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From an entirely theoretical point of view, i can see the point of bogie side control. I can also appreciate the engineering point of view to keep it simple to avoid adding possible problems. But surely it must depend to some extent on the proportion of fixed wheelbase to front overhang from fixed wheelbase. Any normal 4-6-0 should need less side control than a typical 4-4-0. And surely it would be essential in a 4-2-0. But if the fixed wheelbase is extended, e.g. by pivoting the bogie around the rear bogie axle instead of the bogie centre, that must help, provided all the wheels are in the same plane. The usual problem is that the front bogie is far too light and jumps off the rails. Therefore adding a good bit of lead would be much easier, unless the centre of gravity of the body was forward of the fixed wheelbase, causing it to fall forwards. Then either a lot of lead is needed at the back end to balance it better, or support from some part of the front bogie will be needed.

 

I cannot speak from any practical experience, just from engineering logic.

 

Lloyd

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7 minutes ago, Chas Levin said:

Yes, good point: you're right that I was leaping on it as a one-size-fits-all solution. And also a nice point that this is how full size locos work.

 

I didn't meant to start a hoo-hah of course, it's just that the wider subject of chassis suspension systems in all their forms does interest me. I fully realise that I say that as someone who hasn't yet built a loco with any kind of suspension (or even one with a bogie for that matter) and that once I find out how much extra work is involved to balance against how much improvement in running on my particular layout, I too may come around to feeling that simple is better in this case.

Part of the reason it interests me is the challenge of successfully building the more complicated chassis, and the anticipated pleasure of seeing a more intricate and complex machine working well and smoothly (hey - aim at the stars and you might hit a chimney pot, as my old French teacher used to say!).

 

With respect though (the last thing I'd want to do here is offend anyone - we're here for enjoyment, but we're also quite passionate at times!) I feel the word 'Luddite' is a little harsh in this context. A Luddite is one who rejects all modern technologies on principle, whereas here I think there is surely more thought behind the choices... If we assume that the object - below the footplate anyway - is to produce something that runs well, and if I build an entirely rigid loco that runs well on my layout (taking into account my particular competency levels in both loco and layout) then I think I would simply be using one of a number of currently available technologies to achieve the same aim as others do.

 

As it happens however, this is not (yet) the case! My current small layout was originally built by my father in the 1970s. When I inherited it, I wanted to preserve as much as possible (for obvious nostalgic reasons) and build on what was there (in terms of scenics, electrics, signalling etc, none of which were much of a feature). I am also in the process of building an extension to it using contemporary permanent way materials which will )I hope) offer very smooth running, but this does mean that anything I build has to negotiate something of an obstacle course! I have a test track in my workshop using modern track (otherwise despair would take over!) but once they hit the layout as it exists currently, it's a tough world :D. I quite like the additional challenge of building to cope with these conditions, and while I'm also in the process of improving the trackwork with extra shims, guide rails etc, I'll probably leave the basic way in place.

 

My first loco was a DJH J9/10, built entirely rigid and it runs very nicely round the layout... but at the cost of very un-prototypical driver side-play, extra weight and Romford wheels, plus some additional time spent 'honing' one or two layout curves and points! None of which is a problem for me, because the fun and satisfaction I get from seeing it on the move is more than ample compensation (no pun intended!).

But it does make me curious about whether other systems might deal better with what I'm asking them to do...

 

The term luddite is one that Tony uses in reference to himself all the time. I don't think he is being entirely serious, neither am I. I'm proud to say that I don't know much about luddites though.

 

At the end of the day, bogie side control is something that I can get the benefits from but I'm not really interested in pushing it on somebody else. It is something that you really need to discover for yourself. The light will go on, or not as the case may be.

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13 minutes ago, Chuffer Davies said:

Hi Chas,

As soon as I read Andrew's explanation of the benefits of side control I knew this age old argument would kick off again.  There are definitely two opposing camps here with only a few modellers taking the middle ground.  As those who have read my postings previously will know my approach to chassis building is definitely at the opposite end of the spectrum to that of Sir, although there is common ground even here when it comes to the importance of building the chassis square and making sure that the coupling rod centres are exactly aligned with the axle centres in the frames.  

