Locomotive drives

[Chris Higgs]

Interesting thread and I'm certainly one for experimentation outside of the accepted guidelines. For something like joint loco and tender drive, the maths behind it is relatively simple but I would be worried about the real world constraints that such a model would bring along - differing frictions, etc, etc. I think it would be worthwhile building a prototype to get the plan sorted out and highlight the limitations and pracitcalities of building the idea. If it works - ace, bring it on. If it doesn't - it was a good learning exercise.

 

However, it is limited by the fact that gears can have only whole numbers of teeth. So if you choose an arbitrary combination of wheels with different diameters, you cannot guarantee to find two sets of gears that will drive them from the same motor (unless they have very fine teeth). If you adjust the wheel diameters to match your available gears, then yes.   

[(The) Youth]

I don't understand why you would want to drive tender and loco when driving just the loco is perfectly adequate by the sounds of things  

More expense and more things to go wrong 

 

Simon

[Armchair Modeller]

2mm kits are difficult enough for some people to put together reliably, without unnecessary complications. Keep it simple sounds best to me!

[Thos]

There are locos on the market with tender drive, but they don't pull enough, even with traction tyres.

Chris

 

While I would not dream to comment on the other points made, Union Mills use tender drive and are reputed to have excellent pulling power.

[Chris Higgs]

While I would not dream to comment on the other points made, Union Mills use tender drive and are reputed to have excellent pulling power.

 

Yes, but in many cases they had to make the tender far too large for the prototype modelled, and in heavy cast metal, sacrificing much fine detail in the process. Not exactly a finescale solution.

 

Chris

[queensquare]

Yes, but in many cases they had to make the tender far too large for the prototype modelled, and in heavy cast metal, sacrificing much fine detail in the process. Not exactly a finescale solution.

 

Chris

 

It also only has pickups on one side as the other has traction tyres. 

 

Jerry

[Chris Higgs]

It also only has pickups on one side as the other has traction tyres. 

 

Jerry

 

Depending on the loco (and how many wheels it has) this could be OK. My Fleischmann 2-10-0s can afford to have traction tyres on every wheel if it wished, given the ten there are available on the loco. And they can pull one hell of a train as a result. But for a small UK prorotype, it will be an issue.

[Chris Higgs]

Provided they're well-designed and flexible enough to suit a range of locos, etc. (and useable for split frame chassis locos) I can't see why they wouldn't be a good idea.

 

And therein lies the problem. Gearboxes tend not to work that well when running on plastic muffs instead of steel axles. This has been thought about by a lot of people in the past but always with the conclusion that it didn't really work with the current 2mm wheel range. If you have a new range of plastic/FUD wheels with 'normal' axles then it is feasible.

 

The other issue is that unless the prototype is large, there is only one place to put the motor and hance the gearbox probably has to be customised to the loco, rather than a generic one. Even in 4mm where comparatively there is acres of space, you need several configurations.

 

CHris

[queensquare]

Depending on the loco (and how many wheels it has) this could be OK. My Fleischmann 2-10-0s can afford to have traction tyres on every wheel if it wished, given the ten there are available on the loco. And they can pull one hell of a train as a result. But for a small UK prorotype, it will be an issue.

 

I have fitted additional pickups to a lot of these Union Mills locos as although haulage is more than adequate, pickup often is not. They use the so called 'american system' with pickup on one side of the loco and the other side of the tender. In N/2mm on small 0-6-0 or 4-4-0's this is not enough.

 

Jerry

[2mmMark]

 

My range of kits has come about from market research from the many people in both 2mm and n gauge worlds saying this is what they would like.

 

Damien, the N2 you have listed on your web page for LNER kits is actually an N7. An N7 would be of interest to me but given you've got other GNR origin locos listed, I suspect you do mean an N2...

 

Mark

[Ian Smith]

An interesting thread.

 

Damien,  I personally can only echo what many others have said before - Motor in tender driving wheels in engine using a cardan shaft.  I applaud the generous number of potential offerings (although I personally would only be interested in the Dean Goods, but then only if both the loco and the tender were pretty accurately dimensioned - I for one would not want an over-sized tender).  Having said that I would certainly ditch the boiler because I wouldn't want the Belpaire version of firebox either.

