Flexi Chassis an Appreciation

This section allows guests to comment or ask questions. Posts from guests require explicit approval (which generally takes a day or so), before they appear, so that we can prevent unwanted spam.
Proto87Stores

Re: Flexi Chassis an Appreciation

Postby Proto87Stores » Fri Nov 17, 2017 3:44 pm

https://www.nytimes.com/2017/11/10/science/wobbling-bridges-london-brooklyn.html?rref=collection%2Fcolumn%2FTrilobites&action=click&contentCollection=Science&module=Collection&region=Marginalia&src=me&version=column&pgtype=article

An interesting article in the New York Times that indicates that dangerous wobble in otherwise statically stable pedestrian bridges is apparently due to a critical amount of positive feedback created by human gait changes, which is itself caused by feedback from the initial slight bridge wobble.

This rather feeds into the concept of causing/fixing positive feedback in model vehicle roll in my previous posting on the Calcutta sidings thread, due to having much greater positive feedback acting on rolling if the springing center of roll is below the c of g of the vehicle.

Andy

Julian Roberts
Posts: 729
Joined: Sat Jan 09, 2010 11:33 pm

Re: Flexi Chassis an Appreciation

Postby Julian Roberts » Sun Nov 19, 2017 12:41 pm

proto87stores wrote:The etch for the Airfix Mineral Wagon fully equalized Flexichas experiment arrived yesterday.

.......

Providing there are no fatal goofs, I'll post construction progress as I go along.

Andy


I wonder how this is going Andy or are you still in the throes of relocation from marijuana growers?

User avatar
Will L
Posts: 1638
Joined: Sun Jul 20, 2008 3:54 pm

Re: Flexi Chassis an Appreciation

Postby Will L » Sun Nov 19, 2017 1:26 pm

Proto87Stores wrote:https://www.nytimes.com/2017/11/10/science/wobbling-bridges-london-brooklyn.html?rref=collection%2Fcolumn%2FTrilobites&action=click&contentCollection=Science&module=Collection&region=Marginalia&src=me&version=column&pgtype=article

An interesting article in the New York Times that indicates that dangerous wobble in otherwise statically stable pedestrian bridges is apparently due to a critical amount of positive feedback created by human gait changes, which is itself caused by feedback from the initial slight bridge wobble.


Andy

As the article said we are not unfamiliar with the problem in London, and it cost £5m to fix. See
https://en.wikipedia.org/wiki/Millenniu ... #Resonance
I got a chance to walk the Millennium Bridge in the few days it was open and wobbling and it was an interesting experience. The only way to stay upright was to go with the swing, which was exactly the problem.

Our vehicle spring systems are not immune from the problem or resonance, but fortunately, most of the methods in common today include a rubbing surface betwixt axle box and the fixed section of the chassis which introduces enough friction to dampen the springs and avoid the issue, while still letting the springs do their work. I worry about the few ideas about which don't include this feature. The one and only one I built like that, before I learned better, was definitely a sister Kate.



User avatar
Guy Rixon
Posts: 583
Joined: Sun Mar 27, 2011 6:40 pm

Re: Flexi Chassis an Appreciation

Postby Guy Rixon » Mon Nov 20, 2017 10:05 am

I've just built a torsion-sprung chassis for a Geen/GWW kit of a GWR van; it uses MRD parts. As Will notes, it lacks sliding contact and does indeed wobble like crazy. Also, the torsion bars take up the space needed for modelling the brakes.

I arrived at this un-solution due to a need for 3'6" wheels on a 10' wheelbase in a 16' wagon, which doesn't leave room for most other options. I suspect that I'll end up with one fixed axle and one rocking sans springs.

I'm also working on a springing design for some four-wheeled coaches, and I think I will need to add rubbing plates to that for the damping.

Proto87Stores

Re: Flexi Chassis an Appreciation

Postby Proto87Stores » Mon Nov 20, 2017 3:34 pm

Guy Rixon wrote:I've just built a torsion-sprung chassis for a Geen/GWW kit of a GWR van; it uses MRD parts. As Will notes, it lacks sliding contact and does indeed wobble like crazy. Also, the torsion bars take up the space needed for modelling the brakes.

I arrived at this un-solution due to a need for 3'6" wheels on a 10' wheelbase in a 16' wagon, which doesn't leave room for most other options. I suspect that I'll end up with one fixed axle and one rocking sans springs.

I'm also working on a springing design for some four-wheeled coaches, and I think I will need to add rubbing plates to that for the damping.


I'm obviously not familiar with many UK commercial offerings, but I believe I can help you have a very effective solution, possibly even as a fix.

My current working space (and time) issues have not yet been solved, but I think I can set up to take a few photos over the next day or so that will explain what I have done so far. And show how it can help. My personal big time delay block is making some long life tooling that will repeatedly pre-assemble wheel sets and ball bearings quickly and accurately onto the same axle. I don't expect many modellers to be able to do that on their own kitchen table. In the meantime I have proved the suspension works statically, by loosely assembling it with a couple of 5 mm dia rods in place of the wheelsets and bearings. But holding everything together to photograph takes a couple more hands than I currently have ;)

I'll do my best to tackle the picture taking starting today if possible. I appreciate everyone's patience.

