How it works: as the armature rotates and one end with the magnets comes close to the coil of wire, the circuit senses the magnets and turns power on to the coil to make an electromagnet which then attracts the magnet. When the magnet passes to the center of the coil the magnet is turned off, the polarity of the coil reversed and then the coil pushs the magnets away so you get this pull then push effect which rotates the arm.
This simple electronic circuit is about one of the most interesting I have ever built and the only time consuming part is winding the coil of wire which I did by hand and took about an hour. Well worth it.
This link shows how to build this electronic driver circuit: http://www.trainelectronics.com/Pendulum/article.htm
Photo 1: Shows complete motor assembly.
Photo 2: Closeup of end of armature. I hot glued magnets to end of arm which is a piece of hollow fiberglass tube (fishing pole).
Photo 3: View of axle which is a bicycle spoke inside smaller tubing which goes through center of armature. Notice red tape which is just a counterweight so both sides of armature are balanced.
Photo 4: Close up and hand wound coil.
Photo 5: Close up and electronic circuit that drives coil and armature.
Photo 6: Circuit diagram from website that describes how to build electronic driver circuit.