[modeleng] Re: Motor requirements

My initial thoughts are:
A toothed belt for the drive. Available in a wide range of sizes, they allow 
simple adjustment for tension thus facilitating wheel movement etc.

As for speed, 3 -4 mph is about all that you will need as a maximum. There 
are lots of options for motors, and of course for batteries. Probably best 
to decide on one, and then select the other to suit.
At a very rough guesstimate, you will need at least 1/8 HP, preferably much 
more, to use it for passenger haulage.
(depending upon gradiant, track and wagons and many other factors.)

I reckon 6 volt is too low and would look at 12 volt. Thinner cable and 
simpler controls with the lower currant compared to 6 volt at the same 
power.
For the motor, my personal choice would be ex-car motors of some sort. But, 
this depends upon what you have / can scrounge.


Alan Stepney

http://www.alanstepney.info
Model Engineering & steam engine information pages
----- Original Message ----- 
From: "Tony Wells" <oaksfield@xxxxxxxxxxxxxxx>
To: <modeleng@xxxxxxxxxxxxx>
Sent: Tuesday, May 29, 2007 7:50 PM
Subject: [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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