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Sprung chassis, principles and easy applicaton


bertiedog

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After a long dissertation on springing and the idea that it is not needed on models on another thread, I have decided to post on here a little background so that you can decide to use or disregard the idea of copying the real thing and having sprung wheels on models locos.

 

  • First a spot of history, and to define what we mean by a sprung chassis.........

All real locomotives have springing,( Yes, a few exceptions do exist), this is to even out the loads on the wheels and bearings, in a dynamic system as the locomotives rolls over the track.

 

It allows the wheels to shift in position to remain in contact with humps and bumps, the motion of which would lift and lower the whole locomotive if large enough, but is usual confined to acting on only one of the wheels at a time, resulting in the chassis being able to remain level over bumpy track. despite going up and down relative to the frame, the wheel maintains a constant down pressure on the track, firmly in contact.

Toy trains do not bother with springs, early toy trains like
Marklin, Bing Lionel,or Hornby,
relied on large flanges on the wheels to keep things on the track. Any bumps or humps barely mattered,
the huge flanges dealt with it.
Some designs even ran on the flanges through pointwork to prevent frog drop.

 

When Scale modelling picked up in the 1920's most scale model builders like Basset Lowke,Greenly and Lawrence used fully sprung chassis designs on live steam models, and at first most electric steam outline models used sprung chassis.

 

But toy makers continued with the large flanges on more scale models and found springing was not needed, just play in bearings, or sprung guiding wheels on bogied designs.

 

As OO and HO started springing was at first disregarded, as very course flanges were common, such as Trix used. But as scale models became more popular flanges were reduced to smaller sizes and de-railments became a problem.

 

Commercial producers in the 1930's decided that track improvements and play would suffice for OO models in the UK, no commercial models had springing. However many enthusiasts used springing on early chassis, home made systems that used small springs over each axle box, as the real thing.

The first commercial use of springing came from "T
he Dean of HO
",
Gordon Varney
in the US, who decided that he could supply fully sprung chassis with a simple dual wire spring system, which he produced in 1939, and ran till the mid 1950's when it was dropped for cost reasons due to problems after his retirement, and sale of Varney.He worked closely with Robert Lindsay, the motor designers, and had fully floating motors and gearboxes, with all sprung wheels on most of his models.

 

Cost came into the equation, he had to produce cheaper models after the war, and they offered non sprung options on most models as the parts count was lower, and therefore he was able to sell cheaper.

Robert Lindsay provided a partial answer, with model diesel designs, by providing a
flexible chassis without springing,
each axle could rotate along the cross axis of the frame, maintaining a full contact with the rail, without a spring,

 

This flexibility can be done on a simple steam chassis such as an 040, and even a 060, but should not be confused with compensation or fully sprung systems. One axle has to reamain rigid to hold the loco level.

 

It is not a three point system like the Flexi chassis types in the UK either, just a way of pivoting all the axles so that the wheels stay firmly in contact with the track.

 

These improvements were needed in the States as the NMRA was proposing the smaller nearer scale flange for HO, and springing was needed. Some makers disagreed, notably Mantua, who allowed axles to move unsprung and un-fettered in U slots bearings, arguing that this was cheaper to make.

 

Many makers of the 1950's used this method on commercial HO, and it continues to this day on plastic RTR, taking advantage of the flexibility of the mouldings, or oversized bearings, or partial springs like Bachmann.

 

Top quality brass HO locos were usually sprung in later years, early were un-sprung , but with U bearings.

 

In the UK, OO went down a different path, springing was rare on purely cost grounds, Stewart Reidpath used it for a while, but then gave up, saying the track and flanges dealt with de-railments most of the time, but this did not cover the advantages on springing for other factors, like power pick-up.

 

His RTR and kit making was in cast lead, and the weight kept the trains on the track. The same applied to Hamblings RTR and other scale makers, nobody could afford to adopt springing on commercial models.

 

But hand made locos for customers were made with springing, and many enthusiast always built with springing in place in finer class models.

 

After the war, there was a slow movement to adopt springing, especially from people who had seen Varney Models running, and with finer wheels and track, the MRC in London and Birmingham lead the way towards standards that needed springing, like the scale P4 system.

