>Wes Johnston wrote:
>>
>> Last time I was in Germany at the Deutsches Museum in Munich, I saw a steel
>> ball about 1 inch in diameter suspended in a magnetic field.  The electro
>> magnet would come on full force and as the ball rose, it would interrupt a
>> light beam causing the magnet to switch off.  Very simple.  Very power
>>hungry.
>
>If instead a steel ball it was just a rod magnet, the power consume
>would be sensible smaller, since the critical position to interrupt the
>electro-magnet would be when the rod magnet is also acting its field
>over the electromagnet itself, so canceling a lot of gravity effect.  An
>interesting device could be done using a brushless dc motor coils, and
>rotate the field, so the suspended magnet would rotate too... :)  A wide
>assembly of those coils could make the suspended magnet not only rotate,
>but move in an orbital shape since it will try to get out in its
>tangencial vectors (centrifugal force).
>
>Wagner.

I have done that. It was a painted steel globe, a small one. At the bottom
I embedded a small ceramic magnet. The feedback loop was closed with a hall
effect sensor below the globe. When the suspended globe was spun, it would
rotate and eventually stop.

(Note to topic police: this was before PICs)

A couple of years ago I saw an awesome home-built example of the device Wes
described above. The ball was probably three or four inches in diameter; it
must have weighed ten pounds. It was suspended a couple of inches below the
the electromagnet. Huge heat sink for the controller.

Reg Neale