No Andy was.Am i missing somethig here?
Regards
No Andy was.Am i missing somethig here?
proto87 wrote:One other aspect that is presumably important is having sufficient excess wire (and space) to allow for full displacement of all wheels to their upper and lower stops. Will has said that properly fitted CSB's allow for sprung manual depression of the model. So I assume that's not a practical difficulty.
billbedford wrote:proto87 wrote:One other aspect that is presumably important is having sufficient excess wire (and space) to allow for full displacement of all wheels to their upper and lower stops. Will has said that properly fitted CSB's allow for sprung manual depression of the model. So I assume that's not a practical difficulty.
You can calculate the change in length of the spring wire for known displacements with simple trigonometry.
proto87 wrote:One other aspect that is presumably important is having sufficient excess wire (and space) to allow for full displacement of all wheels to their upper and lower stops. Will has said that properly fitted CSB's allow for sprung manual depression of the model. So I assume that's not a practical difficulty.
On the other hand, the surprising apparent ability of CSB systems to not exhibit the far less stable (wobbly) characteristics and difficulties of individually tuned wheels springs may mean that the excess wire length is more critical.
Or that the powerful spread sheets used for CSB's could be used for setting the spring rates of non-continuous individual wheel wire springs, equally successfully, but has anyone tried that?
Will L wrote:A strait line calculation gives the amount that the spring moves to take up a deflection of 0.5mm is rather less than 0.02 per per axle, or 0,06 for 3 axles, which will be shared between the end so the amount of movement through the end fulcrums would be 0.03 which you might be able to measure but you certainly can't see.
Will L wrote:A strait line calculation gives the amount that the spring moves to take up a deflection of 0.5mm is rather less than 0.02 per per axle, or 0,06 for 3 axles, which will be shared between the end so the amount of movement through the end fulcrums would be 0.03 which you might be able to measure but you certainly can't see. Working out the true curved length over those short arks isn't going to change the figures very much.
billbedford wrote:Will L wrote:A strait line calculation gives the amount that the spring moves to take up a deflection of 0.5mm is rather less than 0.02 per per axle, or 0,06 for 3 axles, which will be shared between the end so the amount of movement through the end fulcrums would be 0.03 which you might be able to measure but you certainly can't see.
...which is appreciably less than the slop in the pivot point of a fixed equalisation beam.
proto87stores wrote:The up/down sliding resistance for CSB's was 4 times higher moving upwards than downwards.
Russ Elliott wrote:proto87stores wrote:The up/down sliding resistance for CSB's was 4 times higher moving upwards than downwards.
???
proto87 wrote:Will L wrote:A strait line calculation gives the amount that the spring moves to take up a deflection of 0.5mm is rather less than 0.02 per per axle, or 0,06 for 3 axles, which will be shared between the end so the amount of movement through the end fulcrums would be 0.03 which you might be able to measure but you certainly can't see. Working out the true curved length over those short arks isn't going to change the figures very much.
I agree with all you said except I'm going to quibble with the wire movement amount. I put the axle spacings of my N7 into my CAD program and then just drew simple circular arcs for 0.5 mm and 1mm and measured the differences. While the extension from straight to 0.5 mm is correct, the extension from 0.5 mm to 1mm comes out at over 4 times the amount. Just over 0.1 mm. That would be at least 0.5 mm for an x-10-x loco.
The reason this matters is that the straight line represents the loco off the track. The equilibrium position on the track (no bumps or twist) will be the 0.5 m deflection. And the bumps will cause the +/- sliding around that level.
Also note that the force needed for overcoming the wires sliding is intermittent. I.e you are working against static friction, rather than moving friction, for each track perturbation.
Proto87stores wrote:Russ Elliott wrote:proto87stores wrote:The up/down sliding resistance for CSB's was 4 times higher moving upwards than downwards.
???
See previous post on curvature of wire to hold loco in equilibrium position.
The additional length of wire that has to move into some curve shape from the straight line, off the track rest state, to the sitting on the track, weight carrying equilibrium position is much less than the extra additional amount of wire need to move into the sharper curve shape if the wheel rises from the static equilibrium position to accommodate going over a bump.
I.e. the rate of increase of wire length and friction resistance to upward wheel movement from static equilibrium, is greater than the rate of decrease of wire length and friction resistance to downward wheel movement into a dip. It's considerably non linear.
My error was in using a 25% greater up/down movement range to discover that effect than I claimed. (+/- 0.625 mm instead of the more usual +/- 0.5mm). However, the non linear trend is the same whichever displacement range you use.
proto87stores wrote:IAnd a point I overlooked earlier. The up/down sliding resistance for CSB's was 4 times higher moving upwards than downwards.
