Suspension design for a 2-4-0, CSB?

[MarkS]

Russ, personally, I would be very interested with your ideas on the 2-4-0 configuration, but de-coupled CSB, since I am looking at my efforts so far my Ratio model, and aside from the "knife edge" bearings (which I note are on the first loco in the CSB gallery...), I am looking at springing of the uncoupled axle. (CSB)

- Do I want to go with stiff springing to prevent porpoising or not?
- I assume I should go with the longest span for the spring I can fit in, yes?
- and last, CSB on the drivers, or springy compensation beams for the drivers?

Your thoughts would be very much appreciated, since I am on the verge of rebuilding the chassis again.

[Russ Elliott]

Mark - I really don't know what the best approach for a full-length CSB for a 2-4-0 might be. Options are:

- reduce weight and increase deflection on the front axle;
- reduce weight but keep standard deflection on front axle;
- treat as a standard 'equal deflection' 0-6-0;
- tighten the front axle, but loosen the coupled ones.

All of these will have different pros and cons in respect of pitch stability, coupled traction, horizontality, CofG positioning accuracy. Much will depend on whether you can get sufficient weight over the coupled axles.

Me? I remain of the view (despite vigorous but now more muted opposition from the CSB thought police) that I think I would bottle it and go for strong (0.5mm deflection) front axle springs and soft (0.8mm deflection???) springy equalisers between the coupled axles. Springy equalisers are immune from CofG positioning error. Here's that same old diagram again:



(The 3-fulcrum symmetrical short CSB over the coupled axles is of course viable.)

One thing's for certain though - on a 2-4-0, the more heavyweight crew on the footplate the better!

[grovenor-2685]

One thing's for certain though - on a 2-4-0, the more heavyweight crew on the footplate the better!

Don't forget that you are not limited to a crew of two, you can add an inspector chaperoning an important visitor, eg Hamilton Ellis, and you have doubled the amount of whitmetal in the cab
Regards

[Andy W]

I used that very dodge on a small Midland tank engine. The gear wheel protruded into the cab - not by much, but enough to spoil the model. So I hid it with an extra, bowler hatted, inspector and a hollowed out bucket. No one ever noticed.

[MarkS]

Thanks Russ,
I'll post my progress when I get to it, hopefully next week.
I'll have to google for depleted uranium figures in 4mm... Barring that I could just hang the tender on the loco, but that could be considered a a sign of insanity.
I have the option to use CSB or springy equalizers for the driving wheels, I'll start with equalizers, but how critical would their "springyness" be? (Or is it irrelevant as long as I get .5mm deflection?)

[Russ Elliott]

Hanging the tender on the footplate is feasible, if you can avoid sideplay shorting problems in the leading tender wheels as the loco-tender combination is going around curves, maintain roll and pitch independence of loco and tender bodies, and make sure the front tender wheels get adequate trackholding force. Weightwise, I guess the potential danger is overdoing the weight on the back end of the loco, making its front end too light. A better approach in my view, although I take my cue from what the Manchester boys realised and confirmed over 50 years ago, would be to put the motor in a normal tender, cardan it through to the rear loco driver, and then you've got the whole of the loco firebox to put as much weight above the loco drivers as possible, and balance it out at the front end accordingly.

As far as the 'springyness' of CSBs and springy equalisers is concerned, springrate is springrate, and there is no difference in that respect, except that a springy equaliser will not be as affected by fulcrum friction as the CSB equivalent will be, so the springy equaliser could be a tad livelier.

[zebedeesknees]

Me? I remain of the view (despite vigorous but now more muted opposition from the CSB thought police) that I think I would bottle it and go for strong (0.5mm deflection) front axle springs and soft (0.8mm deflection???) springy equalisers between the coupled axles.

And:-

....a springy equaliser will not be as affected by fulcrum friction as the CSB equivalent will be, so the springy equaliser could be a tad livelier.

Soft leading axle and no damping from the coupled axles springing? That looks like a recipe for a bouncy front end to me.

I would hesitate to advocate a system for others that I hadn't tried, tested and proven for myself.

I have tried both CSBs and springy equalisers (though on an 8-coupled) and would counsel against the latter in a 4-coupled.

On the other hand, if Mark is prepared to break new ground it will be fascinating to see.

Zeb.

