Flexi Chassis an Appreciation

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grovenor-2685
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Re: Flexi Chassis an Appreciation

Postby grovenor-2685 » Sat Feb 11, 2017 6:22 pm

Bill and Andy,
It would help if you agreed on the meaning of the words you use before arguing their respecyive merits.
Equalisation does NOT equal or require springing, nor is it synonymous with compensation.
Firstly we are discuusing suspension arrangements other than rigid chassis, no one is confusing rigid with equalised.

Secondly we can divide suspension systems into those with springs and those without, those without we choose to call compensated.
Equalisation (of axle loads) can be applied to either by appropriate means.
To equalise a compensated system the centre of gravity and the design of the levers etc needs to be done appropriately to achieve that end. You only end up with one axle at double the axleload of the other two if you do it badly.
With a sprung system you can go for an American style bar frame layout of springs and levers to achieve an equalised sprung system but the UK prototype rarely did that and modellers often choose not to either.
Using individual springs for each wheel means that some adjustability is needed to equalise axle loads and the result will only be equal when static. Even so they do work.
The CSB design is aimed at providing some degree of compensation into the springing, the equalisation is optimised at the design stage by the location of the CSB supports.

Andy, do note that bogie vehicles and Bo-Bo locos are much the best configuration for ride and trackholding and good results are achieved with compensation as you have experienced. That does not mean that springs can't improve it further. However other configurations, 4 wheel wagons, steam locos Co_Co dlesels etc are more difficult to get good results without springing.

I'll leave it to Andy to work out the relationship between Zebedees knees and Ted Scannel :)
Regards

John Palmer
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Re: Flexi Chassis an Appreciation

Postby John Palmer » Sat Feb 11, 2017 7:02 pm

grovenor-2685 wrote:With a sprung system you can go for an American style bar frame layout of springs and levers to achieve an equalised sprung system but the UK prototype rarely did that and modellers often choose not to either.
I can only think of the SDJR 2-8-0's as an example of a British design adopting this dual system (on plate frames); what others were there?

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Will L
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Re: Flexi Chassis an Appreciation

Postby Will L » Sat Feb 11, 2017 7:24 pm

Proto87Stores wrote:The outcome was actually good and showed that CSB is definitely a good workable solution, as the model came second in the competition.

The loco that took first place was however, one that used the standard Flexi-chas form of chassis. . . .

Don't think there is any doubt that a well designed flexichassie is capable of producing as much adhesion as is physically possible from a give wheel arrangement and weight. As will a well designed CSB, as both are capable of ensuring an optimum distribution of adhesive weight.

For me at least the advantage of CSB is the improved ride quality obtained by removing the rigid link between the body from the wheels. Some of the more complex flexichassie designs do away with the rigid axle, and can run very nearly as well, but by then the CSB to do the same job could actually be significantly simpler.

And then there are some problems with flexichassie, which originate from the fact that, as such a chassis will always sit level, people don't give much/any thought to weight distribution. Even when they do, when did you last see an article on a flexichassie which mentioned the loco's Center of Gravity.

There is the stability problem. Having set up a the "three leged stool" not getting the CofG well placed in the triangle defined by the three legs can leave you with significant stability problems.

Then there is the weight distribution problem. It isn't particularly difficult for the numerate to work out what the weight per wheel will be, but only if you know where the CofG is. The way this works out isn't necessarily any more intuitive than CSB placement and many a flexichassie loco has proved a disappointing puller as a result.

Finaly if you do the calculations to ensure good weight distribution you can find the solution fails in the stability department.

For anybody interested Russ Elliott has documented all this in digest 41.0 available from the GLAG Web site. The way to calculate the weight distribution is covered here., and the stability issue us coverded here.

This is why I think CSB end up providing a simpler and more reliable solution, but i doubt we would have ever got there without the development of flexichassis first.

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grovenor-2685
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Re: Flexi Chassis an Appreciation

Postby grovenor-2685 » Sat Feb 11, 2017 9:33 pm

I can only think of the SDJR 2-8-0's as an example of a British design adopting this dual system (on plate frames); what others were there?

