According to Jordan :
Test report:
I got a 9 inch diameter thin sheet of Al (ex- pie dish), spun it with a
hand drill. I've got this seriously powerful magnet from an early
voice-coil HDD (much bigger than typical now), that I held up to one
side of the disc.
Good -- experimentation is the way to go.
The magnet slows the drill somewhat - I can hear the change in pitch.
The magnet tends to want to "push off" the disc.
As proof of principle it's encouraging. It'd need a much larger
diameter, especially if I can only get smaller magnets, but multiples
would help of course (I think?).
Also I'm guessing the thickness of the sheets would need to be at least
1/8 inch, as the push-off pressure would likely warp a thinner disc.
Also -- I would expect you to get greater braking from thicker
aluminum -- up to a certain limit at least. Yes -- 1/8" sounds
reasonable.
But hey - all that aluminum is threatening the purse limit again!
I wonder - would it work if a number of pieces were attached to a sheet
of ply? Then we could make a number of "rings" from less material.
I've gone cool on the bicycle rim idea, thinking there's not enough
brake area.
You would lose braking effect as you approached the seams,
because it depends on the ability to conduct electricity in a zone
around the magnet's field. If you have someone who can do a MIG or TIG
job of welding them together, the effect should be better.
But your plywood would be the limiting factor on lifetime. How
long do you need this to work before it is taken down? If you're
talking over a year, I would strongly suggest that you avoid the
plywood, especially since with a tight budget, the odds of someone doing
regular maintenance are pretty poor.
See whether you can find a local shop which needs to make discs
of aluminum from sheet. You may be able to get them to cut from the
center of the sheets and sell you the "drops" -- squares with round
holes.
Enjoy,
DoN.
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