Revisiting Mendocino Motors
Some time ago, we had a great time making a two-part series describing a Mendocino motor. It’s a simple demonstration motor that spins, powered by sunlight. Made with magnets, insulated wire and a few solar panels, it’s a really cool project.
Over the course of explaining and demonstrating how it works, we created a rough prototype to demonstrate the pieces. It wasn’t pretty, but worked well enough to show the concepts. Since then, we’ve been asked about how to build a better one, and what magnets should be used.
Here’s our second try!
The demo we built last time was okay, but there are things we could have done better. We used a lot of wire, which resulted in a really heavy rotor. Copper is heavy – who knew? It was hard for this heavy rotor to get started. Less wire would have been better.
The other problem we found was that the levitating rotor wasn’t very stable. When spinning at slow speeds, the rotor tended to wobble quite a bit. If the wobble motion got too large, it could throw itself off. Unless you build something to constrain the rotor from flying off, this isn’t something that you can build and expect to just leave on your windowsill.
In proposing a better design, we found ourselves divided into two camps. One side wanted to make a vertical motor configuration, where the spinning rotor hangs down. The other side wanted to stick to the horizontal configuration with its pseudo-levitation, arguing that the cool-factor of this was an essential part of the demonstration.
In the end, we built examples of both. We found pros and cons for both.
Here's the new, vertical-axis Mendocino Motor in action:
Here's the more common Mendocino motor, with the rotor axis in a levitationg, horizontal position.
There’s a great technical explanation about how and why these things spin in our original Mendocino Motor article. Here’s the short explanation:
This explanation is true for both the vertical and horizontal motors we made.
Even after building these two working motors, opinions here are still mixed. The vertical setup is easier to recreate, more forgiving, and works quite well. For something that’s going to sit on a windowsill and just run, however, it’s often not facing in the right direction. The horizontal motor is more apt to just spin as long as sunlight is shining in the window.
If you’ve built one of these motors, please let us know. Share your pictures, and maybe we’ll add some of the best here!
In this configuration, the spinning rotor hangs down, making it quite stable. Even if uneven forces push it to the side, gravity tends to keep it hanging down.
Cycle through the pictures to check out our design. We used 30 gauge magnet wire and some inexpensive solar panels from Jameco, which had dangling wires included. They aren't the biggest, but they're affordable. Plus, they come with two wires dangling off, so that no soldering was required!
The structure was printed on a 3D printer. It's a great way to create parts that are accurate and balanced well, though not strictly necessary. You could build a similar device with other materials for your own project. If you'd like to use our 3D model shapes, you can download them here:
You'll also need:
In bright light or strong sunlight, this motor works quite well. To get it to spin in moderate sunlight, we used some very powerful magnets on the sides. The 1" diameter x 1/2" thick DX08B-N52 discs provided a strong field in the gap between them. Be careful handling powerful magnets this large!
This thing spins great. It’s a wonderful demonstration that gets a lot of oohs and aahhhs. That said, there are still some drawbacks that we’d love to improve:
Our earlier horizontal Mendocino motor was constructed out of magnets screwed to scrap wood. It was far from perfect or stable. We assumed that much of the stability issue could be solved by holding the magnets in a more square, stable, tighter toleranced and repeatable way. Armed with a 3D printer, we figured we could print a base to hold the magnets exactly where we wanted them.
Back when we first described these motors, we dedicated the whole first article to describe how the floating rotor is held, balanced and supported. It’s a touchy thing, requiring the right magnets and distances to be stable.
In this round, we found that even with a higher precision setup, getting it to balance was still challenging. Don’t expect to construct one of these things and have it just work right away. It takes a lot of fiddling with the positions of the magnets to get things just right.
Here are the 3D model files you see in these photos:
You'll also need the mirror, the pencil, the 30 gauge magnet wire and the magnets:
After getting the balance right, we ended up with a really nice result. It looks great and performs well.
Ultimately, we still aren’t 100% happy with the stability. Like many magnetic levitation ideas, this stuff is harder than it looks.
Left alone, the rotor can wobble enough during startup to break free and slam to attract to the base magnets. To address the problem, we added a feature that constrains the end of the rotor. It’s a small detail, but an important one for safe operation. It prevents the floating part from flying loose and damaging anything.
In our last article, we discussed a few ways neodymium magnets could be used as magnetic latches or closures for cabinet doors. We ended that one with a teaser about how neodymium magnets might be used to re-magnetize an old closure with a ceramic magnet to be as strong as it was when new. Let’s do it!
Magnetic closures are commonly used to hold doors and drawers closed on everything from furniture to cabinets. Usually, these closures are products made with magnets and other parts (steel, plastic, etc.) that make a magnetic closure. We don’t sell any products or assemblies like this, but that doesn’t stop folks from using powerful neodymium magnets for this purpose.
This month, we’ll take a look at a few solutions that work well.
Star Wars X-Wing Miniatures Game is a tabletop game that’s become popular very quickly over the last few years. It’s a game that’s played on any tabletop (there’s no board), where you enact spaceflight battles using models of X-Wings, TIE Fighters and other spaceships from the Star Wars universe.
In addition to being a fun game, the tiny miniatures are quite detailed and look really great. Some folks buy them for decoration without any intentions of playing the game.
How to re-magnetize a flexible refrigerator magnet...