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How To Balance a
Slot Car Motor:
Balance to a slot car motor is of great importance and makes a
motor great or a dog. Another area of balance that matters to slot
racing and is often not thought about or considered important involves
the running gear. This consists of the rear wheels, gear and axles. Not
many racers put flats on the axles anymore so we can forget them for
now.
Most wheels today have aluminum or magnesium hubs. Many now come with
two setscrew holes opposite each other. They tend to only come with one
set screw though. What we have to balance is the rotational mass of the
set screws and the missing material from the holes as the wheel rotates
at high revolutions.
The set screws can be short or long. Solid or with a thru hole. They
vary in weight and or mass. When a wheel and tire rotates with out holes
it is fairly well balanced. As you remove material for the holes it
tends to affect the rotational frequency and or balance of the wheel.
The then added weight of the one or two set screws will again affect
this balance. The same applies to the gear hubs. The two wheels and gear
combined make for some real unbalanced conditions.
Try this for your self. Just randomly slap some new wheels on a car
and spin it up with a power supply. Listen to the sound pitch and rpm
level with the running gear in motion. Next rearrange the location of
the set screws in the wheels and gear on the axle in relation to each
other. First put them about 120 degrees apart. Spin it up again and see
if your hear a difference. Try next time to put both wheel screws on the
same side of the axle and the gear screw 180 degrees away. Spin it up
again and listen for the difference in pitch and apparent rpms.
The best way to see this is with a good current meter between 1-5
amps. Connect it in series with the plus side of the power supply. Now
spin up the motor and take a reading. Play around a bit with screw
location and when you get it near perfect you will see that the current
draw is at it's least and the perceived rpm level will be at it's
highest level at the same relative power levels. A tachometer would be
nice (dreamer) but impractical for most.
Depending on the number of holes in the wheels and gear, the length,
weight and number of screws used, you may have to play around to find
the best locations. Once you find what works remember them when
replacing with similar wheels and gears. If you can replace them as
close as possible the entire car will sound and run better especially
the fast ones. (have fun)
Larry Shephard
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