How To Make A Paper Clip Motor - Experiment

Building something with our own hands often provides a new quality of insight, not to mention fun. With a few inexpensive materials, you can build your own d.c. electric motor.

The process of fiddling with your motor to get it to work well illustrates the principles of physics as no textbook description can, and watching it actually spin gives tremendous satisfaction. Putting your paper clip motor together takes only a few minutes, and it is worth it!

Materials Needed
2 paper clips
1 small, strong magnet (from Radio Shack; most refrigerator magnets are too weak)
1 C or D battery
1 yard of 20-gauge (AWG 20) coated copper wire
2 rubber bands or tape
1 small piece of sandpaper

Make a tidy wire coil by wrapping it 10 times or so around the battery. Leave a few inches of wire at both ends. Tighten the ends around the coil on opposite sides with an inch or more of wire sticking out straight from the coil to form an axle on which the coil will spin (see figure below).

Attach the magnet to the side of the battery. It may stick by itself, or you may want to secure it with a rubber band or tape. The magnet’s north or south pole should point directly away from the battery (this is the way the magnet naturally wants to go).

Bend the two paper clips and attach them with a rubber band or tape to both ends of the battery so as to form bearings on which the axle rests. The clips need to be shaped so that they make good electrical contact with the battery terminals, allow enough room for the coil to spin in front of the magnet, and keep the axle in place with a minimum of friction.

After checking the fit of the axle on the bearings, use the sandpaper to remove the red insulation coating on ONE end of the wire so that it can make electrical contact with the paper clip. At the other end, remove the coating on only HALF the wire by laying the wire coil flat down on a table and sanding only the top side.

This will interrupt the electrical contact during half the coil’s rotation, which is a crude way to reproduce the effect of commutator brushes. (Ideally, the direction of current flow through the coil should be reversed with every rotation, which would then deliver a steady torque on the coil in one direction; this is what commutator brushes do.

If direct current were allowed to flow continuously, the direction of the torque on the coil from the changing magnetic flux would reverse with every half-turn of the coil. Simply interrupting the current for half a turn interrupts the torque during just that period when it would be pulling the wrong way.

Once the spinning coil has enough momentum, it will just coast through the half-turn without power until it meets the correct torque again on the other side.)

When you place the coil on the bearings with the contact side down and current flowing, you feel it being pulled in one direction by the interaction of the fields of the permanent magnet and the coil (the “armature reaction”). Now give the coil a little shove with your finger and watch it spin.

Many thanks

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