Andy

Proto87stores

Re: Flexi Chassis an Appreciation

Postby Proto87stores » Wed Nov 22, 2017 7:51 pm



Some temporary video of the testing, construction and parts breakdown of the part built simple 4 wheel equalized concept chassis.

Even though the parts are only placed loosely (almost/mostly :o ) together for the demo video, note the floor is completely stable in all simulated twisted track situations (and thus for rail bumps/dips). And the suspension is completely symmetrical for consistent dynamic wagon operation in both directions .

The rocking side arms are intended to held in place by the airfix solebars when they are eventually glued to the floor. Similarly each of the rocking W irons will be held by a centre retaining screw. The rock w iron pegs are standard off the shelf dowels, which would need to be cut in half lengthwise to keep the upper side of the floor flat. I contemplate possibly using the airfix floor upside down.

Plain (not flanged) ball bearings for 2mm id fit completely hidden behind the airfix w irons. If this is not the case for other wagon prototypes, then smaller axle diameters and bearings could be used. I'm not sure if a normal pin point axle bearing could be used n the same way. I've mentally gone beyond using pin points for high inertia reasons, so I wouldn't consider that rout myself.

If a substitute, pre-drilled, wagon floor is provided in a hypothetical wagon kit, there is no skill, tools or soldering required, except for simple manual "put together" assembly of the kit. Nor any adjustments to be made.

A slight extension of the concept would allow for a simple, problem free to assemble and operate 6 wheel chassis kit.

I did make one significant goof. I forgot how large UK wagon wheels are and that they partly overlapped the solebars. So I had to hand cut slots for them (by dremel) in the otherwise originally solid W Iron etches. I will have to turn down the excellent 00 Wheels provided by Dapol to get P87 profiles and width,as I don't have any P4 ones.

Happy to answer questions.

Andy

User avatar
grovenor-2685
Posts: 3142
Joined: Sun Jun 29, 2008 8:02 pm

Re: Flexi Chassis an Appreciation

Postby grovenor-2685 » Wed Nov 22, 2017 11:53 pm

Are the ball bearings supposed to go outside the wheels?
If so I don't see how you can fit such a large diameter bearing into the airfix axlebox, they only just take the usual 2mm od pinpoint bearings, and I don't think there is room to fit the bearings between the wheel and the inside of the solebars. For P4 moving the solebars out to an overscale width is not going to be acceptable.
Regards

Proto87Stores

Re: Flexi Chassis an Appreciation

Postby Proto87Stores » Thu Nov 23, 2017 5:12 am

Unfortunately I'm away (US Thanksgiving) until next week. I did dig out the original CAD for the w iron/bearing /wheel spacing, but I can't process it all for posting until I return.

See y'all next week

Andy
grovenor-2685 wrote:Are the ball bearings supposed to go outside the wheels?
If so I don't see how you can fit such a large diameter bearing into the airfix axlebox, they only just take the usual 2mm od pinpoint bearings, and I don't think there is room to fit the bearings between the wheel and the inside of the solebars. For P4 moving the solebars out to an overscale width is not going to be acceptable.
Regards

User avatar
Will L
Posts: 1638
Joined: Sun Jul 20, 2008 3:54 pm

Re: Flexi Chassis an Appreciation

Postby Will L » Thu Nov 23, 2017 12:08 pm

Proto87stores wrote:

Some temporary video of the testing, construction and parts breakdown of the part built simple 4 wheel equalized concept chassis.

Even though the parts are only placed loosely (almost/mostly :o ) together for the demo video, note the floor is completely stable in all simulated twisted track situations (and thus for rail bumps/dips). And the suspension is completely symmetrical for consistent dynamic wagon operation in both directions .


Hi Andy, hope your having a very good Thanksgiving. I presume you get the same buzz from that, that I tend to get out of Christmas.
For me Issue no. 1 is already, will the dining table be big enough on Christmas day.
Issue no. 2 was trying to get my head around your wagon suspension system, and what is happening at the wheel rail interface.

I see that it ensures you can maintain contact between wheel and rail for any reasonable degree of lack of flatness in the track, but only, it seems to me, because the 4 rocking points on the suspension (2 in mid W iron and 2 in mid sole-bar) are free to move away from the floor. Correct me if I'm wrong but I don't see how it can be otherwise. The floor will still sit firmly on three of the four giving you your firm ride (or will it, see below), but does weight distribution to the wheels vary depending on which of the three (or only if you are very lucky 4) rocking points are actually carrying the weight? Considering our worse case scenario of a sudden 0.5mm deep pit opening up under one wheel, the wheel will be free to drop into it but I had to wonder, what percentage of the wagons weight will it take with it?

I thought about that for a while as well.
The first thought was to wonder about that firm ride. Remembering that in our traditional 3 legged stool analogy, the stool is only really stable if the Centre of Gravity of the weight it is carrying is placed well within the triangle formed by the three points of contact (Russ's explanation/diagram from the CALG site here). When the floor is resting on only three pivot points, assuming that the wagons CofG is dead centre of the wagon floor (and probably some way above it), it will be on the very edge of the stability triangle which ever of the three points are involved, and so your wagon will be subject to a tendency to flip flop between the two. Not quite so firm then.

