Assembly Instructions: Kit #7

Motor, assembled from Kit #7

Difficulty level: 3 (more difficult, requires the use of a soldering iron)

Parts included in this kit

 Printer-friendly assembly instructions in pdf format.

If you want to purchase one of these inexpensive and simple kits, click here.

If you want to understand how it works, click here.

Read all instructions carefully and check the Safety Rules before you start!


  1. Insert the T-pin into one of the caps.
  2. Insert T-pin into the cap

  3. Insert the rotor core into the same cap as shown below. Apply some pressure to push the rotor core approximately 1/2" (10-12mm) into the cap.
  4. Insert rotor core into the cap

  5. Put in the wooden insert.
  6. Put in round wooden insert

  7. Insert the pushpin into the other cap.
  8. Pushpin in another cap

  9. Put everything together as shown below. Push the caps towards each other until they cannot move any more. The T-pin must be secured firmly. This process may require some strength. Be careful not to bend the T-pin or poke yourself.
  10. Assembled rotor

  11. Glue the magnets to the flat surfaces of the rotor core with the letter ‘S’ facing outside. Your kit includes 4 magnets. If you want to try 2 magnets first, glue them to the opposite sides. Straighten the T-pin if necessary. You can check it by spinning the rotor between your thumb and index finger. Again, be very careful.

    All kits have magnets with the South pole marked. If you want this side to look better you may cut out the white glossy round labels that are provided and paste them to the marked sides. You may do it before attaching the magnets to the rotor. It is recommended to use regular white glue or a glue stick on the labels for better results.
  12. Rotor with magnets attached

  13. Cut out the disk (supplied with the kit). Poke a hole in the center, which is marked by a cross. Apply some glue to the middle of the disk and glue it to the cap with a shorter axle (with the pushpin). Slide two sequins as shown below. The sequins act as a spacer between the disk and the stand and work better if their convex surfaces face outwards.
  14. Adding a disk to a rotor

  15. Insert the rotor into the stands marked with blue and silver stars as shown below. Hold the stands and test to see if rotor spins freely. Make final adjustments to the T-pin if necessary.
  16. Rotor on stands

  17. Glue the stand with the silver star to the board. Try to cover the corresponding star completely. Align the marks on the stand with the line on the board as shown below. Note that the star's position and the marks are approximate, sometimes you need to move the stands slightly to achieve the lowest friction. Keep in mind that super glue bonds instantly, so try to be as accurate as possible in these procedures.
  18. Rotor on board (shown without disk)

  19. Insert the rotor into the stand marked with the blue star. Glue it to the board the same way as the first stand. Leave a gap of about 1/16" (1/32", or 0.8mm on each side) between the rotor and the stands. Test again to see if the rotor spins freely. At this time, or later, you may take the rubber plug and fix it as shown below. You can glue different things to the outer flat surface of the plug. Try to be accurate, redo this step if necessary.
  20. Rotor on stands with rubber plug attached

  21. If you purchased the experimentation kit #2 or #3, instead of steps 11-13 for this kit, follow these instructions. After that, please, come back to this page and continue the assembly instructions from step 14.

    Otherwise, insert the nail into the stand with the green star. If it is loose you may apply glue as shown below.
  22. Nail, glued to electromagnet stand

  23. All wire on the spool should be used to wrap around the area between the tape and the head of the nail.
    • Tape one end of wire leaving about 6" (15cm) open. You may use the tape that is already on the nail.
    • Wind all the wire in one rotational direction (either clockwise or counterclockwise) moving back and forth along the nail. Try to be as accurate as possible. Do not let the wire slide off the end of the electromagnet.
    • Tape the second end of the wire using the same tape. Both open ends of wire should be about 6" (15cm) long.
    • Clean about 3/8" (10mm) of the wire tips with fine sandpaper (included) or a sharp knife to remove the insulation.


    Test the electromagnet! Connect one wire to "+" and another wire to "-" of the battery. If electromagnet is assembled correctly the head of the nail should attract metal objects such as paper clips, small nails, knife blade, etc.
  24. Glue the electromagnet to the board as shown below. Turn the rotor slowly to see if the magnets hit the electromagnet. If one or more do, move the electromagnet back until there is a 1/16" (1.5mm) gap between the electromagnet and the closest magnet on the rotor.
  25. Electromagnet position

  26. Locate the optointerrupter pins as shown on the following picture. It is very important to identify all four pins properly. Wrong connection in the motor will destroy the optointerrupter.
  27. Optointerrupter pins

  28. Solder 4 pieces of the hook-up wire to the optointerrupter pins. If your kit includes 1 large piece of hook-up wire, cut it into 4 pieces of equal length. Strip about 3/8" (10mm) of insulation on each end of these wire pieces using a sharp knife. You may bend the optointerrupter leads slightly to move them apart from each other. If you did not use a soldering iron before it is a good idea to practice on soldering two pieces of wire to each other. See the Links page for tips on soldering.

