Flexi Chassis an Appreciation

[Noel]

"4 Wheel Wagons, Compensate, Equalise or Spring"?

How about "Compensate, equalise, spring or don't bother"? Despite all the comments, the last is still a valid option [in the sense of being usable], even if one or more of the others may be preferable, at least in some cases.

[Will L]

I don’t really believe anybody really thinks that current springing methods are in any way a representation of the real thing, and anybody who has tried has quickly found out that the physics of mass related things just doesn’t scale.

I thought the way the original mention was written, it ambiguously implied that model springing followed prototype practice - which was therefore "better" than flexi-chas if only for that reason.

Certainly fitting springing makes you more like the prototype, in as far as all but the most primitive wagons had springs and for very good reasons.
A scaled down representation of a prototype spring is unlike to work as physics assonated with mass just doesn't scale well, so our model springing is going be rather different from that fitted to prototype.
I still think that once you have a practical springing system it is preferable to any simply compensated system given that they are otherwise comparable in terms of the complexity or otherwise of building them. I accept an equalised system containing both elements would be another mater but complexity is more likely to be an issue.

I'm still thinking about the rest.

[grovenor-2685]

I don't really fancy trying to disentangle the springing argument, 4 wheel or otherwise from the Flexi chassis discussion that the topic has in its title.
I suggest just leaving it as is.
Regards

[Will L]

I don't really fancy trying to disentangle the springing argument, 4 wheel or otherwise from the Flexi chassis discussion that the topic has in its title.
I suggest just leaving it as is.

I wasn't thinking of disentangling anything, just splitting and re titling with a sign post connecting the two together, but its not important if your rather not.

[Proto87stores]

"4 Wheel Wagons, Compensate, Equalise or Spring"?

How about "Compensate, equalise, spring or don't bother"? Despite all the comments, the last is still a valid option [in the sense of being usable], even if one or more of the others may be preferable, at least in some cases.

I'm looking to the almost no bother category.




For example these 4 very simple beam etches almost on their own add full (longitudinal) easy add-on equalization to the power bogies of a typical RTR Bo-Bo of a similar range of diesels/electrics. ( Note that these replace the old fixed beams (shown) and require adding replacement bearings as well) . They utilize handy existing fulcrum points on the plastic sideframes (removed- not shown) and the "slightly sloppy" gear clearance of the existing mechanisms. But have been found in practice to work well. As per You tube videos referenced earlier.

These do cause 100% dependable track holding, even if the body connection is only 3 point. I'm not sure that an equivalent primary springing system could be designed and fitted as easily and simply.

Going the extra step of making the body connection 4 point sprung makes the suspension just about perfect. (but that typically requires some additional creative parts and mods). So far I've only done that for certain coaches.

[billbedford]

Certainly fitting springing makes you more like the prototype, in as far as all but the most primitive wagons had springs and for very good reasons.
A scaled down representation of a prototype spring is unlike to work as physics assonated with mass just doesn't scale well, so our model springing is going be rather different from that fitted to prototype.

That is not true. It is just a matter of finding a material that will model the full size spring in our scale.

I have been told that the polycarbonate used in plastic milk bottles will produce acceptable working leaf springs, but I have never tried it myself. There's something about having to make the individual leaves, assemble them and find a suitable colouring solution that puts the exercise into 'maybe in another life-time' category.

[grovenor-2685]

It is just a matter of finding a material that will model the full size spring in our scale

Simplicity itself
Regards

[proto87stores]

Certainly fitting springing makes you more like the prototype, in as far as all but the most primitive wagons had springs and for very good reasons.
A scaled down representation of a prototype spring is unlike to work as physics assonated with mass just doesn't scale well, so our model springing is going be rather different from that fitted to prototype.

That is not true. It is just a matter of finding a material that will model the full size spring in our scale.

If you could find the right material and make a true leaf spring, that could be true statically. But in your strong personal interest of the dynamic (moving along) case, the acceleration due to gravity is the same at any scale. So while the vertical acceleration (and duration) when passing over a bump will be very similar for both prototype and model, the horizontal distance travelled by the model over the same period will be only 1/76.2 of the distance travelled by the prototype.

That's why model trains don't sail way out over collapsing bridges, like the supposed real ones in suspense movies do.

Andy

[Guy Rixon]

Certainly fitting springing makes you more like the prototype, in as far as all but the most primitive wagons had springs and for very good reasons.
A scaled down representation of a prototype spring is unlike to work as physics assonated with mass just doesn't scale well, so our model springing is going be rather different from that fitted to prototype.

That is not true. It is just a matter of finding a material that will model the full size spring in our scale.

