Bargain Geared Motor for motorizing plastic kits

I was at the Edmonton Dollarama store when my eyes lit up on seeing a
handheld battery (2x AA cells) powered pencil sharpener (CDN 2 bucks
only). Right away this was the solution to powering a number of
boats ( Revell Flower class corvette, civilian boats and a fishing
boat) that had bugged me for years as the shaft output is suitably
slow and has a very high torque output. I showed it to my hobby shop
guy and he agreed that it is a real bargain as the motor itself would
have cost more than $2 and the reduction gears more like $15 if sold
in a hobby shop as an independent item.
"the shaft output was suitably slow and had a very high torque
output." Every RC conversion of the corvette on YouTube typically
shows the corvette moving way too fast. This is understandable as
making one's own reduction gears is too complicated and it is
impractical to slow down the motor itself (no guts.) You wouldn't
believe the number of toys and alarm clocks I butchered in my search
for a solution.
I have experimented with several ways to adapt this pencil sharpener
to drive a boat propshaft. This is the best solution, still working
on it, I came up with.
The sharpener comprises a clenched--fist sized conformal plastic
housing. Discard the battery cover and build up (I used foam board
inserts ) the battery recess to be level with the other half of the
flat base. This creates a firm flat base for the sharpener assembly
that I can install with minumum fuss to the bottom of the boat and
with it aligned to the propshaft datum. Solder external wire leads
from the (AA battery) terminals (to the motor) to connect the motor
directly to an external battery power pack.
My battery pack for this sharpener motor is a regular blister pack of
two D cells. I used a solder iron to burn holes into blister plastic
so that I can solder the wires directly onto the D cells inside the
blister packing. Silicone seal the holes to keep water out. Trim the
card to fit the battery pack to the hull equipment installation. The
card should be easy to screw to the bottom of the hull to secure the
battery, a neccessary precaution for RC boating. Fit switches and the
RC equipment connections to the wires. This solution does away with
having to buy a battery holder or the need for a rechargeable
battery. For a buck one should have an hour's or more of motor run
time and just toss the pack away when the juice runs out.
Sharpen a pencil sized wood dowel and let a 3/4 inch stub stick out of
the sharpener. I bought half a dozen sharpeners as they are real cheap
and often Dollarama items don't come around again. Use another
sharpener to make a tight fit point as the taper is slightler longer
than the garden variety pencil sharpener. I haven't done this part yet
but this is my plan. I intend to pare/sand down a 1/4 inch length at
the flat end of the dowel to accept a coil spring The other end of
the spring will fit a metal collet (will make one) attached to the
propshaft. This allows a transition connection from the sharpener's
larger output shaft to a much smaller diameter propshaft . The spring
takes care of any minor motor-propshaft mis-alignment as well as act
as a torque shock absorber. I won't need a universal joint coupler.
At $2 you can afford to take a sharpener apart to see if you can come
up with a better installation. I did and it is still the best to
leave things well enough alone and do what I did.
To fix the sharpened end of the dowel firmly to the gearbox output
remove the steel blade. Replace in the same position, but covering the
whole recess space available, a metal plate bolted down with the same
nut and bolt. Where the plate covers the "sharpener" slot drill two
small holes for tiny wood screws to secure the pointed dowel end. Now
there won't be any slack or backlash.
One more refinement. I am using a brass rod inside a brass tube for
the propshaft and prop tube. The commercial ones are either too
large or too small and don't fit the available props. I have seen
brass tubes soldered vertically on the forward end of the prop tube.
I presume this is a stuffing box to fill with some sort of grease to
keep water from entering through the propeller end of the tube. My
solution is to use a plexiglas square rod (homemade from scrap) large
enough to to drill a hole for the prop tube to pass through it. I'll
drill a reservoir into the plexiglas that will allow cooking oil (non
toxic, biodegradeable) to enter a small hole in the prop tube to lube
the tube as well as keep water out. The plexiglas rod will also serve
as a proptube brace.
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PaPa Peng
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