[MarkS]

Zeb,
I'm Canadian, breaking new ground is something we do, since we have a lot more ground than most...
(It takes more time to fly across Canada than it takes to fly from Toronto to London...)

But I believe Russ said

"go for strong (0.5mm deflection) front axle springs"

not soft. Wouldn't the lively back end be damped by the motor and gear box? But, would the leading driver be dancing all over the place?
Anyway, I've talked enough about it, it is time to finish building the darn thing and get it running...
Remain fascinated my friend, for I have a cunning plan...

[zebedeesknees]

Zeb,
I'm Canadian, breaking new ground is something we do, since we have a lot more ground than most...

That frontier spirit... bring it on!!!

But I believe Russ said

"go for strong (0.5mm deflection) front axle springs"

not soft.

He did... but... 0.5mm deflection is the stated 'default', you might say. So, depending on the weight it carries, which will probably be 'not a lot', then to realise 0.5mm deflection will require a relatively fine wire. Or a long span. Or even both. 'Soft' is a relative term.

Wouldn't the lively back end be damped by the motor and gear box?

Not if that is axle-hung and mechanically de-coupled from the rest of the chassis. The wheels, axles and transmission are unsprung weight. It's the sprung weight that could have a tendency to be livelier than is desirable. The body will be entirely free to rotate about the springy beam pivot axis. CSBs damp this motion.

But, would the leading driver be dancing all over the place?

I doubt that, but the body might be a bit 'noddy'. My main point is, I don't know.
And as far as I am aware, nor does anyone else, because it hasn't been tried before.
I am guessing, and I think Russ is guessing too.
One of my problems with springy equalisers was getting them to have the same behaviour side-to-side. The straightness of the wire is absolutely critical if it is to rotate around its axis in service, or the chassis will list. If the idea is to fix the springy beam, then rotation must be prevented, which means fixing it at the pivot point somehow. Then to adjust the roll level of the loco, which may well be necessary, either the springy beam will need to be adjusted by bending, or a mechanism for independent fine adjustment of the vertical position of at least one of the pivot points in relation with the frames will need to be devised and installed.

Even if you subscribe to the theory, the practice is a minefield...

Anyway, I've talked enough about it, it is time to finish building the darn thing and get it running...
Remain fascinated my friend, for I have a cunning plan...

I shall, and will look forward to the results.

Zeb.
PS, all this messing about with HTML is a right pain. It was so much easier by email...

[MarkS]

So, I have done a bit of work on the 2-4-0, and it is currently sitting on 15 thou springs on the front axle, and 15 thou springy equalizers. Other than the motor and gearbox there is no additional weight. I can push it through pointwork just fine, so it seems the track holding is OK...
With little weight, it is almost on the stops for the drivers, meaning that if I add any weight the springs will need to be stronger. I figure that stronger will be very stiff beams (piano wire compensation) pretty quickly. With enough weight, that might be fine, but I don't want duct tape a chunk of lead to the top of the boiler, it ruins the look...

With CSB's, I figure I will have more options, and since it works well with my 0-6-0t and with my O2 0-4-4t I will fit them.
The cunning plan is that the I have provided for either CSB's or equalizers... and the fitting of lead in the area between the driving wheels.
It will be a handsome wee beastie, with a very high PITA factor. PITA = Pain in the a...

This is what it looks like so far - There is a long way to go...

[Chris Mitton]

Hi all

As I mentioned a little while ago on Paul Willis' blog, I've just embarked on my first P4 loco - an Alan Gibson E4 - and decided, having followed these threads for some months, that CSB is the way to go, using as a basis the High Level gizmos. So it's quite reassuring to read these latest posts, which appear to be saying that things aren't quite as critical as they seem?

My problem, using the CLAG spreadsheet to find where to put the spring anchors, is that it starts off with the weight of the engine, about which I haven't the faintest idea. I can pile up the etches, wheels, bits and pieces on the kitchen scales when Senior Management isn't looking, then guesstimate how much to knock off for the three cab roofs, four cab sides, scrap etch, etc that won't get used - but I could be miles out.