 

When I originally looked at your new website a week (or two) ago apart from thinking "Ooo this looks exciting" my initial concern was the use of 3D printing for the boilers.  I have had a few projects 3D printed in Shapeways FUD so far and whilst the results have been fine (in my opinion) for wagon bodies I would not consider having something round (or indeed completely flat) printed - the stepping between the layers is to pronounced so would need quite a bit of post finishing.  Perhaps you will already be doing that?  I think the 3D printed wheels could be OK assuming they were finished to be concentric to the axles - I have read Missy's recent post on her blog highlighting some of the problems.

 

In conclusion I wish you well with your enterprise, and hope that it takes off.

 

Ian

[Atso]

Funnily enough the idea of both the loco and tender being powered has been done in N gauge using a V2. IIRC from the article I read this was a somewhat fiddly to set up but worked well once the chassis settled in. However, this looks like a lot of work for limited benefits. Be all means experiment but sometimes the simplest and most time honored methods are the best.

 

I would suggest that you design your kits to accommodate those with the most limited skills. This way those with limited skill will feel more comfortable tackling a kit which those more able will be able to modify their model as they see fit.

 

While my own practical experience making working chassis is limited I see the benefits of driving the loco via a motor in the tender. This allows the ability to provide a lot of weight where it is needed, above the driving wheels while keeping things simple and not potentially over taxing the motor. Look at the approach Dapol have taken with their N gauge tender locos, now that they have refined the design there is a lot of credit to their pulling power - although some argue that the motors need better quality control (not an issue I've yet had).

 

Sometimes you can make a refinement to the wheel but it is impossible to reinvent it.

[queensquare]

 

Look at the approach Dapol have taken with their N gauge tender locos, now that they have refined the design there is a lot of credit to their pulling power 

 

Sometimes you can make a refinement to the wheel but it is impossible to reinvent it.

 

Dapol have indeed refined their design including split axle pickup, motor in the tender driving the loco via a carden shaft........sound familiar......... similar to that advocated by the 2mm Scale Association for the last forty years or so.

 

Jerry

[Atso]

Dapol have indeed refined their design including split axle pickup, motor in the tender driving the loco via a carden shaft........sound familiar......... similar to that advocated by the 2mm Scale Association for the last forty years or so.

 

Jerry

 

Hi Jerry, sorry my mistake but that is what I was trying to (badly!) get at. Thanks for the clarification! 

 

P.S. If my 3 A3's are anything to go by, it works very well indeed!

[queensquare]

 

Hi Jerry, sorry my mistake but that is what I was trying to (badly!) get at. Thanks for the clarification! 

 

P.S. If my 3 A3's are anything to go by, it works very well indeed!

 

No worries, I should have made it clear, I was simply trying to emphasise your point 

 

Jerry

[Chris Higgs]

Dapol have indeed refined their design including split axle pickup, motor in the tender driving the loco via a carden shaft........sound familiar......... similar to that advocated by the 2mm Scale Association for the last forty years or so.

 

Jerry

 

Now all Dapol have to do is realise that you don't need a drive shaft arrangement that looks large enough to drive the propellers on the Queen Mary...

 

Also they don't follow the golden rule espoused by leading 2mm modellers such as Mick Simpson, that the two ends of the drive shaft should be within the wheelbase of loco and tender respectively, to avoid instabilities.

 

Chris

[-missy-]

Also they don't follow the golden rule espoused by leading 2mm modellers such as Mick Simpson, that the two ends of the drive shaft should be within the wheelbase of loco and tender respectively, to avoid instabilities.

 

Chris

 

This is something that I always struggle with. Could you expand on this please Chris? I just cannot get my head around where to put the ends of the driveshaft.

 

Thanks.

[Chris Higgs]

This is something that I always struggle with. Could you expand on this please Chris? I just cannot get my head around where to put the ends of the driveshaft.

 

Thanks.

