Because the motor produces such little torque, an extremely low friction support is required. At the "far"
end of the motor are two circular magnets mounted to the base. (Actually, two clusters of magnets. The magnets are doubled-up
These two magnets in the base (two sets of magnets actually) provide a force 'well' for the shaft
to sit in. The magnets on the shaft are repelled by the two magnets mounted in the base.The key part, which is hard to
see in the photos, is that the magnets on the shaft are set slightly to the left of the base magnets (offset slightly toward
the armature's arrow head). This produces a slight force that serves to push the arrow head into the glass plate.
the arrow head the structure is repeated; two magnets in the base and a magnet on the shaft, with the shaft magnet offset
slightly toward the arrow head.
The offsets discussed above, which provide the lateral force pushing the arrow head
into the glass, are actually created and adjusted by the location of the glass plate. If the glass plate is too close to the
base magnets (too far right), the arrow head will not be pushed into the glass plate. If the glass plate is set too far away
from the base magnets (too far left) the armature (the rotating part of the motor) will fall down -- off to the left.It may
sound more complicated than it is.
It is easy to get right, believe me. A look at the pictures will help.
Solar Motor Drive
There is a magnet on the base of the motor (under the armature) that provides a verticle magnetic field for the
part of the coil that is closest to the base. This magnetic field, combined with the current flowing through the coil closest
to the magnet, generates the rotational force.
This motor, like many DC motors, has a requirement that the current
flowing through the coil reverse itself every 1/2 rotation. This solar motor works by having the solar panels automatically
reverse the current in the coil as it rotates.
It does this by having TWO solar panels for each coil. The panels are
on opposite sides of the armature so that when one is on top, the other is on the bottom.
When one panel is illuminated
(the panel on top) the current flows clockwise. When the other panel is illuminated (because it rotated to the top), this
second panel drive current through the coil in the opposite direction as the first panel.
The easiest way to understand
this is to look at the simple schematics picture. It shows two solar cells (panels) connected to the coil.
of this design is that if both panels are illuminated equally (light coming from above and below), the motor will not spin
at all. Can you see why? All of the current flows in a circle around through the cells, with no current flowing through the
Other Useful Information
There are two coils on the armature. The schematic above shows one -- the second
is an exact duplicate of the first. The second coil is mounted at a right angle to the first (rotated 90 degrees with respect
to the first coil).
The coils are wound with 30 gauge wire. I used 200 feet per coil, which turned out to be around
260 wraps around the armature base.
The aramture base is a block of balsa wood. The shaft is an aluminum crossbow
bolt (arrow shaft).
There are three solar cells per panel. Each cell is rated at 100 mA at 0.5 volts in full sun. Buy
them at www.solarworld.com. The three cells are wired in series, so that they generate 100 mA at 1.5 volts in full sun.
The motor does not need
full sun! If built for efficiency, as I did, it easily runs in very low light, such as ambient office lighting.
solar cells are not pre-wired. They are tricky to solder the wire onto them. I recommend searching the web for instructions.
I used regular leaded solder with rosin core. I touched them ever-so-briefly (0.1 second) with the soldering iron to leave
some solder behind, which I could then later quickly tack the 30-gauge wire to.
The arrow head contacts a piece of regular
glass. Nothing special there, just keep the glass verticle to the base.
The magnet in the base is a key bit of the motor.
I used a curved rare earth magnet, purchased surplus, which used to be part of an electric generator. A rectangular flat magnet
will work too.
In summary, there are many little pieces of technology, but the motor is pretty easy to get right. The
construction difficulty is not easy or medium -- definitely "hard." It is best if you have good soldering
skills, and the ability to think about the theory of the motor so that you get the polarity of the cells correct. Make sure
the current flowing through the bottom of the coil flows from left-to-right every time that part of each coil is closest to
the base magnet.
More Detailed Wiring Help
you have wound one of the coils. You have two wire ends. Lets say one wire end is on the right side (near the verticle glass
plate) and the other wire end is on the side of the coil furthest from the glass plate.
Let's call the wire end
closest to the glass plate wire end 'A' and the one on the opposite side 'B'.
I wired three solar
cells in series (+ to -) to form each "panel" of solar cells.
The coil gets wired to two panels
simultaneously. In other words, each of the two coils in the motor is associated with (wired to) two panels. Let's call them
panels '1' and '2'.
Of course, each solar cell panel has two wires, a + output
and - output.
The solar panels
are mounted on opposite sides of the armature. You can think of mounting them on top of the coil wires, one on each side of
the armature, but you want the wire in the coil to be very close to the magnet, so slide them slightly off to the side (in
between the coils).
Connect wire A to the + wire of the panel on top, and also to the - wire of the panel on the
Connect wire B to the - wire of the panel on top, and also to the + wire of the panel on the bottom.
Note that when the armature is rotated 180 degrees (to put the "top" panel on the bottom), you'll notice
that wire A is now connected to the - output of the panel on top and the + output of the panel on the bottom, which is the
opposite of the original wiring orientation.
This is proper. It is through this "reversal" of polarity
that the current through the coil reverses direction, which is required. This is the commutator action that is required of
The second coil,
which is wound 90 degrees to the first, is connected to panels in the exact same way.
This is a tricky project,
but once you understand the principles, it is fun to modify it and make each one you build better than the one before.