It's thirty years since I taught A Level Hard Sums, so while I understand the principles concerned I'm quite rusty juggling the numbers - so the spreadsheets are a boon, thanks! - but it seems to me there are two key points:
One - the location of the spring anchors doesn't depend too much on the actual weight, but does depend critically on the weight distribution, ie what percentage of the weight is carried on each axle. So the initial thought is not to worry about the actual weight so much as where extra weight (lead or whatever) can be crammed in and how it will affect the various loads. [Incidentally, I'm not clear whether the inputs should be axle load or wheel load, which is presumably half assuming we manage to build our engines reasonably symmetrically!]
Two - the thickness of the spring doesn't much affect the locations of the anchor points, but does affect the deflection of the axleboxes.
Therefore, it seems to me, the approach is not to worry too much about the weight, just find suitable anchor points and get on with it by assuming a medium strength spring (around 13-14 thou?). If the result turns out too hard / soft, change the springy beam for a thinner / thicker one.

Using these assumptions, and treating the E4 as a 0-6-0, I've managed to get the CLAG spreadsheet to find anchor points that can use the frame spacers at the outer ends - with a wheelbase of 31+35 mm, anchor points at 12-17-17.5-10 (in Will's terminology). I've assumed very slightly more weight will go on the front axle than the other two, because (a) the boiler is the only practicable place to put significant extra weight and (b) so did the prototype! These give deflections of 0.5 mm on all three axles, up to the third decimal place....if that means the engine sits a thousandth of a millimetre lower at one end than the other, and anyone notices, they've got better eyesight than I!

Is this a sensible approach? If so, I'll just confine my worries to the alarming attrition rate of tiny drills, the Mashima I've just managed to write off, the time it all takes.......

Regards
Chris

[Will L]

.. My problem, using the CLAG spreadsheet to find where to put the spring anchors, is that it starts off with the weight of the engine, about which I haven't the faintest idea.

Absolutely right, so clearly knowing the weight isn't where we start. One of the advantages of CSBs is that we don't have to worry how much the loco will weigh at the design stage.

...it seems to me there are two key points:
One - the location of the spring anchors doesn't depend too much on the actual weight, but does depend critically on the weight distribution, ie what percentage of the weight is carried on each axle. So the initial thought is not to worry about the actual weight so much as where extra weight (lead or whatever) can be crammed in and how it will affect the various loads.

This is true but we have a problem. We do know that a centre of gravity (CofG) at the centre of the wheel base will give us even distribution of weight across all the wheels and, our spread sheet will deal with it nicely. What we don't have is a good way of calculating what effect moving the CofG away form the centre will have on the wheel loads in a sprung chassis. (Oh yes please if anybody knows how to do it) What we do know is the effects are significant and come on with quite small movement of the CofG, so for now the compromise we need to go with is to have the CofG in the centre of the chassis.

[Incidentally, I'm not clear whether the inputs should be axle load or wheel load, which is presumably half assuming we manage to build our engines reasonably symmetrically!]

The spread sheet deals in wheels, the axle load is twice the spread sheet wheel load.

Two - the thickness of the spring doesn't much affect the locations of the anchor points, but does affect the deflection of the axleboxes.
Therefore, it seems to me, the approach is not to worry too much about the weight, just find suitable anchor points and get on with it by assuming a medium strength spring (around 13-14 thou?). If the result turns out too hard / soft, change the springy beam for a thinner / thicker one.

Spot on, that's the way to do it. You can also use the spread sheet to tell you what size wire to use when you do know the weight. I have plans for a posting on this so you'll have to forgive me if I don't go into details right now.

.. treating the E4 as a 0-6-0, ... with a wheelbase of 31+35 mm... anchor points at 12-17-17.5-10 ... I've assumed very slightly more weight will go on the front axle than the other two, because (a) the boiler is the only practicable place to put significant extra weight and (b) so did the prototype! These give deflections of 0.5 mm on all three axles, up to the third decimal place....if that means the engine sits a thousandth of a millimetre lower at one end than the other, and anyone notices, they've got better eyesight than I!

Well done for spotting that implications of small differences in the deflections at either end will produce only a small deviation from level, and can be comfortably ignored.

Is this a sensible approach?

I'm afraid that, as explained above, our current tools don't allow us to calculate our way out of a lopsided weight distribution, despite the fact that solutions to the problem must exist. So, as its not practical to re- jig the fulcrum point once you've built the chassis to get a result by experimentation, I'm afraid that attempting a prototypical weight distribution on an E4 is a journey into the unknown which I can't honestly recommend. I think you would be better off thinking creatively about how to get the CofG in the middle of the wheelbase.

