I took apart my fan to clean it. It has 4 coils of wire that become magnetized when current runs through them. The magnetic differential between them and the central magnet causes the center piece to spin, turning the blades. Flipping over the coils causes the fan to turn the opposite way. I shocked myself real good… tisk tisk…. unplug before opening next time.
Pics from Inside the FanOctober 1, 2007