If you would like to read a bit about how electric motors work, go to step 19. I did not put that information in the earlier steps because some important concepts must be discussed first.
3 inch finish nail or thin steel rod
1/4 inch steel rod (a 1/4 inch carriage bolt from the hardware store would do and costs very little)
Plastic tubing for a fish tank or medical equipment
Enameled magnet wire about 24 gauge (Spools of magnet wire can be bought at Radio Shack, or magnet wire can be salvaged from a number of devices that no longer work, like old transformers or motors. Be careful about going into an old television set. While you can find wire there, you can also encounter a lethal dose of stored electricity.)
#12 copper wire (from some old household electrical cable)
Thin stranded wire to connect the batteries
Spring clothes pins for holding the connecting wires in contact with the motor
Dowel rod (1/2 inch)
Wood for a base
Thin brass sheet or brass hobby tubing
Two ceramic magnets
Batteries or a 3 -- 6 volt AC/DC power supply (2 "D" batteries, a battery holder is suggested)
Motor oil (just a few drops)
Pan head sheet metal screws (two)
Electric hand drill and drill bits (a 1/2 inch spade bit is the best, least expensive option for the larger holes)
Center punch and hammer
Grinding wheel or a concrete face for grinding
Solder gun or iron
Hot glue gun
Fine-toothed handsaw for wood
Files for metal
Multi-meter (helpful, but not necessary)
Step 1: The Armature Shaft
Step 2: Prepare to Drill for the Shaft
Step 3: Drill the Magnet Core
Step 4: Hone the Shaft to Fit
In the event you do not have a grinding wheel available, go outside and hone the finish nail against the edge of a concrete sidewalk. It will take a little longer, but will work if nothing else is available.
Step 5: Cut the Magnet Core to Length
Step 6: Balance the Armature
Step 7: The Commutator
I decided to use clear plastic tubing from a fish tank or from medical equipment for the commutator sleeve. Its internal diameter is too large to fit snugly on the shaft, so I built up the shaft by wrapping it with black plastic electrical tape. When I was sure I had enough, I cut the tape and began to fit the tubing over it. I had to remove tape by half turns until the tubing would slip over the tape, but still be snug and not move. The second photo shows the plastic tubing in place on the commutator.
Step 8: Wind the Armature Coils
Step 9: Balance the Armature Again
Step 10: The Rest of the Commutator
The commutator needs conducting segments so current can flow through the coils and make magnetism. It is time to add the conductor segments. I planned to cut some pieces of brass from a small sheet obtained at a hobby store and bend them to fit the contour of the commutator. But, I discovered that I had some brass hobby tubing just the right internal diameter to slip over the fishtank tubing. (second photo) I cut a piece of brass tubing just a little shorter in length than the core of the commutator. Then I cut it lengthwise to make two pieces that cover just a little more than 1/4 the diameter of the commutator each.
I am trying to use the most simple tools for this, so I used a hacksaw and a vise, not a Dremel tool that many who read this will not have.
The third photo shows the conductor segments of the commutator held in place. I used a file to smooth rough edges left from sawing the brass. The conductor sections will be glued onto the commutator with epoxy glue. I used some sandpaper to roughen the surface of the plastic tubing and the underside of the brass pieces so the epoxy will bond better.
Before gluing, I cleaned one end of each brass piece with steel wool. Then I tinned each with a little solder. I cut the coil leads to length and scraped away the enameled insulation at the ends. Use a knife for this and make the ends shiny and bright. I soldered the coil leads to the brass conductor segments and tested for good connections with a multi-meter. (When soldering do not rest the brass pieces directly on the plastic tubing. It can melt. I used several layers of paper to protect the plastic tubing.
Epoxy can be a sticky mess that coats conductors and creates problems later. I put a small piece of masking tape over each brass piece before gluing. Then I wrapped the whole commutator with masking tape until the epoxy cures. See the fourthphoto. The frosted cellophane tape used in step 9 to keep the coils from unwinding can be removed now. The masking tape can be removed after the epoxy has cured.
Work on the armature is finished. It can be set aside for now.
Step 11: Make a Base for the Motor
I began with this piece from some crating lumber, but had to select a larger piece. I needed more space at the ends of the armature coils to mount the field magnets. There will be more about them later.
Step 12: Motor Bearings
Make the dowel pins long enough so the armature can spin freely without crashing into the motor's base. The shaft of the motor should be parallel to the top of the base when mounted, too.
One of the dowels is drilled only part of the way through. The other is drilled all the way through. The holes are big enough that there is a little play for the shaft to move very freely.
Notice I also marked the base for drilling. The dowels will be glued to the base.
(This is still the first base I tried. It was replaced with one slightly larger.)