Next weight distribution. Having thought through the stability issue, the answer to the weight distribution issue comes from doing principle of moments calculations (I wont bore you), which show that, as the CofG is central on the line between two of the pivot points, all the weight will be carried equally by those two points, with none of it being carried by the third point. Mathematical proof, if any was necessary, of the tendency to flip flop between the two. The good thing from your point of view is that this turns out to mean that equal weight distribution on all four wheels is maintained.

Does the instability issue actually amount to anything? Almost certainly not on decently flat track. How rough track has to be before it begins to show, only experience will tell. Just lets remember that the only reason for indulging in suspension systems at all is because irregular track exists.

I did think briefly about putting springs under the sole bar pivot points, but then considering that your system contains as many moving parts and a lot more moving metal than a Bill Bedford style sprung wagon underframe (courtesy of CLAG again) I wasn't convicted the game was worth the candle.

Enjoy your Turkey

Edited - P.S. On second read that was a genuine wish relating to real poultry meat, and not intended as any sort of comment about your underframe.

proto87

Re: Flexi Chassis an Appreciation

Postby proto87 » Thu Nov 23, 2017 2:18 pm

6.00 before heading to SF.

Will,

The triangular pivot point never leave the floor. The deliberate slight oval slop in the 5 mm bearing holes allow for the 4 linear and transverse "beams" to follow their short curved route as they handle track twist.

I'll list the advantages over springing again later. But not shimmying is one of them ;)

Andy

PS. In the dark and mysterious woods of Waltham Forest, I didn't grow up with Thanksgiving, so I'm even happier with Turkey at Xmas.

Proto87Stores

Re: Flexi Chassis an Appreciation

Postby Proto87Stores » Fri Nov 24, 2017 5:35 pm

Will, no accidental turkey ambiguity offense taken :) But I do weigh a little more than ideal this am.

Respectfully I must disagree both overall an specifically. But I thought I should just comment within your quote to save me a lot of separate typing.

Will L wrote:Hi Andy, hope your having a very good Thanksgiving. I presume you get the same buzz from that, that I tend to get out of Christmas.
For me Issue no. 1 is already, will the dining table be big enough on Christmas day.
Issue no. 2 was trying to get my head around your wagon suspension system, and what is happening at the wheel rail interface.

I see that it ensures you can maintain contact between wheel and rail for any reasonable degree of lack of flatness in the track, but only, it seems to me, because the 4 rocking points on the suspension (2 in mid W iron and 2 in mid sole-bar) are free to move away from the floor. Correct me if I'm wrong but I don't see how it can be otherwise. The floor will still sit firmly on three of the four giving you your firm ride (or will it, see below), but does weight distribution to the wheels vary depending on which of the three (or only if you are very lucky 4) rocking points are actually carrying the weight? Considering our worse case scenario of a sudden 0.5mm deep pit opening up under one wheel, the wheel will be free to drop into it but I had to wonder, what percentage of the wagons weight will it take with it?


The centrally-ish positioned weight of the floor makes it rest of all four rocking points under all circumstances. The four rocking points are designed to be horizontally co-planar to begin with. You can visualize that by considering what happens if two adjacent wheels (side or end) drop the same amount. Their common rocking point drops the same amount also and their adjacent rocking points drop by 50% of that amount, causing the floor to settle down into a tilted, still co-planar position. Obviously that happens for all four orthogonal tilt directions, and with a little extra analysis, it clearly also happens for all four diagonal tilt directions, and so forth, for all tilt directions.

Will L wrote:I thought about that for a while as well.
The first thought was to wonder about that firm ride. Remembering that in our traditional 3 legged stool analogy, the stool is only really stable if the Centre of Gravity of the weight it is carrying is placed well within the triangle formed by the three points of contact (Russ's explanation/diagram from the CALG site here). When the floor is resting on only three pivot points, assuming that the wagons CofG is dead centre of the wagon floor (and probably some way above it), it will be on the very edge of the stability triangle which ever of the three points are involved, and so your wagon will be subject to a tendency to flip flop between the two. Not quite so firm then.


RE stability, the c of g must lie within the "diamond" shape area between the four rocking points for stability, which is pretty much guaranteed for a symmetrical wagon prototype. I tried to show that in the video by my pressing down on the floor ina small circle around the floor centre. kSo no instability if you abide by that rule. This an example of "4 point suspension", which does not have the limiting issues of "3 point" suspension.

Will L wrote:Next weight distribution. Having thought through the stability issue, the answer to the weight distribution issue comes from doing principle of moments calculations (I wont bore you), which show that, as the CofG is central on the line between two of the pivot points, all the weight will be carried equally by those two points, with none of it being carried by the third point. Mathematical proof, if any was necessary, of the tendency to flip flop between the two. The good thing from your point of view is that this turns out to mean that equal weight distribution on all four wheels is maintained.


This is "equalization", so the weight on all four wheels remains constant for all track distortions, statically and dymanically.

Will L wrote:Does the instability issue actually amount to anything? Almost certainly not on decently flat track. How rough track has to be before it begins to show, only experience will tell. Just lets remember that the only reason for indulging in suspension systems at all is because irregular track exists.

I did think briefly about putting springs under the sole bar pivot points, but then considering that your system contains as many moving parts and a lot more moving metal than a Bill Bedford style sprung wagon underframe (courtesy of CLAG again) I wasn't convicted the game was worth the candle.