    Wire colors shown on the picture are used for reference only. You may use different colors or even one color. Just make sure that all the connections correspond to the diagram of the motor as shown in step 21.

    IMPORTANT: Do not overheat the optointerrupter when you solder it. The soldering iron heat may destroy this sensitive device. If you were unable to attach the wire in 3 seconds, let the optointerrupter to cool off, then try it again. Only solder one lead at a time and allow the device to cool before soldering the next connection. Use the same precautions when soldering the transistor.
  29. Soldering wires to the optointerrupter

  30. Locate two marked lines and glue the optointerrupter to the square wooden stand as shown below:
  31. Attaching an optointerrupter to a stand

  32. Glue the optointerrupter stand to the board as shown in the picture. If you rotate the rotor, the disk blades should be in the middle of the slot as deep as possible without hitting the optointerrupter. Wait for the glue to dry. Hold the middle part of the rotor and rotate the cap that has the disk attached until one of the blades is inside the slot. You will need to experiment with it later to find the best position of the disk to provide a good start and the best speed.
  33. Optointerrupter position

  34. Locate the base (B), collector (C) and emitter (E) leads on the transistor:

    IMPORTANT: do not overheat the transistor when you solder it. The soldering iron heat may destroy the transistor. Only solder one lead at a time and allow the device to cool before soldering the next connection. The transistor will most likely be extremely hot during this process, be careful not to burn you fingers.
  35. PNP power Darlington transistor

  36. Locate the 270 Ohm and 4.7 K (4700 Ohm) resistors. The 270 Ohm resistor has red, violet, brown and gold color bands. The 4.7 K resistor has yellow, violet, red and gold color bands. Bend the leads of the resistors as shown below. Tweezers or needle-nose pliers may be very helpful but not required. Trim the leads as necessary (you may use scissors for that purpose).

    Solder these resistors together as shown in the picture. See the Links page for tips on soldering if you do not have enough experience in this procedure. Solder the resistors to the transistor. Do not overheat the transistor. If you were unable to attach the resistors in 3 seconds, let the transistor cool off, then try it again.
  37. Soldering resistors to a transistor

  38. Attach the battery holder to the board. The battery holder allows you to experiment with 4 different voltage settings (1.5, 3, 4.5, and 6V DC). You will need 4 AA size batteries.

    To understand how the jumper wire works let's take a look at the connections inside the battery holder:
  39. Empty battery holder

    The following diagram shows how to get 1.5, 3, 4.5, and 6 Volts using 1, 2, 3, or 4 batteries and a jumper wire shown in blue color. Arrows show the current flow for 1.5, 3, and 4.5 Volts settings. Could you trace the current when all 4 batteries are inserted (there is no jumper wire in this case)?

    Jumper connections

    Insert bare ends of the jumper wire between the spring and plastic case to make a good contact and hold them in place. This is how the jumper wire is actually used for 3 Volts experiments (one end is disconnected and may serve as on/off switch):

    3 Volts jumper wire connection

  40. Follow these steps using the wiring diagram for Kit #7 below. You may trim the wires if necessary.
  41. Your connections should look similar to this:

    Wiring diagram for the kit #7

Check your connections carefully! Even a brief connection of the optointerrupter wires directly to the battery may destroy it.

Start with 3V. While holding the magnets, slightly rotate the cap with the disk in both directions to find the best position where the motor starts easily and spins with the fastest speed. If the motor does not work, increase voltage to 4.5V. If it still doesn’t work, ensure that the rotor can rotate freely and check all the connections – it is important to clean the insulation thoroughly before soldering. Make sure the batteries are fresh and connected properly. If the motor still does not work – click here for troubleshooting.

CAUTION: Do not leave the motor connected to the batteries if the rotor is stalled. High current through the transistor will make it very hot. It may burn your fingers if you touch it and eventually may destroy the transistor.

CONGRATULATIONS! You have finished assembling this electric motor! Click here for Experiments and Applications.