This is a really cool and simple project that makes for an excellent desk toy. It clearly demonstrates the strong diamagnetic properties of bismuth in a really satisfying way.
Ever since I was young I've wanted to make or have something that levitates or floats. I've always been amazed at magnets and their invisible strengths and all the cool things that they could do. And so naturally, when I came across bismuth magnet levitation on the internet, I had to give it a go. So join me on my first instructable and we'll break the laws of gravity together! (not really but it sounds cool)
Step 1: The Science Behind It All
Before we dive into the build, lets just talk a little about how it all works.
Like I mentioned, the levitator works by utilizing the strong diamagnetic properties of bismuth. There are many other diamagnetic materials other than bismuth, however bismuth is very strong, if not the strongest. Diamagnetic materials, when in the presence of a magnetic field, induce magnetic fields that are in the exact opposite direction of the applied magnetic field. Basically, when a magnet gets close to a diamagnetic material such as bismuth, a repulsive force coming from the bismuth will act on the magnet.
This levitator has two bismuth ingots on the top and bottom of the floating magnet, just like in the picture.
However, the bismuth's diamagnetism isn't enough to levitate a little magnet. A "lifter" magnet above the floating magnet must also be used to counteract most of the floating magnet's weight. When the lifter magnet is adjusted to just the right position and the bismuth ingots are the right distance apart, the little magnet can float perfectly in the ingots' diamagnetic fields for a very long time. Eventually, small adjustments would be necessary to account for magnetic losses, but that's years away.
Step 2: Gather the Materials
These are all must-haves for this design to work. You'll need...
- 1 cubic inch N42 magnet (huge magnet!)
- 1/5"-1/4" N42 or N52 magnet cubes
- 2X 3/8" threaded rod
- 4X 3/8" nuts
- Around 5-10 ounces of refined bismuth
For the threaded rods, I bought a 2 foot long one and then cut it in two with a dremel. If you don't have a dremel or disc cutter of any sort that can cut metal, you can use a hack saw. Some hardware stores will cut the threaded rod for you, so don't forget to ask.
Originally I bought these little magnets from Amazon. They ended up being too weak for my taste. The ingots of bismuth had to be brought so close together that it didn't look that impressive. The stronger the better for the little floating magnet. FYI, neodynium magnets' strength are rated with an "N" number. The higher the number, the stronger the magnet. The most popular strong ones are N42 and N52 I believe.
Also just a warning, the really big magnet is really, REALLY strong. Obviously electronics and magnetized cards are not friends with Mr. Magnet. It's also strong enough to fly at a piece of metal so fast that it shatters, so don't let it knock into metal things. As it turns out, the stronger a magnet is, the more brittle it is as well.
For my design, I used my 3D printer to make the main structure. These files are attached to this step. If you don't have a 3D printer, first of all, get a 3D printer! They're very economically priced these days and are sooo much fun to play around with. If you don't have a 3D printer and don't plan on getting one, follow this video on making your levitator. The prototype design in the video is very similar to mine. Basically it's just replacing the 3D printed parts with pieces of wood.
For casting the bismuth, you will need some sort of small container or small box and wet clay-sand mixture to fill it with. You will also need a sort of metal cup or spoon to melt the bismuth. I just bought a cheap metal measuring cup set from Walmart and it did the job.
Step 3: Making the Mold to Cast
I suppose you could get away with not casting the raw bismuth you ordered and just break away two pieces to make your levitator. But where's the fun in that? Bismuth is really easy to cast because it has a relatively low melting point of about 520 F or 271 C. You only need to use a stove top to get things up to that temperature (which is what I used).
The first step with casting is making the mold. You need some kind of container to hold a moist clay-sand mixture. It doesn't need to look good, it just has to work. I just chopped up some wood from an old fence post and dug out some clayish dirt from the ground in my yard. Regular soil might work fine, but I don't know. You want to then wet the clay-sand, but not a whole lot. If it's over saturated with water, the water will boil when the bismuth is poured and could potentially splash everywhere.
Print out this mold I designed and then press it firmly into the clay-sand mixture. Make sure that it is level, otherwise the bismuth will turn out crooked and weird. If you don't have a 3D printer (yet), you can use anything that's 3cm in diameter. Ideally you want a cylinder that is 3cm in diameter and 1cm thick. I know I'm kinda bouncing around between customary and metric, but bare with me.
Another option that I didn't try is to use a small muffin pan as the mold. I'm not sure if it would work with the 3D printed parts however.
Step 4: Melting and Casting the Bismuth
Now the fun part. To melt the bismuth, you need some kind of cup to hold the metal over whatever you are using to heat it. I found that the 1/4 cup from a cheap set of measuring cups works very well. For heat, you can use a stove top, electric or propane. If you don't have access to either, you can buy a small propane or butane torch at your local hardware store and use that (which would probably work better than a stove).
To melt the bismuth...
- Break off a small chunk or chunks that is about 5-10 ounces. Its better to have too much than too little.
- Use a lock wrench or regular pliers to hold the measuring cup over the stove top with the stove on high until bismuth is melted.
- Carefully pour bismuth into molds until they are full. The bismuth may splash and could potentially land on you so I advise wearing an oven mitt.
- Wait 5 or so minutes and then pop the fresh ingots out of the mold.
Like I said before, if you made your clay-sand mixture too wet (like me), the water could boil off and the bismuth could bubble and pop so be very careful and wear an oven mitt or some kind of hand protection.
Step 5: Sanding and Inserting the Ingots
This step is somewhat tedious and makes a mess, but it's necessary. Use course sand paper to grind down the big irregularities in the bismuth ingots and then switch to fine sand paper to buff out the scratch marks. Keep in mind that only one side of the bismuth will be seen if you use the 3D printed design and make the ingots right. You want to make the one side that will be seen very flat. After you've sanded the ingots down, glue them in place with hot glue, epoxy, or whatever else you have. Ideally you want to use a very fast setting glue. While the glue is drying, hold the ingots so that the flat side is level with the frame.
Step 6: Final Assembly and Adjustment
Now for the easy part of putting everything together. The threaded rods slide into the bottom part. You could glue them in place, but it's not necessary. Simply slide in the monster magnet into the top part with one of it's poles facing downwards.
Once you have it all assembled, put a little magnet in between the bismuth ingots and lower the middle part until it is around 1mm from the magnet. Make sure the little magnet is oriented so that it is attracted to the big magnet. Now lower the top part until you notice the little magnet go up and touch the top ingot of bismuth. Now make slight adjustments with the big magnet until the little magnet floats between the two ingots.
The threaded rods might be a little too long for your taste, so you can always take it apart and cut them to length.
It might take a little while playing with the heights of everything, but eventually you'll get it. Every magnet is slightly different. It's fun to try to float different magnets you have laying around the house. Once you get it, sit back and admire it's gravity defying-ness.
bpark1000 made it!