Thanks for that info Will and Jol, that (about skew wound motors) was something I had never learnt in 20 years of modelling and trying to get as near as I can to creating that sense of inertia when trains stop and, particularly with a heavy train, start.
Another thing I still haven't really understood is, what is "cogging"? I have assumed it to be when at the lowest speed and not connected to any power train, the motor tends to move in a series of very small jerks.
Regarding the helpful replies on flywheels, my question was really on the premise, that, having got everything else as good as it can be in terms of a freerunning chassis and power train, as many pickups as possible, that do their job properly, and of course clean track and wheels, does a flywheel add anything more than the larger motor which could fit into the space it takes.
It would be interesting to know how difficult it would be to make this chassis with CSBs given they are not "designed in".
Meanwhile my intention was to make this kit "as is" in the first place, and basically this thread was to highlight any problems I had where a departure from the in instructions had to be made. I will edit one earlier post to explain why I made up the rods John Brighton style rather than just using them as they came.
In the last couple of days modelling time I have been experimenting with bits of lead to see what force the springs exert. The springs sit like this:
2017-08-20 18.03.18-1 (Small).jpg
This is the hornblock bearing as etched. Having removed the etched bearings the bearing sits with the spring uncompressed as pictured on the previous page 1.4mm from the top of its travel. To compress it to 1mm down from the top of its travel takes 30g. To compress it a further 1/2mm, to 1/2mm down from the top of its travel, takes 60g, and to compress it to the top of its travel takes 80g. (The spring is not fully compressed at this point of course.)
These are "ball park" figures, probably not terribly accurate, but give me a handle or general idea on what is needed weight-wise.
I
think the design is that the bearing should ride 1/2mm below the top of its movement, and that the required movement is 1mm - half a mm each way from a centre of travel. So that infers a six wheel loco must weigh 360g to be at the ride height as designed.
I have established my ride height needs to be 1/2mm further down, so 1mm from the top of the travel, and have modified the bearings so that they cannot rise any higher. A 12BA nut is just over 1mm thick and fits over the spring spigot, so the spring can act in just the same way as designed, but my intention is to "bottom out" the front and rear axle springs, and to lighten the centre axle force and give it more upward travel. How I do this will depend on how heavy I can make the loco at the front. The rear will be weighted down by the tender hanging off the back Mike Sharman style so should not be problematic getting enough weight.
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