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Chassis suspension..?

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Ron Laden09/05/2018 08:54:27
1968 forum posts
390 photos

Morning guys,

Yet another beginners question.. sorry.

The 5 inch electric 0-4--0 loco I am designing/building I currently have as a fixed chassis (no axle suspension). I can appreciate that sprung axles can give better running but is it essential or is fixed ok...?

The wheel base I have is 11 inch using 3.1/4" wheels.

Many thanks



Redsetter09/05/2018 11:17:03
132 forum posts

This is not something you should ask model engineers, as many of them will say that of course it should be fully sprung, as per prototype. But you are not making a model - you are making a small locomotive to do a job, and have some fun with.

You can certainly get away without springing on a simple loco that is only going to run slowly, but a bit of "compliance," and not necessarily conventional springs, will improve running as you say, and give better adhesion, and it need not be a lot of extra work.

Look at the earlier Maxitrak 4 wheel locos for ideas. Some have two rigid axles and some have only one axle sprung, or pivoted centrally to provide compensation. These are successful commercial products that pull loads and stay on the track.

Hacksaw09/05/2018 11:35:34
428 forum posts
173 photos

If on a loco one wheel on one side goes over a bump ,and that axle rises, on that side , so that axle is at an angle , why doesn't the axle jam ? Where is the slack ? In the wheel bearing , or axle box sliding bit ?

Redsetter09/05/2018 12:01:56
132 forum posts

It is in the axle box sliding bit.

Ron Laden09/05/2018 14:09:47
1968 forum posts
390 photos

Good question Hacksaw, that had crossed my mind.

I remember looking over a 0-4-0 at a show last year which had sprung axle boxes/blocks, they housed the axle bearing and had two vertical channels machined from top to bottom, one each side of the blocks. The chassis 1/8" steel side frames had a square U shape machined in them which the blocks slid up and down in with two springs mounted at the bottom of the block.

Would I be correct in thinking that the channels in the block sides would have additional clearance to allow the blocks to tilt in and out - top and bottom allowing the angle of axle to change with the movement of the suspension.



Bazyle09/05/2018 17:27:31
5282 forum posts
201 photos

It is a good idea to provide at least one axle with suspension. Model tracks are seldom level and points and joints often have discontinuities.

On a freelance model it is also a good idea to put in guard irons and horizontal stretchers just above the rail level so that when the loco or driving trolley do come off they land on that not crashing down on the sleepers and possibly bending brake gear etc.

Boiler Bri09/05/2018 18:25:58
835 forum posts
197 photos

I made a riding trolley with no suspension. At every bump it de railed. dont know

I now have some. 8 mm travel with springs


Ron Laden09/05/2018 18:40:04
1968 forum posts
390 photos

I must admit I didnt imagine any of this, its all sounding a bit scary...surprise


Redsetter09/05/2018 19:16:51
132 forum posts

Ron, It was certainly not my intention to scare you, as you asked a very sensible question. As you can see there is no hard and fast answer. It depends on what you are trying to do.

For what it is worth, I have two unsprung 4 wheel driving trucks, both give a hard ride but neither is prone to derailments. However the situation with driving trucks is different as they carry more weight than a small electric loco.

It is important for a beginner to get something running, and if you have a simple unsprung design in mind that you can get on the track quickly, why not go for it? It is bound to need improvements of some sort once you have tried it, they always do. I think the key for an unsprung design is to make it as heavy as possible and not to make the chassis too rigid. Others may disagree!

Ron Laden09/05/2018 20:49:49
1968 forum posts
390 photos

Hi Red, well only scary in that my main passengers will probably be both our great grand daughters (5 yrs & 6 yrs) and our local track is a raised one. Not only raised but some of it is on elevated banks so wouldnt want any accidents.

I,m quite happy with my design and I,m hoping that it should run well but I,m now wondering if I should add suspension to improve it further. I went back to my drawings earlier this evening and it wouldnt be that difficult to add spring mounted sliding axle boxes. As it is at the moment the axles are fixed and running in bearings mounted on the chassis side frames.

Will have to give it more thought and decide which way to go fixed or sprung.

Something else which threw me somewhat is the wheel back to back dimension, from GL5 specs I have drawn it up as 4.5/8" - 117.4 mm. I received 2 axles and 4 wheels today and the axles are giving a back to back of 119.2 mm. I,m now wondering if that is too wide but the supplier said it is all to GL5..?



Ron Laden10/05/2018 07:14:35
1968 forum posts
390 photos

Re-visited the design and decided to go with sprung axles, it means some more parts but I think it will be an improvement. My only problem is that apart from a small pillar drill I dont have a lathe or a mill so I have to buy in/get made all machined parts, I do know a couple of people though so that helps.


p.s. Anyone have any thoughts on the back to back measurements..?

Redsetter10/05/2018 07:24:44
132 forum posts

Pm sent.

Howard Lewis10/05/2018 11:26:34
3361 forum posts
2 photos

Am not a loco man as such, but judged by what i saw at the Romney Hythe and Dymchurch Railway, after adjusting the springs on driving axles to give equal loads, they had a lot fewer problems with slippage, and broken springs.

So suspension, properly set up brings benefits.


Bazyle10/05/2018 13:10:17
5282 forum posts
201 photos

Just in case it's not obvious the important thing about back-to-back is for the wheels to pass though the check rails on points but at the same time not be wide enough for the wheel flange to hit the nose of the point frog. However the wheels need a bit of clearance to avoid jamming between two opposing check rails. I suspect your supplier was thinking of this.

Redsetter10/05/2018 13:38:02
132 forum posts

I don't think points will be too much of a problem on a raised track.

duncan webster10/05/2018 14:42:53
2643 forum posts
34 photos

SMEE standard for back to back is 4.687 (119 mm), just looked it up, so is GL5

Edited By duncan webster on 10/05/2018 14:44:15

Ron Laden10/05/2018 19:23:11
1968 forum posts
390 photos

Thanks guys, the GL5 standard I looked at gave 4.625 (117.4 mm) as the back to back but mentions a back to back of 4.687 (119 mm) for better clearance of check rails. Our local track is raised so no points but I may one day visit a ground level track with points.


Neil Wyatt11/05/2018 12:25:19
17970 forum posts
709 photos
77 articles

Springing will improve its adhesion, and therefore its pulling power.

No springing won't stop it working, but it will work better wit at least one sprung axle.

If you want simplicity, copy what I did for my driving truck. Each axle passes through a swinging arm at each end, with a ball race fitted in it. The ordinary ball race happily permits a small amount of mis-alignment over the width of the axle. Springing is just a piece of dense rubber between the arm and the chassis which has the advantage of being progressive and largely indifferent to the exact size and position of the block. It works perfectly, unlike teh original springs with adjusters the blocks replaced (see below).


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