If you could find the right material and make a true leaf spring, that could be true statically. But in your strong personal interest of the dynamic (moving along) case, the acceleration due to gravity is the same at any scale. So while the vertical acceleration (and duration) when passing over a bump will be very similar for both prototype and model, the horizontal distance travelled by the model over the same period will be only 1/76.2 of the distance travelled by the prototype.

That's why model trains don't sail way out over collapsing bridges, like the supposed real ones in suspense movies do.

Andy

I'm not sure what you mean here; could you rephrase it, please? Is your point that the ratio of static and dynamic loads on the spring changes with the scale of the model?

[Alan Turner]

Certainly fitting springing makes you more like the prototype, in as far as all but the most primitive wagons had springs and for very good reasons.
A scaled down representation of a prototype spring is unlike to work as physics assonated with mass just doesn't scale well, so our model springing is going be rather different from that fitted to prototype.

That is not true. It is just a matter of finding a material that will model the full size spring in our scale.

If you could find the right material and make a true leaf spring, that could be true statically. But in your strong personal interest of the dynamic (moving along) case, the acceleration due to gravity is the same at any scale. So while the vertical acceleration (and duration) when passing over a bump will be very similar for both prototype and model, the horizontal distance travelled by the model over the same period will be only 1/76.2 of the distance travelled by the prototype.

That's why model trains don't sail way out over collapsing bridges, like the supposed real ones in suspense movies do.

Andy

That's because a) you can't scale time and b) you don't run your trains fast enough.

This is fundamentally at the heart of springing and why you cannot produce a springing system that is based on the springing system of the prototype (i.e. leaf springs).

regards

Alan

[Russ Elliott]

How strong are Brassmasters ones? Subjectively they feel quite strong. Is the idea of them to rest on the end stop like Gibson ones (but with more downward force perhaps) or to ride in midpoint like a CSB?

The strength of the Brassmasters spring is approx 0.7N/mm. See http://www.clag.org.uk/brassmaster.html. The spring was designed by the late Alistair Rolfe (of No Nonsense Kits). This strength is more suitable to heavier, larger loco, which was Jeff Ayers' design brief. They do not compress to their endstops, like the weak Gibsons do. (i.e. they do not come into the category of 'spring assisted' hornblocks). Indeed, it would take approx 150g to compress them fully.

[proto87stores]

For those who may not have been able to view this earlier, I've uploaded the video clip to youtube, so it displays here.



This rather extreme clip demonstrates the ability of a split, equalized wheels with a separately sprung body, suspension system to stay perfectly and firmly on the track, even if handled very roughly.

In this type of suspension the body springing can be separately set up optimally "soft" for cosmetic smooth riding, without having to worry about the impact of the springing on individual wheel loading and balance..

Andy

[Russ Elliott]

I often think 'equalisation' is a much misunderstood (and misused) term:

nyc254s.jpg

In model terms, this is quite simply:

springy-equaliser.png

[proto87stores]

I often think 'equalisation' is a much misunderstood (and misused) term:

nyc254s.jpg

In model terms, this is quite simply:

springy-equaliser.png

AFAIK Compensation is an UK model society only term which I perceive to be very broadly used for any model track holding suspension of a non springy type that adapts to uneven track. Otherwise it doesn't seem to have a specific reference definition.



For our purposes equalization means what it says. It automatically adjusts the carried weight per wheel equally under a common fulcrum in all track conditions. In both model terms and prototype terms it's even simpler. The bar shown is typically rigid and not springy. On the prototype some (separate) partial springing is often added to rigid bars for (a) Passenger comfort and (b) track and chassis (and delicate cargo) impulse damage avoidance. Neither of those apply in small scale modelling.

Using a springy equalization bar in modelling means you've added some springing to either a body or another fulcrum higher up the chain. You of course now are restricted in what the weight of the carried body can be, without additional adjustment. You've also likely gained several additional model construction and mounting problems.

Andy

[Russ Elliott]

For our purposes equalization means what it says. It automatically adjusts the carried weight per wheel equally under a common fulcrum in all track conditions.

Nonsense.

springy-equaliser2.png

[proto87stores]

For our purposes equalization means what it says. It automatically adjusts the carried weight per wheel equally under a common fulcrum in all track conditions.

Nonsense.

springy-equaliser2.png

Sorry I wasn't clear. I was talking about your earlier single fulcrum diagram as above . As per my earlier comments, I disagree absolutely that a model equalizing bar should ever be springy as well. I certainly didn't submit that concept in my contribution to the digest. If you want to compromise two suspension methods by muddling them up in one component, then you, not I, have the responsibility of justifying it.