Their is nothing wrong with Bill's springing system, but it only operates optimally within at least two constraints that the modeller must be aware of and match fairly well. Those are spring rate and vehicle weight. The suspension system above has neither constraint

I hope this has helped explain the operation better.

Andy
Last edited by John McAleely on Fri Nov 24, 2017 7:38 pm, edited 1 time in total.
Reason: Edited before approval to correctly use quoting

proto87stores

Re: Flexi Chassis an Appreciation

Postby proto87stores » Sun Nov 26, 2017 10:26 pm

grovenor-2685 wrote:Are the ball bearings supposed to go outside the wheels?
If so I don't see how you can fit such a large diameter bearing into the airfix axlebox, they only just take the usual 2mm od pinpoint bearings, and I don't think there is room to fit the bearings between the wheel and the inside of the solebars. For P4 moving the solebars out to an overscale width is not going to be acceptable.
Regards


Hi Keith,

Yes the bearings are intended to be on the outside of the wheels in this example. So I understand your concern. If you assume I'm trying to make a specific kit for the Airfix wagon as is, then there is a clearance issue. But, at the present time, that's not my intention. I'm just trying to show that full equalization suspension of 4 wheel wagon works easily and simply and well. And that it has advantages that make it worthwhile, or even possibly the optimal P4 suspension solution for many P4 society members. And furthermore, to give credit where it is due, that it is just the natural logical progression and successful achievement of Flexi-chas, given the construction and material resources available now, that weren't there when Flexi-chas was first implemented.

I don't know if there is a standard reference dimension for the distance between the insides of the UK wagon w irons? I have only measured the airfix kit and came up with 0.877". Is that prototypical or different based on "00" commercial manufacturing practicality?

And I had assumed from adding up the P4 wheel and BB standards (CLAG) that the overall P4 wheel set width is around 0.857". But, only ten thou clearance either side sounds rather tight if scaled from the prototype. Please advise if that is correct or not.

Since I use a 16.5 mm track gauge, I can definitely fit 1.5 mm depth plain 2mm ID ball bearings for my own use. If the P4 dimensions are such that those end up going too deep in the Airfix w irons, then there is at least one alternative, such as using Exactoscale 1mm axles and 1 mm ID bearings which are shallower. Another low volume manufacturing possibility could even be slotting the bearings partly into the wheels, but there would have to be sufficient need and interest to justify doing that.

But staying in the present. I would only currently expect that it may be of use to those members who are unsure, or experiencing difficulty with the large number of current choices/suggestions for 4 wheel suspension, many of which involve considerable craftsmanship and/or unreliable results. While the equalization concept is universal, individual kits of specific 4 wheel prototypes would almost certainly need specific adaptations.

Andy

proto87stores

Re: Flexi Chassis an Appreciation

Postby proto87stores » Tue Nov 28, 2017 3:20 pm

There is of course one more aspect to using full equalization for 4 wheel vehicles.

It provides a very simple and straightforward way of providing maximum tractive force and track holding for small 0-4-0 locomotives. Best performance is fundamental, with no adjustments of any kind needed.

For steam locos with inside frames, the depth of bearings issue is pretty much non-existent and the moving side beams can actually be the side frames. No complications of sliding hornblocks needed at all. One just needs to make sure the frames are attached sufficiently well to allow the loco to handled off the track for practical purposes. ;).

And of course, unlike sliding hornblock systems, the working length of the coupling rods is fundamentally constant.

Andy

User avatar
Will L
Posts: 1638
Joined: Sun Jul 20, 2008 3:54 pm

Re: Flexi Chassis an Appreciation

Postby Will L » Thu Nov 30, 2017 5:20 pm

Hi Andy

For some reason I'm not seeing your posts under "new post" and only find them a day or so after they arrive. (reflecting time to get administrators authorisation John?)

Proto87Stores wrote:
Will L wrote:I see that it ensures you can maintain contact between wheel and rail for any reasonable degree of lack of flatness in the track, but only, it seems to me, because the 4 rocking points on the suspension (2 in mid W iron and 2 in mid sole-bar) are free to move away from the floor. Correct me if I'm wrong but I don't see how it can be otherwise...


The centrally-ish positioned weight of the floor makes it rest of all four rocking points under all circumstances. The four rocking points are designed to be horizontally co-planar to begin with. You can visualize that by considering what happens if two adjacent wheels (side or end) drop the same amount. Their common rocking point drops the same amount also and their adjacent rocking points drop by 50% of that amount, causing the floor to settle down into a tilted, still co-planar position. Obviously that happens for all four orthogonal tilt directions, and with a little extra analysis, it clearly also happens for all four diagonal tilt directions, and so forth, for all tilt directions.

I am still trying to get my head round the action of your 4 point suspension system. After further thought, I can accept that yes with all 4 pivot points on the floor the wheels will be able to maintain full contact with any (reasonable) track profile, but the quid pro quo is that the vehicle floor (and hence the vehicle body) must tilt one way or another to accommodate it. Perfectly acceptable for a bogie, but may have visible consequences for a typical 4 wheel box van. And lets remember that the whole rational for adopting sprung systems is to decouple the vehicle body from such track induced sudden up or down movements of the wheels. These body movement may be less arbitrary than I original thought but no less real. So my next remark still applies.
Will L wrote:Does the instability (now read tilting) issue actually amount to anything? Almost certainly not on decently flat track. How rough track has to be before it begins to show, only experience will tell. Just lets remember that the only reason for indulging in suspension systems at all is because irregular track exists.

