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Information on the Mendocino Solar Motor

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YouTube video of the motor in action

Note: This version of the motor was optimized for low-light, slow speed applications. It will run faster, with more light, but that was not the goal of this version.

Solar Motor Background

There are two unique features of this solar motor: the magnetically levitated support system and the solar drive mechanism.



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 for strength.)

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.

Near 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.

One implication 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 coil.


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 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.

The 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

Imagine 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 bottom.

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 DC motors.

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.


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