CSB for a Single Driver

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Will L
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CSB for a Single Driver

Postby Will L » Sat Aug 15, 2020 7:06 pm

Following on from a post I placed on his Singles and suspension thread Mike sent me the following PM

Michael Waldron wrote:Will:
Last year I posted an enquiry regarding folks’ approach to getting decent adhesion from a Single.
On the list of subsequent helpful responses was an interesting one from Dave Bradwell, and a kind offer from you to discuss a CSB option, which, I think was apparent from my wording, I had summarily discounted.
Would you be kind enough to elaborate on how this might be done successfully, as I am a newcomer to CSBs, having not yet made a chassis using that method of suspension, but having gratefully read your very voluminous and helpful input, and now actually working towards applying my brain to the idea of Singles actually being a possibility with CSBs.
You may possibly have seen my recent post enquiring about spur gears for the last etching project I undertook before divesting myself a couple of years ago of E B Models, namely a gearbox system for tender drive and adjustable loco gear frame. A photo of the test arrangement of that system is on that thread.
I am also in touch with Barry Luck, as a fellow member of the Brighton Circle, who has has varying experiences of success with tender drives (now abandoned!) for his single, as he illustrates on his copious website.

Anyway, after a lengthy introduction, the floor is yours! Convince me!

Thanks
Mike


I thought this was an interesting question and others might be interested in my answer, so I decided to put it in a thread of its own.

Why CSBs?

Well he did ask so I think a recap on the basics is worthwhile.
1. Well sprung locos visibly run better, that is more smoothly, than locos that are not. They also run quieter if track noises bother you.
2. Once you have decided that all wheels will have some form of suspension, fitting CSBs to a loco is certainly no more difficult than any other method, and rather simpler than some.
3. A CSB loco will deliver a specified weight distribution across the driving axles, and getting this weight distribution right is key to getting good pulling power from your loco. See this detailed explanation of why weight distribution affects pulling power . A loco sprung with individual springs is capable of the same levels of performance but setting it up to do so is much more hit and miss.

Any Down sides?

The only downside, if downside it really is, is the fact that you need to ensure your loco centre of gravity is where you planned it to be. However, I think being aware of the implications of the weight distribution of a loco and its impact on pulling power is worth thinking about for any loco, rigid, compensated or sprung. So I could argue forcing you to think about it is a positive too.

CSB and single drivers, getting the wire in.

Having looked back at your previous posts, I see you are doing Stroudly LB&SCR G class singles where the wheel sizes are 4’ 6” and 6’ 6”. The wheelbase is 15’ 9” which I am assuming is equally divided (i.e 7’ 10.5” or 31.5mm).

The question that immediately arises with singles like this is where the CSB wire is going to go. Typically, we expect to hide it behind the loco frames. In theory the wire can just as well be above or below the axles, or in the case of a 2-2-2 single below the driving axle and above the carrying axles. To judge by the pictures I can find, it looks as if we will only be able to hide the wire on a G class if we adopt the over and under option.

Given the 1’ 0” difference in axle hights, you have a 4mm gap to thread the wire through. Assuming a 3mm (or 1/8) drive axle and a 2mm carrying wheel axle, 2.5mm of that gap is occupied by axles. Axle fulcrum points 2mm above the carrying axles and 2mm below the driving axle will do the trick. You can play with those a little bit (0.5mm) but they must add up to 4mm. Therefore the axle block fulcrum points are going to be a bit closer to the axles than normal. This is by no means impossible, but it does mean you won’t be using any of the currently available readymade components without modification.

I would still used the Highlevel hornblock/axle block combination. I’m only using the full size hornblocks for my example below, although much the same thing can be done to the Miniblock versions that may be a better fit for the 2mm axle of the carrying wheels. It would be necessary to make (probably get etched) new CSB Carrier tags to suit the 2mm axle centre to the CSB wire dimension. These would not fit onto axle blocks as they come, which would need to be reduced in size along one side until the new size carrier tag does fits. That would mean the removal of very nearly all the metal below the bottom of the driving axle, and there will be very little metal in the tag above the fulcrum hole, but as these are both on the side away from where the weight is carried, it should all be perfectly workable. There should be less difficulty getting them on the carrying axles given the smaller axle size, but some metal still needs to go. The diagram shows what I mean.

Modified Highlevel.jpg
Modified Highlevel.jpg (151.5 KiB) Viewed 1058 times


The Hornblock cheeks will also need to be filed back a little bit to allow the CSB wire to pass. The CSB arrangement is illustrated below.

