Stripped Down Motor

Date: Mon Feb 24 2003 - 11:05:06 PST

Greg -- My first reaction is to be sure the coil is well balanced, so that it
doesn't sit in one place and draw all that current. If the clips are getting
red hot while the motor is actually running, I guess I'd just try it with
fewer batteries. Below you'll find a general reply that I've sent over the
past couple of years to a few people who have had questions about the motor
-- it covers several aspects, and hopefully will help:

Sorry you had problems. This motor has a reasonably high success rate, but
few motors that you make from scratch are completely foolproof, and their
temperamental nature can indeed be frustrating. Here are a few things to

1. The coil needs to be well balanced. When you spin it by hand it should
turn freely several times, and not immediately settle in one position. If
it's noticeably heavy on one side, try adjusting the positions of the wraps
where the ends wrap around the main coil.
If you're using fairly heavy wire, try making a lighter coil using smaller
wire. If you only have a very few turns in the coil, try adding a few more.

2. The electrical contacts need to be good. Be sure you've removed the
insulation from the ends of the coil where they contact the paper clips. Be
sure the contacts aren't dirty or charred (sometimes this occurs if there's

3. The "painting" of the upper part of ONE of the ends (when the coil is held
with its flat sides vertical) with a felt pen can be important. Be sure you
paint only the top side of ONE of the ends, NOT both ends! This is sometimes
the most temperamental part of the whole thing. I've seen motors where
redoing this painting makes the motor go -- but I've also actually seen
motors also where removing the painting makes it go!! -- some motors tend to
bounce as they go, and if the paint stops conduction on one half of the
cycle, and the bounce stops it on the other, then there's no conduction at
all! So if all else fails, try sanding BOTH ends of the coil!

4. Be sure you aren't using bare wire for the whole coil! The coil itself has
to be insulated. Only the ends should be stripped bare.

5. Be sure that your battery is good. I've seen these motors run on one D
cell, but I've also seen ones that required two or even three D cells, and
I've also seen students put D cells in parallel to provide more current if
needed. A good 6-volt lantern battery should work well.

6. Be sure that your magnets have some reasonable strength, and aren't
extremely weak.

Hope this helps. Good luck!

Don Rathjen
Exploratorium Teacher Institute

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