 

In larger scales springs had remained in use by scale modellers in O gauge and was always in used in live steam in 2 1/4 and other larger sizes.

 

As P4 came forward, and fine scale OO took off, springing started to be fitted, using separate springs and horn blocks, but also the CSB system of wire springing came about, perhaps not realising this was just a modified Varney system, but was highly thought out, and based on calculations.

 

Compensation systems started to be considered for Models as well, this is the idea that any pressure on one part of the suspension should result in a shift of the pressure to another part of the system to compensate for the change.

 

It equals out changes, but does nothing to better a fully sprung chassis in model terms, however it can be used with light springing or without springing, Mike Sharman advocated this mixed approach.

 

The ideas were based on the three point principle, that any three points will always find a way of standing on any surface under them, they will adopt a firm contact.

 

Applied to an 040 chassis, one axle would be rigid to the body and chassis, and the other able to pivot about it's centre point, the loco will remain quite stable over very rough track.

 

Taking it one further, the un-sprung pair can be sprung to the body and chassis, and the pivoting one can have springs added, this is complex, and not actually needed.

 

What is done is to have for hornways with sprung axleboxes and connect the axle on one side by a beam pivoted to the chassis side.

 

This is a compensated chassis, any movement of any wheel is allowed, but the system keeps all in very equalised contact with the rail.

 

Although it does not seem to be a three point system in fact it is, as the axles connect the forces in the same way, really a doubled up three point system.

 

Such a model in any scale will stick to the track under all circumstances, and therein lies the advantage, we need constant electrical pickup, and firm traction, and springing provides the answer, (as does a compensation system without springs).

 

Others argue weight will work in the same way, it does with commercial models and toys, but we are talking about fine scale models here, and many other factors apply.

 

Gear wear is higher with excess weight, noise is higher, and general wear and tear is higher without a sprung chassis. RTR get away with it to an extent, but the running qualities of even the best RTR cannot be compared to a good well assembled kit or hand built loco.

 

It is not difficult to achieve, just plain common sense and home mechanics are needed.

 

I will post some examples in drawing of chassis springing and compensation ideas, all applicable to existing chassis, kit chassis or home brew. understanding the principles, which are very basic, helps understand why kit makers do things in a certain way, some times they over do a design in complexity, and a little thought can simplify or improve a kit., but you have to know the basics and make a reasoned judgement.

 

But one thing is absolutely certain, springing is better than none.........you may get away with no springs on RTR, but it would be so much better with them. It's an integral part of a decent design.

Stephen.

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The reference is very useful, it covers most systems , especially CSB, but this does muddy the water with kits a bit, which can be a bit of a curates egg in some designs, in one case I know the suspension had no fixed datum, ad the loco rocked on the chassis. The designer had forgotten to have at least one rigid axle, or at least have all adjustable springs,, not common on OO locos due to the small sizes of springs an adjustment parts.

 

If you want to follow the Compensation path Mike Sharman's book is very good, but the methods may be complex to apply to existing models and may require extensive modifications to kit designs, which is why a grasp of the basics is needed.

.

The most basic point, and not grasped by lots of people is it is the chassis weight (plus body),that we are springing, to float on the wheels which are always in firm contact with the track.

 

The wheels do not move up and down with the suspension, the chassis moves up and down, and this very basic point is often missed.

 

The wheels, bar a few thou, remain parallel to the line between the two contact points on each supporting rail, which off course may not be level.

 

The movement of the hornblock, the bearing tube etc., will be very slight, in the order of .5mm max in each direction, (and some suspension is set to only move down or up).

 

If pressure is applied up wards by the wheel "rising", then the wheelset reacts, as one wheel rises the other does so slight, and the axle is no longer parallel with the track. The wheel is no longer parallel vertically with the frame, twisting against it, but this effect is very slight in 4mm scale, and play and slack will be enough to allow free suspension movement.

 

The usual arrangement for suspension, is hornblocks, with a bearing in the, floating in hornways in the frame, but it can be a sleeve bearing in the same way. it does not matter whether the bearings are attached to each other or loose, they are moved as a pair by the axle.

