All-mechanical magnetic levitation
WARNING WARNING WARNING
Note that when many pounds of copper tube is spinning at 5000RPM, it is EXTREMELY DANGEROUS. If you bump your fingers against it, it could EAT YOUR ENTIRE ARM INSTANTLY. Or if the sharp edges of a magnet get caught, the magnet could explode and the pieces fly out like bullets. It's FAR more dangerous than any power tool. For safety I made a close-fitting plexiglas box to cover the tubes: I heated a sheet of plexi on a greased aluminum foil sheet in an oven, molded it over the top of the tubes while wearing heavy gloves, then carved it square and used it as the top plate in a plexiglas box. The magnets only hover about 1/4" above the spinning tubes, so if you build a cover, it must be close-fitting without touching. The cover isn't required for initial testing, just for operation around curious fingers.
Try to avoid using steel for anything except the ball bearings, otherwise
the hovering magnet will be sucked to the end of the tubes. If you decide
to make the tubes lots shorter than 12", be aware that the magnet might
become unstable and drift towards the steel ball bearings. This
might be fixable: put a small piece of iron below the tubes, close
enough to attract the magnet to remain centered, but not so close
that it pulls the magnet down into the tubes.
Other notes: neodymium-iron-boron (NIB) cylinder magnets are required.
Ceramic or alnico magnets are too weak, although they might hover if the
RPMs of the tubes could be doubled or tripled. Samarium-Cobalt magnets
work, but are too expensive. One source for rare-earth NIB magnets is
Force Field, www.wondermagnet.com.
I know that their 3/4" dia, 3/8" thick NIB
disk works well. I haven't tried the small cylinders, but they PROBABLY
work OK. See my NEODEMO file
for more fun things to do with
NIB supermagnets. Heed the safety warning!
How does it work?
Another way to make a magnet hover: use a superconductor. When a magnet
approaches a superconductor plate, it induces a circle of moving charge.
Since the superconductor has no resistance, the current will never be
slowed, the repelling fields will not die away, and the magnet will hover.
But superconductors require super-cold liquid nitrogen for their
operation. They are also fairly expensive: $10 to $20 for a 1" disk.
If we could just MOVE our magnet suddenly sideways across the copper,
a new pattern of current would be induced, and the magnet would be
repelled again. If we could move the magnet rapidly across the metal
plate, it would lift up and fly. One form of "Maglev Train" uses this
effect, it contains powerful magnets in its lower surface, and "flys" over
a thick aluminum trough.
The magnet-roller device turn the train idea upside-down. The "train"
stays still and the track moves fast.