Paperclip Motor

This is a simple electric motor powered by a single AA battery. It can be used in science, physics, or technology classes to help convey some basic principles of electromagnetism or with your own kids on the weekend for a bit of science fun.

The motor does not utilize commutation. Rather, it uses inertia and magnetic attractive and repulsive forces to maintain rotational motion. In the electromagnetic coil, magnetic flux F = N * I where N = number of turns of wire around the bobbin and I = the current flowing through the wire. Increasing the number of turns or increasing the current increases the magnetic field generated. Increasing the number of turns requires more wire, which increases the resistance of the circuit resulting in a decrease in current. Can you find the optimum balance of turns/current to maximize the magnetic flux :-)?

The motor consists of the following 3D printed parts:
(1) Simple Bobbin (you wrap the copper wire around this part)
(1) Fan (optional; for decoration)
(1) AA battery holder - I remixed this from enif's Flexing battery holders with integrated spring - http://www.thingiverse.com/thing:456900 (thanks enif for a wonderful design!). The changes I made to enif's design for this application include:
-Raised the height of the "box" so that magnets will sit flush across it and the battery
-Implemented an indentation and holes at the + and - ends to hold the paperclips in place.

Additional materials needed to construct the paperclip motor:
(2) Number 1 size paperclips
(1) AA Battery
(1-4) Magnets (suggest >18mm or 5/8" in diameter (or square)). Experiment with more or fewer magnets to see the effects!
(~50cm or 20" of 22AWG enamel coated wire) - This is sometimes called magnet wire. 22AWG works well - slightly smaller or larger may also work; smaller wire will have a more difficult time maintaining a straight axle and larger wire will consume more current and take up more space in the bobbin "tray".
(1) small cork or piece of foam - this helps provide balance if the fan blade is used on the other end. It also helps keep the motor from "walking" too far.

To assemble (reference attached pictures for details):
-Straighten one leg of each paperclip so that it is relatively straight. Bend the other loop of the paperclip to that it makes a "U" shaped cup for the axle to sit in.
-Insert one of the paperclips into the hole and indentation at the negative end of the battery holder and then insert the AA battery slightly to hold the paperclip in place.
-Insert the other paperclip into the hole and indentation at the positive end of the battery holder and push the AA battery so that it is completely inserted. This should hold the two paperclips securely, but allow them to be twisted around and slightly raised/lowered for positioning.
-Place the magnets on top of the battery in the center.
-Wind the wire around the small bobbin; leave enough wire at each end to form the axle (about 40mm or 1.5"). Start by inserting about 40mm of the wire through one of the two small bobbin holes (this is one side of the axle) - this should be inserted from the inside towards the outside and then wrapped around from the inside, around the side, then into the "tray" of the bobbin. The wire should then be continually wrapped around the "tray" of the bobbin until about 40mm is left at the other small hole of the bobbin. Then, wrap the wire around the side of the bobbin and through the small hole from the inside towards the outside (this is a little tricky as you have to go through all the wrapped wire; but, it is possible) - this makes the other end of the axle.
-Remove the enamel from each axle end of the wire using sandpaper or a small precision file. If you don't remove enough enamel, the motor won't spin as it will get no power from the battery.
-Straighten the axles - the straighter and more balanced you get them, the better chance you have of getting continual rotation.
-Install the fan (if desired - may require glue depending on wire gauge size) and cork/foam.

To Operate:
-Place the wire/bobbin assembly so that the axles rest in the "U" shape of the paperclips and the bobbin is positioned directly over top the magnet(s). Position the paperclips so that the bobbin comes as close as possible to the magnets without hitting them.
-Give the axle a little twist to get it started (if you use the fan blade, you can blow on it to get it rotating).

Sometimes it is a bit difficult to get started. If you have trouble, observe the axle/bobbin as you manually rotate the motor. If you notice excessive wobble or if the weight of the bobbin/wire is off-center, then readjust and try again. Adding more magnets side-by-side on the battery (with the poles all facing the same direction) can provide more force. Once the motor has run for awhile, carbon buildup can occur on the copper axles and paperclips where they contact; simply clean with sandpaper or a file to remove the carbon buildup and restore conductivity. If the wire/bobbin does not get warm to the touch after a few seconds of sitting in the paperclips, either there is poor conductivity (sandpaper the axles and paperclips again) or the battery is too dead to power it (replace the battery).

My prototype ran for over four hours straight on a single AA battery.

I hope you enjoy this fun and easy to make project.