 

When it comes to side control it is not incorrect for Tony to say that it is un-necessary  but I cannot agree that it offers no benefit.  A particular case in point for me where side control proved highly beneficial was for loco's shunting the yard on our Hungerford exhibition layout.  Initially I could not shunt into the rear siding in the goods yard using a small prairie's front buffers without buffer locking occurring.  As soon as I fitted side control to the front pony truck the problem was solved.  Before anyone suggests I could have restricted the side play on the front driven axle to achieve the same outcome, I'd already tried that. 

 

I can also say with confidence that side control on a bogie does definitely improve the passage of a locomotive through point work.  It is only a small incremental improvement, but an improvement none the less and I am very happy to spend an extra hour fitting side control for this small benefit.  It can also be the difference between needing to remove material from the back of the cylinders or not.  Tony says he is happy to do this as it can't be seen.  I personally hate doing this if I can avoid it.   

 

Not all layouts are suitable for models built with side control.  I anticipate that it is only suitable for, and you will get benefits with, models that are built to run on fine scale track, if you are using Peco points then the incremental benefit will be lost.  If your layout has curves tighter than 3ft here again I think you are expecting too much for a model with side control to work. Whilst I always ensure that the models I build will go round 2ft 6in radius I never run them in anger around anything under 3ft.

 

Fitting side control is not complicated but it does require the modeller to take the time to understand the mechanics of it.  If its not thought through it is unlikely to work (i.e. derailments will occur).  Here again I'm more than happy to take the time to think it through and it gets easier to get it right the more I do it. 

 

If you have a personal dislike of side control then don't do it, for me I see the benefit and I will continue to employ it for as long as I model.

 

Back to you Sir....

 

Frank  

 

Thanks Frank, also very interesting. All aspects of loco suspension do seem to cause excitement, but perhaps your comment here is a nice point of compromise:

 

"When it comes to side control it is not incorrect for Tony to say that it is un-necessary  but I cannot agree that it offers no benefit." 

 

I just posted a reply to Andrew where I explained that part of my layout is old vintage track (and highly demanding of modern stock) and part of it (currently under construction) is modern track, so I either have the best of both worlds, or the worst, depending on your point of view! I say this with particular regard to your comments below:

 

"Not all layouts are suitable for models built with side control. I anticipate that it is only suitable for, and you will get benefits with, models that are built to run on fine scale track, if you are using Peco points then the incremental benefit will be lost.  If your layout has curves tighter than 3ft here again I think you are expecting too much for a model with side control to work. Whilst I always ensure that the models I build will go round 2ft 6in radius I never run them in anger around anything under 3ft."

 

I think the long and short of it for me is that my curiosity about side-control, springing and compensation has become so great that I'm going to have to have a go at building locos using these systems, just for the fun of it :) and if they run less well than rigid ones with floppy bogies on some parts of my layout, I shall still love them!

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59 minutes ago, Tony Wright said:

Good morning Chas,

 

I'm not saying that all side-control bogies/ponies don't run as well as ones which offer no guidance, but they're certainly not the panacea for all running ills by their guiding the locos into curves. As I've mentioned, I have none, and all the 'unrestricted' ones ride perfectly, don't derail and probably don't contribute anything to loco-guidance. They don't need to - those same locos ride beautifully just as 0-6-0s. 

 

As for 'running tests'.............. In my professional loco-building days, a popular one (prior to a decent RTR version) was an original Bulleid Pacific, of all three types. I always used Crownline kits to make these (Ian Rathbone painting them), and the chassis on those was compensated at source, including a recommendation that the bogie be sprung. I built the first one as prescribed, and it ran 'all right'. However, what a fiddle to get it to run to my satisfaction. The drive was on the rear axle, with jointed rods. It limped, wobbled, swayed from side to side and slipped excessively when starting a train (just like the prototype!). I did eventually get it to ride 'properly' (with its sprung bogie), but never again. The others I made had everything soldered rigid (rods included), driven off the centre axle and the bogie packed with lead. All done in probably a third of the time, and 'perfect' running every time. 

