Which axle to motorise on 4-6-0?

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jon price
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Which axle to motorise on 4-6-0?

Postby jon price » Mon Nov 28, 2022 1:18 pm

Are there any specific reasons why a particular axle is better for motorisation of a 4-6-0 tender engine, or a 4-6-4 tank which are likely to be built with fixed axkles, no suspension?
Connah's Quay Workshop threads: viewforum.php?f=125

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zebedeesknees
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Re: Which axle to motorise on 4-6-0?

Postby zebedeesknees » Mon Nov 28, 2022 5:34 pm

jon price wrote:Are there any specific reasons why a particular axle is better for motorisation of a 4-6-0 tender engine, or a 4-6-4 tank which are likely to be built with fixed axkles, no suspension?

The one that was driven on the real loco? Better modelling, and less strain on the rods than driven from one end.

Ted.
(A purists' purist)

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Jol Wilkinson
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Re: Which axle to motorise on 4-6-0?

Postby Jol Wilkinson » Mon Nov 28, 2022 8:28 pm

Not all 4-6-0s were driven on the centre axle, but as Ted implies, driving the centre couple axle is best as it also reduces the effect of clearances in the crankpins and bearings.

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John Bateson
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Re: Which axle to motorise on 4-6-0?

Postby John Bateson » Tue Nov 29, 2022 7:10 am

And of course there were prototypes that were driven on the leading and centre wheels, leaving the rear wheel to keep up as a coupled wheel to the centre driver. :twisted:
Anybody for two synchronised motors in one of these?
John
Slaving away still on GCR stuff ...

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jon price
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Re: Which axle to motorise on 4-6-0?

Postby jon price » Tue Nov 29, 2022 7:24 am

Thanks for this advice. I will go for the center axle.
Connah's Quay Workshop threads: viewforum.php?f=125

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jim s-w
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Re: Which axle to motorise on 4-6-0?

Postby jim s-w » Tue Nov 29, 2022 8:21 am

A few things not mentioned is will the gearbox be visible on the center axle and the center axle is usually the one set up with the most side to side movement (ot the most flexibility generally).

The RTR guys tend to use way more flimsy coupling rods than we do and they tend to go for the rear axles. There must be hundreds of thousands of 4-6-0 out there and it's not a problem you ever really hear about.
Jim Smith-Wright

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davebradwell
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Re: Which axle to motorise on 4-6-0?

Postby davebradwell » Tue Nov 29, 2022 9:18 am

Driving the same axle as the prototype might be the ideal - the coupling rod will have a longer bearing in this crankpin - but that doesn't necessarily exclude the rear as long as you don't use those separate bits of coupling rod that overlap on a crankpin. The leading axle will usually be a no no as we often end up with a thin boss and short bearing.

If there's some clearance in the rods, it doesn't look good if the wrong axle turns first when starting.

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Proton
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Re: Which axle to motorise on 4-6-0?

Postby Proton » Tue Nov 29, 2022 11:34 am

And just to be a smart a55, the UP Challengers were driven on the last axle...

John

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Will L
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Re: Which axle to motorise on 4-6-0?

Postby Will L » Tue Nov 29, 2022 12:45 pm

In our fine scale lives, where jointed rods are the order of the day, there is always the possibility of a little lost motion on each joint. Thus It is marginally more difficult to ensure you get a bind free chassis if you drive the first or last axle on any 3 driven axle chassis. However no worse than is inevitable if you want to build anything with more than 3*. A little extra care needed perhaps but nothing we shouldn't be able to overcome, so in my life I tend to put the drive were I can best hid it, which tends to be under the cab on the 3rd axle. This also means you not trying to put side play on the driven axle.

* That said I think the centre (flange less) axle of a 9F maybe the only sensible choice. 4 coupled locos are best driven on the third axle as this leaves you able to put side pay on the 2nd and 4th axle which works well

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zebedeesknees
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Re: Which axle to motorise on 4-6-0?

Postby zebedeesknees » Tue Nov 29, 2022 3:52 pm

Proton wrote:And just to be a smart a55, the UP Challengers were driven on the last axle...

John


As were the USA 0-6-0 tanks on the Southern. So that's where I would drive mine if I ever got round to building one.

But oh! - the prototype equalisation...

Ted.
(A purists' purist)

Enigma
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Re: Which axle to motorise on 4-6-0?

Postby Enigma » Tue Nov 29, 2022 3:54 pm

Will L wrote: 4 coupled locos are best driven on the third axle as this leaves you able to put side pay on the 2nd and 4th axle which works well


Er, a 4 coupled is an 0-4-0. I presume you mean an 8 coupled 0-8-0?

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Will L
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Re: Which axle to motorise on 4-6-0?

Postby Will L » Tue Nov 29, 2022 11:11 pm

Enigma wrote:
Will L wrote: 4 coupled locos are best driven on the third axle as this leaves you able to put side pay on the 2nd and 4th axle which works well


Er, a 4 coupled is an 0-4-0. I presume you mean an 8 coupled 0-8-0?

Depends if your counting wheels or axles. Doing CSB calculations has meant I tend to think in terms of axles But yes I could have expressed it better


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