It remains true that
Proto87Stores wrote:
Will L wrote:...your system contains as many moving parts and a lot more moving metal than a Bill Bedford style sprung wagon underframe (courtesy of CLAG again)...


Their is nothing wrong with Bill's springing system, but it only operates optimally within at least two constraints that the modeller must be aware of and match fairly well. Those are spring rate and vehicle weight. The suspension system above has neither constraint

And while that final point is also true, with with both the Bill Bedford et al wagon springing and CSB, I think we have methods in place which mean that realtionship between spring rate and body weight are well managed and no more significant on practical applications than the failure to decouple body from wheel movement implied by a pure equalisation system. (Not true for all sprung systems I will agree, particularly attempt to apply individual springs to multiple axle loco chassis, as Julian's current machinations (onwards) tends to illustrate)

For anybody considering supplying components, I suspect that for the audience were are considering, (the getting it all right P4 crowed who might actually be interested in fitting suspension to anything) the desire to populate the underside of wagons with a full set of brake rigging safety straps and will mean that the minimal intrusion of the sprung system make it much more attractive.

proto87stores wrote:There is of course one more aspect to using full equalization for 4 wheel vehicles.

It provides a very simple and straightforward way of providing maximum tractive force and track holding for small 0-4-0 locomotives....
For steam locos with inside frames, the depth of bearings issue is pretty much non-existent and the moving side beams can actually be the side frames. No complications of sliding hornblocks needed at all. One just needs to make sure the frames are attached sufficiently well to allow the loco to handled off the track for practical purposes. ;).

And of course, unlike sliding hornblock systems, the working length of the coupling rods is fundamentally constant.

The point about all that moving metal applies here too I think. I'd wonder how easy it would be to get your drive train in and pivoting. Also I'd wonder how much slop in the bearings was necessary to ensure the movement of the frames wasn't restricted by bearing clearances and what impact that would have on the "fundamentally constant" coupling rods lengths.

User avatar
Le Corbusier
Posts: 1198
Joined: Wed Feb 11, 2015 3:39 pm

Re: Flexi Chassis an Appreciation

Postby Le Corbusier » Thu Nov 30, 2017 5:38 pm

Reading all of this with interest .... just one question though - is this an either/or debate or an and/also debate? Is the aim to try and develop an additional system which works and enriches choice? or argue the merits of one system over another? I find it all fascinating but at times it does feel more akin to a political debate !

Just thought I would ask.
Tim Lee

User avatar
grovenor-2685
Posts: 3142
Joined: Sun Jun 29, 2008 8:02 pm

Re: Flexi Chassis an Appreciation

Postby grovenor-2685 » Thu Nov 30, 2017 6:31 pm

proto87stores wrote:Hi Keith,

Yes the bearings are intended to be on the outside of the wheels in this example. So I understand your concern. If you assume I'm trying to make a specific kit for the Airfix wagon as is, then there is a clearance issue. But, at the present time, that's not my intention. I'm just trying to show that full equalization suspension of 4 wheel wagon works easily and simply and well. And that it has advantages that make it worthwhile, or even possibly the optimal P4 suspension solution for many P4 society members. And furthermore, to give credit where it is due, that it is just the natural logical progression and successful achievement of Flexi-chas, given the construction and material resources available now, that weren't there when Flexi-chas was first implemented.
As shown the design has two layers of brass for each W iron which with the large holes for the bearings cannot act as the visible W-iron so 3 layers in total. Its going to be hard to disguise that. Normal, fine scale practice is to replace the plastic W iron with a brass version to improve appearance, with sprung versions the bearing carrier is designed to be hidden behind.

I don't know if there is a standard reference dimension for the distance between the insides of the UK wagon w irons? I have only measured the airfix kit and came up with 0.877". Is that prototypical or different based on "00" commercial manufacturing practicality?

Generally the W-irons were 6ft between inside faces and the journal centres 6'6" apart so to fit between the solebars the W-ironsshould be kept to an outside dimension of 24.5 mm. Most current offerings are close but do vary a bit.
And I had assumed from adding up the P4 wheel and BB standards (CLAG) that the overall P4 wheel set width is around 0.857". But, only ten thou clearance either side sounds rather tight if scaled from the prototype. Please advise if that is correct or not.
Commercially available wheels do vary a bit in width, for maximum compatibilty you need to allow 2mm for wheel width and BB at 17.89 (S4 max) so wheelset width 21.89 mm or 0.862"
Regards

User avatar
jjnewitt
Posts: 226
Joined: Sat Jan 02, 2010 5:04 pm

Re: Flexi Chassis an Appreciation

Postby jjnewitt » Thu Nov 30, 2017 7:57 pm

grovenor-2685 wrote:
proto87stores wrote:I don't know if there is a standard reference dimension for the distance between the insides of the UK wagon w irons? I have only measured the airfix kit and came up with 0.877". Is that prototypical or different based on "00" commercial manufacturing practicality?


