Backpack Science with Ken Finn: Stripped-Down Motor

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Backpack Science

Backpack Science is a summer series of easy at-home experiments geek dads can perform with their kids while school’s out. It is written by (San Francisco) Exploratorium science educator Ken Finn. This article is #8, and the final in the series; you can find the whole series here.

Stripped-Down Motor

I find this electrically-powered contraption fascinating — almost magical. It’s a very powerful experience to gather some common objects (wire, paper clips, some magnets and a cup) and, along with a battery, assemble them so they “spring to life.” This electrodynamic rotating ring will pull you and your kids into an afternoon of tinkering.

What you’ll need:

  • 5 small disk or rectangular ceramic magnets
  • 2 large paper clips
  • plastic, paper or Styrofoam cup
  • solid (not stranded) enameled or insulated 20-gauge copper wire, about 2 feet (60 cm) long
  • masking tape
  • battery or power supply
  • 2 electrical lead wires with alligator clips at both ends
  • wire strippers (if you are using insulated wire)
  • sandpaper (if you are using enameled wire)
  • black waterproof marking pen
  • battery holder

How it’s done:

  1. Wind the copper wire into a coil about 1 inch (2.5 cm) in diameter. Make four or five loops. Wrap the ends of the wire around the coil a couple of times on opposite sides to hold the coil together. Leave 2 inches (5 cm) projecting from each side of the coil, and cut off any extra.
  2. If you are using insulated wire, strip the insulation off the ends of the wire projecting from the coil. If you are using enameled wire, use the sandpaper to remove the enamel.
  3. Color one side of one of the projecting ends black with the marking pen.
  4. Turn the cup upside down and place two magnets on top in the center. Attach three more magnets inside the cup, directly beneath the original two magnets. This will create a stronger magnetic field as well as hold the top magnets in place.
  5. Unfold one end of each paper clip and tape them to opposite sides of the cup, with their unfolded ends down.
  6. Rest the ends of the coil in the cradles formed by the paper clips. Adjust the height of the paper clips so that when the coil spins, it clears the magnets by about 1/16 inch (1.5 mm). Adjust the coil and the clips until the coil stays balanced and centered while spinning freely on the clips. Good balance is important in getting the motor to operate well.
  7. sd_motor_1

  8. Once you have determined how long the projecting ends of the coil must be to rest in the paper-clip cradles, you may trim off any excess wire. The length of the projecting ends depends on the separation of the paper-clip cradles, which in turn depends on the width of the base of the cup you are using.
  9. If you are using a battery, place it in a battery holder. You can make your own from a block of wood with four vertically-inserted nails. Use the clip leads to connect the battery or power supply to the paper clips, connecting one terminal of the battery to one paper clip and the other terminal to the other paper clip.
  10. sd_motor_2

  11. Give the coil a spin to start it turning. If it doesn’t keep spinning on its own, check to make sure that the coil assembly is well-balanced when spinning, that the enamel has been thoroughly scraped off if enameled wire has been used, that the projecting end has been painted with black pen and that the coil and the magnet are close to each other but do not hit each other. You might also try adjusting the distance separating the cradles, as this may affect the quality of the contact between the coil and the cradles.
  12. Keep making adjustments until the motor works. Have patience! The success rate with this design has been quite good.

Stripped-Down Motor (images included), excerpted with permission from Exploratopia, 2006, published by Little, Brown Books for Young Readers © Exploratorium, All Rights Reserved.

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2 thoughts on “Backpack Science with Ken Finn: Stripped-Down Motor

  1. Hi Ken Finn, I knew you a million years ago as Kenny Finn, my name, it was Nicky Penney, now I go by Nichola Fitzsimmons…. I found an old picture you gave me in an old trunk a few days ago & thought, I sure do miss that guy & here you are!!! I’m leaving my info below, contact me!;-)

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