I did't know of any offhand but I have learned not to make absolute statements on such things as there will always be someone who knows better, as you did!
Regards

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Guy Rixon
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Re: Flexi Chassis an Appreciation

Postby Guy Rixon » Sat Feb 11, 2017 11:32 pm

John Palmer wrote:
grovenor-2685 wrote:With a sprung system you can go for an American style bar frame layout of springs and levers to achieve an equalised sprung system but the UK prototype rarely did that and modellers often choose not to either.
I can only think of the SDJR 2-8-0's as an example of a British design adopting this dual system (on plate frames); what others were there?


It was quite common in 19th-century locos. I've seen in on Sturrock designs for the GNR, on earlier SER and LCDR locos and (IIRC) on some MR tank engines. Notably, all the examples I can bring to mind have outside frames.

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Re: Flexi Chassis an Appreciation

Postby Julian Roberts » Sun Feb 12, 2017 6:57 pm

Does anyone know why is it not possible to make an attachment to a reply on this thread?

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Re: Flexi Chassis an Appreciation

Postby garethashenden » Sun Feb 12, 2017 7:28 pm

Julian Roberts wrote:Does anyone know why is it not possible to make an attachment to a reply on this thread?

It might be because it's a Guest Book thread.

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Re: Flexi Chassis an Appreciation

Postby John McAleely » Sun Feb 12, 2017 7:46 pm

garethashenden wrote:
Julian Roberts wrote:Does anyone know why is it not possible to make an attachment to a reply on this thread?

It might be because it's a Guest Book thread.


Correct. However, I have now changed that, so that we can use attachments as usual. Guests posts still require approval before they will be seen.

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Re: Flexi Chassis an Appreciation

Postby Julian Roberts » Sun Feb 12, 2017 9:48 pm

Tnanks John :P

These discussions always seem to focus down to how much load can be pulled.

Proto87Stores wrote:
Actual or supposed "superiority" of wheel springing in either theory or practice, for model track holding, is a very difficult process to demonstrate in practice, and I suspect even more so to prove in theory.


Andy




I suppose the problem is, the track is just as critical a component as the loco.

Below is my third layout plank, the sum total of my layout building, as I so far make stock for running on our club layout. The planks are made to give a vicious test of what a loco can do - the first one being to my previous minimum of 4ft radius curve.

Here is my incomplete visually Barclay Tank at its full speed on a reverse 600mm curve I made in an afternoon after it turned out that the loco would be required to go round such a curve on a proposed layout. It is made using the standard P4 triangular gauge to give appropriate widening on the curves. The track needed no fettling other than rail ends smoothed off.

The loco is made as per what I have written in the Snooze, this one has moving axles all round.

The loco shows no inclination on many repetitions to jump the rails and I am confident that when on the intended layout, at an appropriate speed for such a curve, any problems will be not be the fault of the loco.







Below shows a short freight train (with suspension as per my 3rd article) including a long wheelbase SR CCT type van, and a Caledonian Railway 6-wheel guards van, being put through its paces. Similarly there is no inclination to jump the rails on many repetitions.


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Re: Flexi Chassis an Appreciation

Postby QuentinD » Sun Feb 12, 2017 10:59 pm

Can someone please clarify for a beginner what the flexichassis system is? Is it different from 3-point compensation? I've heard much talk but seen little documentation, only the occasional photo.

CSBs, on the other hand, are well-documented online and seem relatively simpler

Quentin

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Re: Flexi Chassis an Appreciation

Postby grovenor-2685 » Sun Feb 12, 2017 11:36 pm

QuentinD wrote:Can someone please clarify for a beginner what the flexichassis system is? Is it different from 3-point compensation? I've heard much talk but seen little documentation, only the occasional photo.
CSBs, on the other hand, are well-documented online and seem relatively simpler
Quentin

As I understand it "Flexichas" is the name used by Mike Sharman, Rod Neep and Perseverance as a trade name for 3-point compensation.
Mike Sharman wrote the book, Rod Neep drew up etching masters and Perseverance sold the parts. The principles are covered pretty thoroughly in the Digest 41.0 by Russ Elliott.
Regards

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John McAleely
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Re: Flexi Chassis an Appreciation

Postby John McAleely » Sun Feb 12, 2017 11:50 pm

grovenor-2685 wrote:The principles are covered pretty thoroughly in the Digest 41.0 by Russ Elliott.