If you've accepted that, then I would also suggest that a very slight adjustment to the fulcrum plot to 12, 16.5, 17.5 9.5 will give a more evenly balanced loco which would minimize the adhesion penalty of having the front axle un-driven.

Will

P.s. I have plans for an E4 of my own and I'm thinking about mounting the gaerbox on the front driving wheel with the motor further forward still in the front of the boiler and smoke box. This leaves the firebox and below the cab floor free for added weight.

[David Thorpe]

When I first heard about CSBs, I thought that the idea sounded great and that it was the obvious way to go with my next chassis. I have to say, however, that I find the mathematical complexities utterly off-putting and totally beyond me - it seems to me that if a system that I first perceived as relatively simple is in fact this complex, and requires this amount of mathematical knowledge and precision, then it just isn't for me, which is very disappointing. Or is it just being made to seem more difficult than it actually is?

Chris - the E4 loco body (without the detailing and smokebox door, but otherwise complete), plus the completed chassis including wheels, coupling rods, motor and gearbox weighs in at 88g.

DT

[MarkS]

Since I was painting some locos for a customer, I decided to paint my Ratio 2-4-0 before the chassis was complete.

P1030279.jpg

However, I am now finishing the remaining items on the chassis - first off, pickups.

P1030283.jpg

The pickups are between the drivers, but are well hidden under the valences of the body. The wire comes through a hole drilled through the copper clad and the loco chassis to remain invisible, but will take a bit of careful work to clear the lead weight between the frames under the motor.
The chassis sits on two sets of CSB's, one set for the front wheels, and the second for the drivers. Currently though, the front drivers are "cantilever sprung" since the wire is not anchored at the front.
I suspect that this arrangement will lead to excess slipping when it comes time for running trials, but then a class '1' loco doesn't need to be too strong... I'll report back...

[David B]

Mark,

I like your pick-up arrangement. Any chance of a close-up and/or a bit more description. (Apologies for jumping in on a different thread).

You may have seen that I was enquiring about top wipers in the thread in this same category - http://www.scalefour.org/forum/viewtopic.php?f=19&t=1247

I have made some up but am not completely happy with them. How do you insulate the carrier from the chassis? Do you find the tips of the wires sufficient contact for good pick-up?

David

[MarkS]

Thanks David,
The idea comes from Ted @ CLAG - http://www.clag.org.uk/tedpick01.html ...
My version has differences due to the nature of the footplate, valence and space between the frames.

Here is a close up of the other pick up that I am about to install. Note, I have not yet bent the tips.
Basically I have a piece of copper clad sleeper, clipped to length, to which I soldered the centre part of the pickup. I drilled a hole through for the wire, the end of which is bent over and soldered to the copper face as well. Having the wire go through the loco frame adds some strength to the joint. (Which is glued with CA)
And finally, yes, there is more than sufficient contact with just the pin point, honest!

[David B]

Thanks, Mark. I feel some experimenting coming on!

David

[MarkS]

Further developments with the Ratio 2-4-0, the original gearbox at 80:1 resulted in a screaming motor, so that the loco sounded like a R/C airplane at full throttle...
It has been replaced with a HL Roadrunner + and at 54:1, is much quieter.
The configuration is the same as shown in the instructions - download/file.php?id=2835 and powers the rear axle.

The problem I am having is that when power starts to be applied, the loco will rise (or lower when direction is reversed) on the rear (powered) axle.
How does one control that kind of torque reaction? Does a torque reaction rod have to be attached to the swing arm?
Or should I be thinking of bolting the motor down so that it cannot move? Would a couple of hours of running in help?
I don't recall any discussion of torque reaction on the the swing arm / extension type gearbox configuration, so I am at a bit of a loss at the moment.

On the other hand, the pickups work beautifully!

[Russ Elliott]

I don't recall any discussion of torque reaction on the the swing arm / extension type gearbox configuration, so I am at a bit of a loss at the moment.

There was an extensive and tortuous discussion on P4_talk in mid-May 2005, initiated I believe by a query from David Knight. I posted up 3 diagrams in the course of the exchange, as a means of trying to picture what we were talking about:









I'm not sure the discussion reached any kind of unanimous conclusion, but Andrew Jukes drafted an interesting set of guidelines and principles that could apply to such cases. (Which are worth revisiting in due course.)

The problem I am having is that when power starts to be applied, the loco will rise (or lower when direction is reversed) on the rear (powered) axle. How does one control that kind of torque reaction? Does a torque reaction rod have to be attached to the swing arm? Or should I be thinking of bolting the motor down so that it cannot move?