Generally the W-irons were 6ft between inside faces and the journal centres 6'6" apart so to fit between the solebars the W-irons should be kept to an outside dimension of 24.5 mm. Most current offerings are close but do vary a bit.


The figure I've seen on drawings (proper ones) for the distance between the insde faces of the axleguards (that's the terminology that always seems to be used for 'W-Irons') is 5' 11.5". As keith says the distance between journal centres is 6' 6" though I'm not sure how useful that is to modellers. Perhaps more importantly the distance between the inside faces of the solebars, at least on on steel underframes stock, was 6' 3" (the axleguards were cranked just below the solebar). The limited drawings I have for wooden underframes would suggest this dimension was the same on those as well. If solebars are anything like scale (which admitedly, if they're plastic, is unlikely) the distance over the outside faces on the axleguards in 4mm scale can quite legitimately go up to 25mm. This does make life easier if you are using pin point bearings with spring carriers.

Justin

User avatar
grovenor-2685
Posts: 3142
Joined: Sun Jun 29, 2008 8:02 pm

Re: Flexi Chassis an Appreciation

Postby grovenor-2685 » Thu Nov 30, 2017 9:32 pm

(the axleguards were cranked just below the solebar). The limited drawings I have for wooden underframes would suggest this dimension was the same on those as well.

I think the crank in the W-iron on steel frame vehicles was introduced to bring the W-iron axlebox guides into the same position as with timber frames, the timber solebars being thicker they had need of a crank in the W-iron.
I was going by the drawing here http://www.norgrove.me.uk/history_files/Sep72/Sep-72.htm, looking more closely, the 6 ft figure is to the W-iron centre which would be 5'11.5" inside.
Regards

Proto87stores

Re: Flexi Chassis an Appreciation

Postby Proto87stores » Fri Dec 01, 2017 3:33 am

Will L wrote:Hi Andy

For some reason I'm not seeing your posts under "new post" and only find them a day or so after they arrive. (reflecting time to get administrators authorisation John?) There is also the 8 hour time shift that means you automatically see my evening posts dated a day later

The centrally-ish positioned weight of the floor makes it rest of all four rocking points under all circumstances.... SNIP.... it clearly also happens for all four diagonal tilt directions, and so forth, for all tilt directions.


I am still trying to get my head round the action of your 4 point suspension system. After further thought, I can accept that yes with all 4 pivot points on the floor the wheels will be able to maintain full contact with any (reasonable) track profile, but the quid pro quo is that the vehicle floor (and hence the vehicle body) must tilt one way or another to accommodate it.

Yes, but it will tilt almost exactly the same amount as does the same wagon if sprung instead ;) Both sprung or equalized vehicles will tend to follow the average angular distortion of the track immediately below the wheels. .

Perfectly acceptable for a bogie, but may have visible consequences for a typical 4 wheel box van.

The only difference is if the tilt makes the c of G move significantly to one side. Then of course the sprung wagon would tilt MORE than the equalized version.

And lets remember that the whole rational for adopting sprung systems is to decouple the vehicle body from such track induced sudden up or down movements of the wheels.

First consider the extent of "decoupling". Because of the equalization beams dividing their wheel movement effect by two, the overall body movement will only be one quarter of the movement of the wheel. Yes the (pretty much) same movement of sprung body (to about the same position) would be delayed by a few milliseconds, but only provided the wagon is moving very fast. At normal shunting plank speeds, I don't think a normal human would notice much, if any, difference. And the total movement at the end of the milliseconds is going to be the same, except for the added springing possibility of "overshoot" and subsequent (hopefully damped) oscillation. (Shimmy). Because we can't scale weight, any model sprung roll/shimmy, etc., will occur at a much faster (and noticeably unrealistic) rate. The only way to slow down such movement is to greatly increase the model weight - which incidentally this design will happily accommodate. Further, a significant weight increase will begin to simulate some of the rolling inertia of the real thing.

Just because I had a random shape chunk of steel handy, I did as a quick test, place it roughly on one of the new equalized Amfleet car bogies and, even though it apparently rubbed one wheel, it still managed to roll quite presentably. This particular piece of metal weighed around 800 gm.
See


These body movement may be less arbitrary than I original thought but no less real. So my next remark still applies.

I’m sorry, but I must disagree as compared to a sprung chassis.

Will L wrote:Does the instability (now read tilting) issue actually amount to anything? Almost certainly not on decently flat track. How rough track has to be before it begins to show, only experience will tell. Just lets remember that the only reason for indulging in suspension systems at all is because irregular track exists.


It remains true that
Proto87Stores wrote:
Will L wrote:...your system contains as many moving parts and a lot more moving metal than a Bill Bedford style sprung wagon underframe (courtesy of CLAG again)...


Yes, just two identical pairs of merely etched moving parts. But they are all on a single, simple, inexpensive fret and require no sliding precision. Nor do they need to hold (or solder) any bearings in correct alignment. While two items are longer than the wheelbase, their cost is still low and the assembly much faster and less critical.

