A motor in 10 minutes
Back in the 1960's my father taught me how
to make the little electric motor we will make
here. Sometime in the 1980's I saw a
description of it in the magazine "Physics
Teacher". Lately I have seen it described as
Beakman's motor, after the science oriented
TV show on which it recently appeared.
The motor is simply a battery, a magnet, and
a small coil of wire you make yourself. There
is a secret to making it (which I will of
course share with you) which is at the same
time clever and delightfully simple.
What you will need:
A battery holder, such as Radio Shack
#270-402 (holds a "C" cell) or #270-403
(holds a "D" cell).
A battery to fit the holder.
A magnet such as Radio Shack #64-1877,
#64-1895, #64-1883, #64-1879, or
#64-1888.
Some magnet wire such as Radio Shack
#278-1345. We want enamel coated 22
gauge (or thicker) wire. We will only need
about a yard of wire, so the Radio Shack
package will make a dozen motors or more.
Some heavier wire such as Radio Shack
#278-1217 or #278-1216. We want bare
wire of 18 or 20 gauge, so we will be
removing the plastic insulation from the
wires listed above. We will need less than a
foot of this wire per motor.
A quicky motor
We start by winding the armature, the part
of the motor that moves. To make the
armature nice and round, we wind it on a
cylindrical coil form, such as a ball point pen
or a small AAA battery. The diameter is not
critical, but should be related to the wire
size. Thin wire requires a small form, thick
wire requires a larger form.
Leaving a couple of inches of wire free at
one end, wind 25 or 30 turns arounf the coil
form. Don't try to be neat, a little
randomness will help the bundle keep its
shape better. The coil will end up looking
like the photo below:
Now carefully pull the coil off of the form,
holding the wire so it doesn't spring out of
shape.
To make the coil hold its shape permanently,
we will wrap each free end of the wire
around the coil a couple of times, making
sure that the new binding turns are exactly
opposite each other, so the coil can turn
easily on the axis formed by the two free
ends of wire, like a wheel.
It is not necessary, but I usually wrap a
couple turns around these binding turns as
well, threading the wire into the space
between the large coil and the small coils
that hold it together. This makes for a neat,
tight package, as in the photo below:
If this method of holding the coil together is
too difficult, feel free to use scotch tape or
electrical tape to do the job. The important
thing is to keep the coil together, and to
have the two ends of the wire anchored
well, and aligned in a straight line, so they
form a good axle.
Now is where the secret trick comes in, the
thing that makes the motor work. It is a
secret trick because it is a small and subtle
thing, and is very hard to see when the
motor is running. Even people who know a
lot about motors may be puzzled until they
examine it closely and find the secret.
Hold the coil at the edge of a table, so the
coil is staight up and down (not flat on the
table), and one of the free wire ends is lying
flat on the table. With a sharp knife, remove
the top half of the insulation from the free
wire end. Be careful to leave the bottom half
of the wire with the enamel insulation
intact. The top half of the wire will be shiny
bare copper, and the bottom half will be the
color of the insulation. A quick sketch may
help:
Do the same thing to the other free wire
end, making sure that the shiny bare copper
side is facing up on both wire ends.
The idea behind the trick is that the
armature is going to rest on two supports
made of bare wire. These supports will be
attached to each end of the battery, so
electricity can flow from one support into
the armature and back through the other
support to the battery. But this will only
happen when the bare half of the wire is
facing down, touching the supports. When
the bare copper half is facing up, the
insulated half is touching the supports, and
no current can flow.
The next step is to make the axle supports.
These are simple loops of wire that hold up
the armature and allow it to spin. They are
made of bare wire, since they will also act to
get electricity to the armature.
Take a stiff piece of bare wire (copper or
brass will work, as will a straightened paper
clip) and bend it around a small nail to make
a loop in the middle, as shown in the photo
below. Do the same to another wire, so you
have two supports.
The base for this first motor will be the
battery holder. It makes a nice base because
it is heavy when the battery is installed (so
the motor won't wobble) and because it has
convenient holes in the plastic where we
can attach the bare wire armature supports.
Attach the support wires securely to the
battery holder by winding the free ends
several times through the small holes in the
plastic at each end. Bend the support wires
so the rings are just far enough apart for
the armature to spin freely. Bend them apart
a little and insert the armature into both
rings, then bend them back so they are close
to the coil, but not touching it.
Insert the battery into the holder. Place the
magnet on top of the battery holder just
underneath the coil. Make sure the coil can
still spin freely, and that it just misses the
magnet.
The finished motor looks like this:
Note that there is a strip of paper stuck in
between the battery and the electrical
contact in the holder. This is the on/off
switch. Remove the paper to allow electricity
to flow into the motor, and replace the
paper when you want to stop the motor
and save the battery.
Spin the armature gently to get the motor
started. If it doesn't start, try spinning it in
the other direction. The motor will only spin
in one direction.
If the motor still doesn't start, carefully check
all the electrical connections. Is the battery
connected so one support touches the
positive end of the battery, and the other
touches the negative end? Is the bare
copper half of the armature wire touching
the bare support wires at the bottom, and
only at the bottom? Is the armature freely
spinning?
If all these things are correct, your little
motor should be spinning around at a pretty
fast rate. Try holding it upside down. The
motor should spin in the opposite direction
if the magnet is on top instead of on the
bottom. Try turning the magnet upside
down and see which direction the motor
spins. If you want a motor that has the
magnet on the side instead of the top or
bottom, you can simply make a new
armature, but this time lay the coil flat on the
table when you scrape the insulation off of
the top half of the free wire ends.
