Step 4: Magnets
I used twelve 1 x 2 x 0.5 inch rectangular magnets from Magnet4less.com (very reasonable prices). On the back of the rotor, I also used an aluminum plate to keep the magnets separated (this plate is also available from Otherpower). We used heavy duty epoxy to ensure that the magnets won't fly off at high RPMs. Be VERY careful when you put these magnets into place - they have enough power to severely injure or break your fingers! I found that a little caution and a rubber hammer were invaluable tools.
The magnets are placed in alternating polarities on the back of the rotor. We used a small magnet to test each magnet's polarity.
I left the magnets exposed, but I am planning on a possible renovation soon. I should've cast the magnets in some sort of resin to prevent corrosion. There is plenty of good information on the internet on how to do this, and it's very similar to casting a stator coil.
Once all the magnets are on the rotor, remember that the whole disk is now one gigantic magnet. Do not set it on a workbench with metal shavings or magnet-sensitive materials!
Also, you may notice that the pictures are a bit out of order (the rotor is painted already) but I am trying to lay this out in the most logical order... not necessarily the order we did it in!