Demo Classroom Induction Motor

There are many DIY Permanent Magnet (PM) motors, demonstrated online, usually simple DC motors that have a loop of wire spinning between poles of a PM. In real life most electric motors in actual use today (as at Apr 2026) are actually Induction Motors. They have no PMs in them! I set out to build a classroom-safe demonstration induction motor that shows how a simple copper wire frame rotor can be made to rotate with a couple of stator coils and electro magnetic induction.

Induction motors are fascinating, because it's not immediately obvious how they work. I was a small boy watching a UK Open University Electrical Engineering TV program with my dad, when I first saw a demonstration induction motor. A copper wire frame just appears to spin. I couldn't see how it worked, what makes it go around, but I did notice the presence of two electromagnetic coils. I kind of knew something magnetically was going on but I did not understand the details, and would not for another 10 years!

This Demo Induction Motor uses a really low friction bearing. This is crucial as this enables it to run on a 9 volt AC supply thus making it completely safe to touch and operate in a classroom setting. The bearing consists of an upside down Indicator Pin, that is held magnetically by a couple of small neodymium magnets with a tiny piece of thin glass in between the magnets and the drawing pin. The glass and a little bit of light oil lowers the friction of the bearing.

The motor has two stator coils near to the rotor, with their axes at right angles. One coil is fed from the safe 9 V AC supply through a capacitor, which limits the current so the coils do not overheat, and wastes less energy than using a resistor. The second coil has an extra capacitor, in series, so its current is shifted in time compared with the first coil. The two coils are at right angles in space and their currents are out of phase in time. This generates a magnetic field that sweeps around the rotor, sometimes called a rotating magnetic field. This rotating magnetic field induces current flows in the copper wire rotor, which in turn generates a magnetic field, which interacts with the moving magnetic field from the stator coils to generate torque, thus causing the rotor to spin.

1. Small block of wood (ca 4cm x 4cm x 1cm) to make a jig for constructing the "birdcage" copper wire frame rotor.
2. 50cm of Copper Wire 16 SWG (1.63mm) for making the rotor.
3. Large Indicator Pin for the bearing.
4. Solder, soldering iron, small butane flame lighter for soldering copper wire joints.
5. 16cm x 10 cm x 1.5cm wood to mount the overall motor.
6. 2 x wood supports (2cm x 2cm x 8cm) and 2cm x 13cm x 0.5cm to create the rotor support.
7. 2 small neodymium magnets (1.5mm x 1cm diameter) to create the bearing.
8. A small fragment of glass (the kind used for protecting mobile phone screens) to make bearing.
9. Old discarded power supply unit with transformer inside to create primary stator coil.
10. Copper wire (varnished) 33 SWG (0.25mm) to create the auxiliary stator coil.
11. Some wood bits or lego bricks to mount the stator coils.
12. 6 x Non-Polarized 100uF Electrolytic Capacitors: https://www.amazon.co.uk/dp/B0F1FTF6G9
13. One mains to 9 Volt (1 Amp) power supply.
14. A couple of small LED's and a resistor to indicate power is on.
15. A 3 way screw terminal block (choc-block).
16. Wire to connect the components.

1. Most Induction motors have what's called a Squirrel Cage. Because of the bearing design mine looks more like a Birdcage, than a Squirrel Cage. It starts with cutting a small square block of wood, about 4cm x 4cm x 1cm to act as a jig.
2. Use a round object to draw a circle onto the wood, with a diameter of 3cm.
3. Drill 8 x 2mm holes, 0.5cm deep, into the wood, placed equidistant on the circumference of the circle.
4. Fashion 8 identical "L" shapes from 16 SWG Copper Wire. The long part of the "L" is 4cm, and the short part of the "L" is 1cm. The copper wire I bought was varnished, so I also had to use sand paper to remove the varnish at the ends of the "L" shape. It helps if you also use a soldering iron and apply some molten solder to tin the ends of the copper wires so they are ready for soldering later.
5. Make two copper rings, (if needed remove all varnish using sand paper before bending the wire to make the ring). Tin the rings at each point where there will be joints. The first ring needs to be 1cm in diameter, and the second needs to be 3cm in diameter. Also make sure the ends of the wire used to make the rings are soldered together so that you have a continuous ring conductor.
6. Insert the 8 x "L" shapes copper wire pieces into the jig. Orientate the "L" shapes to support the smaller copper ring, and then solder each "L" shape to the smaller ring. I found I had to use a small butane burner to get the copper hot enough to enable a good solder connection. This will make the birdcage structure.
7. When the copper has cooled, use a contact glue to affix an Indicator Pin onto the small copper ring, pointing upwards, as shown in the picture. This will become part of the bearing. Then remove the birdcage structure carefully from the jig. Bend the 8 copper wire legs slightly outwards so that when you put the larger copper ring onto the birdcage the 8 legs hold it in place. This makes it much easier to solder each leg onto the large copper ring.

