Re: gEDA-user: Magnetic bike operation

[John Doty <jpd@xxxxxxxxx>]

On Mar 29, 2010, at 10:23 AM, Rob Butts wrote:

> So I'd lke to make this programable; therefore, in lieu of a permanent
>   magnet and bringing it closer to the disk to increase the resistance I
>   could use an electromagnet and increase the magnetic field?

Yep. Current in the disk is proportional to the current in the electromagnet, and power dissipation in the disk is proportional to the square of the current. 

But I'd guess the electromagnet will get hot, too, in reasonable cases. You need a shallow "skin depth" in the disk material, thinner than the disk: otherwise the field penetrates without inducing much current. That drives you to high conductivity materials there. But to keep the dissipation in the magnet down, you want it to be wound of much higher conductivity material than the disk is made of. That gets hard if you're already using something like aluminum for the disk...

John Doty              Noqsi Aerospace, Ltd.
http://www.noqsi.com/
jpd@xxxxxxxxx




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