepdown from a worm, hiding it all in the firebox.

 

Then if it's arranged so that the weight of the loco and tender can fall on that rear axle, some reasonable tractive effort should be available.

 

Mark

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In one of the early MRJs, Allan Sibley wrote about powering a 4mm kit for a Midland Spinner using an RG4 motor/gearbox combo to drive the trailing axle rather than the driving wheel.

 

Now we can't get a 2mm equivalent of an RG4 but it should certainly be possible to do something similar by bringing the drive forwards and then back onto the trailing axle with a 2 stage spur stepdown from a worm, hiding it all in the firebox.

 

Then if it's arranged so that the weight of the loco and tender can fall on that rear axle, some reasonable tractive effort should be available.

 

Mark

 

What are the wheel diameters? If the driver is say, 14mm and the trailing wheel 7mm then how about a 2:1 gear between the two, and drive both? ;)

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What are the wheel diameters? If the driver is say, 14mm and the trailing wheel 7mm then how about a 2:1 gear between the two, and drive both? ;)

They would have to dead exact for that - otherwise welcome to the wonderful world of transmission lockup.

Does work ok on tractors with hydraulic drive though.

 

I think I recall a suggestion many years ago - applicable to single drivers only - of mounting the drivers on stub axles then using a central motor driving leading and trailing axles via cardan shaft to allow bogie swing. Even allows the tender wheels to be driven!

 

This was done on full-size 2ft gauge locos built by Chance in the USA for pleasure railways, many of which worked in the UK at Butlins and elsewhere. Think they also had the 'drivers' slightly above rail level and driven but not quite in sync as if they'd been in rail contact.

Edited by decauville1126
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I'm not sure that driving the trailing wheel is any better traction-wise than the main wheel. Perhaps this is a case where tender drive would actually produce more - however little it may be - than the loco. Or you could just reverse things, put the motor in the loco and drive the tender via a carden shaft, so the tender could be filled with weight. A thought perhaps?

 

Izzy

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What are the wheel diameters? If the driver is say, 14mm and the trailing wheel 7mm then how about a 2:1 gear between the two, and drive both? ;)

 

Arise, Sir Cumference!

 

I think π might have some influence on that...

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Arise, Sir Cumference!

 

I think π might have some influence on that...

 

Is Mark getting very obscure, or did his New-Year tipples knock out the O-level maths neurons ?   

 

   π just drops out in the sums, so isn't important;   Ratio of circumferences: 14π / 7π = 2 / 1

 

 

That said, I don't think I'd bother with such a drive system.  If lacking tractive effort which can't be solved with weight and balancing, then Izzy's idea of motor in loco driving gears in tender seems the most promising option. 

 

- Nigel

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Since the tyres are coned, the rail head is curved and the wheels can slide slightly from side to side within the track gauge, you can never guarantee exactly what wheel radius is in use at any one time.

 

As that applies to wheels of the same diameter, what's the relevance ?   

 

For anyone who cares, the difference of wheel diameter taken over the full width of the tyre cone is 0.1mm. 

 

- Nigel 

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I'm not sure that driving the trailing wheel is any better traction-wise than the main wheel.

 

Izzy

 

Possibly not. But it certainly could be easier to balance the loco to get enough weight bearing onto the rear axle. I should imagine it difficult to stop a Single simply rocking about the centre axle. 

 

Against driving the rear axle is that it will not take a very large final gear. When I designed the Class 03 chassis, it was impossible to get anything other than a minimal amount of extra gear reduction from the spur gear stage.  So in effect you are probably left with 30:1. However this would give the same top speed as 60:1 on the main axle.

 

If driving the main axle, one might consider the Ultrascale worm sets which offer higher ratios than was available in the varieties the Association stocked. 46:1 or even 50:1

 

https://www.ultrascale.uk/eshop/products/view/CAT015/218

 

Chris

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You can stop a single rocking on its centre axle by using beam compensation as I did with 1A. You can also adjust the weight distribution, within limits, by how you arrange the pivots.

Jim

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Is Mark getting very obscure, or did his New-Year tipples knock out the O-level maths neurons ?   

 

   π just drops out in the sums, so isn't important;   Ratio of circumferences: 14π / 7π = 2 / 1

 

 

That said, I don't think I'd bother with such a drive system.  If lacking tractive effort which can't be solved with weight and balancing, then Izzy's idea of motor in loco driving gears in tender seems the most promising option. 

 

- Nigel

 

It's often difficult to implement these systems. Typically the secondary spur gears on locos have to sit to the side behind the frames as the worm wheel is on the centreline. But the narrow firebox on a pre-grouping loco like a Single may not allow this.

 

Chris

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Loads of stuff to think about, thankyou everyone. I'm keen to power the large single drivers; the ultrascale gears look interesting and simple. I have also dug up my copies of the 2mm magazine in which Tony White shows how he built a T9 with a beautiful little gearbox driven by a shaft from the tender...with lots of pictures! Hurrah!

