These are common steps in troubleshooting your motor:

  1. Make sure that your rotor spins freely if you give it a slight push with your hand.
  2. Test your electromagnet. Connect one 1.5V battery to electromagnet wires briefly. The electromagnet should push the closest magnet on the rotor. The rotor should turn 45° if you have 4 magnets on a rotor, or 90° if you have 2. If it does not – switch the wires.If your electromagnet does not work, it may be shorted. Sometimes re-winding the electromagnet may solve this problem.
Problem Cause Solution
Newly assembled motor does not work: rotor does not spin. In the starting position the light from the LED reaches the phototransistor because the disk blade is not in the optointerrupter slot. Make sure that in the starting position one of the blades is inside the optointerrupter slot and does not allow light from the LED to reach the phototransistor. While holding the magnets, slightly rotate the cap with the disk to find the proper disk blade position.
Rotor is jammed. Find the exact cause and fix the problem. This may require breaking off the stands and reattaching them to the board. You may try to lubricate the axles with WD-40 or any other lubricant.
Electromagnet attracts the magnets instead of repelling them. Switch the electromagnet wires.
Bad connection in wiring. Thoroughly clean the wires to remove the insulation before soldering. Re-solder the connections.
Intersecting connections in wiring. After soldering check all the connections to make sure that they do not touch each other.
The battery is dead or battery voltage is low. Get a new battery. Increase the voltage by adding an extra battery. The lowest voltage for this motor is 3V, though sometimes it may not start at this voltage.
One of the magnets is not repelling. Tear this magnet off and glue it upside down. All of the magnets should have the same pole facing outside.
The optointerrupter is connected incorrectly. Make sure that you connected the optointerrupter wires according to the wiring diagram.
The optointerrupter was burnt and does not work. This may happen if you connected it improperly or used high voltage. Even a brief connection of the optointerrupter wires directly to the battery may destroy it. Replace the optointerrupter.
The transistor is connected incorrectly. Make sure that you connected transistor leads according to the wiring diagram.
The transistor was burnt and does not work. This may happen if you overheated it while soldering, connected it improperly, or had the rotor stalled on a high voltage. Replace the transistor.
The light from the LED reaches the phototransistor because the disk is semi-transparent. Blacken the blades with permanent marker or glue additional pieces of opaque material, such as aluminum foil, to the blades.
Motor worked fine for a while but then stopped working. The battery is dead or battery voltage is low. Get a new battery. Increase the voltage by adding an extra battery. The lowest voltage for this motor is 3V, though sometimes it may not start at this voltage.
The transistor is burnt. Get a new transistor and re-solder it. Try not to leave the motor stalled, this may be a reason the transistor was burnt in the first place.
The optointerrupter is burnt. Replace the optointerrupter.
The transistor is getting too hot even when the motor works. The rotor has too much friction. Make sure that the rotor spins freely. You may add a heat sink to the transistor for better heat dissipation. You may also try to lubricate the axles with WD-40 or any other lubricant.
The disk blades are too wide. (If you made a disk yourself or glued the pieces of opaque material to the blades) Trim the blades with scissors.
Dirt in the optointerrupter slot may interfere with the light beam. Clean the optointerrupter slot.
The electromagnet gets hot. Not enough wire used for the electromagnet. Make sure that the electromagnet coil has enough wire. Use all the wire from the spool.
Short connection inside the electromagnet. Re-wind the electromagnet. It is better to use a new spool of wire, but sometimes the old wire may still work.
The motor speed is too slow. The disk blades are too narrow. Make the blades wider by cutting the disk with wider blades or gluing 4 pieces of opaque material to the disk blades.
If you need to disassemble the rotor…   This operation requires quite a bit of strength. Disassemble the rotor with a rocking motion as if trying to break it and at the same time pulling the ends out.

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