My prototype example picture is clearly a combination, mainly because it's a passenger vehicle. There are actually double equalizing beams, of which you can just barely see the inner of the pair behind the auxiliary coils springs. The main car springing is in the center and may or may not bear on the center of the equalizing bars. But I don't have an engineering drawing to substantiate either possibility and I'm not going to speculate.

I'm not sure what your picture of the outside 3rd rail locomotive with the trucks partly hidden, or the second diagram are actually intended to show? I'm certainly not proposing building anything like the latter. Or describing it as model "equalizing".

Andy

[Russ Elliott]

As per my earlier comments, I disagree absolutely that a model equalizing bar should ever be springy as well. I certainly didn't submit that concept in my contribution to the digest. If you want to compromise two suspension methods by muddling them up in one component, then you, not I, have the responsibility of justifying it.

The Digest is necessarily eclectic, so it's not surprising individuals will have their different preferences.

Ted had a bunch of springy equalisers in his S&D 2-8-0. Worked perfectly.

[proto87stores]

As per my earlier comments, I disagree absolutely that a model equalizing bar should ever be springy as well. I certainly didn't submit that concept in my contribution to the digest. If you want to compromise two suspension methods by muddling them up in one component, then you, not I, have the responsibility of justifying it.

The Digest is necessarily eclectic, so it's not surprising individuals will have their different preferences.

Ted had a bunch of springy equalisers in his S&D 2-8-0. Worked perfectly.

I'm reluctant to just agree with that example, without first knowing you and Ted's test criteria and on which layout(s) the loco ran its trials. But with Ted's terrific mechanical capabilities and skills, I would expect him to be able to make anything work, even if it wasn't perfect initially. The only comparison I can offer is apparently so do a large sample of similar Flexi-chas locos and presumably nowadays many similar CSB fitted locos, or people wouldn't keep on making them.

The interesting question that arises from your comment though, is why then bother to go the extra trouble and complication of making such perfectly working springy beams continuous? There must be many places on a model steam loco where different springs rates and equalization effects are more appropriate and better implemented with non-continuous beams.

And just to repeat my perspective. I'm interested in making things simpler for the less skilled newcomers by keeping any unnecessary and/or undsireable springing out of the parts cost, the extra assembly work and the weight adjustments..

Andy

[grovenor-2685]

is why then bother to go the extra trouble and complication of making such perfectly working springy beams continuous?

Well, actually because it is less trouble and simpler to install two wires rather than 4 or 6.
regards

[proto87stores]

is why then bother to go the extra trouble and complication of making such perfectly working springy beams continuous?

Well, actually because it is less trouble and simpler to install two wires rather than 4 or 6.
regards

If linear springy beams with equalization appear perfect, substituting free sliding loose wires through holes gives a different form of springing with much less equalization. I'm not going to stoop to use springy equalizing beams as the new standard for perfection, but clearly both forms are springing can't give exactly the same static and dynamic results. There have to be some trade offs of one versus the other. So what are they and which one is understood to be better for model performance, and how?

I still claim that only the physics of equalization maintains constant wheel weighting over the various track imperfections and dynamic impulses. And AFAIK, only (vertical plane fixed) pivoting beams can avoid the need for vertical sliding bearings. Both advantages of the Flexi-chas design taken to its logical modern possibilities.

Andy

[Julian Roberts]

Thanks for the answer to my question (on Page 4!) re Brassmaster springs Russ. The link was informative. I will have further questions arising in a while which will probably demand a new topic heading.

It seems to me, while not wanting to be drawn into the present to and fro, that compensation is a lot easier to understand. And it is easy to alter the ride height without any effect on the weight borne by each wheel.

The Amtrak passenger coach video is impressive. Prompts me to wonder whether the model passengers have sprung cushions or modern foam type seating material

[Will L]

Continued

...What I don’t understand is why your so set against using primary springs? The reason why vehicle get sprung is that it decouples the mass of the body from shocks transmitted when the wheels hit any irregularities.

That certainly sounds like obvious "common sense", but for simple linear springs, this is where the devil is in the details:....

I've read over your post a several times now and I think I have understood most of your points. Details there most certainly are although I have yet to find the Devil there in. Our experience of supernatural beings tends to be a very personal thing, and I think we may need to agree to differ as to the relevance or otherwise of your concerns.

There are however a few points I would like to take issue with.

1. A real wagon weighs very much more when loaded than when empty, it is this that requires non linear springs, not the performance at any one given weight, which, for most modellers, is our only concern.

2. It is true that the springing systems I am talking about will not maintain equal weight distribution in all circumstances. But, so long as they maintain sufficient weight on each wheel to ensure the vehicle stays on the track, and, where appropriate, maintains electrical continuity, I don’t see that any momentary laps in ultimate pulling power when going over a bump is a significant issue.

