On 03/27/2010 01:32 PM, Stefan Salewski wrote:
On Sat, 2010-03-27 at 16:28 -0400, Rob Butts wrote:
I'm having a debate with an ee friend about how the magnetic resistance
works on an excersice bike.
May be something like
http://de.wikipedia.org/wiki/Wirbelstrombremse
http://en.wikipedia.org/wiki/Eddy_current_brake
Yes, this.
I've had one apart before - they use permanent magnets and a thin
aluminum rotor that's usually geared up from the pedals so it spins
pretty fast. To adjust the brake tension a pair of laminated iron poles
are brought close to the spinning rotor - the narrower the gap between
them, the more resistance. Note that the pole pieces don't actually
touch the rotor (except in an old bike I had where the rotor warped from
resistive heating - then I got a lot of aluminum shavings everywhere).
Eric
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