Introduction: Levitating Solar Motor
In this tutorial, we will create a magnetically levitated, solar powered electric motor...woah! That is a lot of cool things in one sentence. This type of motor is called a Mendocino Motor, named after the city in which it was invented, Mendocino, California.
The motor consists of a spinning shaft that is held up by repelling magnets, stabilized by resting a point against a wall. It is powered by solar panels mounted on the spinning shaft, which generate currents through coils of insulated wire.
First, let’s acknowledge that this motor isn’t very powerful. It isn’t useful for getting much work done. You’re not going to power a car with it. But it is a fun science project and a cool conversation piece. We like it because it is a great demonstration of the principles involved in most electric motors.
Step 1: Parts List
Here is a brief list of what we used to build our Mendocino Motor. For the rotor (the spinning portion of the motor):
- 1/2" diameter wood dowel rod, purchased from a local hardware store
- Thin wood from a craft store, able to be cut with a hobby knife
- Hot glue to hold the pieces together (do not use hot glue on neodymium magnets!)
- 30 gauge insulated magnet wire, MW30-4 or MW30-8
- Four solar cells from Futurlec, SZGD5433
- Two RX088 ring magnets
For the base:
- Wood for the base and wall
- Thin piece of aluminum for the wall
- Twelve RX033CS-N magnets. Alternatively, RX038DCB-N52 magnets might also have worked well. Still, we like planning on stacking multiple thinner magnets. This lets you adjust the strength by altering the number of magnets used in each stack.
Step 2: Step 1: Put Magnets on the Shaft
Though it isn’t the most perfectly straight or balanced motor shaft, we used a ½” diameter wood rod that is 10" in length. Wood rods like this are commonly available at hardware or home improvement stores.
For this light load, we placed RX088 ring magnets on the shaft in two locations, near either end. For this demo, the north poles of both magnets are facing the wall. For help identifying the north pole, see Which Pole is North. We used a single D68PC-RB magnet to help in the video.
In the video, we used smaller magnets on the rod and base, but this was just to levitate the rod. In order to effectively levitate the copper wire and solar cells, we need stronger magnets!
Step 3: Step 2: Put Base Magnets in Place
For this demonstration, we chose four sets of 3 RX033CS-N countersunk ring magnets in the base, as you can see in the previous drawing. These magnets are countersunk on the north pole side, which helps to identify which pole is north.
What spacing should be used for the two base magnets?
If the two magnets are very close together, the floating magnet is held higher but isn’t stable. If the two magnets are too far apart, they won’t hold much load. There’s definitely a “just right” distance in the middle. In the video below, we hold up the back end of the shaft by hand, while experimenting with various magnet-to-magnet distances.
After this distance is chosen, the video also shows how the base magnets are set a little further away from the wall than the floating magnet on the shaft. This provides stability, since the shaft tends to tip into the wall. With our setup, we found it to be about 3" center to center.
That’s it! The shaft now spins freely. We've made a pseudo-levitating shaft, which is a great start for making a Mendocino motor.
Step 4: Technical Info- Pseudo-Levitation
There is a common theory in the magnetic world called Earnshaw's Theorem, which basically states that repelling magnets are not stable, and adding more repelling magnets will not make it any more stable. You need some other stabilizing force to make a magnet float in a stable way.
But there is a loophole. Pseudo-levitation constrains the movement of the magnets using some form of a tether or wall. This works because the theorem shows only that there is some direction in which there will be an instability. Limiting movement in that direction allows for levitation with fewer than the full 3 dimensions available for movement.
If we set 2 axially magnetized disc or ring magnets side by side, with their axes parallel, there is a pocket of stability above them. A third magnet can sit in this pocket, but the shaft is free to move along its axis.
If we add a wall to stop this motion, where the levitating shaft starts to move away from the highest point, the wall stabilizes the levitating shaft. By setting the floating magnet slightly closer to the wall than the magnets in the base, the shaft tends to lean against the wall.
With two sets of magnets like this, the shaft is held levitated. It is stable with only one point of contact with the wall.
Step 5: Step 3: Winding Copper Wire
Once you get the rod to levitate and spin nicely, it is time to add the copper wire.
We constructed the rotor frame from light wood, held together with hot-glue-gun glue. It may not be the most accurate construction method, but it was a fast way to experiment with an easily modifiable prototype quickly. We used thin wood from a craft store that was easily cut with a hobby knife.
Start winding the copper wire around the rotor. We made ten turns while keeping the wire on one side of the 1/2" diameter shaft and then ten turns on the opposite side of the shaft.
Winding the wire, we kept a tally on paper to avoid losing count. Make the same winding on the opposite position, crossing the first winding.
We chose 30 gauge (30AWG) magnet wire and used about 1,000 turns in each coil. This was more turns of wire, and heavier than most motors we’ve seen. There are some great looking motors online that use as little as 100 turns. That’s a good thing if you don’t want to use such big magnets – our floating piece weighed in at half a pound. Copper is heavy!
You can find 30 gauge wire like this as MW30-8 in our Magnet Wire section.
Step 6: Step 4: Wire Solar Cells
Once the wire is wound, label the wires so that you can keep track of the direction of the coil and which wire is which. Here we show the first solar cell with wires soldered in place. The tape is only there to prevent tugs on the solder joint during assembly.
We chose a solar panel with higher voltage and lower current ratings. We ordered them from a distributor called Futurlec. We don't have a relationship with them; they're just a place we found solar panels online for a great price.
We wired the panels as shown in the sketch. The sketch shows just one set of panels with a single coil of wire. The coil only shows a few turns, for clarity. In the motor we constructed, we added a second set of panels and coil of wire in the same fashion.
Step 7: Step 5: Technical Details!
What solar panels should be used? How many turns in the coils of wire? What wire gauge should be used? This is where things get complicated. The answers to all these questions are interrelated in all sorts of interesting ways.
We found a few Mendocino motor examples online, where builders include details about what kind of wire they used and how many turns. Many of them show some really dazzling workmanship, much better looking than our rough example! It seems like 100 turns of wire is most common in the descriptions we’ve seen online. What we couldn’t find was a justification that explained why that many turns were used.
By the way, magnet wire is the common name for the single-strand, solid copper wire that has a laquered-on insulation around it, commonly used for motors, transformers, etc.
Before ordering parts for the motor, we had to somehow decide: What solar panels should we get? What gauge of wire? We did some theoretical analysis, comparing various solar cell specifications with various wire gauges and number of wire turns. The results really depended on the interesting ways solar panels work, as well as the shape and design of the motor.
For more technical details, including some analysis and mathematical things, check out our full article here.
Step 8: Step 6: Watch It Go!
In the video below, we set the completed rotor on top of the motor base. Because the rotor assembly was so heavy, a bit over half a pound, we increased the size of the magnets used for both the rotor and the base. The rotor uses two RX088 ring magnets, 1" outside diameter x 1/2" inside diameter x 1/2" thick. On the base, we stacked three RX033CS-N magnets together to form a taller magnet, in four locations.
We show two different magnets set beneath the coil to provide the magnetic field. By hand for our initial testing, see the 1-1/4" diameter x 1" thick DX4X0 magnet held in place. A shorter, 1-1/4" diameter x 1/2" thick DX48 magnet was attached more permanently to the base.
There is a lot more research that can be done on these motors, but hopefully this Instructable can give you some insight into how it works and how to build a cheap version of one! We think its very cool.