 

I know Roy Jackson built two identical A3s, one solid, one compensated. Tony Gee knows more of this than I do, but Roy told me (in his unique way) that he found no advantage in compensation/spring (in EM), and that the 'floppy' one took at least three times longer to build. He was going to write about his experiences, but I never saw anything.

 

Regards,

 

Tony. 

Good morning Tony, like you, Andrew picked me up on assuming that side-control was a panacea rather than something to be selectively applied; and I realised you weren't rejecting side-control full stop.

 

Your Bulleid Pacific experiences are an interesting addition to the data and I have to say that the entire body of your experiences with no side-control and rigid chassis and (mainly, I think?) rigid rods is very persuasive for me, in large part because you have the number of years and the number of builds to make the data surely representative. Roy Jackson's non-identical A3 twins might well furnish some very interesting data too...

 

 

As I just wrote in another reply however, my imagination has been caught by the idea of working suspension systems in a 4mm loco, so I think I'm going to have to give them a try, even if the work-vs-improvement ratio is poor (:banghead:). At least I'll be able to stand back and say 'Look, I built that sprung / compensated / side-controlled loco', even if I have to add that in all honesty, I probably won't be building another like it!

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23 minutes ago, jwealleans said:

One or two pictures would be worth several thousand words here.

Hi,

i’m not sure that pictures will help, it really needs  diagrams with explanations.  I’m sure there are books written in the past which have already explained the principles far better than I could do. For me the pioneers and exponents of these techniques included Guy Williams and Mike Sharman.  I had several conversations with Mike when I was a young modeller but sadly never met Guy.

I’ll see what I can find in my book collection and report back.

Frank

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23 minutes ago, FarrMan said:

From an entirely theoretical point of view, i can see the point of bogie side control. I can also appreciate the engineering point of view to keep it simple to avoid adding possible problems. But surely it must depend to some extent on the proportion of fixed wheelbase to front overhang from fixed wheelbase. Any normal 4-6-0 should need less side control than a typical 4-4-0. And surely it would be essential in a 4-2-0. But if the fixed wheelbase is extended, e.g. by pivoting the bogie around the rear bogie axle instead of the bogie centre, that must help, provided all the wheels are in the same plane. The usual problem is that the front bogie is far too light and jumps off the rails. Therefore adding a good bit of lead would be much easier, unless the centre of gravity of the body was forward of the fixed wheelbase, causing it to fall forwards. Then either a lot of lead is needed at the back end to balance it better, or support from some part of the front bogie will be needed.

 

I cannot speak from any practical experience, just from engineering logic.

 

Lloyd

 

You have hit at least one nail firmly on the head. A fixed pivot in the centre of a bogie is the worst of all worlds, yet I see it many times in kits and models that people have built. There is no way all the wheels can stay aligned with the rails when the bogie turns.

 

I do exactly what you have said, making the pivot point for the bogie somewhere between the rear bogie wheels and the front driver. The further forward the pivot is, the longer the effective wheelbase becomes. One of the Buckingham 4-4-0 locos doesn't even have a proper bogie. The front bogie wheels are a pony truck and the rear bogie wheels are part of the main mechanism and are lightly sprung up and down only, with no side to side play or turning left or right at all. So it is an outside frames 2-2-4-0 that will go round a 2ft radius curve in EM gauge and you can shunt with the buffers at the front of the loco around tight curves with no problems, simply by doing what you say and effectively extending the fixed wheelbase

 

If the pivot is immediately behind the bogie wheels, the rear bogie wheels hardly move at all, which is ideal for avoiding them hitting frames and cylinders. The front bogie wheels move a small amount but the overall wheelbase stays roughly in line with the rails.

 

I think there is a possible case of misuse or two different uses of some terminology here.

