Proto87Stores wrote:While the subject of vehicle weight is currently being discussed, I would like to try and re-stress the importance of understanding the effect of spring rate in relations to vehicle weight.
So to recap the basics:
In order to safely ride over even small bumps and twists in track, each wheel must be able to independently and freely move up and down relative to the chassis/body of the vehicle.
This movement can be achieved by a) equalization/flexichas moving beam/levers, as already well covered, or by b) relatively free springing.
However, what doesn't seem to be mentioned much on the forum is that merely fitting springs to wheel bearings does not itself provide a springing motion unless the spring rate is low compared to the weight of the vehicle supported by that wheel.. For those using horizontal wires, what seems to be the only consideration, even for CSB's, is balancing the wire thickness to achieve the required 50% static displacement position. But the thickness of the wire and its length between fixed supports affects its spring rate. You can therefore accidentally, or deliberately end up with different spring rates while still achieving the 50% balance position.....
While in the past I would have tended to agree with your basic thesis (details omitted for clarity), that it was hard to match the characteristics of a sprung suspension system to the needs of a 4mm steam outline loco, and most of the attempt in the past did suffer from the sort of issues you described. None the less in the 3000 or so years of human wheel transport history, there are very few occasions where a wheeled vehicle hasn’t been improved by fitting some sort of sprung suspension, the issue being how best to achieve it. I think that the time has come even for 4mm scale steam outline models and that, in your certainty that CSBs really can't work as well as I would like to think they do, you seem to be missing a couple of salient fasts.
1. When you use the spread sheet to set up a CSB, the whole point is that you have designed a springing system that ensures, for the weight of a given loco, the springs over each axle will be depressed by the same amount (half the designed full movement) with the same load applied at each axle. I would have said that, however you push your balloons, this implied the same effective spring rate for each spring. As the result is that the required amount of deflection is produced by the same load for each spring segment, for the life of me I can't see why you think that any one span will suddenly become more or less resilient that any other over the rest of the permitted movement range.
2. I'm not the only person who builds these things, a number of competent modellers have adopted them and find that they work well as advertised*. This is no longer a theoretical exercise, there is practical experience to back it up. Which, with respect, is more than can be said for your concept of a fully equalise multi axle 4mm steam outline chassis. I'm not saying you can't make it work Andy, just that you haven’t yet, and, till you do, you can't demonstrate that it is any way simpler to produce or more effective in action than the CSB based locos we already have running round in ever increasing numbers. When you have achieved it, I expect the performance will be good enough to make it comparable with a CSB based loco, and the deciding factor as to whether it gets commonly adopted will end up being how easy it is to implement.
*OK I'm sure you can find people on RMWeb who have never built a CSB who tell you why it doesn’t work, and probably somebody who has built one but made a pigs ear of it, but then there is always one isn’t there.
Changing topic, I would also like to have a think about the uses for ball bearing bearings, but so as not to loose the discussion at the end of a very long thread I've started a new one called Low Friction Bearings in 4mm