eddy current brake

[Todd King]

  <<<
  Pardon my ignorance, but what effect does a magnet have on a non
  metallic element like aluminum or copper.
  How's it work?
  And what kind of drag can you expect from such a device?
  
  Todd Knighton
  Protomotive Engineering
  >>>
  
  The magnet causes a drag force on the non-magnetic rotating disk (in this 
  case) because of currents induced by the motion of the disk through the 
  magnetic field; the currents "swirl" (thus the eddy term) about and dissipate 
  as heat due to the small amount of resistance in the conducting disk. But of 
  course a current in a conducter also generates a magnetic field so you get the 
  drag force. It's really neat- you can brake the rotating disk without 
  contacting it. If you happen to have an old hard drive platter laying around 
  you can demo the effect. Give the platter a good spin and just bring a magnet 
  close to the surface of the upper disk. You'll see the thing slow noticeably. 
  BTW, if you have an older model drive dig out the (big) magnets from its arm 
  motion control assy; you'll be Astonished by how strong they are if you have 
  never seen these magnets before. Put two of them together (don't get your 
  finger caught as they snap together!) and you will not be able to pull them 
  apart without sliding them parallel! Anyway I think that another app for eddy 
  current brakes was the diesel-electric locomotive?
  
  Todd    Todd_King at ccm.co.intel.com