 

I think the key is the length of the driveshaft. If a loco with a driveshaft goes around a curve, the driveshaft is no longer straight compared to the motor shaft in the tender, and the worm shaft in the loco. This angle of deflection causes a twisting force on both loco and tender, which might be so large as to cause a derailment. The longer the driveshaft, the less the angle of deflection and so the less instability. Also I think this gets worse when the ends of the shaft lie outside the fixed wheelbases of loco and tender, and so start to swing away from the track centre line, like the ends of a bogie coach do when it goes around a sharp curve.

 

So I think the position should be that the further forward the UJ that drives the worm can be, and the further back the UJ the drives from the motor can be, the better. Or simply put, make the driveshaft as long as you can manage.

 

The rule adopted by Mick Simpson et al is that the rear end of the driveshaft should not be further forward than the front axle of the tender, and the front end should be no further back than the rear coupled axle of the loco. Driving the middle axle of the loco rather than the rear one helps in this regard.

 

A quick look at a Dapol steam loco will show that they do not follow this rule, as they have that very obtrusive drive bush hanging a long way in front of the front tender axle.

 

Following the rule is not always possible due to the physical limitations of the prototype. For example on my Collett Goods chassis I drive the rear axle, because otherwise you would have to have gears visible under the boiler. And you may need to have the motor in the tender in the coal space because of its size, rather than further back.

 

People often overcome the problem of having a short driveshaft by making both loco and tender as heavy as possible, as this makes them more difficult to twist off the track. If you were adding weight only for traction purposes, you would probably only put it in the loco.

 

Chris

[CF MRC]

An interesting thread!

 

I think the only situation where driving the locomotive and tender simultaneously might be useful is for a single wheeler to get it out of trouble if the driving wheel falls down a hole in the track: which is inevitable with N gauge track standards.  I mused on this 35 years ago with the Johnson single but didn't do it  This engine  wouldn't / couldn't pull anything in N gauge because of the sloppy wheel / rail profile and so was converted to 2mm fine scale early in its life (1979): it s reasonably powerful.

 

The Stirling 8' single also doesn't have tender drive and will pull very long trains on straight track, but is very sensitive to our generous curves as there is probably not quite enough clearance at the front end.  In fact there is b****r all clearance at the front end (also on the prototype).  It will be interesting to see how Damian will overcome this in his loco range.  

 

The most recent Ivatt-modifed Stirling 7' single has Triumph Herald type suspension and will go through anthing and pull anything - but - it is a relatively simple design with a massive amount of weight incorporated: e.g.copper tungsten frames.  The best solution on Copenhagen Fields is to have both singles together roaring up the Holloway Bank!

 

Tim

[Rhys]

I think the key is the length of the driveshaft. If a loco with a driveshaft goes around a curve, the driveshaft is no longer straight compared to the motor shaft in the tender, and the worm shaft in the loco. This angle of deflection causes a twisting force on both loco and tender, which might be so large as to cause a derailment. The longer the driveshaft, the less the angle of deflection and so the less instability. Also I think this gets worse when the ends of the shaft lie outside the fixed wheelbases of loco and tender, and so start to swing away from the track centre line, like the ends of a bogie coach do when it goes around a sharp curve.

 

One question I've always wanted to ask about tender drives is 'how long is too long for a drive shaft?'

 

I've aways thought that this should work fine with an 0-6-0 with a 6 wheel tender, but what happens if your prototype (say) is a 4-6-2 with a bogie tender. The loco UJ would have to be quite a ways forward to line up with the rear driving wheels. And in this case, would the tender UJ be level with the front wheels or aligned with the forward bogie pivot?

[CF MRC]

Suppose the shaft shouldn't be too long otherwise if it is made of the usual thin wire it could start to whip. To be honest I have found that most drive shafts end up in about the right place after all the other factors such as where the motor will fit and the back end of the gear head are taken into account.

 

Another factor to consider is what sort of pivot you are putting between the engine and tender: a rigid single axis e.g. for solid transfer of weight between engine and tender, a double pivot or a single pivot. My one experience of a bogie tender was no problem with a rigid single axis coupling between engine and tender. The front bogie floats and has a bit of side play; the back bogie simply pivots and takes the weight of the tender. The drive shaft coupling is somewhere near the front of the tender within the coal space.