1. I used a contact adhesive "Gorilla" glue to construct a simple wood bridge, as shown in the photos. The pillers were 2cm x 2cm x 8cm and the top part of the bridge was 2cm x 13cm x 0.5cm
2. I then used the contact adhesive glue to attach one small neodymium magnet (1.5mm x 1cm) to the center and underside of the bridge.
3. Once the glue had dried then I added a second neodymium magnet (I found by experimenting that 2 magnets were sufficient to hold the weight of the birdcage rotor, about 11g)
4. Finally I had an old unused mobile phone tempered glass screen protector. I broke a small fragment off and glued this to the underside of the neodymium magnet to complete the bearing, as shown in the photo. There's a tiny bit of light oil in the contact between the needle and the glass to try to reduce friction further.

1. You need to find an old power supply unit, one that has a transformer in it. Ideally it would be converting mains AC electricity to somewhere between 6-12 Volts, and be capable of delivering between 0.5 - 1 Amps. The one in my demo happen to be 6 Volts and 0.5 Amps.
2. Carefully cut and split the unit open, in order to extract the transformer, making sure not to damage the coils or the connections to the transformer. Often there is a small board with a few diodes and a capacitor to convert AC to DC, but this will be disconnected later and is not required.
3. Put the transformer into a vice and then use a hacksaw to start cutting the transformer in half, as shown in the photo. Every transformer has a Primary coil, and a Secondary coil. The Primary coil is connected to the mains electricity, and tends to be made of very fine copper wire, where as the Secondary coil that generates the lower output voltage uses less turns of a coil made from thicker copper wire. As you cut the transformer in half make sure that the secondary output side of the transformer is NOT damaged. We're going to be using that later. The Primary mains facing coil will almost certainly get damaged but this doesn't matter as that coil is going to be replaced.
4. When you are about half way through cutting the transformer in half surround the Primary side of the transformer in electrical tape, and use a G clamp to hold the transformer together. The transformer core is made of lots of steel plates. As your hacksaw gets close to splitting the transformer in half, there is a risk that all the plates will fall apart. The tape and G-clamp are there to ensure that the end result is that you have two halves of a transformer core, with the low voltage Secondary coil still intact.
5. Once the two halves are separated, you will have two "E" shape transformer half cores. Remove all of the Primary Coil from its "E" shape transformer core, leaving what's called the coil former, or bobbin.
6. Clean up the coil former. I had to remove the outer parts of the coil former, and glue another flat piece of plastic onto it to replace the plastic destroyed by the hacksaw.
7. Use 33 SWG (0.25mm) copper wire to wind a new coil onto the coil former. I didn't aim for a specific number of turns, instead I aimed to fill the available space. My winding space was a square shape, the outer square being about 23mm x 23mm, and the inner square being about 15mm x 15mm with a coil depth of about 12mm.
8. Finally I used some old lego bricks from my sons toy box to make a couple of stator coil stands to mount the transformer "E" halfs and used contact adhesive to glue everything in place. The stator coils are placed at right angles to each other, and are about 7mm from the rotor, as shown in the photos.

The Demo Induction Motor requires an AC voltage supply. Unfortunately the only power supply unit (PSU) that I could find was an old 9 Volt DC Sinclair Computer PSU, rated at 1.4 Amps. When I opened the Sinclair PSU up I found it was a transformer with a standard full wave rectifier and smoothing capacitor. I removed that rectifier and capacitor to derive an AC supply, but I still needed to limit the current flow through the demo motor. One could use a resistor, capacitor, or inductor to limit the current. I experimented with all three options and eventually settled on using a capacitor. This wastes less energy, and doesn't result in a resister that gets quite hot.

1. The circuit above shows how the Demo Induction Motor is wired up.
2. C1 reduces the current flow down to the required level.
3. C2 causes the current flow in Stator Coil 2 (SC2), to be out of phase with the current in Stator Coil 1 (SC1).
4. To create 300 uF capacitors, I bought 3 x 100uF capacitors and wired them in parrelel. The Capacitors need to be Non-Polarised, because of the AC, and electrolytics, because of the size. The Capacitors I used were rated for 100V which is plenty for this application.
5. The LEDs show that power is on, the resistor limits current flow to a milliamp or two.

1. I found the following web-page for explaining how "Induction Motors Work".
2. Shown above is a picture from my osciloscope with the voltages across each of the status coils, which illustrates how there is a phase shift.