Continued as promised
David Thorpe wrote:,,,Meanwhile of course you've had to calculate how to ensure that the loco is properly weighted (I still don't understand how you can do that before the loco is even built) and with a bit of trial and error decide on what size of guitar strings to use. Once all that is done all may be well.
There is no doubt that this is what tends to bother newcomers to CSB. How do you match your springing to the loco weight at the design stage when you haven’t the faintest idea what that weight will be. The truth is you can’t, so you don’t. What you can do is design the chassis for a loco with its Centre of Gravity (CofG) in a specific place, and it is the location of the CofG which dictates how the fixed fulcrums need to be placed, not the absolute weight. That’s what makes the whole idea practicable. The final adjustment to suit the actual loco weight is the choice of the right size wire. As we saw last time this should/need not be by trial and error.
For me adopting CSB also illustrated something more basic, which is that once you stop using rigid chassis, where you have little choice, you really ought to consider how the suspension will affect the weight distribution of you’re loco. This is true whatever form of suspension you choose, as failure to do so can lead to disappointment and unintended consequences. Like locos unable to pull their own tenders.
On the other hand you may have a loco that dips down in the front or rear because you haven't got the weights right
Not if you’ve got the loco CofG in the right place, and a simple see saw device will tell you where it is. Of course It is necessary to weight the loco carefully to achieve this, and, people do worry, often unnecessarily, that this won’t be possible,
(Quoted out of order) or you may find that because you haven't been able to add much weight (none in the front because you can't put any in the open cab at the back, and not much in the boiler above the drivers because all the space is taken up with motor and gearbox) haulage is disappointing.
Weighting the loco to get the balance right is rarely as big an issue as some make out. It just needs a little thinking about. Do remember that the right place for the CSB is where you’d expect it to be, right in the middle. I agree this does preclude the desire to add weight at random to improve adhesion, but I would point out that just adding extra weight anywhere, without thinking how the suspension is going to distribute it, may not be all that effective.
Adding weight in the wrong place can produce axles with significantly different loadings, and having one axle significantly more lightly loaded than the rest can adversely affect adhesion.
See this post for an explanation of how this sort of thing affects the adhesive performance of a . To achieve maximum adhesion, you really need equal weight on each driven axle, and a properly designed CSB will achieve this, and means the loco need not weigh as much as it would if the weight distribution isn’t considered.
If you really are having trouble getting sufficient weight aboard, remember that two smaller weights at either end of the chassis are as just as effective a single larger weight at the centre. Then, as the problem only really occurs with smaller prototypes, have you considered if you really need a motor that big, taking up boiler space? Experience has shown me that quite small motors will produce all the power necessary to pull prototypical length trains, and the desire to fit the largest possible motor is really unnecessary. Until they became unavailable, I had standardised on the Mashima 1024 and I never found them wanting. Both locos described in the
“Haulage Challenge” section of this post are 1024 fitted
If you really insist, the most recent iteration of my CSB spread sheet will allow the design of a CSB with the centre of gravity away from the optimum place. I wouldn’t necessarily recommend doing it but if needs must I can show how it’s done.
, or you'll find that one or more of the hornblocks are sticking (also possible with compensation, of course)
Just as much a problem for any suspension system. We need to learn how to get them right.
or you may find, as with my whitemetal Mackintosh 0-6-0T, that the loco is much too springy (curable, possibly, with thicker guitar strings but I don't happen to have any).
Makes me wonder what would happen if you ran out of wire for say, the hand rails.
Major advantage, of course, is that you can drop out all the wheels if necessary - can't do that with a fixed axle but hopefully you won't need to!
Once dropping the wheels out becomes a practical thing to do, its surprising how often you find it a valuable and convenient facility.