 

One axle, usually the driven and an outer axle, is left rigid with the frame, and the other float. This provides the reference datum level and positioning, stopping rolling side to side.

The one stiff axle makes little difference to the action of the suspension, if all are sprung instead, with a fully floating motor, then adjustable springs must be provided, or a CSB system chosen

 

The Varney method used a fully floating system, but was ingenious, it used taut wire to suspend the chassis on the bearings, and they are adjustable, allowing levelling and level side to side as well. The motor floats in a nose suspended way, fully able to bounce with the chassis movement, note, chassis movement, not wheels going up and down, they don't, it's the chassis that does.

 

The Varney chassis allowed a rather generous 2mm up and down, far more than later experience showed was needed, but this was 1939!!

 

Each side of the frame has a wire, about 15 thou,stretched the full length of the frame, crossing and touching all the bearing sleeves ends. In between each wheel is a stud in the frame, which acts as a support, just like CSB method, but the big difference is the other end of the wire, it runs though an adjusting screw or clamp stop, allowing a small coil spring on the end of the wire to be tensioned.

 

This allows adjustment, wind up the tension till the loco floats, that all that's needed, no calculations, no individual settings, unless the wheels are not symmetrically spaced, with such arrangements the studs may have to be adjustable as well. or moved slightly off centre. Most average designs float correctly first time, and the performance of this method is truly magnificent.

 

The heavy Pacific they made, or the Mikado could run over the roughest track, bumps, jumps, miss aligned gaps, no trouble at all, it simply glides over the track.

 

The CSB method does the same, but needs a bit of reading up to set correctly, the studs need careful siting , and the wire diameter is important, no auxiliary coil spring is used, as the wire acts as compensation beams as well as basic springing. The previous posting has the reference to the site with details.

 

more soon,

Stephen.

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I thank you for putting all the time and effort into set out the history and principles of springing.

 

I would just question one point. You say that the wheels don't go up and down but that the frames do (sorry - pet hate of mine - locos don't have chassis!). I always thought that the whole point of springing or compensation was to smooth out the effects of and bumps/joints in the track. I can't quite get my head around the concept of a loco running along plain and level track with the wheels staying level and the frames going up and down.

 

To me, springing is a way of ensuring that the frames (and the rest of the loco) move along smoothly by allowing the wheels to move up and down slightly over track irregularities, with the springs taking up the movement and cushioning the frames and body against lurches and bumps.

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As previously noted, many thanks Stephen for the effort in your excellent precis of 'the principles'. If the other thread that you refer to is the one that I think it is, this is a refreshing and understandable read compared to some of the argumentative postings on there!

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The drawing shows for a 3mm axle raised .5 mm on an arc from the other end of the axle, at 14mm nominal , a block 8mm high,(only top shown), 4mm above the axle line will move out of true by approx a half thousandth of an inch.(..012mm).

 

 

post-6750-0-17097000-1295194357_thumb.jpg

 

 

No known model hornblock would jam, or bind. with this amount out of true in any practical situation.

Stephen.

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I thank you for putting all the time and effort into set out the history and principles of springing.

 

I would just question one point. You say that the wheels don't go up and down but that the frames do (sorry - pet hate of mine - locos don't have chassis!). I always thought that the whole point of springing or compensation was to smooth out the effects of and bumps/joints in the track. I can't quite get my head around the concept of a loco running along plain and level track with the wheels staying level and the frames going up and down.

 

To me, springing is a way of ensuring that the frames (and the rest of the loco) move along smoothly by allowing the wheels to move up and down slightly over track irregularities, with the springs taking up the movement and cushioning the frames and body against lurches and bumps.

 

The wheels move in relation to the frames, not the track, although the track on which they sit may bump up and down relative to the ground, the whole thing floats, and we are supporting the chassis,(this includes the frames!), as a unit floating on the springs.

 

 

The reason I put is this way is that many people have described wheels rising up in the hornways as if there is no reaction from the frame, or the other wheels etc., it is all a dynamic system interrelated, but the concept is easy to visualise as a chassis floating on springs, supported by the wheels standing on the track.