 

I see side control and limiting bogie movement as two distinct things. Side control, to me, is using some form of spring to keep the bogie centred and to allow the bogie to guide the loco round a curve. Limiting movement to just stop the bogie moving about and shorting is quite different and plays no part in guiding the loco. 

 

If there are no clearance issues, such as with an inside cylinder 4-4-2T, I mount the bogie on a pivot arm and attach it just forward of the front driving wheels. The more clearance problems, the further the pivot moves forwards.

 

I have built mechanisms with various springing, beams, bogie side control springs and suchlike. I could make them all work but the difference in running was not noticeable and I would challenge anybody to look at the locos on Narrow Road and tell me which have some form of springing or guidance on bogies and which do not. I can't tell myself most of the time and I built most of them!

 

I am pretty sure that the advocates of some sort of bogie steering mechanism probably hold the engineering "high ground" and I am certainly not against it in any form but having run layouts with both "fancy" and "simple" mechanisms, I have no doubt which suits me best.

 

 

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31 minutes ago, FarrMan said:

From an entirely theoretical point of view, i can see the point of bogie side control. I can also appreciate the engineering point of view to keep it simple to avoid adding possible problems. But surely it must depend to some extent on the proportion of fixed wheelbase to front overhang from fixed wheelbase. Any normal 4-6-0 should need less side control than a typical 4-4-0. And surely it would be essential in a 4-2-0. But if the fixed wheelbase is extended, e.g. by pivoting the bogie around the rear bogie axle instead of the bogie centre, that must help, provided all the wheels are in the same plane. The usual problem is that the front bogie is far too light and jumps off the rails. Therefore adding a good bit of lead would be much easier, unless the centre of gravity of the body was forward of the fixed wheelbase, causing it to fall forwards. Then either a lot of lead is needed at the back end to balance it better, or support from some part of the front bogie will be needed.

 

I cannot speak from any practical experience, just from engineering logic.

 

Lloyd

Thanks Lloyd, I saw your post just as I'd copied this line from a previous reply of Andrew's and it's very relevant:

 

"The 0-6-0 that you mention, lacks the overhang of the 4-6-0 running as an 0-6-0, thus not an applicable example."

 

There is something here I don't fully understand: I know that on a full-size loco the bogie plays a part in supporting the body (for instance in the case of a 4-6-0), yet we frequently build models (not to mention RTR examples) where that's not the case, where the bogie is largely (in the case of a trailing pony truck perhaps entirely) cosmetic.

So two questions occur to me:

First, I too cannot see how a 4-6-0 model running bogie-less can behave exactly the same way as an 0-6-0 in terms of weight distribution and therefore running, yet it seems to be a widespread assumption that they are effectively the same. Is this simply because the differences in behaviour between the two are considered so small they can safely be ignored?

Secondly, even though we're dealing with sizes, weights and forces that are so much smaller than full size that they may well not follow many of the same behavioural trends (e.g. when negotiating curves) I can't help thinking that abandoning bogie support altogether is - or might be - a very significant sacrifice and that it must be worth a try...

 

Anyway, I don't mean to prolong this debate to excess and take up Tony W's 'bandwidth': thank you to all those who have contributed, as it's given me a great deal of food for thought :scratchhead:

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Hi Andrew,

 

Thanks for your explanation.  I thought side-control was always a matter of lateral springs between the bogie and the front of the loco.  Am I right in now understanding that the bogie pivot alone, if properly positioned, can introduce side-control (vide Frank's C1)?

 

I don't think this is really that contentious.  Different layout styles, track standards, coupling types and operating choices would influence the need (or not) for "enhanced engineering" such as springing, compensation or bogie control, let alone the pleasure some folk take in the build and in problem solving.  Some locos had quite a bit of kit dangling outside the bogie (cylinders, steps, piston tail rods) and, without controlling sideways movement, the adjustments would be a significant compromise.

 

Alan

 

While I was writing this further comments from @t-b-g and others have clarified this and noted what I think is a useful a distinction between controlling the movement of the bogie in relation to the loco and the bogie imparting some control to the movement of the loco.