I think any number of factors might be going on here. First of all, I'm guessing that your current cantilevers on the front carrying axle are way too soft, hence the instability you report in one direction, but I'm not sure I understand why the loco should pitch in the other rotation when the loco direction is reversed.

Maybe it's something obvious, as Ted pointed out:

No, the motor must not make contact with the body. I learned my lesson on this (more trial and error!) many years ago with a Portescap fitted 7F. It lifted the driven (rear) axle under load in reverse, because the torque reaction of the motor bore down on the bottom of the boiler, 'jacking' the axle upwards.

Andrew Jukes later noted:

The most obvious solution would seem to be to make the swinging gearbox link rigid and so integral with the motor assembly, detach the motor from the chassis and then to put one of those nifty horizontal links from the motor to an attachment point at or above the top of the chassis. The overall geometry could be much the same but the forces would follow different paths.

And this was followed through by David Knight:

The added link does a fine job of giving flexibility to the final positioning of the motor so that backheads and such do not need to be removed but once a place has been found the link needs to be soldered up solid. I found this out the hard way <vsg> and this was with a rigid axle! The effect on a sprung one would be even more pronounced IMO.

The above are extracts from a long series of exchanges, and perhaps need to be read in their full context.

For starters, I'm curious where your overall CofG is.

[David Knight]

Gee Russ, talk about a blast from the past! The engine in question of my original posting back on P4_talk was a compensated Comet framed Jinty and the motor was in fact fixed solid so no torque link as such, or certainly nothing appropriate for springing. My J72 uses the same gearbox as the Jinty, a 54:1 Roadrunner + and once again I have soldered up the extension once I established the optimum position for the motor. I have used the torque link as suggested by Bills drawing and it seems to work fairly well although on close inspection the motor does contact the crossmember and one of the PCB pickup strips. I just went down and ran the engine while carefully watching for motor movement and there was none. A pic follows of the setup used.

hooked up.jpg

The torque link looks like this;

torque reaction link etc..jpg

Note the ears on the gearbox just below the motor which are part of Bill's etch, not on the original HighLevel box
Hope this helps.

Cheers,

David

[MarkS]

Russ, for starters, the CoG is over the leading driving wheel axle.
Last night I exchanged the CSB wires (cantilever front drivers) to long ones for both driving wheels (ie 3 anchor points) and noted no change in the way that the body lifted when power is applied.
Note - the body lifts when the power is applied, and returns to a normal attitude when the power is reversed. The motor cannot lift at the front, but can slide fore and aft a bit.

I had a torque link installed per your first diagram, but have removed it since it didn't help, and there is no difference without it. (The motor could move fore and aft, I think Dave's horizontal link should help in this case)

I was thinking that friction in the axle washers might be having an effect, so removed one on each side between the gearbox sides and the axle bearings. No difference noticed...

It seems that soldering the extension (along with a torque link) as postulated by Andrew, and proven by Dave may be the best way to make this thing work...

On my O2 0-4-4T, I have the same motor gearbox combination, with the swing arm 'reversed' and tucked under the motor. This has had none of these problems and the motor is simply held down with a piece of double sided foam tape!

[MarkS]

Today, I soldered the swing arm in the same manner as Dave Knight suggests. The loco now runs as smoothly as it should.
Now, it does not pull a whole lot, but it does, oddly enough, stick to the track like glue...

[David Knight]

A final (?) thought about the gearbox extension. To the best of my knowledge there is no flexible option on any of the bespoke gearboxes that Chris does. It is only on some of the generic variety that have to fit a multitude of situations that include the moveable extension. I suspect this would indicate Chris's thinking on the matter.

Cheers,

David

[MarkS]

Today I changed the CSB wire for the drivers one size 'softer' (13 thou) and that seems to have given the little loco a bit more grip, not significant, but noticeable.
The wire for the front wheel set remains one size larger at 14 thou.
I have abandoned the cantilever idea, the loco was prone to slipping as I suspected it would be.

[Russ Elliott]

Today, I soldered the swing arm in the same manner as Dave Knight suggests.

I think this probably confirms, for anything other than a fixed axle, that any loose swing arm on a HL box needs to be made solid with the gearbox.

Did you do the soldering in situ, Mark, and how is the motor now constrained on the chassis?