Gear Ratios

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simon - 29 Jan 2010 23:32 GMT

Putting a new motor and gears in a K's Johnson 0-4-0T. Its tiny, about
length of tender so need tiny motor. But was wondering gear ratios. Now in
simple terms if its an
Express with big wheels then use 38:1
Slow freight eg 4F with heavy load, 20mm wheels then 50:1
Express freight eg cauliflower with modest load, 20mm wheels 38:1

But what would the team recommend for Johnson 0-4-0 T with its expected slow
speed, just few wagons, wheels 15mm ?

Suggestions wellcome and corrections to basic assumptions.

Cheers,
Simon

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Nigel Cliffe - 30 Jan 2010 08:38 GMT

> Putting a new motor and gears in a K's Johnson 0-4-0T. Its tiny, about
> length of tender so need tiny motor. But was wondering gear ratios.
[quoted text clipped - 7 lines]
>
> Suggestions wellcome and corrections to basic assumptions.

I'd be looking at higher ratios. Similar sized locos are available in kit
form from High Level, they come with 100:1 (or thereabouts) gearboxes. High
Level kits are very good, run superbly; I have built quite a few.

High Level's gearboxes are available as components; try one with a small
Mashima motor.

http://www.highlevelkits.co.uk/

- Nigel

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Nigel Cliffe,
Webmaster at http://www.2mm.org.uk/

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Paul Boyd - 30 Jan 2010 13:09 GMT

> Putting a new motor and gears in a K's Johnson 0-4-0T.

> But what would the team recommend for Johnson 0-4-0 T with its expected
> slow speed, just few wagons, wheels 15mm ?

I'd agree with Nigel 100% - I would use something like 80:1 or 100:1
using one of High Level Kits gearboxes. There isn't a model that one of
these won't fit one way or another, and there's a PDF you can download
showing the various gearboxes actual size for planning. I use these
almost exclusively.

Cheers

Signature

Paul Boyd
http://www.paul-boyd.me.uk/

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simon - 30 Jan 2010 21:37 GMT

>> Putting a new motor and gears in a K's Johnson 0-4-0T.
>
[quoted text clipped - 8 lines]
>
> Cheers

I know, I know, thats how should do it. Tis just that had enough of learning
curve without doing more. Will ponder.....Did read last night that these
engines were rated to pull 35 empty wagons or 25 full at Burton shed so
maybe you are right.

Cheers,
Simon

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Paul Boyd - 31 Jan 2010 10:25 GMT

> I know, I know, thats how should do it. Tis just that had enough of
> learning curve without doing more. Will ponder.....

Well, if you're on a learning curve than High Level Kit's gearboxes are
ideal because they go together nicely without lots of faffing about
trying to mesh gears. About the only "specialist" tool you'll need is a
broach to ease out the bearing and idler shaft holes to be a snug fit -
and that's true of any quality etch.

Taking Greg's point, yes, if you do want occasional bursts of speed then
60:1 might be better. It's really up to you! If you do go for an HLK
gearbox, then the worm stage can be changed at a later stage if you
change your mind about the ratio. Incidentally, HLK's gearboxes use
multiple stage reduction gearing so there are no high reduction worm and
pinion gears so setting up is easy.

Cheers

Signature

Paul Boyd
http://www.paul-boyd.me.uk/

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simon - 01 Feb 2010 21:54 GMT

>> I know, I know, thats how should do it. Tis just that had enough of
>> learning curve without doing more. Will ponder.....
[quoted text clipped - 13 lines]
>
> Cheers

Must admit was a bit concerned about the speed cos of small wheels. Had made
that mistake with Cauliflower by putting a 60:1 gear and it didnt half whirr
when trying to go express freight speed. Just so happens that cauliflower
has a small diameter motor with that 60:1, so have removed them and put it
into the Johnson tank. Had to do a bit of fettling but its in and the
enclosed motor will look excellent as bottom half of boiler when painted
black. Swapped pickups from (steel ?) wire to phosphor bronze and its now a
nice little runner. Will see what its pulling power is when add couplings.
Doubt if ran on mainline very often as some of them only carried 400 galls
of water and no coal bunker.

Thanks for advice
Simon

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Greg.Procter - 31 Jan 2010 00:59 GMT

> Putting a new motor and gears in a K's Johnson 0-4-0T. Its tiny, about
> length of tender so need tiny motor. But was wondering gear ratios. Now
[quoted text clipped - 10 lines]
> Cheers,
> Simon

The K's motor was fairly low reving whereas any modern
small motor will run to impossible revs. (say double the K's)
If you want the 0-4-0T to occasionally run on the mainline
then 80:1-100:1 will be too great a reduction because
the loco will take forever. The other downside of high
reduction ratios is the noise (you might not care, of course)
The high revs will wear the motor bearings much quicker
than a lower reduction.
High reduction worm and pinion gears are much finer than
the common ratios and so require much more careful setting up.

If you can change the gear ratio later I would suggest
trying 60:1.

One system I've made use of is putting a large pinion
(spur gear) on the driven axle and a small pinion or
spur gear on the gearbox axle so that a lowish
reduction ratio is multiplied 2 - 2.5 - 3 times.
I have to admit I first did this because I
only had a Tri-ang worm/pinion in my parts box
and nothing suitable could be bought in NZ.
The gearbox axle mounted gear can sit anywhere around
the driven axle gear so it gives a better choice of
motor location.

It's apparently common to use a spur gear reduction
before the gearbox, but I reject that as being too
buzzy with the spur gears running much faster than after
the worm-drive gearbox.

Regards,
Greg.P.

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Model Forum / General / Railroads / February 2010

Gear Ratios