Which Russ publishes on the CLAG website: http://www.clag.org.uk/41-0rev.html

(Members can also get a copy from the Digest Archive, but since this is a guest book thread, I thought the public link would be more useful...)

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Will L
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Re: Flexi Chassis an Appreciation

Postby Will L » Mon Feb 13, 2017 12:06 am

QuentinD wrote:Can someone please clarify for a beginner what the flexichassis system is? Is it different from 3-point compensation? I've heard much talk but seen little documentation, only the occasional photo.

CSBs, on the other hand, are well-documented online and seem relatively simpler


Flexichassis was the name given to 3 point suspension by Mike Sharmans in his book of book titled "Flexichas, A Way to Build Fully Compensated Model Locomotive Chassis" Copies are still obtainable https://www.amazon.co.uk/Flexichas-Buil ... 0860930726 explaines in fairly simple terms the principle of three point suspension, how it can be applied. In particular how it can be used to build good working chassis on the kitchen table. Seminal is not to big a word.

Another source of information is Scalefour Digest 41.0 - The principles of model locomotive suspension To understand the basics you only need get through the first 7 sections (out of 21). This isn't such an easy read and covers most of what you need to know on suspension subsystem, although it predates the continued development of CSBs.

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Re: Flexi Chassis an Appreciation

Postby Julian Roberts » Mon Feb 13, 2017 5:01 pm

QuentinD wrote:Can someone please clarify for a beginner what the flexichassis system is? Is it different from 3-point compensation? I've heard much talk but seen little documentation, only the occasional photo.
Quentin



Quentin
I was totally converted to railway modelling and later to P4 by reading Iain Rice's three books on loco construction published in the '80's by Wild Swan. Locomotive Kit Chassis Construction in 4mm is the one relevant to your question. He explains fully how to make rigid and compensated chassis, and leaves you in no doubt as to the merits Mike Sharman's brilliant Flexichas concept.
Mike Sharman's own book gives the innermost essentials but if I had read that first I might not have really understood or been gripped with enthusiasm. If I had read the Scalefour Digest first I may not have understood anything nor been interested! Simply depends what kind of mind you have. Iain explains everything really fully with lots of sketches and explanations, and not least loads of photos of excellent modelling that whetted my appetite. He doesn't assume any prior knowledge and doesn't talk down to you if you have none, makes everything really logical and thought out yet without glossing over the problems and over-simplifying. Obviously I don't know how much of a beginner you are, I doubt you are as green as I was when I read those books first 20 years ago if you already model in P4, and may not need the spoon feeding that I did back then.
Some things I have since then learned from further reading, my own experience, from this Forum, and friends, particularly Allan Goodwillie and David Franks, and changed from the way he goes about things.

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Re: Flexi Chassis an Appreciation

Postby Le Corbusier » Mon Feb 13, 2017 5:44 pm

Julian Roberts wrote:
QuentinD wrote:Can someone please clarify for a beginner what the flexichassis system is? Is it different from 3-point compensation? I've heard much talk but seen little documentation, only the occasional photo.
Quentin



Quentin
I was totally converted to railway modelling and later to P4 by reading Iain Rice's three books on loco construction published in the '80's by Wild Swan. Locomotive Kit Chassis Construction in 4mm is the one relevant to your question. He explains fully how to make rigid and compensated chassis, and leaves you in no doubt as to the merits Mike Sharman's brilliant Flexichas concept.
Mike Sharman's own book gives the innermost essentials but if I had read that first I might not have really understood or been gripped with enthusiasm. If I had read the Scalefour Digest first I may not have understood anything nor been interested! Simply depends what kind of mind you have. Iain explains everything really fully with lots of sketches and explanations, and not least loads of photos of excellent modelling that whetted my appetite. He doesn't assume any prior knowledge and doesn't talk down to you if you have none, makes everything really logical and thought out yet without glossing over the problems and over-simplifying. Obviously I don't know how much of a beginner you are, I doubt you are as green as I was when I read those books first 20 years ago if you already model in P4, and may not need the spoon feeding that I did back then.
Some things I have since then learned from further reading, my own experience, from this Forum, and friends, particularly Allan Goodwillie and David Franks, and changed from the way he goes about things.