 

Tim

[Chris Higgs]

Suppose the shaft shouldn't be too long otherwise if it is made of the usual thin wire it could start to whip.

 

I think if you have the case of a LNER Pacific for an example, that a significant portion of the drive shaft will be hidden from view within the cab and firebox, and so can be made of a thicker material in that area (by putting a sleeve onto the wire?).

 

The reality is though, not many people are building Pacifics!

 

Chris

[Donw]

There is quite a difference between the modeller building a loco who can tweak and fettle parts by hand to achieve a satisfactory result and a manufacturer who will tend to use prescision machine to produce something that shouldn't need careful assemby as that is expensive. It is interesting that the Motor in the tender driving by a shaft developed by the modellers should be proving a sucess for Dapol. It is also a fairly flexible set up.

I also model in 0 gauge an buy ABC motor gearboxes ( not cheap) however even in the larger size one configuration doe not fit all and several gearbox configurations are offered. Even so in order to keep the final drive wheel under the cab footplate Brian had to make up a special. With the restrictions of space in 2mm this may be more of an issue.

If the gearbox is multi stage it is possible to make a number of configurations using the same gears but adjusting the angle of the motor and gears. With suitable machinery is should be possible to design a motor gear combination then prescision drill the gearbox sides. However whether this would be economic in 2mm is another matter. A while back Steve Bedding was experimenting with driving a miller by CAD. That sort of approach should make doing things like this more feasible.

However at the end of the day the sort of achievable tolerances may mean the modeller tweaking and fettling may be the best answer in a lot of cases.

 

Don

[Nig H]

 

I think the key is the length of the driveshaft. If a loco with a driveshaft goes around a curve, the driveshaft is no longer straight compared to the motor shaft in the tender, and the worm shaft in the loco. This angle of deflection causes a twisting force on both loco and tender, which might be so large as to cause a derailment. The longer the driveshaft, the less the angle of deflection and so the less instability. Also I think this gets worse when the ends of the shaft lie outside the fixed wheelbases of loco and tender, and so start to swing away from the track centre line, like the ends of a bogie coach do when it goes around a sharp curve.

 

So I think the position should be that the further forward the UJ that drives the worm can be, and the further back the UJ the drives from the motor can be, the better. Or simply put, make the driveshaft as long as you can manage.

 

The rule adopted by Mick Simpson et al is that the rear end of the driveshaft should not be further forward than the front axle of the tender, and the front end should be no further back than the rear coupled axle of the loco. Driving the middle axle of the loco rather than the rear one helps in this regard.

 

A quick look at a Dapol steam loco will show that they do not follow this rule, as they have that very obtrusive drive bush hanging a long way in front of the front tender axle.

 

Following the rule is not always possible due to the physical limitations of the prototype. For example on my Collett Goods chassis I drive the rear axle, because otherwise you would have to have gears visible under the boiler. And you may need to have the motor in the tender in the coal space because of its size, rather than further back.

 

People often overcome the problem of having a short driveshaft by making both loco and tender as heavy as possible, as this makes them more difficult to twist off the track. If you were adding weight only for traction purposes, you would probably only put it in the loco.

 

Chris

I have 19 2mm tender locos and none of them follow this rule, and the tenders have no additional weight, just the motor in the coal space. I try to keep the drive shaft in the tender as far back as possible to hide as much as possible from view, and the loco drive shaft as far forward in the cab as possible for the same reason. All these locos work fine.

 

Nig H

[Rhys]

 

I have 19 2mm tender locos and none of them follow this rule, and the tenders have no additional weight, just the motor in the coal space. I try to keep the drive shaft in the tender as far back as possible to hide as much as possible from view, and the loco drive shaft as far forward in the cab as possible for the same reason. All these locos work fine.

 

Nig H

 

Would it be possible to post some photos of the more extreme cases?

 

Cheers,

Rhys.