Any ideas for a 2-2-2 Single chassis- how to compensate or spring

[michaeld]

Dear all,

I'm looking at building a chassis for a "Single" 2-2-2 loco in p4 and would be grateful for some thoughts on how to compensate or spring?

Any ideas or pitfalls? At least theres no coupling rods and quartering to worry about !

thanks in advance

Michael

[bertiedog]

The best would be sprung, on wire beams, or individual springs, but the key to good performance is to use Mike Sharmans method, put the weight of the tender on the driving wheels.

 

The tender wheels are rigged so that only the rear pair bear any weight, the front two float in slots, or a "bogie".

 

A stiff beam is taken under the cab from the tender to a pivot point right under the drivers. The weight is applied unsprung, any springing merely acts on the body and chassis of the loco.

 

It will now pull well, and ride very well indeed. The beam can be permanently coupled, or a socket made in the tubes to allow dropping the tender.

The tender should be packed with lead shot etc to give as much down force as possible.

 

The trailing wheel can be sprung to get the loco to ride "even" (really an 040), and the front wheels lightly sprung enough to ride the track properly.



I have built several P4/S4 222 and 422 locos and all used this excellent approach from Mike Sharman, some with no springing on the driven axle, which makes things even easier to arrange.

 

The transfer beam can be 3mm square brass tube or rod etc., The tender pull can be taken by the transfer beam.

 

I would not spring the rear tender axle, why bother, it hardly makes a difference. The locos simply glide along, and the weight makes haulage with a single driver a pleasure.

[N15class]

I was going to say look at the Sharman book on compensation, but I am too late.

[DLT]

Hi Michael,

 

Is the drive actually on the driving wheels?

I've not tried it myself, (never built a 2-2-2!) but I have seen a 2-2-2 with 4-wheel drive, on the front and rear axles via a layshaft, and the prototype driving wheels left to do their own thing with very light springing.

 

Not sure if this helps, but might be worth a try!

Dave.T

[Jol Wilkinson]

Allan Sibley wrote up building a single (MR I think) where he drove the rear axle IIRC and loaded the tender onto the rear of the loco for good adhesion, put a single pivot on the front axle and let the driving wheels go along for the ride. I think that the driving wheels axle had a large flywheel on it to keep it on the rails, but light springing would obtain the same result.

[N15class]

I suppose if the leading and trailing wheels are the same diameter you could drive the trailing and use a chain drive to the leading, leaving the drivers sprung. This would mean you could weight the loco, and it would work like a 0-4-0

[burgundy]

The best would be sprung, on wire beams, or individual springs, but the key to good performance is to use Mike Sharmans method, put the weight of the tender on the driving wheels.

 

The tender wheels are rigged so that only the rear pair bear any weight, the front two float in slots, or a "bogie".

 

Ouch! I had not really thought that bit through when I did the shopping at Expo EM last weekend for my next winter's project. See

http://www.mjwsjw.co.uk/page24.html

I have bought High Level hornblocks for all the axles, with the intention of using a compensating beam between the driving and one of the carrying axles (giving two points of suspension) and a centre pivoted rocking mechanism on the other carrying axle (to give the third point of suspension). I guess that it would still be possible to apply a Sharman style "free bogie" to the front of the tender and transfer the tender weight to the middle of the loco chassis?

Good job I have a couple of months to think about this before I am likely to start work on the kit.

Best wishes

Eric

[bertiedog]

Some people use Sharman's system with a small alteration, have the hanging pivot between the driver and the rear wheels, both sprung or un-sprung. This makes a front heavy loco sit up straight, without the front wheels or the bogie bearing any weight, bar enough to stay on the track.

Personally I find just hanging the weight on the driven axle is straightforward and it always works.

Driving the front and trailing wheels means a complex solution, chains would be easy in O gauge, but in 4mm?..it would have to be a shaft drive, or two small motors one for each axle.

Or just go for a tender drive!!

The pulling power of a single with Sharman's system is good, several coaches, but also the smoothness and steadiness has to be seen to be believed, especially at speed.

Stephen.

[Jol Wilkinson]

[/left]

 

Ouch! I had not really thought that bit through when I did the shopping at Expo EM last weekend for my next winter's project. See

http://www.mjwsjw.co.uk/page24.html

I have bought High Level hornblocks for all the axles, with the intention of using a compensating beam between the driving and one of the carrying axles (giving two points of suspension) and a centre pivoted rocking mechanism on the other carrying axle (to give the third point of suspension). I guess that it would still be possible to apply a Sharman style "free bogie" to the front of the tender and transfer the tender weight to the middle of the loco chassis?

Good job I have a couple of months to think about this before I am likely to start work on the kit.

Best wishes

Eric

 

 

Eric,

 

you would need twin side beams for the two axles and a single pivot point for the other. If you have the twin beams between the rear and centre axle you can move the side beams pivot points towards the driven axle which will put more of the load on it. You could then hang the front of the tender onto the loco drag beam for extra adhesion.

 

Not so good as the Mike Sharman system but easier (that's one of the options provided in the London Road Models Lady of the Lake 2-2-2).

