In a message dated 6/2/00 10:49:06 PM Pacific Daylight Time,
<< determining motor RPMs >>
For HOn3, motor RPM may be the most limiting factor for engine speed. In
brass models almost all of the manufacturers seem to have used a gear ratio
of around 28:1m the NWSL gearboxes designed to fit HOn3 models typical axle
size of 2.4mm also use this gear ratio. Some older Japanese models have axle
gears virtually identical to the NWSL gearbox. Unlike standard gauge, the
wheel diameter for narrow gauge engines seems to be within a fairly limited
range of 36" (C-16) to 44" (K-36), for example. with the same gearboxes and
a driver size range of 20% + / -, the big variable in model operations tends
to be motor rpm.
AS an example, the sunset C-16s and the WSM k-36 used completely different
motors but both had 12 volt RPMs around 5,000. By comparison a Sagami 1420
had a 12 volt rpm of 28,000, and a Sagami 1630 (about the strongest, best
running Sagami motor for HOn3 use) has a 12 volt rpm of 15,000. Comparing
the sunset C-16 mashma motor to a similar sized Sagami 1420 you see that for
HOn3 models you can find motor rpms varying by almost 600%, far more than can
be oversome by the typical gearbox and driver diameter changes. Unfortunately
the coreless 1230 used in the WSM K-36 is pretty gutless and needs the
increased gear ratios typically found only in geared (logging) steam engine
By the way counting teeth on the gears in a model shay, climax or heisler
can lead you to a big mistake. For instance the WSM Westside Lumber Co. #3
used two worm/worm gear reduction sets in the gearbox; each worm gear had 15
teeth, I calculated the total gearbox reduction as 225:1 (15x15=225), boy was
I wrong. These models used a double spiral worm (instead of the typical
single spiral worm), so the gear reduction was only 7.5:1 and the total
gearbox was only about 56:1, a big difference.
The big problem with small motors, is that some run slow normally and others
only because they are underpowered and overloaded by the mechanism. With
NWSL motors having published specs, this can be determined, but many of these
models have motors for which the importers/builders have not furnished data.
A lot of modelers use the trial and error method of motor selection, while
others stick to 'if it ain't broke, don't fix it...'