I would second this ... and I am still a beginner. I found Iain Rice's Chassis building a fascinating introduction to the things that need to be considered and it massively aided in my overall understanding, whilst just making you itch to have a go yourself.
Last edited by Le Corbusier on Tue Feb 14, 2017 8:44 am, edited 1 time in total.
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Re: Flexi Chassis an Appreciation

Postby Proto87Stores » Tue Feb 14, 2017 1:12 am

billbedford wrote:
Proto87Stores wrote:
So far, given a few days to allow for extra consideration, no-one seems to have found fault with the above Physics.

However, if instead we consider the methodology of pure Equalization, the static weight carried on each wheel of a similar well balanced vehicle remains constant, regardless of track twist or any combination of bumps/dips in the track. Flexi-chas is of a course a methodology based on equalization, but was somewhat affected by the limited range of practical and economic options and parts available to modellers back at that time.

Quoting from the suspension section of the Digest:
. . . .
"2 Introduction

The term 'better running' may be looked at from several viewpoints; of these, the most important is freedom from derailment, followed closely by controllability of locomotives and their performance in terms of balance, stability and haulage capacity."
. . . .

My ongoing concern is why almost all the other threads on this forum are heavily into recommending some form of chassis springing, when equalization clearly and fundamentally is better at providing consistent wheel weighting over less than perfectly flat track, and meets the primary goals of better running as expressed above?

Andy


After 15 or 20 years of explaining to you why springing is superior to 'equalisation' you still don't get the point, and I suspect that most people that have tried to help you have just given up.

To recap: Springing is a dynamic system, and while the static loads may vary within small limits, the benefits of the absorption of minor perturbations in the ride height due to irregularities in the track or wheels gives a smoother ride.

Flexi-chas does not provide any equalisation, except in the case of four wheeled vehicles, and even then sprung or rigid systems provides better road holding than rocking 3-point suspensions. Flexi-chas is compensation system where the proportion of weight carried by each axle is fixed by the geometry. So in the case of a flexi-chas three axle loco frame one axle carries as much weight as the other two combined.

For equalisation both springing and compensation are used so that loads are shared and averaged between springs. This is evident on US designed bar-framed locos where springs are linked together by compensation beams, or on many diesel loco bogies.


Bill,

You are getting quite far ahead of me here. I'm only interested in first getting agreement on the basic underlying physics. That of multiple wheels on axles sharing the weight of the vehicle they are carrying. If that Physics isn't understood by all interested parties, then there is no way of assessing comparisons of existing methods, or validating potential improvement suggestions.

My understanding of any form of LINEAR springing on a wheel without intermediate stops is as follows:

The recommended needed range of movement = +/- 0.5 mm
When resting on the track, the correct default static equilibrium position under the per wheel weight of the vehicle is the 50% (midway) compression point.
The spring is essentially unloaded when and while the vehicle is lifted off the track.
Setting the required spring rate vs. the wheel position and the location of the c of g in the chassis to obtain the correct/desired per/wheel weight carried requires a smart computer program.

It then follows that if the wheel drops a full 0.5 mm relative to the chassis, there is zero weight carried by the spring and the wheel. And if the wheel rises 0.5 mm relative to the chassis, the max weight the wheel carries while still sprung is twice its equilibrium per wheel weight before it becomes merely rigid.

If the spring is softer than required for the full movement range, then there will either be rigid stops at the top and bottom of the =/- 0.5 mm movement range, or a larger range of movement for the same loads. So, in the former case, a dropping wheel will hit the lower stop before there is zero weight and hit the higher stop before carrying twice the equilibrium weight.