 

Edited by Buhar
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12 minutes ago, Buhar said:

Hi Andrew,

 

Thanks for your explanation.  I thought side-control was always a matter of lateral springs between the bogie and the front of the loco.  Am I right in now understanding that the bogie pivot alone, if properly positioned, can introduce side-control (vide Frank's C1)?

 

I don't think this is really that contentious.  Different layout styles, track standards, coupling types and operating choices would influence the need (or not) for "enhanced engineering" such as springing, compensation or bogie control, let alone the pleasure some folk take in the build and in problem solving.  Some locos had quite a bit of kit dangling outside the bogie (cylinders, steps, piston tail rods) and, without controlling sideways movement, the adjustments would be a significant compromise.

 

Alan

 

Afternoon Alan,

 

That is correct, as you are altering the way the bogie in conjunction with the chassis performs. Side control works in conjunction with general bogie control that may involve additional weight or springing.

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2 hours ago, Tony Wright said:

 

 

I know Roy Jackson built two identical A3s, one solid, one compensated. Tony Gee knows more of this than I do, but Roy told me (in his unique way) that he found no advantage in compensation/spring (in EM), and that the 'floppy' one took at least three times longer to build. He was going to write about his experiences, but I never saw anything.

 

Regards,

 

Tony. 

 

Ah! You refer to "The strange tale of the Flying Scotsman and the Gay Crusader".

 

The article was written. I know because I wrote it as Roy's "ghost writer". It was going to be the final part of the "Locomotives of Dunwich" series that were spread over several decades.

 

It was about the time that Roy and I had a bit of a disagreement over our involvement with MRJ. I think after that, he was a bit reluctant to submit the article and it never appeared. After he died, I did mention to one or two people that it might be appropriate to see if it was till on his computer and might be published as a sort of posthumous tribute but nothing came of it.

 

This was a photo I took to show the home made adjustable spring arrangement that Roy used.

 

818949096_Retford019.jpg.602d595d0f0bbfaf16fd0788607406be.jpg

 

When completed, both locos ran very nicely. The rigid one pulled the heaviest train with no added weight. The sprung one slipped like mad until the boiler was filled with lead. It would then pull the train with a trace of slip on starting.

 

The sprung one was marginally quieter through the complex crossings.

 

 

 

 

Edited by t-b-g
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1 hour ago, Chas Levin said:

 

Thanks Frank, also very interesting. All aspects of loco suspension do seem to cause excitement, but perhaps your comment here is a nice point of compromise.

 

I think the long and short of it for me is that my curiosity about side-control, springing and compensation has become so great that I'm going to have to have a go at building locos using these systems, just for the fun of it :) and if they run less well than rigid ones with floppy bogies on some parts of my layout, I shall still love them!

Hi Chas,

Good for you.  Welcome to the dark side.

Frank

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13 minutes ago, t-b-g said:

 

Ah! You refer to "The strange tale of the Flying Scotsman and the Gay Crusader".

 

The article was written. I know because I wrote it as Roy's "ghost writer". It was going to be the final part of the "Locomotives of Dunwich" series that were spread over several decades.

 

It was about the time that Roy and I had a bit of a disagreement over our involvement with MRJ. I think after that, he was a bit reluctant to submit the article and it never appeared. After he died, I did mention to one or two people that it might be appropriate to see if it was till on his computer and might be published as a sort of posthumous tribute but nothing came of it.

 

This was a photo I took to show the home made adjustable spring arrangement that Roy used.

 

818949096_Retford019.jpg.602d595d0f0bbfaf16fd0788607406be.jpg

 

When completed, both locos ran very nicely. The rigid one pulled the heaviest train with no added weight. The sprung one slipped like mad until the boiler was filled with lead. It would then pull the train with a trace of slip on starting.

 

The sprung one was marginally quieter through the complex crossings.

 

 

 

 

 

Would it not have been the case that, with the boiler filled with lead, the springing was negated?

