On Fri, 2011-09-09 at 13:37 +1000, Geoff Swan wrote: > > So if I have an electromagnetic and I hold it next to the spinning > > metal disc as I increase the intensity of the magnetic field the metal > > disc should be harder to spin? > Yes. > > > Define conductive? The eddy current breaks says non-ferromagnetic which > > means to me not having any magnetic properties like aluminum. > Conducts electricity. Doesn't magnetise. Eg aluminium, copper. NOT iron. 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. If you're fitting this onto a bike (e.g. to make an exercise bike), you might be able to do something clever with a bike designed to take a disk brake. Have your eddy brake disk machined with a matching hole and thread to the hub, and screw onto that. (Or, for hubs which have bolt-holes for the brake disk - bolt to it). Obviously this would mean you couldn't use the disk brake, so I hope the whole assembly is going to be stationary ;) -- Peter Clifton Electrical Engineering Division, Engineering Department, University of Cambridge, 9, JJ Thomson Avenue, Cambridge CB3 0FA Tel: +44 (0)7729 980173 - (No signal in the lab!) Tel: +44 (0)1223 748328 - (Shared lab phone, ask for me)
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