There is nothing wrong with Bill's springing system, but it only operates optimally within at least two constraints that the modeller must be aware of and match fairly well. Those are spring rate and vehicle weight. The suspension system above has neither constraint.
[/quote]

And while that final point is also true, with with both the Bill Bedford et al wagon springing and CSB, I think we have methods in place which mean that realtionship between spring rate and body weight are well managed and no more significant on practical applications than the failure to decouple body from wheel movement implied by a pure equalisation system. (Not true for all sprung systems I will agree, particularly attempt to apply individual springs to multiple axle loco chassis, as Julian's current machinations (onwards) tends to illustrate)

The “well managed” requires a linear spring rate to give 50% spring deflection when in weight equilibrium. That means that just a small dynamic deflection results in a major change in wheel weight on the track. Not good for either track holding or stability. As a similar performance comparison, In my youth, all cars used Bias Ply tyres. Within their constraints, they worked well enough for most users. But now they all use Radial tyres. Mostly due to users appreciating and choosing better road holding.

For anybody considering supplying components, I suspect that for the audience were are considering, (the getting it all right P4 crowed who might actually be interested in fitting suspension to anything) the desire to populate the underside of wagons with a full set of brake rigging safety straps and will mean that the minimal intrusion of the sprung system make it much more attractive.

I can’t tell if that is an issue or not yet. I haven't proceeded to cosmetics. The current first attempt metal is just a proof of concept. But at least when I eventually complete a rake of say 10 wagons, which might take only an evening or two to assemble, they will all perform identically without any further work.

proto87stores wrote:There is of course one more aspect to using full equalization for 4 wheel vehicles.

It provides a very simple and straightforward way of providing maximum tractive force and track holding for small 0-4-0 locomotives....
For steam locos with inside frames, the depth of bearings issue is pretty much non-existent and the moving side beams can actually be the side frames. No complications of sliding hornblocks needed at all. One just needs to make sure the frames are attached sufficiently well to allow the loco to handled off the track for practical purposes. ;).

And of course, unlike sliding hornblock systems, the working length of the coupling rods is fundamentally constant.

The point about all that moving metal applies here too I think.

No. If I use the inside frames as the moving beams, it’s the same metal

I'd wonder how easy it would be to get your drive train in and pivoting.

See the pictures of the gearbox drive in the bogie examples in earlier topics. With typical 0-4-0 small drivers, a motor with Neodymium magnets and bemf control, even my small 14:1 ratio should work very well.

Also I'd wonder how much slop in the bearings was necessary to ensure the movement of the frames wasn't restricted by bearing clearances and what impact that would have on the "fundamentally constant" coupling rods lengths.[/quote]

The slop in the Ball Bearings is too small to measure in 4mm scale. All that is needed is that their mounting holes are vertically minutely oval-ed, so the bearing outer can tilt

Andy

User avatar
Will L
Posts: 1638
Joined: Sun Jul 20, 2008 3:54 pm

Re: Flexi Chassis an Appreciation

Postby Will L » Fri Dec 01, 2017 3:52 pm

Proto87stores wrote:
Will L wrote:
The point about all that moving metal applies here too I think.

No. If I use the inside frames as the moving beams, it’s the same metal

It was also the rocking frames on each axle I had in mind Andy.

Experience has also shown that you concerns about getting the spring rate right are not bourn out in practice.

proto87stores

Re: Flexi Chassis an Appreciation

Postby proto87stores » Fri Dec 01, 2017 5:33 pm

Will L wrote:
Proto87stores wrote:
Will L wrote:
The point about all that moving metal applies here too I think.

No. If I use the inside frames as the moving beams, it’s the same metal

It was also the rocking frames on each axle I had in mind Andy.

Experience has also shown that you concerns about getting the spring rate right are not bourn out in practice.
.

The end linking bars of small rocking loco frames would just be tiny, maybe just flat hook in etched beams. No need to duplicate the complex rocking W iron scheme. I only duplicated the "shadow" w irons on the wagon chassis to save the usual more thorough lengthy design time and effort of creating smaller alternative linking methods. Twin holes around the same bearing seemed to be a no-brainer for what I'd hoped was just a rapid evaluation. There's actually no need for them to be w iron shaped, or as big.

As to the claimed working success of current methods, I can only point to just the latest report of track holding problems on this forum. E.g. Multiple derailments on one of the newest, team-built, well run in, major P4 layouts, Mostyn, at it's latest exhibition outing. And we know Mostyn's trackwork isn't something that is continually being changed :? But more to the point, the Mostyn spokesperson, in responding, seemed to think of that as a normal good performance. E.g nothing needs fixing. Is that the same "not borne out in practice" criteria you are using?

Even after 15 years or so, this is forum is notable for the number of topics still relating to trying out yet more ways to build sprung or compensated chassis successfully. That doesn't make sense if there is no problem

Andy

proto87stores

Re: Flexi Chassis an Appreciation

Postby proto87stores » Fri Dec 01, 2017 6:18 pm

Le Corbusier wrote:Reading all of this with interest .... just one question though - is this an either/or debate or an and/also debate? Is the aim to try and develop an additional system which works and enriches choice? or argue the merits of one system over another? I find it all fascinating but at times it does feel more akin to a political debate !

Just thought I would ask.


