billbedford wrote:
Joe Brook Smith had nothing to do with this dimension. It was a purely empirical value used by Chris Pendlenton on his early sprung locos and subsequently adopted as a de facto 'standard'.
The 0.5mm is not the wheel movement allowance, whatever that is, but a designed
static deflection of the carrying springs under load. There is also a dynamic deflection which is added to the static deflection and this can be plus or minus. Since this dynamic deflection is closely tied to the rail top, then there is no reason to calculate it.
You have been told this so many times now that repetition is becoming somewhat tedious.
Since no-one else has picked up on this, I'll just mention the problematic issues raised here again.
If 0.5 mm is the static deflection of a simple linear Hooke's law sprung wheel bearing, which is carrying some of the weight of vehicle, then as little as as a + or - 0.1mm rail height variation below that wheel will alter the weight carried on that wheel by a whopping + or - 20%. And I doubt even the flattest laid P4 trackwork is with +/- 0.1 mm. So yes, there is every reason to be aware of it's high value.
And since this thread is about discovering and handling vehicle wobble (roll), rather than Flexichas in general, it should be pointed out that springing at the wheel bearings means the center of roll is then the same height above the rail as the wheel axle. Whereas the center of gravity of any unmodified model vehicle is difficult to get below floor level and almost impossible to get to axle level, let alone below.
The problem with a center of roll on level track, that is below the center of gravity, means the vehicle is roll unstable without additional restraints and that even with restraints, will likely have two stable positions, rolled slightly left and rolled slightly right. An extreme analogy would be balancing a broom on its handle.
If the vehicle suspension is equalized at the axle bearing level but sprung at the body to chassis level, then the center of roll is at the body mounting level, which is typically twice as high, and much more likely to be above, or at least much closer to, the center of gravity of a sensibly weighted model vehicle. If the center of roll is above the center of gravity, then the vehicle will be statically roll stable and tend to roll back to a single vertically upright position after any deflective force.
Merely posting a description of a particular mechanical linkage, does not demonstrate or validate the performance of that linkage for a particular purpose, nor does it provide a means of comparison with other linkage implementations. Just guessing or coming up with limited extent anecdotal examples is wishful thinking, not engineering to create and prove an optimal, all cases, design.
Andy
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