A 3D printed electric motor with a built in AA battery holder. The last step has the necessary .STL files.

Materials needed:

14 gauge wire (or large paper clip)
3x12mm neoydynium magnet
2-3 feet of enameled magnet wire
AA Battery
M3 Bolts

Step 1: Introduction — How It Works

An electric motor has two primary parts: A permanent magnet and a coil loop of some kind. When an electric current passes through the coil, the coil produces a magnetic field which interacts with the permanent magnet.

The coil ring experiences a torque causing it to rotate. The coil ring's magnetic field wants to line up with the permanent magnet's magnetic field. If the current stayed on, the coil ring would just find that position and stay there. The trick is turning off the current at just the right time and having momentum carry the ring until the current switches on again, torque is applied to the ring, and it does it over and over.

Step 2: The Coil Ring

One of the hardest parts of making a homemade electric motor is making a symmetric loop so it doesn't wobble. A 3D printed ring makes it much easier.

You will need maybe two feet of enameled magnet wire
First thread about two inches through the center hole and wrap the ring, fish about 3 inches back through the top or bottom hole on the other side, and fish through the center hole
Completely sand one shaft end, but only sand the bottom of the other. See illustration above for clearer instructions.

Step 3: The Base

Please note: The version shown is without a switch holder.

The blue rods is where the 14 gauge wire is inserted. The metal rod of a large paper clip would likely work as well.
The shafts of the coil ring (shown in green) rotated very well in the cavity.
The battery is held in place with two M3 bolts gently applying pressure. The battery could also be held in place with some aluminum foil making electrical contact with both ends of the battery.
Electrically it is very simple: The circuit simple connects the positive and negative ends of the battery to the 14 gauge wire ends (the blue rods in the diagram)