S4News 200 0-4-4 and 4-4-0 article.

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

S4News 200 0-4-4 and 4-4-0 article.

Postby Julian Roberts » Sat Feb 04, 2017 3:09 pm

Optimizing Suspension for Roadholding - 0-4-4s and 4-4-0s


There are one or two corrections I would like to make to my article as it appeared in Scalefour News 200, and I will take the opportunity to try to explain rather more clearly one of the topics of the article, bogie compensation, and add more photos than possible for the magazine.

First, on Pages 13 and 14, I refer frequently to the pivot of the compensating beam being better placed at a 1/3rd or 2/3rds position rather than at a half way point. This figure should be qualified with the word "roughly". As I said in the first article, the exactness of this placing isn't critical and can be adapted to suit the practicalities of the situation. 1/4 of the distance is fine, as is 3/5ths. The point is perfectly simple, the closer the fulcrum or pivot to the "steering wheels" the more weight is on those steering wheels, and the more sure will be the steering of the loco round curves or at track irregularities.

Page 15

1. Bogie pivot placing.

The further back the pivot is placed, the less sideplay is required on the inner driving wheel - but the buffers will move further from the centreline on curves. The further forward it is placed, the more sideplay will be required, and the less buffer overhang there will be.
Bogie wheel swivel movement will be least if it is pivoted at the bogie centre like a coach.

BOGIE COMPENSATION AND CLEARANCE

Here is the diagram from Page 13 again. It shows how the bogie can be compensated with the inner driving wheel. The idea is that when the bogie goes up, the inner driving wheel axle goes down, and vice versa. This is all very well in theory, but in practice isn't so easy.

CaptureCompensation 4-4-0 diagram.JPG
CaptureCompensation 4-4-0 diagram.JPG (39.18 KiB) Viewed 1034 times


Typically with the normal Flexichas set up, the driving wheels on our models have an up and down movement of say 1mm available each way, and are normally in a midpoint of this travel. However on the bogie we have a problem - while it can fall away from the loco frames, there isn't room for it to move upwards unless we are to have unsightly gaps at its normal midpoint of travel, between the bogie frame and loco frame, and above the wheels. When my suggested placing of the compensation beam pivot nearer the bogie than half way is adopted, the movement will be less, but some is still required.

A look at a real Compound shows how little gap there is between bogie frame and loco chassis frame.

2017-02-04 12.17.25.jpg


Midland Compound 035.jpg


On the real thing there is no cut out to allow the bogie to swivel - it is not designed to be able to take curves that would require so much bogie movement

Midland Compound 009.jpg


Midland Compound 008.jpg


The same is evident from photos of the CR Class 439

img044.jpg



img045.jpg
This picture refuses to upload the right way up!


This picture shows the 439 model with its far larger than scale wheel cutouts. On the prototype the cut outs clear the bogie frame, not the wheels. Even with this much clearance I found that sometimes on uneven track the bogie wheels touched the framing, and could cause short circuits. I have had to yet further enlarge the already unprototypical gap.

IMG_0282.JPG



Page 16

[The first photo caption in the magazine refers to all three of the photos. The second caption does not refer to any photo and should be part of the script.]


From photos of the Class 439 and the LMS Compound it's clear to me that loco mainframe cutouts large enough to clear the bogie wheels are a modelling cliche born of the typical modeller's desire to make trains take curves far sharper than the prototype, and that the prototype had cutouts large enough for the bogie's inner frames only. I don't know if this applies to other classes with this wheel arrangement, and to other wheel arrangement types.

If we are to have any suspension and wheel movement, and expect our locos to go round curves tighter than the real thing would have done (as most modellers expect), these mainframe cutouts are going to have to be appreciably larger than the wheel circumference, worsening what is already a visual inaccuracy.

Particularly where I put the pivot behind the bogie thus increasing the swing, reducing the width of the framing could help solve some of these issues. But a more elegant solution was apparent in the CR Class 113 that I bought ready made. Here the chassis mainframes no longer exist on the loco itself, but have become part of the bogie. This subterfuge is entirely invisible from any normal perspective. Where there is a gap along the top it is hidden by the valancing, and where there is a vertical gap it is hidden by the footstep.

Thus there is no longer any problem of the wheels hitting the frames on curves however unrealistically sharp they are. Although this bogie is not compensated with the inner driving wheel, it shows how to begin to go about solving the problem of upward movement of the bogie and its wheels.

A few more pictures than were in the magazine can illustrate these and related points.

The bogie has a roller at the front which takes the loco weight. Some weight is probably also taken where the pivot is, at the back. The front is filed into a gentle arc where it will meet the bufferbeam.
2016-05-08 22.28.23.jpg

2016-05-08 22.27.53.jpg

2016-05-08 17.32.29 (Large).jpg


Where false framing meets real framing is concealed by the footstep.
2016-05-08 17.30.21 (Large).jpg

A few more pictures of the model show how invisible this subterfuge is.
DSC02298.JPG

DSC02309.JPG


I include the following one to show (?) the unprototypical removal of brake yokes on the bogies of this coach, as per my article in Snooze 201
DSC02307 (Large).JPG


Finally another photo to show how little we will normally notice this whole area, depending on the painting, the light, the viewing angle, and so on.