High level G Class layout.jpg
High level G Class layout.jpg (70.41 KiB) Viewed 1058 times

CSB and single drivers. Weight distribution considerations.

There are a few choices here. I believe that the G class had roughly equal weight distribution across all three axles, and that’s what we would aim for with a standard CSB plot. However, given all the drive is coming from the centre axle, I think it would be worth considering biasing the weight distribution to put a bit more weight on the driving axle.

Classically we have always tried to keep the centre axle that little bit softer than the ones at the end to avoid any tendency of the loco to oscillate around the centre axle. That said, I have never seen a CSB loco that showed any sign of doing that, and I have come to believe that there is enough friction in the works to dampen down any tendency to do it. So, if it was me, I would go for a 30% 40% 30% weight distribution.† This may produce a tendency for the front of the loco to lift visibly when accelerating away with a heavy train. All sprung locos do this to some extent (see Russ Elliot’s explanation of why), but it is normally too slight to be noticeable. If it becomes an issue, a tender connection which stops the back of the loco going down relative to the tender should cure the problem.

In the table that follows I have given three CSB plots, The first is for an even weight distribution. The second gives a 30/40/30 weight distribution, but may take the end fixed fulcrums a bit too close to the back of the loco, so the third plot achieves the same thin while bringing the end fulcrums a bit closer in. For each plot there is a wires size to loco weight table. You choose the wire size closest to the actual loco weight (less wheels and motor if you want to be purist about it). In all cases the loco Centre of Gravity needs to be directly over the driving axle.

G class plot.jpg
G class plot.jpg (82.84 KiB) Viewed 1057 times


† You will note I don’t go along with Julian’s idea that we should overweight the leading axle to avoid derailments.

Michael Waldron
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Re: CSB for a Single Driver

Postby Michael Waldron » Thu Sep 10, 2020 8:08 pm

An excellent treatise!

Just one small point... 1/8” axles are used throughout Stroudley’s G class, that Will correctly deduced I was enquiring about, even on the tender, as it uses the same wheels as leading and trailing wheels on the loco.

Mike

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Will L
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Re: CSB for a Single Driver

Postby Will L » Thu Sep 10, 2020 10:25 pm

In which case the same axle block modification will work on the carrying axle as well as the driving axle, just the other way up. They will be a bit thin above the carrying axles but fortunately ware isn't usually a problem for us.

Michael Waldron
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Re: CSB for a Single Driver

Postby Michael Waldron » Fri Sep 11, 2020 5:48 am

Just checked, and the G singles wheelbase was:-

8’ 0” + 7’ 9” for the unique large boilered ‘Grosvenor’ (with 6’ 9” drivers).

The same for ‘Abergavenny’ - the smaller version, with 6’ 6” drivers.

And 8’ 0” and 7’ 11” for the ‘production’ G class.

Mike

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Will L
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Re: CSB for a Single Driver

Postby Will L » Fri Sep 11, 2020 8:51 am

Michael Waldron wrote:Just checked, and the G singles wheelbase was:-

8’ 0” + 7’ 9” for the unique large boilered ‘Grosvenor’ (with 6’ 9” drivers).

The same for ‘Abergavenny’ - the smaller version, with 6’ 6” drivers.

And 8’ 0” and 7’ 11” for the ‘production’ G class.

Mike

Just to be sure I've re run the numbers. It does not make a significant difference.

Grosvenor would give you an extra 1mm to play with between the axles.

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zebedeesknees
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Re: CSB for a Single Driver

Postby zebedeesknees » Mon Sep 14, 2020 11:17 am

If I may put my oar in...

My 'Spinner' uses separate springs for the drivers and the trailing axle, though they could have been connected with a CSB, but having a bogie complicated that somewhat. For a 2-2-2, CSBs will do a great job for the ride of the chassis, but for traction the concept limits the weight on the driving axle.

I would suggest that the chassis be sprung as indicated, but as much unsprung weight as possible be added to the driving axle, by wrapping the gearbox and/or loading the bearings with a transverse weight. This would need to be even round the axle, of course.

Ted.

Michael Waldron
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Re: CSB for a Single Driver

Postby Michael Waldron » Wed Sep 16, 2020 4:38 pm

Ted:
Apologies for delay in response, as temporarily in a 4G signal-free area on Galloway peninsula, as opposed to Gloucestershire, where 4G and home WiFi abounds!

Please could you elaborate on your thinking regarding weighing the axle? I’m not sure I quite follow what you’re saying in your final paragraph.
Thanks
Mike.