 

I'm afraid that this account only reinforces my firmly held opinion - based on experience - that equalisation and springing are a complete waste of time.

 

I have a part-built Brassmasters Black 5, bought and started when they first came out. The chassis took ages to assemble and is very lightweight and flexible; I foresee soldering the floppy bits solid or, more likely, buying a Comet chassis.

 

John Isherwood.

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28 minutes ago, t-b-g said:

Ah! You refer to "The strange tale of the Flying Scotsman and the Gay Crusader".

 

Roy delighted in telling me the tale on my one and only visit to Retford.

 

May I be the one to say that chassis compensation and side control of bogies are actually different things?

 

IMG_0067_LR.jpg.e3b328050ea63a1a3549e27e8795c226.jpg

This loco is my only essay (to date) in bogie side control - it has a 'proper' lateral springing between the bogie frames, acting on the bogie pivot pin exactly as per the full-size thing. It rides like a Rolls-Royce and negotiates curves down to two foot radius with ease.

 

One interesting aspect, being a pacific, is whether to do anything similar for the rear pony truck? This one on this loco just flops around and I think it is quite noticeable when curving through pointwork how much the cab swings out in relation to the tender, particular when in reverse.

 

My take? Fun to do and satisfying when it all works - but I can fully understand when there is a time imperative for a professional builder then, unless the buyer is prepared to pay extra, then not really worth doing.

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21 minutes ago, cctransuk said:

 

Would it not have been the case that, with the boiler filled with lead, the springing was negated?

 

I'm afraid that this account only reinforces my firmly held opinion - based on experience - that equalisation and springing are a complete waste of time.

 

I have a part-built Brassmasters Black 5, bought and started when they first came out. The chassis took ages to assemble and is very lightweight and flexible; I foresee soldering the floppy bits solid or, more likely, buying a Comet chassis.

 

John Isherwood.

Hi John/Tony,

there is something strange happening here.  There have been carefully designed experiments to establish whether compensation improves the tractive potential of a model.  These were written up in the EMGS Newsletter some years ago.  The experiments demonstrated that there is absolutely no difference between rigid and compensated chassis.  It’s simple physics, a combination of weight and coefficient of friction acting on the driven axles.  In the Retford experiment if the compensated loco needed additional ballast to pull the same train as the rigid locomotive then some other variable must have been at play here. 
Frank
 

Edited by Chuffer Davies
Didn’t initially spot it was TBG who described the Retford experiment.
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1 hour ago, t-b-g said:

 

Ah! You refer to "The strange tale of the Flying Scotsman and the Gay Crusader".

 

The article was written. I know because I wrote it as Roy's "ghost writer". It was going to be the final part of the "Locomotives of Dunwich" series that were spread over several decades.

 

It was about the time that Roy and I had a bit of a disagreement over our involvement with MRJ. I think after that, he was a bit reluctant to submit the article and it never appeared. After he died, I did mention to one or two people that it might be appropriate to see if it was till on his computer and might be published as a sort of posthumous tribute but nothing came of it.

 

This was a photo I took to show the home made adjustable spring arrangement that Roy used.

 

818949096_Retford019.jpg.602d595d0f0bbfaf16fd0788607406be.jpg

 

When completed, both locos ran very nicely. The rigid one pulled the heaviest train with no added weight. The sprung one slipped like mad until the boiler was filled with lead. It would then pull the train with a trace of slip on starting.

 

The sprung one was marginally quieter through the complex crossings.

 

 

 

 

Thanks for this! The results seem to be as liable to interpretation and the influence of many factors as lots of other information, but at least we know, rather than wondering. Very interesting photo too...

And the title - "The strange tale of the Flying Scotsman and the Gay Crusader" - is worth the price of admission on its own!

