BL Workshop

Build an Electric Motor





This simple motor operates by turning a magnetic field on and off at the proper time.


VIDEO: Watch our simple electric motor in action.

When current flows through the motor’s rotor coil, it generates a magnetic field. (Picture an invisible magnet extending through the center of the ring-like rotor coil.) When you put a permanent magnet near the rotor, the rotor will try to align itself so that the north pole of the “invisible magnet” will face the south pole of the permanent magnet (or vice versa). If the current is turned off before alignment occurs (but while the rotor is still turning), the invisible magnet will cease to exist and momentum will cause the center of the rotor to swing past the permanent magnet. Eventually friction will bring the rotor to a standstill.

If the electrical current is restarted at just the right time, the invisible magnet will re-form and the rotor will continue to spin. This on-off-on-off pattern of the invisible magnet drives the rotor like a small “putt-putt” boat motor.

WHAT YOU’LL NEED

  • 2 Paper clips
  • 4 Tacks
  • 1 Soft wood block, 5 inches long
  • 2 Small round magnets
  • 1 15-inch length of lacquered bell wire (we used 26-gauge wire)
  • Nail polish (any color!)
  • Needle-nose pliers
  • Sandpaper
  • Masking tape
  • White glue or hot glue gun
  • Magic marker or a half-inch diameter dowel
  • 1.5-volt flashlight battery (you might need two batteries)

WHAT YOU’LL DO

Step 1: Rotor Assembly

motor-11.jpgA) Using the sandpaper, scrape one inch of lacquer insulation from each end of the bell wire. This is a critical step.

B) Wrap the wire around the marker or dowel, leaving one inch of each wire end extending from the resulting coil. Use a bit of masking tape to keep the coil from unraveling. The two wire ends must be aligned in a straight line passing through the center of the coil.

motor2.jpgC) Holding the rotor so the coil is vertical, coat the upper half of one of the wire ends with nail polish. Set aside until the nail polish is thoroughly dried. The nail polish will control the flow of current through the coil as the rotor spins, turning the invisible magnet on and off at just the right time.

Step 2: Base Assembly

motor3.jpgA) Using the needle-nose pliers, bend the two paper clips into the shape shown here.

B) Using white glue or a hot glue gun, glue one of the magnets onto the center of the wooden block. When the glue has dried, place the second magnet on top of the glued magnet.

motor4.jpgC) Attach the two bent paper clips to the wooden block on either side of the magnets using the tacks. The upright parts of the paper clips should be about 1 1/2 inches apart.

Step 3: Final Assembly

A) Carefully insert the wire ends of the rotor through the loops of the upper parts of the paper clips.

motor5.jpgB) Run a wire from one of the paper clips to the positive terminal of a flashlight battery. Run a second wire from the other paper clip to the negative terminal of the battery. The rotor should start to spin after being gently flicked with a finger.

TROUBLESHOOTING

This motor is not a precision device, so it might be necessary to fiddle with it in order to get it to work. If the rotor does not spin or spins poorly, try the following:

A) Check the charge on the battery. You might need to connect two 1.5-volt batteries together to get enough power. Never connect more than three volts to your motor.

B) Check the wires connecting the battery terminals to the paper clips. Hint: An easy way to connect the motor to the battery is to use wires fitted with alligator clips, as we did here. Alligator clips can be purchased at hardware stores and electronic outlets.

C) Check the wires extending from the rotor for insulation. If a poor job was done removing the insulation in Step 1, current will not flow in the rotor and the magnetic field will not form.

D) Check the inside loops of the paper clips for dirt, especially if the rotor was inserted before the nail polish dried. Dirt will block the flow of current through the rotor.

E) Check distance of the rotor from the magnet. When the rotor coil is turned vertical to the face of the magnet, the distance between the coil edge and the magnet should be less than 1/8 of an inch. Bend the upper sections of the paper clips slightly to bring the coil closer to the magnet.

F) Center the coil over the magnet. Reposition the coil by bending the upper sections of the paper clips.

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