Flexi Chassis an Appreciation

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proto87stores

Re: Flexi Chassis an Appreciation

Postby proto87stores » Mon Dec 18, 2017 5:57 pm

billbedford wrote:
Will L wrote:3. The CSB spread sheets came about because of the need to work out where the fixed fulcrum points must go.


We need a spreadsheet because the deflections on a beam with more that two supports is mathematically indeterminate. ie there aren't enough equations to be able to solve the problem.


And there I was thinking that suspension bridges were designed rather than injuneered by trial and error. :o

I'm still more interested in your response on spring rates vs. weight though.

Andy

billbedford
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Re: Flexi Chassis an Appreciation

Postby billbedford » Mon Dec 18, 2017 8:05 pm

Proto87Stores wrote: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.


Sorry. 50% of what exactly?
Bill Bedford
Mousa Models
http://www.mousa.biz

proto87stores

Re: Flexi Chassis an Appreciation

Postby proto87stores » Mon Dec 18, 2017 9:36 pm

billbedford wrote:
Proto87Stores wrote: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.


Sorry. 50% of what exactly?


grovenor-2685 wrote:Somewhere among Bertiedog's postings in the RMweb archive there was a better description of the Varney system complete with an illustration from a Varney catalogue. If applied as intended it should not hold everything on the bottom bump stop, the adjustment allows the spring force to be set so it rides at the mid point like a CSB.
Regards


From Scalefour Suspension digest

5 Requirements for model locos

The main requirement for good running consists in maintaining continuous and consistent contact between all wheels and the track:

Continuous contact is achieved by allowing wheelsets to have vertical movement with respect to each other; this vertical movement is achieved by hornblocks or axleboxes (or tubular bearings) that can move up and down in the loco frames or chassis (see figure 1).


Bill,

This is the absolutely basic stuff of working suspension.

As per Keith's above, and others earlier posts on this topic, CSB's and and other spring systems, even such as your wagon springs, typically want and assume that the static on perfectly flat track spring position for each wheel is at least approximately at the 50% point of it's up-down movement - So that there can be Up-down movement.

I thought we'd moved on enough so that I could show that lightweight vehicles, such as you just previous suggestions for empty open wagons, need very much softer spring rates than normally weighted vehicles.

Andy

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grovenor-2685
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Re: Flexi Chassis an Appreciation

Postby grovenor-2685 » Mon Dec 18, 2017 11:07 pm

So what's new? We have mentioned innumerable times that the diameter of the spring wire is adjusted to get the required static deflection with the actual vehicle weight, so the lighter vehicle gets a softer spring.
Regards

proto87stores

Re: Flexi Chassis an Appreciation

Postby proto87stores » Tue Dec 19, 2017 3:02 pm

grovenor-2685 wrote:So what's new? We have mentioned innumerable times that the diameter of the spring wire is adjusted to get the required static deflection with the actual vehicle weight, so the lighter vehicle gets a softer spring.
Regards


billbedford wrote:

proto87 wrote:
That's the fundamental difference between equalization and springing hitting a bump. A sprung wheel sees proportionally increasing resistance as the wheel tries to rise, while an equalized wheel sees no difference in resistance as the wheel rises. Basically it is free to follow the rail height profile without incurring extra loading. Hence the track holding excellence.

billbedford mistakenly replied:

You have that backwards. An equalized wheel has to lift the whole of the weight it supports as soon as it hits a bump, while as sprung wheel only has to deflect the spring and the energy stored in the spring deflection will lift the supported weight at a later time.



Actually I was trying to get Bill to understand the basics of there being an independently controllable dynamic spring deflecting rate by picking the spring length and dia. in co-ordination, as opposed to just achieving static balance with the spring length that happens to fit easily in the chassis.

As I understand the general spring fitting and CSB instructions, after you have set the balance by choosing the wire dia., you have no way of then choosing the dynamic spring rate and you are stuck with the one that happens to come with the spread sheet fixed fulcrums and the wire dia. that balances the weight.

It's highly unlikely that there is some "Goldilocks" like situation for Spring Physics in 4mm scale, that the dynamic spring rate you end up with happens to be just the right value for the dynamic springing of each wheel on that vehicle.

Andy

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Will L
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Re: Flexi Chassis an Appreciation

Postby Will L » Wed Dec 20, 2017 12:33 am

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.....


Andy

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

billbedford
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Re: Flexi Chassis an Appreciation

Postby billbedford » Wed Dec 20, 2017 12:27 pm

proto87stores wrote:Actually I was trying to get Bill to understand the basics of there being an independently controllable dynamic spring deflecting rate by picking the spring length and dia. in co-ordination, as opposed to just achieving static balance with the spring length that happens to fit easily in the chassis.


What is there to understand?

If the dynamic deflection under load is less than the designed static deflection any combination of spring rate and weight is going to accommodate the dynamic deflection. And because CSBs are partially equalised the dynamic deflection can even exceed the static deflection on some axles without detriment.
Bill Bedford
Mousa Models
http://www.mousa.biz

Proto87stores

Re: Flexi Chassis an Appreciation

Postby Proto87stores » Sun Dec 24, 2017 4:26 pm

billbedford wrote:
proto87stores wrote:Actually I was trying to get Bill to understand the basics of there being an independently controllable dynamic spring deflecting rate by picking the spring length and dia. in co-ordination, as opposed to just achieving static balance with the spring length that happens to fit easily in the chassis.