Edited by Chas Levin
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Knowing Roy they were probably put in that order quite deliberately.:rolleyes:

 

I'm not getting involved in this debate.  Several of the contributors are aware of my predilections on this topic so I'm not sticking my head above the parapet! ;)

 

However, I do have a 2-6-0 (with a tender!) in my pile of projects and some sort of control for the pony truck may be on the cards.............:unsure:

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27 minutes ago, Chas Levin said:

 

And the title - "The strange tale of the Flying Scotsman and the Gay Crusader" - is worth the price of admission on its own!

 

If I remember correctly, Roy's original title was to have been "The queer tale of the Flying Scotsman and the Gay Crusader" !!

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53 minutes ago, Dr Gerbil-Fritters said:

A fascinating subject.  I found this on side control, from the Scalefour Digest.  

 

868410566_sidecontrol.JPG.20d9684e2c8f37f6aa325f17fc9e569c.JPG

 

Seems simple enough...

 

The length/diam of the springs is critical, too short or too thick and the amount of movement on the bogie will be very limited which can lead to derailments. 

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39 minutes ago, pete55 said:

 

If I remember correctly, Roy's original title was to have been "The queer tale of the Flying Scotsman and the Gay Crusader" !!

 

It was but we were not sure if we would get it published (in MRJ at any rate, "other" publications may have been interested) with that title, so it was changed.

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I think something that Frank mentioned is very important in the bogie discussion. Apart from the riding qualities through pointwork and curves, which I think if done correctly, the bogie side control gives, possibly the most important gain is for those people who use screw and 3 link couplings.  It provides mitigation to reduce front buffer beam overhang experienced on a curve or even worse a reverse curve to stop buffer locking when propelling by reducing the overhang by leading the engine into each curve with the bogie or pony. I don't off hand remember exactly how it's worked out, but the biggest offenders for overhang are those with the greatest distance between the buffer ends and the mid point between the leading and trailing (rear) driving axles, if I remember correctly.

 

On the topic of sprung versus rigid, it's a fact that on my layout I have three J39s. Two are sprung and one is rigid. They're all roughly weighted the same but the sprung ones don't slip on loads on my very tight curves where the rigid one does. I'm sure other people have anecdotes that provide evidence of the opposite but this has been my experience in spite of the fact that the tests Frank mentioned concluded no difference between the two methods. The bottom line is, we all do what works for us.

Edited by Clem
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1 hour ago, Chuffer Davies said:

Hi John/Tony,

there is something strange happening here.  There have been carefully designed experiments to establish whether compensation improves the tractive potential of a model.  These were written up in the EMGS Newsletter some years ago.  The experiments demonstrated that there is absolutely no difference between rigid and compensated chassis.  It’s simple physics, a combination of weight and coefficient of friction acting on the driven axles.  In the Retford experiment if the compensated loco needed additional ballast to pull the same train as the rigid locomotive then some other variable must have been at play here. 
Frank
 

 

There could well have been other factors. One loco had nickel silver tyres on Markits wheels and the other was on steel tyred ones, either Sharman or Gibson, I can't remember which now. What surprised us greatly was that it was the steel tyre one that slipped. I always thought they were supposed to be better.

 

I would never be able to do the sums to work it all out but I do have a theory.

 

With the sprung mechanism, that included the bogie so at least some of the weight was taken on that. Plus the fact that unless you are a genius, you will never get a dead even weight distribution over 6 sprung axles. Some will be doing more work than others.

 

What has always baffled me, from a physics point of view, is that you can get a pair of tweezers and lift an individual wheel on a sprung mechanism really easily. If you try to lift an individual wheel on a rigid mechanism, you have to lift the whole loco up and it is much harder to do.

 

So the rigid one must grip the track better. Obvious innit!   

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Rigid vs suspension

 

Less wheels touching track for same weight. More very small deformations causing more contact?

 

Possible?

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To be slightly more serious about it, part of the problem with the sprung loco was that the train was very heavy and the drawbar/coupling was well below the axle height. As the loco started, the whole body sat up like a speedboat in the water on the springs. The cab went down and the front went up.

 

Not a good way to put the power onto the driving wheels evenly and one of the reasons why the GWR preferred a 4-6-0 to a Pacific!

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