2017-02-04 12.06.58.jpg
Another photo that refuses to upload the right way up


PS Many thanks to Alan Turner for turning the errant photos the right way up, below...
Last edited by Julian Roberts on Sat Feb 04, 2017 6:00 pm, edited 1 time in total.

Alan Turner
Posts: 479
Joined: Sun Jul 20, 2008 4:24 pm

Re: S4News 200 0-4-4 and 4-4-0 article.

Postby Alan Turner » Sat Feb 04, 2017 3:18 pm

img045.jpg


2017-02-04%2012_06_58.jpg
2017-02-04%2012_06_58.jpg (129.82 KiB) Viewed 1031 times


regards

Alan

billbedford
Posts: 600
Joined: Tue Oct 02, 2012 2:40 pm

Re: S4News 200 0-4-4 and 4-4-0 article.

Postby billbedford » Sun Feb 05, 2017 1:37 pm

Julian Roberts wrote:[b] Optimizing Suspension for Roadholding - 0-4-4s and 4-4-0s

A look at a real Compound shows how little gap there is between bogie frame and loco chassis frame.

download/file.php?id=13487&mode=view



But that picture does not show the bogie frame. What is shown is the outer face of the compensation beam. The real bogie frame is set 6" inside the main frames on both sides. This gives the bogie enough room to pivot on any reasonable curve.

Perhaps 'Getting it all right' should include bit which says that it's a good idea to know what you are trying to model before you start.
Bill Bedford
Mousa Models
http://www.mousa.biz

Julian Roberts
Posts: 571
Joined: Sat Jan 09, 2010 11:33 pm

Re: S4News 200 0-4-4 and 4-4-0 article.

Postby Julian Roberts » Sun Feb 05, 2017 9:21 pm

Bill
Thanks for that clarification.

What I was saying about the gap refers to upward movement not being available if compensating the bogie with the inner driving wheel.

Having lost a day's modelling composing that post yesterday morning I don't know if what I meant is still unclear. The issues are the tighter than real curves, combined with Flexichas up and down movement of wheels plus suspension movement to accommodate track irregularities.

A "reasonable" curve means different things to different people. Do you know (I don't) what the minimum radius was the Compounds were designed to take? A four foot model radius curve is an approx prototype 4.5 chains. If we just had curves as on the prototype (and totally rigid suspension) there would be far less problems all round, except finding space for a layout perhaps - nor would there need to be unprototypical wheel cut outs in the frames.

The solution to the problems of tighter than realistic curves plus suspension and Flexichas compensation, I was suggesting yesterday, is in that Class 113's bogie approach.

Here are some pics of what must be the front of that inner frame - is that right? But we don't normally bother to model what is invisible.

Midland Compound 082.jpg

Midland Compound 083.jpg


The view from the front shows not much of this is visible, though whether these baffles (?) are on all the class I am not sure.

Midland Compound 081.jpg


In case you didn't refer to the article in the Snooze here is the pic of the model on a 4ft RH bend showing wheel cut outs and what is a too large gap between the compensating beam and the chassis above. Upward movement is possible at the beam, but the front wheel will (has already perhaps) clout the mainframes despite the cutout. If the pivot was in the middle of the bogie rather than behind the issue might be less, but the Class 113 (made by a well known modeller) shows how all the problems can be got round.
2016-10-28 08.57.23.jpg

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grovenor-2685
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Re: S4News 200 0-4-4 and 4-4-0 article.

Postby grovenor-2685 » Mon Feb 06, 2017 9:19 am

but the Class 113 (made by a well known modeller) shows how all the problems can be got round.

The 113 though, does not have outside cylinders in the way.
Regards

Alan Turner
Posts: 479
Joined: Sun Jul 20, 2008 4:24 pm

Re: S4News 200 0-4-4 and 4-4-0 article.

Postby Alan Turner » Mon Feb 06, 2017 10:46 am

Also don't forget that Midland frames were reduced in width ahead of the leading driver to give clearance for the bogie.

regards

Alan

billbedford
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Joined: Tue Oct 02, 2012 2:40 pm

Re: S4News 200 0-4-4 and 4-4-0 article.

Postby billbedford » Mon Feb 06, 2017 11:06 am

Julian Roberts wrote:
In case you didn't refer to the article in the Snooze here is the pic of the model on a 4ft RH bend showing wheel cut outs and what is a too large gap between the compensating beam and the chassis above. Upward movement is possible at the beam, but the front wheel will (has already perhaps) clout the mainframes despite the cutout.


Yes, but if you use a prototypical pivot for the bogie and twin side beams for the drivers you not only avoid all these problems, you get better traction.
Bill Bedford
Mousa Models
http://www.mousa.biz


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