The Worlds Simplest Electric Motor


I was very impressedthat you could actually build a working electric motor with so few parts.I built one and brought it to work where it was a big hit with all the engineers around here. This writeup was for a friend of mine who wanted instructions that his son could follow for a science fair project. Here's how to build one. If you are using a text only browser, you can click on the "Figure" links to downloadthe drawing s (GIF files). BTW, my friend's son won second place in theschool's science fair.

Instructions:

  1. Starting about 3 inches from the end of the wire, wrap it 7 times aroundthe toilet paper tube. Remove the tube (you don't need it any more). Cutthe wire, leaving a 3 inch tail opposite the original starting point. Wrapthe two tails around the coi l so that the coil is held together and thetw o tails extend perpendicular to the coil. See illustration below:

                                  

    Note: Be sure to center the two tails on either side of thecoil. Balance is important. You might need to put a drop of glue wherethe tail meets the coil to prevent slipping.

  2. On one tail, use fine sandpaper to completely remove the insulationfrom the wire. Leave about 1/4" of insulation on the end and wherethe wire meets to coil. On the other tail, lay the coil down flat and lightlysand off the insulation from the top half of the wire only. Again, leave1/4" of full insulation on the end and where the wire meets the coil.

                                  

  3. Bend the two paper clips into the following shape (needle-nosed pliersmay be useful here):


                                  

  4. Use the rubber band to hold the loop ends (on the left in the abovedrawing) to the terminals of the "D" Cell battery:


                                  

  5. Stick the ceramic magnet on the side of the battery as shown:


                                  

  6. Place the coil in the cradle formed by the right ends of the paperclips. You may have to give it a gentle push to get it started, but itshould begin to spin rapidly. If it doesn't spin, check to make sure thatall of the insulation has been remove d from the wire ends. If it spinserratically, make sure that the tails on the coil are centered on the sidesof the coil. Note that the motor is "in phase" only when it isheld horizontally (as shown in the drawing).

  7. For display, you will probably need to build a small cradle to holdthe motor in the proper position. It might also help to bend the ends ofthe coil a bit so that as it slips right or left, the bends keep it inthe proper position:


                                  
  1. Here is a diagram of the finished motor:

                                  

Further Experiments:

Since this is an existing design, you might want to do some furtherexperiments to make it more of a Science Fair experiment instead of justa model. Here are some suggestions:

  1. Try to adjust the phase angle of the motor so that it will operatein a vertical position. This involves removing a different area of insulationfrom the partially bared tail of the coil.
  2. Try making different shaped coils and seeing how they work. Is thecircle the best shape? Try squares, ovals, etc. Make a display showingeach of the coils you tried with a short summary of the results underneaththem.
  3. Try varying the number of turns of wire in the coil. I don't know wherethey came up with seven. Does even or odd number of turns matter? Doesthe number of turns determine the speed? Again, include the different coilsin the display and describe the results.
  4. How long can you get the motor to run before it falls off the cradle?
  5. Turn the coil slowly by hand and feel the magnetic attraction at eachposition of the coil. Make drawings showing the different coil positionsand describe how the attractions vary at each position.
  6. HARD ONES: Can you think of an interesting way of determining the speedof the motor (in RPM)? Can you make the motor do any work?

Final Notes:

You can get the magnet wire and ceramic magnets at Radio Shack. I thinkthe wire comes in a pack of three spools of different gauges, you wantto use the medium gauge, not too heavy, but thick enough to hold its shape.

Be sure to bring a fresh (extra) battery to school with the project.