For springs that are proportionally harder, the wheel will not hit an upper stop, or movement limit, unless the weight on the wheel is proportionally increased. Correspondingly,, the wheel will become unloaded proportionally before the lower stop.

My understanding of purely longitudinal (chassis) equalization is as follows:

Consider each side of the loco or passive vehicle chassis separately.
Divide up the wheel bearings identically along each side into separate adjacent pairs, or triplets of overlapping adjacent pairs

Each adjacent pair of wheel bearings on one side of a chassis are then connected by by a rigid beam which is pivoted at a fulcrum point between them. The weight to be carried by the pair of wheels is applied to the beam at the fulcrum point. A similar duplicated beam on the other side if the chassis connects the matching wheel bearings on the other side. But the two beams may move independently. Add as many beams and fulcrum points separately per side as needed to cover all the load carrying wheels fitted to the vehicle.

Set the fulcrum of each beam where it will divide its downward force in the weight ratio between the pair of wheels that you want. (default is 50:50 for a pair weighted equally, or 66:33 for each beam of an over-lapping pair triplet all weighted equally).

If you end up with more than two fulcrums per side, add another layer of similar beams pressing down on those fulcrums (again your choice of ratio) until you end up with only 2 fulcrum points per side.

The necessity of going beyond chassis only pure longitudinal equalization.

Pure longitudinal equalization alone will not solve any of the “twisted track issues”. But there are several options for going beyond just equalizing the chassis sides and mounting the body to the chassis. I have listed three possible options below. There may well be others. The best option in a particular case typically will be based on where the c of g of the vehicle is and the performance/stability desired.

The three options I considered include:

1. Attach/support the body and/or chassis fixed sideframes on the four remaining fulcrum points via vertically flexible joints or springs.

2. Add a single transverse equalizing beam to two opposite fulcrums on each side. Support the body on the center fulcrum of the transverse beam and the two remaining fulcrums. Springs optional.

3. Add or use one more beam layer to the sides so that you only have one fulcrum on each side. Add two transverse equalizing beams to both ends of the top longitudinal side beams. Attach/support the body at four points on the fulcrums of the two side beams and the center fulcrums of the two transverse beams. Springs optional.

Now the body will be stable on the all equalized chassis.
To keep this post of manageable size, I’ll stick with just the descriptions above for now. This is still checking to make sure we have common ground as to what springing and equalization are and do. And of course these are open for comment.

I’ll save what I believe are the various justifications and advantages for later.

Andy

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Re: Flexi Chassis an Appreciation

Postby Horsetan » Tue Feb 14, 2017 8:13 am

John Palmer wrote:
grovenor-2685 wrote:With a sprung system you can go for an American style bar frame layout of springs and levers to achieve an equalised sprung system but the UK prototype rarely did that and modellers often choose not to either.
I can only think of the SDJR 2-8-0's as an example of a British design adopting this dual system (on plate frames); what others were there?


Did the SNCF 141R 2-8-2s have the same system?
That would be an ecumenical matter.

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Re: Flexi Chassis an Appreciation

Postby junctionmad » Tue Feb 14, 2017 12:00 pm

Personally , I'm a fan of the Varney springing technique . I'm building Co-Co. Diesel bogies with this method .

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Re: Flexi Chassis an Appreciation

Postby David Knight » Tue Feb 14, 2017 2:48 pm

Horsetan wrote:
John Palmer wrote:
grovenor-2685 wrote:With a sprung system you can go for an American style bar frame layout of springs and levers to achieve an equalised sprung system but the UK prototype rarely did that and modellers often choose not to either.
I can only think of the SDJR 2-8-0's as an example of a British design adopting this dual system (on plate frames); what others were there?


Did the SNCF 141R 2-8-2s have the same system?[/quote

Ivan,

If this article is anything to go by I think the answer is yes. https://en.m.wikipedia.org/wiki/SNCF_Class_141R

Cheers,

David

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Re: Flexi Chassis an Appreciation

Postby Will L » Tue Feb 14, 2017 6:47 pm

junctionmad wrote:Personally , I'm a fan of the Varney springing technique . I'm building Co-Co. Diesel bogies with this method .