What is there to understand?


Actually all the following common-sense, and long established very basic engineering :(

Unless you know the vehicle weight and then choose the needed spring rate first, you have no idea whether you are designing in very hard springing, medium springing or very soft springing for that vehicle weight And only once you have the spring rate, can you then decide to how to implement that spring, bearing in mind it can only be achieved as some a combination of spring length and appropriate wire diameter.

And BTW, the overall effective vehicle spring rate (ratio of weight against spring rate) is what dramatically affects and determines the track holding reliability of a sprung vehicle.


For any given spring rate, thick wire needs to be longer, thin wire needs to be shorter. Obviously you are limited in that you have to choose a wire length that will fit the space available. FINALLY, only then can you set the wire support point heights so that the axle bearing, with the wire you are using, is around the suspension movement mid point.

All the above is the very fundamental basis of why and how springing works. Yet none of that spring rate importance is explained in the suspension digest, nor the 4 point suspension of full equalization that is the natural progression of Flexichas. And nowhere is there any numeric table of worked out spring rates for the various wire lengths and sizes recommended for 4mm model use, so that individuals can quickly find the right wire size for their particular vehicle weight and application.

So your particular justification for recommending switching from Flexichas to springing, without first knowing and understanding this stuff, seems particularly risky and unsubstantiated.

If the dynamic deflection under load is less than the designed static deflection any combination of spring rate and weight is going to accommodate the dynamic deflection. And because CSBs are partially equalised the dynamic deflection can even exceed the static deflection on some axles without detriment


If you don't know or care how much dynamic deflection you get when you hit a bump, then sure any off the wall wire size suggestion will do. But that's how you get unexplained derailments for vehicles that are too light weight, or just wrongly sprung. If you don't the know the numbers your proposed solutions will give, they can't be depended upon to be the right answers.

And separately: Of course, CSB's do not correctly partially equalise an 0-8-0 axle configuration, or greater, even though they are frequently recommended here for such. Anyone who bends a piece of wire running through 5 fixed supports will see that.

Andy.
Last edited by John McAleely on Sat Jan 06, 2018 9:32 pm, edited 1 time in total.
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proto87stores

Re: Flexi Chassis an Appreciation

Postby proto87stores » Wed Jan 10, 2018 5:53 pm

Will L wrote:
Andy

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.


See my immediately previous answer to Bill. Whether for an individual wheel, or the whole loco, the spring rate you end up with is the one that statically balances the weight for the support spacing, not necessarily the one that could/should have been chosen to give the best dynamic smoothing of bumps. Physics is an uncompromising Mistress. "You only get what you weigh for", not "everything comes to those who weight" ;)


Will L wrote:
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.


I have looked over the impressive galley at http://www.clag.org.uk/csb-gallery.html . And great and prolific work it all is. However, that's not a valid argument to claim that any one them would have better static or dynamic performance than an equivalent fully 4 point equalized version. In fact, it's had to imagine how a system that doesn't keep constant equal weight on all drivers, can ever reach the tractive and track holding performance of an equivalent appropriately equalized vehicle.

Will L wrote:
*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.


I've learned not to be a reader of advertising funded forums. :(
Will L wrote:
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


Slow be it ;)

Cheers

Andy
Last edited by John McAleely on Wed Jan 10, 2018 7:06 pm, edited 1 time in total.
Reason: Reformatted to quote correctly

billbedford
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Re: Flexi Chassis an Appreciation

Postby billbedford » Thu Jan 11, 2018 9:38 am

proto87stores wrote:See my immediately previous answer to Bill. Whether for an individual wheel, or the whole loco, the spring rate you end up with is the one that statically balances the weight for the support spacing, not necessarily the one that could/should have been chosen to give the best dynamic smoothing of bumps. Physics is an uncompromising Mistress. "You only get what you weigh for", not "everything comes to those who weight" ;)




Some worked examples would be useful here, just to prove your point.
Bill Bedford
Mousa Models
http://www.mousa.biz

proto87stores

Re: Flexi Chassis an Appreciation

Postby proto87stores » Thu Jan 11, 2018 3:47 pm

billbedford wrote:
proto87stores wrote:See my immediately previous answer to Bill. Whether for an individual wheel, or the whole loco, the spring rate you end up with is the one that statically balances the weight for the support spacing, not necessarily the one that could/should have been chosen to give the best dynamic smoothing of bumps. Physics is an uncompromising Mistress. "You only get what you weigh for", not "everything comes to those who weight" ;)




Some worked examples would be useful here, just to prove your point.




This explains why spring rate matters most for dynamically handling bumps. Your favorite subject. ;)

Andy

billbedford
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Re: Flexi Chassis an Appreciation

Postby billbedford » Fri Jan 12, 2018 9:21 pm

Oh dear, more road vehicle stuff. No wonder you are confused.

The problem with this stuff is that railways, in general, keep any bumps in the track to a minimum. So we can ignore ignore most of what he said, apart from one thing that he implied, but didn't say explicitly. This was that if the wheels are to stay on the track/road the dynamic deflection has to be less than the static. Something I may have mention here before.
Bill Bedford
Mousa Models
http://www.mousa.biz


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