Re: gEDA-user: Electromagnetic bike

[Rob Butts <r.butts2@xxxxxxxxx>]

   Wow, this is fantastic everyone.  Thanks!



   I knew I came to bthe right place!



   Rob

   On Fri, Sep 9, 2011 at 12:41 PM, John Doty <[1]jpd@xxxxxxxxx> wrote:

   On Sep 9, 2011, at 5:29 AM, Peter Clifton wrote:
   > If you're after significant resistance, I would go for a copper disk,
   > about 5mm or thicker, with strong magnets - either an electromagnet
   on
   > an iron core - placed quite close (within a few millimetres) of the
   > spinning disk, OR - some neodymium hard-disk magnets (for example).
   >
   > You could use an aluminim disk (much cheaper, and easier to obtain
   I'd
   > imagine) - but I would up the thickness.

     The torque will fall off at low speed, when the magnetic diffusion
     depth exceeds the thickness of the disk. The diffusion depth is
     given by:
     sqrt(dm*t)
     where dm is the magnetic diffusion coefficient, about 130 cm^2/s for
     Cu, 230 cm^2/s for Al. The time parameter, t, is essentially the
     time a point on the disk remains in the vicinity of the magnet.
     This is, of course, just dimensional analysis: a detailed model of
     the field configuration is needed if you need to be more
     quantitative.
     The same physics leads to the concept of "skin depth".

   John Doty              Noqsi Aerospace, Ltd.
   [2]http://www.noqsi.com/
   [3]jpd@xxxxxxxxx
   _______________________________________________

   geda-user mailing list
   [4]geda-user@xxxxxxxxxxxxxx
   [5]http://www.seul.org/cgi-bin/mailman/listinfo/geda-user

References

   1. mailto:jpd@xxxxxxxxx
   2. http://www.noqsi.com/
   3. mailto:jpd@xxxxxxxxx
   4. mailto:geda-user@xxxxxxxxxxxxxx
   5. http://www.seul.org/cgi-bin/mailman/listinfo/geda-user


_______________________________________________
geda-user mailing list
geda-user@xxxxxxxxxxxxxx
http://www.seul.org/cgi-bin/mailman/listinfo/geda-user