 Hi, I'm Zor. Welcome to Unizor Education. Today, we will talk about practical usage of direct current electricity in DC motors. Well, this lecture is just part of the course. The course is called Physics for Teens. It's presented on Unizor.com. Every lecture is accompanied by very detailed notes. It's basically like a textbook which you can read synchronously with listening to the lecture, or as synchronously. The website also contains the prerequisite course called Mass for Teens. Mass is absolutely mandatory to know a certain extent to know the physics. But today's lecture will be more, I would say, practical. No calculations, no formulas. So, we will talk about how direct current motors are actually created. What's their basic design, ideas, etc. By all means, I'm not going to talk about all the minute details of how contemporary DC motors are used. But I will try to bring you as close to this as possible without going into the smallest details. So, you will not be able to master every detail. But you will understand the principle. And that's what I believe is very important. Also, I'm not going to talk about how it's done now. I will try to present the construction of these motors as they were historically invented. Because everything starts with a simple idea. And then this idea is being developed a little bit better and better until it reaches contemporary level. I think it's very important to understand how it comes from the original idea. Because actually that's how every creation is made. First, you have an idea. And then you start implementing this and you find this little thing and that little thing which may be an improvement. But there is an idea in the very beginning which is extremely important and I will pay some attention to this. Okay. Now, what's the idea of DC motor? Well, first of all, do we use and where do we use DC motors? Well, wherever the source of electricity is direct current, which mostly batteries. So wherever the batteries are used, we use direct current motors. For example, when you start the car, you turn the ignition key or press the button. Something starts rotating the main engine, the internal combustion. I'm not talking about electrical motors, automobiles right now. I'm talking about electric combustion. So at that particular moment, you have starter and starter is supposed to start the main engine. Well, starter is DC motor. Now, I just mentioned electric cars. Well, obviously, all the motors in the electric cars are DC motors. Also, obviously in all the toys where you have small batteries, AA batteries, AAA batteries that power some kind of motors like little cars moving. Drones, for instance, they work off batteries, obviously. And the direct current motors. In computers, hard disks, for instance, are rotating. That's DC motor. So it's very important to have nice DC motors. And we do have nice DC motors right now. But the idea is much simpler than contemporary construction. If you will open right now the DC motor of, let's say, hard disk of a computer, you will see a lot of different things. And you might not actually understand that everything is actually based on simple principle. And let's start with the simple principle. So what is the simple principle? Well, you'll know that if you have two poles of a magnet, well, let's say it's something like this. This is my magnet, okay? Now, in between you put a conductor, let's say a copper wire, and you connect it to electricity. So we have electrons moving this way. The current moves from positive to negative moves this way. The magnetic lines go from north to south. And we know that in this particular case, every electron which is moving here acts a force, a lens force. And basically that actually creates the force on the entire wire. So the entire wire would be moving either this way or that way. It doesn't really matter. It's a rule of the right hand, rule of the left hand, whatever it is. But it will be perpendicular. That's what's important. Perpendicular to both the direction of the magnetic lines and the direction of electricity, current. So in this particular case, if my magnet is like this and if my current is, let's say, perpendicular to the board, then the force will be vertical, up or down depending on the direction of the current in the wire. So that's the beginning. What does it mean? It means if you have electricity and magnetic field, you will have the force which will move the conductor which carries this electricity. Great. So this is the first idea. We can convert mechanical and we can convert electrical energy and magnetic energy into mechanical movement. Now, from this, we have to build the engine, the motor. Well, in all the practical cases, the motor must actually rotate. So that's the most practical thing. So we have to find out how to rotate something. Well, next idea. Next idea is, instead of just single wire, you will have a frame and you will put this frame on some kind of an axis. And this will be my battery, plus and minus. Now, what happens in this case? Look, the current goes this way, goes here and goes this way. So these two sides of a frame carry the current in opposite direction. What does it mean? Well, it means that the force which acts on the current from the magnetic field would move, would force actually one of them in one direction and another side would be in another direction. As we were saying before, the direction of the force depends on the direction of the current. Well, and obviously the direction of the magnetic field, but magnetic field is constant. With the current, we have in two different directions, two opposite directions. The first will be in the opposite direction. Now, if you have a frame which is freely rotating around the axis and we have two different forces, well, it will start rotating. Okay, so we are making some progress towards rotating. Okay, now, designed by itself will work only until both forces will rotate significantly enough to position when these forces will be opposite to each other. Because if you will look at this from the top, so from the top it will be what? This is one magnet, this is another magnet. So these are lines of magnetic field. Now, if my frame from the top looks like this, which means there is a wire from here to behind the board and from wire from here behind the board, we are looking from the top. Now, in this particular case, this wire will be moved in one direction and this wire will be moved to another direction until it will turn in such a way that the frame would be perpendicular to the magnetic field lines. So let me just draw this differently. So when it perpendicular direction of the current, so in this case my force will be perpendicular to both direction of the magnetic lines and direction of the current, which means it will be to the right or to the left. So this one, let's say, would go to the right and in this one let's put the letters A, B, C, B. So A, B would be moved to the right, C, D would be moved to the left and it will start rotating. When it will reach the position when this frame is perpendicular, it will be the biggest actually, a rotating moment. But when it will be parallel to these lines, what happens in this case? Well, one of them would move, would push this way, another would push this way, they would neutralize each other. There would be no rotating momentum relative to the axis. So if it's this way, there is a rotating momentum. If it's this way, there is no rotating momentum. So our frame would turn like up to a certain position and then it might actually oscillate a little bit and stop. So there is no rotation, there is no permanent rotation. We need to do something to make it permanent. Next idea. Next idea is the following. So let's say in this particular, in the leftmost position, when it's really parallel, it looks something like this. In this