 

As the track alters as the loco rolls forward the springs adjust the pressure on the chassis, and a new average position is constantly adopted as bumps and humps are crossed by each wheel.

 

Compensation helps even out the effects resulting in a steadier average position. by adjusting the pressure across pairs etc.

 

Stephen.

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I should add that we usually interfere deeply with the floating chassis, by having one of the axles rigid to the chassis to maintain easy stability across the frames.

 

 

This is just the "usual" practice, not needed as such as Varney showed, but if left off the springs are all going to have to be adjustable to level things in all axis.

.

At least with one rigid axle, we gain cross stability, and we have a fixed axle to add a gearbox to should you wish to. Personally I prefer all axles are sprung, with the motor floating as well, it is smoother.

 

A practical addition would be the spring pressure on the gearbox axle would be increased to help act against torque reactions, which tend to both twist, and raise and lower pressure on the axle, as the motor varies in speed.

Despite advocating the all springing, 040 are often better with a single rigid axle, and the other simply pivoted and unsprung completely,

 

It works very well in such a simple set-up and suits diesel bogies designs straight away. No springs, no real compensation, but the wheels are hard on the track all the time.

 

The same can be done on an O60, front axle rigid, the other pivoting, or the centre rigid and outer pivoted, again no springs needed.or very light wire springs added to damp the pivoting.

 

Even an 080 can be done this way, or any larger loco really there's no limitation.the chassis and body will roll a bit with the rigid axle, but on decent track the whole action is very smooth, and passage over points much smoother than un-sprung, and electrical contact is excellent, and still no springs!

 

By a Pivoted axle, I mean one in a total sleeve bearing from one side to the other, with a pivot connection to the chassis in the middle, just like a bogie would be attached to a bolster.

 

Springs next.

Stephen.

 

 

.

 

 

 

 

 

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Please, Stephen, continue with what you are doing. Your posting are helping me understand the principles of what I'm doing without having to work it out all by myself, so saving me a lot of time.

 

I totally agree, and I am all for constructive criticism. So being all grown up's let's all agree to disagree before this interesting thread is locked ;).

 

ATB, Martyn. P.S. The Mods are watching B).

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Thanks, Andy - I know that this is essence a 'non-post' but public thanks need saying.

Agreed. It was this sort of issue that brought my O scale Class 14 project to a halt - in more ways than one! I'm hoping to learn a lot from this thread... :)

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the wheel maintains a constant down pressure on the track

 

I hesitate to interrupt Bertie, because I usually understand where he's going to in one of his expansive soundbite modes, but I think the above notion requires clarification. Taking the simple case of a balanced sprung 4W-wagon, each wheel gets 25% of the sprung weight in a static situation. Dips and bumps in track will effect relaxations and compressions in the springs as they absorb and discharge their potential energy. In an extreme momentary case, 2 wheels might become completely unloaded and the other 2 will take in the region of 50% of the sprung weight. The forces are in a constant state of dynamic change (change = attempting balance), the only proviso being that the sum of all those forces is a constant 100% of the sprung weight.

 

The unit of measure of the difference between a spring's fully relaxed and fully (but static) compressed state is significant. For driving wheels in 4mm scale, the value of 0.5mm has been suggested and seems to have gained a wide acceptance amongst the springing community. The 0.5mm notion is entirely arbitrary, and merely a vague consensus of what might be required on the actuality of averagely-awful and awfully-averaged homemade 'finescale' track.

 

In terms of traction, the difference between unloaded and fully loaded axles will produce a changing set of normal forces, and therefore tractive forces, at the wheel/rail interfaces.

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First, the really easy one, a diesel bogie, the design was sorted in 1948, by Robert Lindsay in California, who designed the motor as a five pole skewed slot design with 16:1 worm drive in HO.(note the flanges are NMRA and this was 1945, where were the UK and Euro designers?)

 

 

post-6750-0-64597800-1295204391_thumb.jpg

 

 

One end gearbox is attached to the motor and central tube, and the other gearbox floats on the tubular extension, able to rotate a few degrees, allowing the wheels to ride over bumps and humps. The bolster is rigid to the rigid axle.

