Hi Andy as promised further thoughts.
For anybody else inclined to want to read on, the following contains detailed consideration of how a CSB fitted loco may or may not work. Such discussions amuse me, but your not obliged to read it and I promise you any failure to read or understand what follows will in no way effect how well your P4 train set works.
Proto87stores wrote:Both Will and I published you tube clips showing a vehicle being pressed down by hand to demonstrate that its body was sprung. It’s interesting that both videos appeared to show a similar (strong?) downward force being applied before the vehicles dipped. And no “shimmies” in either case. Yet the Amfleet car body was supported by the same 8 springs shown in the freight bogie. I.e. At one end, it needed a greater than 4 oz push to cause the downward movement. And that would be quite hard springing for a model of that weight.
Admittedly hazarding a guess that Will’s model needed a similar heavy push, then it could be construed that the springiness of the CSB’s is not the method that small bumps are handled., and that instead some form of self equalization is occurring partially or instead.
As to the downward force needed to further compress a CSB, no need to guess. As you have pointed out in the past, a CSB spring is not progressive. Therefore, as the full weight of the loco is required to compress the springs by 0.5mm, then to get a further 0.1mm compression on all wheels will require a push equal to 1/5 of the loco weight, etc. etc. The difference between my loco and your coaches was that the loco was already standing on springs matched to the weight of the loco and designed to be compressed by a given amount, and it is movement in the springs that produces the desired road holding performance; while your coach springs are not so matched to the vehicle weight, are not required to provide the road holding, and may well have been barely compressed at all until you pressed on the end.
...We already know that CSB’s only work if the wire slides freely between the support pins. The wire is much too strong to stretch between fixed points. So the entire springing capability is limited to the extension or shrinking of the loops of sliding wire above each wheel. For the static support of the vehicle it’s reasonable to accept that the loops expand (as springs) until the overall vehicle weight is balanced.
The usually suggested way that equalization occurs in a CSB is by the principle of springy beams…
I think that perhaps describing to you what CSBs do as equalisation was never a good idea. From where you are coming from, equalization has a very specific meaning about the equal distribution of weight which I don’t think is entirely what CSBs do. They certainly transfer weight from one wheel to the next, but the distribution will only be equal if the wheels are on level track.
…However, any beam that is pivoted in its centre, only “springs” if a changing load is applied to both ends of the beam at once. Then it stabilizes in an equilibrium bent shape and becomes effectively rigid at that loading. If the load at one only end changes, then the springy beam will try to rotate as a rigid beam until a new equilibrium position is reached.
This is where we are going to part company. The CSB is continuous through a series of fulcrums so it clearly isn’t going to pivot around anything, and wheel loads are applied to the beam at a point partway between two fulcrums, so I’m unclear where your idea of applying force “at one end” comes from. So I don’t accept your conclusion…
... that CSB’s are seriously misnamed and their dynamic operation not yet fully understood. In the dynamic case, they are fundamentally a single wire acting as a series of flexibly joined dynamically rigid equalizing beams. And as such they pass the movement of small bumps upward to the vehicle body in almost exactly the same manner and amount as would a series of separate rigid beams. They only time and manner they act truly as springs is in the static balancing of the body.
The only way any wheel moves relative to the chassis is by changing the curvature of the bit of the beam it is in contact with. Curving the beam is exactly where the springiness comes from, so changing the curvature means the load being applied to the wheel has changed. In my mind there is no doubt that irregularities in the track will result in slightly different deflections in each spring segment, which further implies slightly different loadings on each wheel. Certainly, true in the static situation.
I think what may be on your mind is that in the dynamic case, the shifting weight balance resulting from uneven track would mean a that the CSB need to move significantly through the fixed fulcrums to take up the different profiles needed, and that you doubt that can happen fast enough to accurately follow the track profile. Hence you think that some other mechanism explains the fact that CSBs do work.
I agree there is a potential friction issue involved in the fact that the length of CSB required must change as the loads on the individual wheels change and thus must slide across (some of) the fulcrum points. For this reason, Russ Elliot has always been keen to advise that fulcrum points are lubricated, but personal experience says this is unnecessary.
In the static situation it is quite clear that my CSB fitted locos do sit down on their springs as the CSB theory would lead you to believe, and any friction between wire and fulcrum point is insufficient to show any noticeable reluctance to settle to the full static deflection. This is of course when most of this movement must occur and movements in the dynamic case will inevitably be small in comparison. Then as taking more weight on one wheel inevitably means taking less on another, the necessary movement is likely only to involve a subset of fulcrums.
Any failure of this sliding movement to occur, or to not occur fast enough, would inevitably compromise the locos ability to deal with track irregularities. Now remember this is P4 we are talking about where the scale flange size means we become only too painfully aware of locos that have problems in this area. Finally remember my very first CSB loco, which did do much to convince me CSB were the way to go, was an 8 coupled loco with a long rigid wheelbase, the very thing most likely to show up any difficulty in keeping wheels firmly on the track, and with additional sets of fulcrums to exacerbate this problem if it was a real concern.
In passing, I did used to wonder if these movements of the CSB wire through the fulcrums would cause the wire to work one way or the other during an exhibition day. For a while I used to check for evidence of such movement, but I never found any.