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