 

The same arrangement can be home built, a tube with no motor and the drive applied to the end with a shaft, or gears or belt from above the bottom tube.

 

All simple and very effective, no springs and superb running, and applies to all scales. It also works with 6 wheeled types, the bolster pivot being placed between the middle and outer pair, the outer axle rigid..

To aid a six wheeled bogie the swinging axles can be lightly sprung with wires, to damp the movement a touch., as quick acceleration, can give a torque reaction and wheels lift a bit. This happens more with O scale bogies, with powerful motors.

 

I should point out that Hollywood Foundry does similar designs with the motor on the top, but not the ingenious tube design from Robert Lindsay.

 

Stephen.

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Guest jim s-w

Hi all

 

Before anyone reading this thinks that for finer scales springing is essential it isn't. Not in all cases. Desirable? Absolutely but not essential.

 

One thing I would say in my experience is that springing has totally replaced compensation in wagons. My own approach is to try vehicles in their rigid from first and fit springing only if required. Compensation may mean the wheels stay in contact all the time but the movement looks worse than rigid.

 

As always though theory is theory and often falls down in the real world. What I mean is a well build rigid chassis will be better than a badly built sprung chassis but all things being equal, springing will ALWAYS be better than compensation or rigid.

 

Having said all that the subject is about springing so back to you Stephen

 

Cheers

 

Jim

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name='Miss Prism' timestamp='1295203848' post='306375'

 

In terms of traction, the difference between unloaded and fully loaded axles will produce a changing set of normal forces, and therefore tractive forces, at the wheel/rail interfaces.

The effect is very, very, slight, it is not a constant value, but as the spring is about in the middle of it's range, the amount of difference over .5mm is very, very tiny indeed. We are not moving away from a zero value but are mid scale in simple terms, so forget it!! Wagon springing is slightly different, the lighter loadings may reveal the rate of the spring altering, resulting in bounce. Locos mass damps the bounce..

 

 

.5mm seems the accepted limit, 1mm in all, up and down, this is generous for P4 and tight frog 16.5 and 18mm track, In fact I built several P4 locos with no springing at all, and they worked fine on good track, but I repeat good track.

 

Gordon Varney used a movement of about 3mm, but for reasons later explainable, he allowed the movement in up direction only, the wheels could not "drop", they are bottomed in the slot by the keeper plate.

 

The chassis in that condition could ride bad track, but any individual wheel would not drop on frogs crossings.

with a six or 8 coupled chassis this works fine, but if you wanted you could adjust the spring wires to allow the loco to float freely on the wheels, and in this condition the wheels would go down relative to the frames .

Th reason he chose two methods was to make it easy to set, wind the springs up fully and all the axle boxes are bottomed to the keeper plate, and the loco stands upright and steady, but the springs will deflect over bumps etc.

 

Slack the Varney Wire springs off and the axleboxes float, and the whole loco will rock and roll a bit as it runs, but very smoothly and it simply cannot de-rail!! It glides along, but some people do not like the ideas of no restraint to side to side rocking being there, and again torque reaction can rear up and as the power is increased and decreased the loco may lean slightly.

 

I'll dig out some drawings on the Varney method.

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On wagons it is all different, they are light and bounce when sprung, especially if the suspension is not set against a stop but fully floating, this makes the trucks lurch all over the place as they are pulled over bumps,, and appearance does suffer.

 

The answer is to set against a stop, in effect at rest the chassis is rigid, only an upward pressure will deflect the spring, the wheel will not travel down, but it is not actually needed that much, ad a touch of bearing play and the wagon with springs and a stop will roll better and not bounce and lurch so much.

 

 

Also the weight of the wagon should be brought up to a reasonable level with ballast, this will damp movement

 

Stephen.

 

 

 

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post-6750-0-57482300-1295220443_thumb.jpg

The Gordon Varney way to provide easy springing, with steel 15 thou wire stretched from the front to the back, over the sleeve bearings on the axles, via the buttons on the inside frames. The front is clamped, and the rear, , via the small coiled spring on the end, is secured to a cross bar. To adjust the front screw is slackened and the wire pulled and the clamp tightened, but you can add screw shackles to ease this, allowing micro adjustment.

