How does an Electric Motor work?

Electric motors can remain very mysterious! How do they use electricity to start rotating? Let's break it down step by step to understand how it works. Topics covered in this video: circuits, current, magnets, electromagnets, armature, commutator, brushes, stator, and rotor. This video only covers DC motors. 

If you look around your house, you will see many devices that have electric motors, such as kids toys, table fans, toothbrushes, hairdryers, and this electric cutting knife. But how does the electric motor work? You turn it on and somehow it starts rotating. Why is that?

Let’s start with something called a circuit. You have a battery, some wires and a device that uses electricity, such as a light bulb. Electricity flows through the circuit. But as soon as there is a break in the wire, the electricity stops flowing and the light bulb goes off. The path must be complete for the circuit to work. This is best down through the use of a switch. Electricity is flowing down the wire. This is called conventional flow. If we take the battery out and flip it, then the current will flow the other way. The light bulb will still work in either case but there are some devices that will work differently depending on which way the current flows.

Okay, so that’s the basics of a circuit. Now let’s come over here. This is a magnet. It has a north pole and a south pole. And it likes to attract other metal objects like these paperclips. If you bring another magnet towards it, opposite poles attract, and the same poles repel. The magnets don’t have to be in this shape, for example, some magnets might be more flat, like this. You can think of this magnet as always on, It’s always working, you can’t really turn it off.

That’s why it’s sometimes called a permanent magnet. It’s made up of any smaller magnet domains that are lined up in the same direction but later, I’ll show you a type of magnet where this not always the case. Let’s take one of our permanent magnets and drill a hole in the center and put it on something that will allow it to spin.

Now, bring another magnet towards it. Our spinning magnet will immediately line up until opposite poles are right next to each other. Now switch out the side magnet. The same poles repel and opposite poles attract. If we keep switching out these side magnets, then our spinning magnet will just keep spinning. This concept of the spinning magnet is really important. Well come back to it in a moment. Here’s a metal bolt which is not a magnet. It’s made up of magnetic domains but they’re pointing in random directions. Now let’s take a wire, wrap it around several times and then create a circuit. The current through wires forces the magnetic domains to line up. That means we’ve just made a magnet, or more specifically, an electromagnet.

It can do the same things that a permanent magnet can. It can pick up pieces of metal and it has a north and a south pole, which will attract or repel other magnets. But the electromagnet is special in the sense that it can be turned on or off, just like the light bulb. You can’t do that with a permanent magnet. Now watch what happens when we flip the battery. 

The electric current was flowing this way but now it flows the other way. This will cause the poles on our magnet to switch places. North will become south and south will become north. This is called reversing the polarity of an electromagnet. Instead of flipping the battery, an easier way to do this is to just switch the wires. You should be aware that the electromagnet will get very hot if it’s on for a while, just a caution in case this video inspires any science projects.

Let’s come back to our spinning magnet. This time well replace the spinning magnet with our electromagnet. As soon as we connect the wires, the magnet turns on and it lines up with the side magnet. Now, in reality, connecting these wires would prevent the bolt from spinning freely but what’s important here is the concept of the spinning electromagnet. Now let’s switch the wires to reverse the poles on the electromagnet. The same poles repel and opposite poles attract.

Now, reverse the polarity again. Same poles repel and opposite poles attract. If we keep switching the polarity, our electromagnet will just keep spinning. To make this strong, let’s bring in another permanent magnet on the side. Notice how this side has the south pole towards the center and this side has the north pole towards the center. The side magnets work together to spin the one in the middle. This right here shows the very basics of an electric motor but we need to make a few improvements. The two side magnets can be replaced with stronger curved magnets.

And instead of a bolt with wires, we’re gonna use a metal loop. This is called the armature. Connect our wires and we have a circuit again. This time, you can think of the electromagnet as flat like this with the south pole pointing up.

Now the armature will spin until opposite poles are lined up. We can keep it spinning by switching the wires just like we did before. But this is a lot of work to sit here and manually switch these wires. We need to add something to the armature called a commutation. It’s a ring with gaps in the opposite sides. The commutation will spin along with the armature. Now we connect the circuit with two brushes on the side. These brushes will slide along as the commutation spins. And they are spring loaded so that they always maintain contact. The current flows from the wire through the brush, the commutation ring, the armature loop and back through the other side. Now we have our electromagnet and the armature spins.

As we come around this time, the brushes will switch contact to the other side of the commutation ring. And remember, there’s two brushes so this is happening on both sides. Before the switch, the current in the armature is flowing this way.

After the brushes switch sides, current will flow the other way. This means the electromagnet switches polarity, which will cause the armature to keep spinning. This commutation ring does the same thing as switching the wires like we were doing before but this time, it does it all on its own. It will continue to spin as long as were connected to a battery. Disconnect the battery, no more electromagnet and the spinning stops. Now, so far, we’ve only used one loop on the armature.

This will cause our motor to have an irregular speed and in fact, we could get stuck in this position with the brushes halfway between commutation segments. What we can do is split the commentator ring and then add another loop, so first, the brushes are in contact with these commentator segments, which turns on this selector magnet, which causes it to start spinning. Once we get to here, the brushes switch contact to the next pair of commentator segments, which means this loop turns off and the next loop turns on.

Now, this electromagnet wants to spin. The brushes switch contact and the next loop turns on. This keeps happening as our motor spins. It’s almost like the loops will take turns being an electromagnet. Some electric motors will add many loops to the armature. This ensures that there will be a continuous spinning motion on the motor. This spinning force on the armature is called a torque. Stronger torque means a faster spin. There are some things we can do to improve the torque of the motor. Electromagnets are stronger when there are more wires. 

This is true when we wrap more wires around the metal bolt and it’s also true when each of our armature loops are made of many wires. The motor will have stronger electromagnets, which means it will spin faster. If you look at some pictures of real electric motors, you can see lots of wires wrapped around and yes, this is the same reason. More wires wrapped around means stronger electromagnets. Another way to make this stronger is to use more electricity.

Let’s learn a few more terms here. The part that doesn’t move is called the stator. In this case, it’s the two permanent magnets on the side. These fit inside the edges of the motor case. The armature in the middle is also called a rotor.

Remember, this is the part that spins. The axle goes through the middle here and then sticks out the back of the motor.  Other types of electric motors will work a little differently than what I’ve shown here. No matter the type of motor, most of them will produce some type of spinning motion. Once its spinning, we can use this to make different devices move. In this case, a kids toy. Or even a fan that cools your room. The spinning of the motor can be converted to other types of movement, such as the side-to-side motion that we see in this fan. Or how about this electric cutting knife?

Each blade is going back and force. It all starts with the spinning of the motor to turn a gear, which then pushes these two pieces back and forth. So hopefully this video has made a few light bulbs go off in your brain. If you like learning new things, head on over to Brilliant. This is a problem-solving website and app that focuses specifically on math and science. The idea here is that you learn by doing. Pick a topic, it starts with the basics but gradually gets more complex as you go. For me, I’ve enjoyed how you can see these concepts visually, like the area of a circle.

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