Step 13: Preparing the Field Magnets
It is very important that they not present like poles. Unlike poles attract. Allow the two magnets to attract each other and stick together. Use small pieces of tape to mark the faces that stick together. These faces will each point toward the armature when mounted on the motor.
Suitable magnets like these can be purchased at Radio Shack. Or you can salvage magnets from some junk equipment, like an old hard drive. You can even take them from refrigerator magnets no longer needed.
Step 14: Mounting the Field Magnets
I drilled a hole about 3/16 inch in diameter through the center of each dowel where the center of the magnet would be. This allowed a socket for hot glue to make a big rivet. In the photo you can see the back of one field magnet and the front of the other.
Step 15: Mounting the Field Magnets on the Base
Step 16: The Commutator Brushes
Strip the plastic insulation from a piece of #12 household copper wire. Bend it as you see in the photo. The "U"-shaped bend will fit around a mounting screw. The tension provided by this wire against the commutator can be adjusted by bending the wire a little. The brushes should have enough tension against the commutator that there is never a loss of contact. But, they should not be so tightly against the commutator that they make it difficult for the armature to turn. Mark the location for the brush mounting screw. Drill a hole for it. Fasten the brush to the motor base with the screw. The upward bent end of the brush near the screw is for making electrical contact with the motor.
Step 17: Lubricate the Motor Bearings
In this photo you can see the completed motor, including the brushes mounted to the motor base. If there is ever a problem with the brushes, it is very easy to loosen one screw or the other and bend or replace the brush. Dust and corrosion will appear between the commutator and the brushes. If the motor begins to perform poorly, remove the brushes. Clean them and the commutator. Also, bend the copper wire for the brushes just a little so there is a little more tension against the brass conductor strips. The tension can become weak, even though they appear to make good contact.
Step 18: It Runs!
I used some jumper wire to connect to two "D" cells from a flashlight. 3 volts is about the minimum voltage on which this motor will operate. I expect you could use up to about 6 volts with no problem. I would not want to exceed 6 volts, though. Running it a long time could cause the commutator to become hot, and that could cause the plastic tubing under the brass sleeves on the commutator to loosen.
Regular use of this motor would make a battery holder a very desirable thing to have. It appears to draw quite a bit of current, but I have not checked for an exact number with an ammeter. I did notice the flashlight batteries I have been using seem to be going down more rapidly than I would have expected. I want to try powering it with a 6 volt auto battery charger.
If you want the motor to run in the opposite direction, reverse the battery connections. When you start the motor, it works best if the armature is almost vertical.
Step 19: How This Motor Works
The magnet at the left shows a black spot in its center. This is to represent an axle about which the magnet can revolve. The two red ends are pushing away from each other. Because the magnet at the left has an axle, the direction it moves is in an arc, which turns the axle. This is already a very simple motor. But, it is also a very limited motor. As soon as the gray end swings around to be opposite the red end of the right magnet, the two unlike poles will lock onto each other and the motor will freeze.
But, suppose that by some magic the polarity of the left magnet could change just as the gray end was about to lock onto the red end of the right magnet and become a like pole instead of an unlike pole. The left magnet would be repelled by the end of the right magnet again and the left magnet would continue to turn for another half turn. Suppose the ends of the left magnet reversed their polarity each time one was about to lock onto the magnet at the right. The left magnet would continue to spin on its axle.
It is impossible to change the polarity of a permanent magnet rapidly as hypothetically suggested in the last paragraph. But, it is possible to make magnets that can be reversed very rapidly and at will. Electricity flowing through a wire makes a weak magnetic field around the wire. By wrapping many turns of wire around a steel core, this weak magnetic field can be concentrated in the steel core to make a very powerful magnet. Suddenly changing the direction of the current flow in the wire reverses the magnetic polarity so that the north pole of the magnet becomes the south pole, etc. That is what the commutator does. As the motor's armature turns, the brushes and the commutator constantly reverse the current flow in the armature coil, which reverses the magnetic polarity just before the magnetic poles would lock onto each other and freeze. The result is that the armature continues to spin and spin. The efficiency of the motor increases when another permanent magnet is added to the left side of the graphic. In addition, the magnets do not only repel each other. Unlike magnets can also pull toward each other during part of the rotation, just as like magnets push away from each other during other parts of the rotation. A motor becomes even more powerful and efficient by adding more pole sections to the armature with more segments on the commutator and more magnets around the circumference of the field. Although this motor is very simple and not very powerful, it illustrates how very large and powerful motors work.
Note: Most large electric motors run on alternating current and are designed a bit differently than this motor so that the current flow reversals that are characteristic of alternating current naturally cause the magnetic polarities in the motor poles to reverse many times per second without the use of a commutator. An exception is the many direct current electric motors used in an automobile to raise and lower the windows, to adjust the seats and mirrors, and to start the car's engine. Those motors work very much like the motor described in this Instructable.