Crepello wrote:There's also the consideration that the friction generated in the changing of the suspended wire length only leads to changes of wire tension. These tensile forces (one each side of an axlebox) then need to be resolved into their vertical components to arrive at the contribution to axlebox load perturbation. The calculation would be simple if infinitely flexible strings were involved, but our wires have continuously changing gradients. Nevertheless, the worst case would be at the point of inflexion between positive and negative curvature in the spring wire. Taking the sine of that gradient angle multiplied by the frictional force each side of an axlebox, that's a miniscule amount, because even the maximum wire gradient is so shallow.
proto87stores wrote:I would suggest that low force wire linear tensioning is not a contributing factor in sliding CSB suspension operation.
Crepello wrote:proto87stores wrote:I would suggest that low force wire linear tensioning is not a contributing factor in sliding CSB suspension operation.
Why are you worrying so much about friction in the supports then??
Will L wrote:proto87stores wrote:IAnd a point I overlooked earlier. The up/down sliding resistance for CSB's was 4 times higher moving upwards than downwards.
And there is another reason why that' isn't a valid interpretation. I agree the increase in wire length will accompany the deflection increase and hence the frictional resistance to that movement, but the increase in wire length between no deflection and 1mm deflection isn't linier, it's actually a segment of a sign curve with the wire length increasing most quickly as the 1mm limit of deflection is approached, as your diagram shows. As I have shown above, the actual practical movements are both small and close to (either side of) the 0.5 static deflection point. So while there may be a difference between the upward and downward resistance it won't be anything like the x4 you suggest, and as it isn't the only frictional resistance to the up and down movement of the axle, it just gets lost in a general and very desirable dampening effect.
This is all very interesting, if this sort of thing turns you on, but whatever theoretical objections you may see we have practical experience of CSB producing reliable sprung steam era loco chassis, which:-
1. are truly riding the springs and not, either the top, or the bottom, stops
2. fully decouples the body from the wheels, with the improved ride characteristics you expect from functional suspension
2. give good weight distribution and hence good haulage characteristics
3. are mechanically and constructionally simple, when compared to other methods which implements suspension on all wheels.
I will be interested to see just how well your N7 gets on. Compared to a CSB, I'm sure you ought to be able to get it to pull just as well, and we may be hard put to differentiate the ride quality. It can never be decoupled like a sprung loco and I have questions about just how mechanically and constructionally simple implementing equalisation on a rigid steam loco chassis will prove, but the proof as they say.....
Will L wrote:It should also be remembered that even a 0.5mm step under one wheel will not produce an additional defection of anything like 0.5mm for exactly the same reasons.
I'm not sure I understand what you are saying above?
The calculations aren't that strait forward but I reckon an additional 0.25 for a static 4 wheeled vehicle. Actually the ability to deal with steps of that size is really only a party trick and is not required by any competent track builder. The true "detrimental to reliable running" issue that we ought to be thinking about isn't steps in the track at all, but the "rate of change of cant". That is the rate at which the height of the top of one rail changes in relation to the other. On the real thing this is limited to never more than 1 in 600 (1 in 1200 for high speed line) see this Network Rail document A Guide to Permanent Way Design, although a rather more extreme but perhaps more easily attainable limit for model railways of 1 in 300 has been suggested in the past. Using that, even a real monster (long fixed wheelbase) loco like a 9f with a 21' 8" wheelbase, will see no more than 0.3mm over the full coupled wheelbase, resulting in deflections of ± 0.15 from the static point over the rigid wheelbase of the vehicle.
proto87stores wrote:I'm not sure I understand what you are saying above?Will L wrote:It should also be remembered that even a 0.5mm step under one wheel will not produce an additional defection of anything like 0.5mm for exactly the same reasons.
FWIW, we have a cant issue in the US due to so many larger layouts having curves on grades...
proto87stores wrote:[re a 0-10-0 ... if you did that "press down test" We talked about earlier to show that you do have full springing. If you just allowed for the expansion of one wheel loop, you wouldn't be able to push down any noticeable distance on the loco at all.
If you want that to "net out", then that will have to move the wire along and out of the curvature over three other wheels.
There is a practical issue with only designing a CSB model to have a much smaller up/down movement than +/- 0.5 mm.
Again this is where leaving the fixed beam designs behind creates new added complications. None of the above is any concern for a properly equalized flexi-chas. It's just a case of build it, and it will run perfectly on completion.
proto87stores wrote:.....Given the large number of P4 Steam Loco Builders in the Society, did anyone build a steam loco chassis with single independent sliding wire springs per wheel and do a running comparison with a similar model with the then new CSB's? ....
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