For those that don't know, the Varney system was applied original by one or two American RTR companies in the late 40's (I understand). A relavent RMweb thread is here.

Superficially it looks like a sort of CSB, in as far as it has a wire running down each side under fixed fulcrum point in the chassis and over fulcrum points on axle bearing blocks (or over the axle?). It differs in as far as this wire is held under tension by an additionally (usually) coil spring(s) and has a mechanism to allow the adjustment of the tension applied so as to adjust ride hight. The RTR originals were VERY HEAVY and the spring wire was nowhere near being able to support the body weight and the effective sprinkling it was all down to the tension in the wire. Being American prototypes they tended to have lots of axles. The version being proposed on RMweb are said to be rather closer to CSBs because the body weights are significantly less and as they use CSB style spring steel wire. However as any axle depression can only occur by compressing the adjustment spring, now much the spring wire adds to this is unclear (to me at least). I have no direct experience of any of them, but those who do say they ride well over track irregularities.

While I am comfortable that I understand how CSB distributes a loco weight over its wheels, I'm afraid I can't get my head round what the Varney system does but I presume it is just as dependant on the Centre Of Gravity being in the right place. There is a suggestion that the Varney system is adjustable while the CSB system isn't but I think that is a failure to understand CSB theory. I would have thought the mechanics of CSB were easier to implement, but then I would say that wouldn't I.

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Re: Flexi Chassis an Appreciation

Postby billbedford » Tue Feb 14, 2017 7:39 pm

Proto87Stores wrote:My understanding of any form of LINEAR springing on a wheel without intermediate stops is as follows:

The recommended needed range of movement = +/- 0.5 mm
When resting on the track, the correct default static equilibrium position under the per wheel weight of the vehicle is the 50% (midway) compression point.
The spring is essentially unloaded when and while the vehicle is lifted off the track.
Setting the required spring rate vs. the wheel position and the location of the c of g in the chassis to obtain the correct/desired per/wheel weight carried requires a smart computer program.


The were lots of blokes working in loco weigh shop who would have disagreed with this, though perhaps their skills have been lost.



It then follows that if the wheel drops a full 0.5 mm relative to the chassis, there is zero weight carried by the spring and the wheel. And if the wheel rises 0.5 mm relative to the chassis, the max weight the wheel carries while still sprung is twice its equilibrium per wheel weight before it becomes merely rigid.

If the spring is softer than required for the full movement range, then there will either be rigid stops at the top and bottom of the =/- 0.5 mm movement range, or a larger range of movement for the same loads. So, in the former case, a dropping wheel will hit the lower stop before there is zero weight and hit the higher stop before carrying twice the equilibrium weight.

For springs that are proportionally harder, the wheel will not hit an upper stop, or movement limit, unless the weight on the wheel is proportionally increased. Correspondingly,, the wheel will become unloaded proportionally before the lower stop.



You have completely misunderstood the way springs work. The static deflection for a model loco is given as ± 0.5mm, but the dynamic deflection is much smaller than this, probably in the range of less than ± 0.1 mm for reasonably well laid track. If the spring become unloading in service there is something very wrong with the application that the springs are being put to. I would never expect to see a springs on a model loco either completely unloaded or rigid, after all we are modelling a railway, not all-terrain vehicles.


My understanding of purely longitudinal (chassis) equalization is as follows:

...

If you end up with more than two fulcrums per side, add another layer of similar beams pressing down on those fulcrums (again your choice of ratio) until you end up with only 2 fulcrum points per side.



Which gives a four point suspension...


The necessity of going beyond chassis only pure longitudinal equalization.

Pure longitudinal equalization alone will not solve any of the “twisted track issues”. But there are several options for going beyond just equalizing the chassis sides and mounting the body to the chassis. I have listed three possible options below. There may well be others. The best option in a particular case typically will be based on where the c of g of the vehicle is and the performance/stability desired.

The three options I considered include:

1. Attach/support the body and/or chassis fixed sideframes on the four remaining fulcrum points via vertically flexible joints or springs.

2. Add a single transverse equalizing beam to two opposite fulcrums on each side. Support the body on the center fulcrum of the transverse beam and the two remaining fulcrums. Springs optional.