 

Looking at the drawing of the frames in the link to the instructions, then anothe option comes to mind. If you are building in one of the wider gauges with more space between the frames, then CSBs might be the solution. You can set the mounting points for the wires to get more load on the driven axle. The wires could pass above the outer axles and below the centre driving axle. See http://www.clag.org.uk/beam-annex3.html

 

Jol

[Michael Edge]

Normal compensation does not work very well for singles, you need to get much more weight on the driving axle (which is what was actually done in full size practice). The Sharman method quoted above should work though.

Michael Edge

[billbedford]

A 2-2-2 is a 0-6-0 with different sized wheels -- what's the problem? Just use standard CSBs, though younmif=ght have to be a bit clever about how the bearings are attached to the spring wires.

[N15class]

Surely if you use CSB on a 2-2-2, you would need to load the centre driving wheel more, which I would see resulting in the loco pitching on soft front and rear springing.

[billbedford]

I've just looked up the weights of the GNR 7'6" single. They had a total weight of about 40tons and a driving axle load of about 17 tons. So either the pitching is not a problem or it is entirely prototypical. There is enough friction in the bearings slide to damp out any oscillations. Though it may be advisable to balance the loco prototypically, i.e. that there is more weight on the leading axle than the trailing

[N15class]

That is interesting Bill, it is strange how somethings fool logic.

[t-b-g]

I have seen CSBs up close and been mightily impressed but I am not sure that they are the answer to maximising haulage on a single. I would have thought that shifting possible adhesive weight onto the front and rear wheels would be the last thing you wanted to do.

 

I have an old Ks Midland Single, which happily shifts 8 Ratio Midland carriages. The loco driving wheels are rigid (and have the motor/gearbox on them), as are the rear tender wheels. The front 2 pairs of tender wheels are in a "free bogie" which could easily be compensated but current P4 protagonists seem to be advocating that it is probably not necessary. The rear loco wheels ride up and down in a slot and are very lightly sprung, just enough to keep them on the rails. The front bogie just hangs there with a bit of weight on it to keep it on the rails. For a 2-2-2 you could put that in a slot too. What stops it pitching fore and aft is the design of the loco to tender coupling. If all the other wheels can move up and down, you can make the coupling pretty rigid, so that it can turn from side to side but can't move up and down more than is needed for clearance/free movement.

 

With that sort of arrangement you can put extra weight wherever you like in the loco or the tender and it will all add to adhesion.

[billbedford]

The easiest way to maximise the haulage capacity of any loco is to ensure that all the rolling stock runs with correctly adjusted pin point bearings.

[Michael Edge]

Quoted axle weights are what the civil engineer thought they were, as far as I know they were promptly adjusted on arrival at running sheds. I've tried just about every possible method of building singles over the years, compensation produces a very smooth running loco which will barely pull its own tender. Best results have been with individual springing, with just enough weight on the carrying axles to stop the loco pitching.

Michael Edge

[michaeld]

Thank you everyone for your thoughts and ideas,-really interesting and helpful.......

The loco in question is the LB&SCR "Grosvenor" a very handsome beast! I like the simple idea of using one of the high level mini gearboxes (micro miser) on the rear fixed axle, rocking the front axle and weighting and springing the big driver,I'm guessing this will allow a lot of weight to be put on and around the driver and centre of gravity. To be honest I can't quite get my head around the mathematics of the CSB's :-)

cheers Michael

[N15class]

You are not the only one. All the things I have read are all for 4mm I work in 7mm. Plus I have never figured out how you can work out all the positions and loadings when you have not built the thing.

[buffalo]

You are not the only one. All the things I have read are all for 4mm I work in 7mm. Plus I have never figured out how you can work out all the positions and loadings when you have not built the thing.

Scale is irrelevant as you are dealing with measurements along a single axis (the frame). Admittedly all the examples on the clag site are 4mm, but you just need to start from the correct wheelbase dimensions for your scale. As to weights, well, you use experience to design to an estimated target weight and try to stick as close as possible to the designed weight distribution. If your end result is heavier or lighter, you add or remove weight and/or adjust the spring thickness. AFAICS there's no reason why the clag spreadsheet should not work at any scale.

 

Nick

[billbedford]

To be honest I can't quite get my head around the mathematics of the CSB's :-)

 

Maths? what Maths?

[bertiedog]

I think things are getting too complicated, the Sharman method places extra weight on the driver, leave it un-sprung, and just spring the lead and trailing wheels, if a drawbar is used between the tender and the loco in addition to the transfer beam this will stop any pitching under load. the track being P4 should be accurate, and you are just aiming at as much weight as possible on the driving wheels.

 

The lead and trailing springs will be there to balance things, that is all.

 

Even less complex, make the main driver unsprung, along with the trailing wheels, and just get the loco level, the only moving sprung wheel would be the lead axle, lightly sprung to ride the track. The Sharman pivot point moves to under the firebox with this variant, pulling the driving axle and the trailing against the track.

P4 track should allow this to work just fine,

 

The trailing wheel could be cross pivoted, a sleeve bearing pivoting about the middle, no springs, but able to adjust to the track, and still maintain the loco level without pitching.

 

The final effect is a rigid pair of drivers, pivoting trailing axle, with weight transfer from the tender to between the axles, and a lightly sprung front axle, I am willing to bet that this is the easiest and least complex solution, and the ride and traction would be superb.