I'll be helping to run the Luton club's 7mm "Central Works" layout at Stevenage on the 14/15th Jan. Is there someone from the 2mm Society stand I could have a chat with and who might be able to show me some gears! And the associated jigs and tools?

 

My N Gauge Spinner has sprung, slimmed-down 4mm Gibson drivers running in High Level hornblocks with a sprung, weighted pony truck. The rear wheels are allowed about 0.5mm movement up and down in oval filed bearings.

 

post-7598-0-18009400-1483291570_thumb.jpg

 

 

 

Regards

Simon

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Loads of stuff to think about, thankyou everyone. I'm keen to power the large single drivers; the ultrascale gears look interesting and simple. I have also dug up my copies of the 2mm magazine in which Tony White shows how he built a T9 with a beautiful little gearbox driven by a shaft from the tender...with lots of pictures! Hurrah!

I'll be helping to run the Luton club's 7mm "Central Works" layout at Stevenage on the 14/15th Jan. Is there someone from the 2mm Society stand I could have a chat with and who might be able to show me some gears! And the associated jigs and tools?

 

My N Gauge Spinner has sprung, slimmed-down 4mm Gibson drivers running in High Level hornblocks with a sprung, weighted pony truck. The rear wheels are allowed about 0.5mm movement up and down in oval filed bearings.

 

 

 

Regards

Simon

 

Hi Simon, I will be at Stevenage demonstrating 2mm loco building and will have various finished and part built locos with me. If there is anything specific you want to see let me know and I'll try to remember to bring it up. Julia Adams, another excellent 2mm modeller will also be there demonstrating. Do come and introduce yourself, it would be good to meet you - I thoroughly enjoyed your book.

Tim Watson built a beautiful Spinner which was written up in the old Model Railways magazine back in the 80s I think, I will dig out my copy of it. Tim will be at Stevenage on Copenhagen Fields.

 

Have you looked in some of the other 2mm threads on RMWeb. As well as the chassis one mentioned above there is my Bath Queensquare thread which currently has posts about loco building - Im building a small SDJR 4-4-0 at the moment.

 

Jerry

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No problem with single drivered locos so long as there is as much weight as possible on the driving wheels. The two singles on CF will each pull the train that they run with, they just look better double heading (and very typical of the GN in the 1900s).

 

The Ivatt rebuilt Stirling 2-2-2 single uses a 50:1 worm and wheel: you can't see the worm in side view.

 

3136t6c.jpg

 

The tender has a coupling with the engine that only allows movement in one direction, as can be seen by the way it can be held by the tender alone.

 

ngojrn.jpg

 

The fall plate between engine and tender helps to achieve this rigidity.

 

2e531wg.jpg

 

With this coupling the tender chassis has to be able to float independently, using the slack screw at the back to support it on one point and a piece of studding at the front to keep it centred.

 

xqgpzo.jpg

 

Interesting that you made an N gauge model of 672, Simon. My Johnson single started off as 672 in 1977, but was re-numbered as 663 when it was converted to 2mm finescale in 1980. The bogie wheels on 672 are much bigger than on 663, so it was simpler to use the correct size Association wheels and change the number and a slight modification of the front frames. I would also add that as an N gauge single the driving wheels spent more time going sideways than forwards, as there was too much slop between wheel and rail, so a tender drive for N is probably not unreasonable.

 

2u4kimr.jpg

 

See you at Stevenage.

 

Tim

Edited by CF MRC
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Thanks very much Tim and Jerry. I've really enjoyed reading through the 2mm threads having had my interest piqued by the recent kind gift of a baseboard from the late Steve Sykes' last 2mm layout project. I hope to use it to build an LSWR/Midland based station; (no Great Western, not one of Steve's favourites!). I look forward to meeting you, Jerry, at the show. What I need to do is to be able to visualise the size of the gears, then I can build things. (Perhaps a set of pictures/diagrams of the available gears would be a nice thing to add to the 2mm Society's web-site?) So if you're demonstrating building 2mm locos that would be brilliant!

And Tim, when Dave C., gives me some time off the stewards' rota I'll pop over to CF for a chat, it would be good to see you and the Spinner if it's around!

 

Cheers

Simon

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I'm not sure that driving the trailing wheel is any better traction-wise than the main wheel. Perhaps this is a case where tender drive would actually produce more - however little it may be - than the loco. Or you could just reverse things, put the motor in the loco and drive the tender via a carden shaft, so the tender could be filled with weight. A thought perhaps?

 

Izzy

 

I had a quick play in CAD and have concluded doing a tender drive (with or without motor) is not easy using Association methods. In order to keep the gears below the footplate to allow a motor to be present above, you need to use a lot of small gears as RTR tender drives do. Using a single idler between axles means a gear sticking up well above the footplate and is in any case infeasible on tenders with relatively long wheelbases. And the idelrs would be very visible below the frames if viewed from side on. So expect a lot of gears, and hence expense.

 

I would probably go for a rewheeled and remotored RTR tender drive if I really had to do this.

 

Chris

Edited by Chris Higgs
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