3. Despite your suggestion otherwise I can promise you CSB locos, designed according to the spec, are truly suspended near enough mid way through their suspension movement. Their USP (sorry, Unique Selling Point) is that it is the only springing system that can guarantee that this is true. They may not be (don’t need to be) as bouncy as your coach but they will pass your push down test.

4. I’m afraid I did loose the relevance of your argument on spring rates. Russ and I have this ongoing discussion as to whether it is better to have shorter softer wires or longer thicker ones. But, given that they both produce the same deflection for a given applied weight, I’m not at all clear what else there is to worry about.

I have a lot of respect for the quality of the thought and design that goes into your product range, and given the, regrettably, unlikely event of me needing an appropriate vehicle on short wheelbase trucks my thoughts will turn to you.

[Alan Turner]

I still claim that only the physics of equalization maintains constant wheel weighting over the various track imperfections and dynamic impulses. And AFAIK, only (vertical plane fixed) pivoting beams can avoid the need for vertical sliding bearings. Both advantages of the Flexi-chas design taken to its logical modern possibilities.

Andy

But sprung suspension systems cannot produce equal weigh distribution in the dynamic phase - only when the system is static can that be so.

When a spring compresses the load in that spring rises, so any bump in the track that causes a spring to compress will cause weight to be transferred to that spring and therefore causes load to be shed from other springs in the system.

regards

Alan

[Crepello]

But sprung suspension systems cannot produce equal weigh distribution in the dynamic phase - only when the system is static can that be so.

Neither do rigid beams! When a beam rotates to a new equilibrium point, it must necessarily be due to unequal moments at its ends.

[proto87stores]

Continued

...What I don’t understand is why your so set against using primary springs? The reason why vehicle get sprung is that it decouples the mass of the body from shocks transmitted when the wheels hit any irregularities.

That certainly sounds like obvious "common sense", but for simple linear springs, this is where the devil is in the details:....

I've read over your post a several times now and I think I have understood most of your points. Details there most certainly are although I have yet to find the Devil there in. Our experience of supernatural beings tends to be a very personal thing, and I think we may need to agree to differ as to the relevance or otherwise of your concerns.

There are however a few points I would like to take issue with.

1. A real wagon weighs very much more when loaded than when empty, it is this that requires non linear springs, not the performance at any one given weight, which, for most modellers, is our only concern.

2. It is true that the springing systems I am talking about will not maintain equal weight distribution in all circumstances. But, so long as they maintain sufficient weight on each wheel to ensure the vehicle stays on the track, and, where appropriate, maintains electrical continuity, I don’t see that any momentary laps in ultimate pulling power when going over a bump is a significant issue.

3. Despite your suggestion otherwise I can promise you CSB locos, designed according to the spec, are truly suspended near enough mid way through their suspension movement. Their USP (sorry, Unique Selling Point) is that it is the only springing system that can guarantee that this is true. They may not be (don’t need to be) as bouncy as your coach but they will pass your push down test.

4. I’m afraid I did loose the relevance of your argument on spring rates. Russ and I have this ongoing discussion as to whether it is better to have shorter softer wires or longer thicker ones. But, given that they both produce the same deflection for a given applied weight, I’m not at all clear what else there is to worry about.

I have a lot of respect for the quality of the thought and design that goes into your product range, and given the, regrettably, unlikely event of me needing an appropriate vehicle on short wheelbase trucks my thoughts will turn to you.

Thanks for the kind thoughts and taking the time to think about my ideas.

My only concern now is that you may have missed my point about hard and soft linear springing being both required and opposite in effect.

Relatively hard spring rates are needed to hold the weight of the vehicle closely to the 50% height level. Which means that any bump forced spring range movement to say the 75% level will involve another 50% loading at that wheel. which will have quite a force upwards impact on the body. E.g It's a "short throw" suspension.

But if you want to have the wheel spring "absorb" bumps more, then you want a small bump to cause a much larger spring deflection (e.g. a soft rate) without having much so impact on trying to move the body up. However, in order to still have the strength to hold up the body statically at 50% height, then it has to have a much longer spring movement range overall. Or "long throw" suspension.

Having a long thick horizontal wire or a short thin horizontal wire hold the same weight between to fixed end points doesn't mean they are necessarily different Hard or Soft rate Springs. You have to have the SAME wire diameter held fixed between DIFFERENT lengths to change the spring rate significantly. Or vice versa.

An ideal non-linear rate spring will have a soft rate for large bump absorbing deflections around the 50% mid position, but much harder rates and very little additional deflection once the movement tries to exceed the expected desirable amount. I've assumed that the sliding wire construction of CSB's have a similar non linear effect to explain their observed stability.

Should you ever have need of a P4 bogie tram, let me know.

Andy