I'm looking at the technical aspects of model suspension as a non-member, non UK resident, outsider, who basically needed to invent suspension systems from scratch for Proto-87 and/or 16.5 mm gauge ONLY, without any of the accumulated experience of working with the existing society long established, assumptions, ideas, methods, components and/or issues. My own investigation however became conflicted somewhat with the large portion of the membership's tendency to abandon Flexichas before it had fully evolved into a very stable 4 point suspension system, that was able to take advantage of more modern economic technology. E.g.much lower cost, miniature ball bearings, for one.

So I have nothing to gain in changing what the Society wishes to do, except to offer what I have discovered on my own, as input for additional options for you. In so doing, as an engineer, I have tried to include full theoretical back up and practical operation testing records for my own now preferred direction, so that I'm not just offering an unsupported personal opinion.

I think, that in trying to explain the non-obvious aspects of the theory, it may have seemed like a debate, but it's really just an attempt to lay out the theory and evidence, so that it can be correctly understood and compared with what you have already. After that it's still your choice, but hopefully a fully informed one.

Andy

User avatar
Flymo748
Posts: 2175
Joined: Sun Jul 20, 2008 6:00 pm

Re: Flexi Chassis an Appreciation

Postby Flymo748 » Fri Dec 01, 2017 6:21 pm

proto87stores wrote:As to the claimed working success of current methods, I can only point to just the latest report of track holding problems on this forum. E.g. Multiple derailments on one of the newest, team-built, well run in, major P4 layouts, Mostyn, at it's latest exhibition outing. And we know Mostyn's trackwork isn't something that is continually being changed :? But more to the point, the Mostyn spokesperson, in responding, seemed to think of that as a normal good performance. E.g nothing needs fixing. Is that the same "not borne out in practice" criteria you are using?


Hi Andy,

To comment on this, in an observational way, and to neither defend or attack any suspension system or layout.

At Warley, I sat with Richard Oldfield at the Mostyn workbench whilst he went through the coach which had just derailed. We had a good conversation whilst checking over every aspect of the vehicle.

We went through (or Richard did whilst I watched and made occasional suggestions):

- back to back on each wheeset
- fixing of the tyre on each wheelset
- dirt on the tyres
- bits stuck to the back of the wheels
- concentricity both lateral and vertical on each wheelset
- security of bogie fixings
- free movement of bogie fixing, for swivel and tilt
- removing the bogies and checking for visual defects
- checks for any infringement of any free movement
- security and freedom of movement of couplings
- flexibility of corridor corrections

and probably quite a few other things which I have forgotten we prodded and poked at...

At the end of all of that, the coach was put back onto a spare road in the fiddle yard and propelled by a push at quite some speed through a turnout. Where it was rock steady. The conclusion? We didn't have a clue what caused it to fall off.

It might have been something from one of the adjacent coaches which pushed it off, and kept itself on the rails. It might have been a coincidence of movement and rail joint. At the end of the day, we couldn't find it and the coach went back into service where as far as I know it performed faultlessly for the rest of the weekend.

So the moral of the tale is that sometimes, just occasionally, these things "just happen", on models as in real life...

Cheers
Flymo
[edited for typo]
Beware of Trains - occasional modelling in progress!
www.5522models.co.uk

proto87stores

Re: Flexi Chassis an Appreciation

Postby proto87stores » Fri Dec 01, 2017 6:29 pm

Keith,

Thanks for the W Iron spacing info.

The current etch is of 0.010" stainless steel, so the two shadow w iron shapes only take about about 0.022" thickness behind the Airfix ones I did include versions with 4mm and 3mm OD bearing holes on the same etch sheet, so there is still room for more cosmetic experiment in the short term. The current shadow irons struts are a tad less wide than Airfix's, so do manage to disappear completely,even with some typical suspension movement. I wouldn't know they were there, if I was merely watching the wagon on track.

Andy

User avatar
jjnewitt
Posts: 226
Joined: Sat Jan 02, 2010 5:04 pm

Re: Flexi Chassis an Appreciation

Postby jjnewitt » Fri Dec 01, 2017 6:45 pm

grovenor-2685 wrote:I think the crank in the W-iron on steel frame vehicles was introduced to bring the W-iron axlebox guides into the same position as with timber frames, the timber solebars being thicker they had need of a crank in the W-iron.
I was going by the drawing here http://www.norgrove.me.uk/history_files/Sep72/Sep-72.htm, looking more closely, the 6 ft figure is to the W-iron centre which would be 5'11.5" inside.


Yes that's what I'd always assumed. I must admit I was a little thrown when the only drawing I could find of a wooden solebar wagon (an LMS D1950 single bolster) showed 6' 3" between solebars and joggled axleguards.

I think the joggle in the axleguads was as much to do with the fact that the springs (at 4") were wider than the steel solebars. Otherwise I can't really see any reason why they couldn't have had the same dimension between solebars for both steel and wooden underframe stock.

Nice to have something interesting to dicuss on this topic. :-)

AndyI wouldn't assume that the endless tinkering with the basic springing concept has anything to do with whether it works or not. P4 modellers generally like to have a go at things and will more often than not come up with their own take on something simply because they can. That's one of the nice things about the Scalefour Society, it is filled with people with ideas. It would be really boring if everyone did the same thing. :-)

Justin


Return to “Guest Book”

Who is online

Users browsing this forum: No registered users and 2 guests