[modeleng] Motor requirements

Well, I have finally surcumbed to the lure of the loco, and gone loco! My 
3.1/2" gauge train now has a chassis, and both front and rear bogies, all in 
wood in true Richard Blizzard fashion though, so perhaps I should not be 
mentioning it here .... <VBG>
It is a scratch built 4-6-2, with 3-axle tender, all to be made from polished 
hardwoods, and not "hard words" as I just mistyped - they will come later! As I 
am working from the bottom up, I need to decide on the drive train next, so as 
to be able to design the body around it. The idea is for it to look like a 
steam loco, but be electrically driven, but more Basset Loake than Hornby 
Triang, hopefully! With an overall length of nearly 30", at least I have given 
up on the Basselt Loake clockwork motor idea though .... I am therefore 
thinking of putting a battery (or batteries) in the tender, with a disguised 
power cable through to an electric motor in the loco proper.

Chatting to Al and Tel off list, I have come round to the idea of either a 
cordless electric drill or a recycled windscreen wiper motor, though whilst out 
shopping today, I saw some of the big 6-volt zinc lamp batteries, the ones 
(very) approximately 2" square and 3" high, for only £2 each and so may look 
into a 6-volt motor as well. I had thought about trying to find such as a small 
motocycle battery to fit into the tender, but decided that the additional 
weight made matters worse, not better, taking me into the lands of diminishing 
returns, incidentally. My problem is that while I have the bit of garden where 
the fruit trees are for some track, it is only 30' x 40' at the most, and so it 
would be a very twisty one at this size, round those trees, and so what design 
speed should I aim for please, so that I can determine how powerful a motor 
will be required?

From my working days, the clearance times for pedestrian crossings were based 
on 1.2 metres (4 feet) per second, so should my train go faster or slower than 
that, bearing in mind the lack of long straights where an express could be 
wound up to maximum speeds? Should I be able to keep up / catch up with it in 
the event of an accident, such as when Unka Jesse fell off his and could then 
only watch it disappear into the distance until it (literally) ran out of steam 
? As my driving wheels are 2.1/2" diameter, I did a bit of mental arithmetic to 
work out that at 3mph, a brisk walking pace but not rushing, the wheels would 
be doing around 225rpm.

If I was to use a cordless drill with a natural speed of 900rpm to 1,000rpm, it 
would need to be greared down rather than using the standard sort of speed 
control, as these are inclined to over heat if used for a prolonged period of 
time. I would need a pulley ratio of 4:1 if I was to use the flexible drive 
belt that I am looking for. 1" to 4" would give me problems in housing the 4" 
pulley, whereas 1/2" to 2" might well give me slippage problems on the 1/2" 
one, however. Physical gears has (for me) the problem of achieving alignment as 
well as maintaining it due to possible moisture movement of the timber frame 
and chassis. This as well as being far noisier, though nylon gears might get 
around that if they could take the loadings.

I am open to any help, ideas and suggestions that the Group may come up with, 
please, but precision engineering is just not possible for me I am afraid, as 
bittter experience has shown far too often.

Thank you,

Tony.

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