3. Add or use one more beam layer to the sides so that you only have one fulcrum on each side. Add two transverse equalizing beams to both ends of the top longitudinal side beams. Attach/support the body at four points on the fulcrums of the two side beams and the center fulcrums of the two transverse beams. Springs optional.


Sure these will work, but springing especially CSBs, will be more efficient, more elegant and more prototypical.
Bill Bedford
Mousa Models
http://www.mousa.biz

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Re: Flexi Chassis an Appreciation

Postby grovenor-2685 » Tue Feb 14, 2017 8:31 pm

Bill said: The static deflection for a model loco is given as ± 0.5mm

Assuming here that the static deflection is for the springs when the vehicle is standing on level track, then it will never be negative.
We aim for +0.5 mm, at least in the design guide for CSBs but Andy was talking about the range of movement designed into the axleboxes between the top and bottom bump stops which may well be ± 0.5mm or thereabouts as it is a non-critical dimension.
If that is the case and the static deflection is +0.5 mm then with the wheelset on the lower bump stops the CSB will be straight and thus applying 0 downforce as Andy said. But, as you say this is irrelevant in operation as the bump stops should never be reached in running.
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Re: Flexi Chassis an Appreciation

Postby Julian Roberts » Thu Feb 16, 2017 9:37 am

Quote Iain Rice from his aforementioned book, pre CSB days

So what of sprung chassis, also to be found in commercial kit form? Well I'm not going to argue that they're an unworkable waste of time, as that patently isn't true. However, I would argue... that the majority of commercial sprung chassis don't work in the way that most people think they do, and that the proper design and construction of a truly effective sprung chassis is no simple matter. Doubters are referred to the writing in MRJ of Chris Pendlenton, who produces some remarkably effective examples of the breed, but not , be it noted, using any commercial coil-sprung hornblock. Mr Pendlenton also comes from the North-East of England, where , as is well known, they eat a lot of fish from a early age, which makes him, like Jeeves, in need of a hat -size considerably above the average.

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Re: Flexi Chassis an Appreciation

Postby grovenor-2685 » Thu Feb 16, 2017 10:38 am

As you say, pre CSB.
At that time there were, I think, two commercial designs.
1. The original MRSG design taken up by Alan Gibson that relied on a small, weak coil spring intended that the axles would sit on the top bump stops just like a rigid chassis except when the track irregularities allowed the spring to push the axle down to remain in contact with the rail.
2. The common 'Japanese/Korean brass' where the opposite usually applied, the springs were strong enough to keep the axles on the bottom stops and hence were not effective unless the user substituted weaker springs.

The single leaf guitar springs and CSBs do a better job easier, the Brassmaster's coils also used by Comet are also simple if the spring rate is correct for the loco weight.
Regards

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Will L
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Joined: Sun Jul 20, 2008 3:54 pm

Re: Flexi Chassis an Appreciation

Postby Will L » Thu Feb 16, 2017 3:33 pm

As Keith says, the USP (business jargon sorry - unique selling point) of CSB is that it is the only system I am aware of which guarantees a sprung suspension where the loco is properly supported by the springs, that is with a range of movement available above and below the static position, with out a great deal of very careful adjustment and guess work. I'm told the Brassmaster system does this but as it is really isn't adjustable (see posting about the Varney sytem above) this can't be true for any weight of loco. The Brassmaster system is certainly reasonably simple to apply. The Varney sysem may achieve it, but I believe they are inclined to run with the axles held against a keeper plate so that effectively only upward displcment of an axle is actually available, and we are left of speculate what the true weight distribution characteristics actually are.

However to revert to the Thread topic, I think it is reasonably clear that we a can see CSB as a direct descendant of Flexi Chassis, as Flexi Chassis gave rise to the development of working hornblocks, and the construction methods that go with them, which make CSB practicable.

To pick up Julian's point, I too am a great fan of Ian Rice's writings and was inspired by him to...

I was going to say "greater things", but I rather wonder if that might not get me accused of elitism or of denigrating the efforts of those not so inspired?


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