Joseph Gwinn wrote:
In article ,
Jordan wrote:


Joseph Gwinn wrote:

Aluminum will work only as an eddy brake, and the drag will vary as the
square of speed (rpm).

A sheet of hard steel will in addition act as a hysteresis brake,
increasing the drag at lower speeds. Mild steel is too soft
magnetically to get much hysteresis effect, but a flat sheet of hardened
spring steel ought to work. It doesn't need to be pretty.


So they're two variations - eddy brake and hysteresis brake?
I think aluminum would be easier to work with, and the speed squared
characteristic of eddy sounds good.
Should the magnets be mounted either side of the disc, with opposite
poles facing each other?


That would work. You will need some iron too, to make a complete
magnetic circuit.

One variation is an aluminum cylinder with the magnetic field being
radial.

I would look into the patent literature for ideas.

Joe Gwinn




Easy demo. Drop a magnet through a chunk of Al. pipe. Slow-mo drop.

Slide same magnet down an inclined sheet of Al. Slow-mo slide.

Pretty sure this works with about any metal, but having the magnets
sticking to the disk is problematic.

Faster it goes, the bigger the eddy currents formed and resisting
movement.

Think simple.

Simple disk. Simple magnet holders under the disk, out of sight.

My two bits worth, anyways.

If complicated works, a bit, anyway, I would look at gearing up the
output shaft with a couple sets of bicycle gearing/chains, and having
the brake at the end of the train of gearing to do its thing with a
geared advantage. Salvaged bike parts are cheap to aquire.

Or a generator with a variable load, rpm dependant.

Or running the LEDS planted up the blades.

Or...:-)

Just ideas.

Cheers
Trevor Jones