Build a Simple Electric Motor from Scratch

Every electric motor — from a toy car’s tiny vibration motor to a Tesla’s traction motor — works on the same principle: a current-carrying conductor in a magnetic field experiences a force (the Lorentz force). This homopolar-style motor builds that principle from first principles using wire, a battery, and rare-earth magnets.

What You’ll Need

• 1.5 V AA battery
• Enamelled copper wire (0.3–0.5 mm diameter, about 60 cm)
• 2 × neodymium disc magnets (strong)
• 2 large metal paperclips or stiff bare copper wire (for supports)
• Sandpaper (fine)
• Tape for temporary holding

Step-by-Step Instructions

1. Wind the coil: Wrap 15–20 turns of enamelled wire around a AA battery to form a circular coil about 1.5 cm diameter. Leave ~4 cm straight tails on each side. Slide the coil off the battery.
2. Secure the coil shape: Wrap the tails around the coil body twice each to keep the shape — the tails should stick out from opposite sides along the same axis (the rotation axis).
3. Sand the tails: Sand the entire insulation off one tail (both top and bottom). Sand only the TOP half of the other tail — leave the bottom half insulated. This asymmetric stripping creates the commutator effect that keeps rotation going.
4. Build the frame: Bend two large paperclips into U-shapes to form bearing supports. Stand them on each end of the battery with the top loop as the bearing the coil axle rests in.
5. Place magnets: Stack the neodymium magnets on top of each other and place them on the centre of the battery top, below where the coil will hang.
6. Start the motor: Rest the coil axle tails in the paperclip bearings above the magnet. Give the coil a small spin to start. If wired correctly, it will continue spinning on its own.

Safety Notes

• Neodymium magnets are extremely strong for their size — keep away from fingers (pinching hazard) and from credit cards, pacemakers, and electronics.
• The battery will drain quickly — disconnect when not demonstrating.

Tips & Troubleshooting

• If the coil doesn’t spin after a nudge, check that the half-insulated tail truly has ONLY the top half sanded — the bottom half must be insulated.
• Lower the bearing height so the coil hangs closer to the magnets — stronger field = more torque.
• This works best with very strong neodymium magnets; weak ferrite magnets won’t produce enough force.