 

The frames are a keeper plate type, with U shaped, slots to allow the bearings to move up and down.

As supplied the spring is set tight to hold the bearings against the keeper plate when at rest., therefore the loco stands upright.and requires no adjustment.

 

Wheels can deflect upwards against the frames, but not down, and this actually helps running over points( think about it), no drops. In practice there are slight drops, and good electrical pickup.

 

Most enthusiasts slacken the wires to allow the loco to float completely on the wires, and then it is fully sprung, but may suffer torque reaction effects under load, but these are very slight.

 

The frame spacers are each side of the bearing tube , this position is not important, it is purely the sleeve bearings, the wire and the buttons that are vital.for this excellent system to work....and boy does it work, the locos simply glide!! and this was 70 years ago...Why, Oh, why, do we put up with modern rubbish, when this design showed how to do it.

 

Stephen

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And this is the complete 1948 loco, the Super Pacific , which has sleeve bearings that contain oil, full springing, including sprung self centering bogies,and the Robert Lindsay designed motor with ballraces, five pole skewed slot armature, the casing fully floating on the sprung bearings, with fully sealed gearbox.. This motor was the basis of Hornby's Ringfield motor in the Castle, but they simplified the design. The wheels fitted D step ends, and were retained by screws.

Expensive to make, but sold well, it was dropped after Varney retired in the 1950's. Why do people produce less these days when they got it right first time?

post-6750-0-50106000-1295222525_thumb.jpg

 

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First, the really easy one, a diesel bogie, the design was sorted in 1948, by Robert Lindsay in California, who designed the motor as a five pole skewed slot design with 16:1 worm drive in HO.(note the flanges are NMRA and this was 1945, where were the UK and Euro designers?)

 

Maybe they has more important things to worry about at that time.

 

Jim.

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It was 1948 when produced, long after the war,..... the 1945 reference was to an article in the US model press, even in the UK a full model press ran throughout the war.and UK makers were waiting to resume production only to be stopped in the UK by Board of Trade rulings that forbade new model production till about 1950/51.

 

 

Despite knowing of the US designs, the UK makers cut costs or decided they knew best, which drove Hornby to some odd designs.which became too expensive to make. Even Gordon Varney got caught with costs, but the demise was due to his retirement., and Japanese made brass locos took up springing across the board in the 1960's....in the UK there were none.......

 

When etched kits started in the UK the designs tended towards the complex when springing was fitted, Varney's design seemed to have escaped notice.

 

It applies equally to the use of scale horn blocks and hornways by the way, and works in very fine scale chassis, it does not foul brakes etc, and suits plate framed locos like most British outlines, and it is completely hidden from view., the same as the CSB system., which is a version of the same idea, but based on compensation ideas as well.

 

Gordon Varney never mentioned Compensation in his books, instructions and articles, but others have pointed out his system does act as compensation, as any wheel rises the pressure on the wire increases and the other axles are subjected to increased down pressure, maintaining the level. This is un-calculated, but it seems reasonable from the CSB principles.

 

Stephen.

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Thank you, Stephen

 

When you get chance could you say something about motors driving a non-rigid axle, please. I've seen notes about torque bars on gearboxes with a flexible drive to a fixed motor. How about where the whole shebang is hung off the axle, or is that not a good idea?

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Very interesting! How many times have we tried to re-invent the wheel when pioneers like this were doing all the hard work for us all those years ago. Certainly the CSB seems to have been forgotten about for decades but there it is!

 

I can't lay my hands on a copy right now but I recall that the Ahern "bible" on loco constrution included details of springing.

 

Another pioneer who was very big on springing was the late Rev. Peter Denny. All his rolling stock is sprung as are several axles on locos although he found that the answer to good running locos in EM (and his locos do run extremely well after 50 or in some cases 60 years) is good pick ups (and lots of em), accurate construction and lots and lots of weight. His 0-6-0 tanks weigh as much as a modern RTR pacific!

 

Many thanks for the very interesting information bertidog! We can still all learn something from these sorts of people after all these years!

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