Julian Roberts
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Re: CSB for a Single Driver

Postby Julian Roberts » Wed Sep 16, 2020 8:15 pm

As I have the honour to have my name mentioned by Will above :) let me just say my philosophy that I wrote about in Snooze 199 was primarily in the light of my experience with 0-8-0's, 0-6-0's and 4-4-0's or 0-4-4's. My experience with a 2-6-0 is that carrying wheels need a lot of weight but I wouldn't say more than that... ;) I've kept a vague eye on the writings on this topic as I've got a single to make, a 4-2-2, sometime. Being in the compensation camp I've tended to think on beamy lines, but sure, it's got to have an imaginative solution if we're not to cheat and drive from the tender wheels. One heresy I've toyed with is, what about (somehow) making the loco and tender one rigid unit!? :o The single driver and the centre tender wheels act as an 0-4-0, all the other wheels go along for the ride. It would depend on the minimum radius of the track curves whether it would be possible, sure on straight track no one would know!

I'm just back from the wonderful Galloway peninsula!

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Horsetan
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Re: CSB for a Single Driver

Postby Horsetan » Wed Sep 16, 2020 10:55 pm

Julian Roberts wrote:.....I've got a single to make, a 4-2-2, sometime. ...


MR Spinner?
That would be an ecumenical matter.

Jeremy Suter
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Re: CSB for a Single Driver

Postby Jeremy Suter » Thu Sep 17, 2020 6:45 pm

Been watching this thread carefully I have already rebuilt the chassis on my GCR 422 Single.

When I built it many years ago I sprung the wheels although not CSB style I used Alan Gibson sprung hornblocks. The basic problem was tractive effort, it struggled to pull the tender. I got round it by changing to a fixed driving axle and rocking the rear axle giving the classic 3 point balance, Then I packed the boiler with weight making it front end heavy and weighting the tender onto the link with the loco to counter balance the boiler putting all the body weight onto the driving axle which I think gives the best tractive effort for a single.

The tender has a fixed rear axle with a beam compensation on the other two which are lightly sprung aswell

My problem now is that the front bogie needs to be rebuilt to make it heavy enough to stay on the rails and not affect the body weight which it did when the chassis was sprung.

What I am really saying is that I needed to get all the body weight over the driving axle

If I redo it again with the CSB style I would spring only allowing it to go down not up as in effect I'm driving an 022 with a loose 040 truck pushed along in front

IMG_5773 (3).JPG

Please could you elaborate on your thinking regarding weighing the axle? I’m not sure I quite follow what you’re saying in your final paragraph.
Thanks
Mike.

I made a small bucket of lead to go under the driving axle and gear box to give more un-sprung weight to that axle its still there and can be seen between the spokes.

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Will L
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Re: CSB for a Single Driver

Postby Will L » Thu Sep 17, 2020 11:58 pm

Have to say that from a CSB point of view a 4-2-2 is a rather more complicated prospect than a 2-2-2, as weight carrying bogies complicate things. It certainly requires more thought than I have currently given to it, but I think I could do it OK. When done I would at least know what the weight distribution was going to be, which would at least put me one up on any other way of doing it. What an appropriate weight distribution might be is one of the things which would require that additional thought. As a starting point I would probably seek to replicate something like the % weight per axle they had on the prototype.

I'm not very fond of trying to transfer tender weight to the loco. Bin there in my compensation days, made it work sort of, but I wasn't very happy with the result. In any event it isn't compatible with CSB and the attempt to design in a weight distribution. For any single driver I think I would be more inclined to go for a tender drive as this would allow the boiler to be a big heavy weight in the right place, just like a boiler full of water would be on the prototype. I would also consider a heavy bogie which didn't need too much of the loco's weight to keep it honest.

Stephan.wintner
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Re: CSB for a Single Driver

Postby Stephan.wintner » Fri Sep 18, 2020 10:54 pm

Been following with great interest.

It seems to me that even 30/40/30 might put too much weight on the leading & trailing. Clearly, going too far would lead to oscillating. 1/98/1 for example. But I'm wondering if 20/60/20 would work, or 25/50/25.

Stephan

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Will L
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Re: CSB for a Single Driver

Postby Will L » Fri Sep 18, 2020 11:18 pm

Stephan.wintner wrote:Been following with great interest.

It seems to me that even 30/40/30 might put too much weight on the leading & trailing. Clearly, going too far would lead to oscillating. 1/98/1 for example. But I'm wondering if 20/60/20 would work, or 25/50/25.

Stephan


I'm afraid I only know one way to find out.


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