position, it doesn't move, right? Now, what if as soon as we are coming close to this position, as soon as we will turn off electricity completely in the frame? What happens? Well, it will, by inertia, it will pass this position of nullifying forces. But there are no forces because there is no electricity. And then as soon as we pass that particular point, we will turn the electricity on again in the frame, but in the opposite direction. So if before, this was moving this way and this was moving this way, but when they are in this position, it makes a rotation. But now we have passed this rotation, this point and we change the direction of the current. Well, now this side of this frame will be moving to this direction and this line will be moving in this direction. So after we pass this point, it will continue rotating in exactly the same direction. So in this position, my lines, my sides go this way, now they go that way. In this position, there is no current at all, so we just move by inertia this way. And now we change the direction of the current and now this line will be moving that way and this will be this way. And it will continue rotating the frame. Good idea. Now if we will accomplish this, if we will switch off electricity immediately before this lead point, as we can see, and then turn it in a different direction immediately after, then we would have this rotation. The question is how to accomplish this. Well, actually there is a relatively simple device which was invented for this particular purpose and it's called Commutator. Well, Commutator is something like this. Imagine a ring. Now what we will do, we will make these empty things. Here we will have contacts, less than minus. Now this ring would be rotating with the frame. So frame is actually connected to this piece of the ring and to this piece of the ring. These two, this will be connected to this half and this will be connected to that half of this ring. But now this ring would rotate with the frame on the same axis. Now as it rotates, you see when it rotates at some point, at some point if you rotate it this way, let's say, these two contacts, they're called brushes, these two brushes will hit the empty spot and there will be no electricity. But then as we continue rotating, the brush which used to connect one side, one side of the frame to a positive sign would actually, if we would turn it this way, to this dead zone, this positive would be feeding this one. So that's change of polarity. And this one which feeds the negative electricity, right now it's connected to this one. Let's say this one. But as we turn it a little bit after the dead zone, it will feed the other part with negative electricity. So that's how we change the direction of electricity. Now in the text for this particular lecture on Unizor.com, I have some nice pictures, much nicer than these ones. This is just to demonstrate the idea. Over there you will have a little bit better, maybe understanding if you will look at those pictures. But that's really relatively simple. This is, again, idea. The implementation can be different. How we range these rings, how we put it on the same axis with this frame. These are all, I would say, technical details. But the idea is this, to have this kind of a contact ring which has two empty spots here and then how we basically change the direction of electricity in the frame from one direction to another. Okay. So that's good. And to tell you the truth, if we will just implement this, it will work. And that's how most of DC motors were really implemented. And obviously there are, I mean, first motors. And then there are obvious improvements. For instance, instead of a wire loop, you can have something more solid. Like you have a coil of wires. The more coils you have, the more magnetic properties this particular thing has. And that's why the action will be a little stronger, if you wish. But that's details. I mean, what kind of a material you use for these coils. Well, copper probably. Can aluminum work? Yes, probably it can, but worths. So there are different technicalities, I would say. But this is the idea. The frame connected to a commutator, and that's how it would work. Okay, but we have to progress, right? What's basically really wrong with this kind of a design? These brushes. These brushes are, it's not really the good idea. Why? Because, first of all, they wear off, obviously. It's mechanical part which is moving. I mean, whenever you have mechanical part moving, it's obviously a problem with wearing, with putting some kind of maintenance through this, etc. It requires attention. So brushes are not really good. Another problem with brushes, they might actually produce sparks. When we are talking about powerful DC motors, sparks, well, that might be dangerous. I mean, what if you have some kind of flammable gases around you? Sometimes you have to. And it's not a good design for this particular reason. So we need mechanical rotation, but we don't need this connection problems with this very, very weak connection between the brushes and the ring of the commutator. So we need some other design. Okay, so let's continue. We will continue with brushless design. Okay, first of all, what we can do, and this is easier, we can do a completely reverse model. We will reverse the rows. So right now in this design, we have permanent magnets statically installed, and this static part of the DC motor is called stator, stator, stator, whatever. And then we have this frame or a coil inside, which is rotating. And it's called, obviously, rotor, because it's rotating. So stator and rotor. Now let's reverse. What if we will do the following? We will have one frame here, and the frame here. Now, frame acts as electromagnet. We know, right? So there is a magnetic field, which is going, let's say, this way, this way, this way, and this way. So this is Norse, this is South, this is Norse, this is South. Now, we will use these as static part, as a stator, and we will use magnet inside on the axis. Actually, it's exactly the same thing, because in this particular case, Norse and Norse, they are going into different direction. They repel each other, and South and Norse will attract each other. Same thing here. North and South, and South and South, attracting, repelling. So this thing will move this way, until it reaches this position. Well, and stop. Well, oscillate a little bit by inertia, because it will turn and a little bit inertia, but then it will go backwards and stop. So what's necessary to do in this case? Well, we will change the direction of the current. So instead of plus-minus, we will have minus-plus. Instead of North-South, we will have South-North. And instead of North-South, we will have South-North. What happens now? Well, this will repel, and this will repel, and this will attract. So it will turn this way. If, and it will do exactly the same trick, at the time when this permanent magnet almost reached this particular horizontal position, it will turn off the electricity. So it will just by inertia, it will move a little bit here. It will pass this dead point. And as soon as it passes that point, we will turn the electricity in an opposite direction like it is right now. So North will go to South, and South will go to North. The same direction, so it will be rotating. Sounds good? Why is it better? Because we had to change the direction of electricity in the first design and in the second design. Well, it's much better. Because in the first design, this frame in between two magnets was moving all the time, and all these contacts are supposed to be in the moving ring of the commutator, which is kind of mechanically difficult, these brushes, etc. Here what we will do, we will put these two terminals of some kind of device which can switch statically. So these contacts are not moving, as in the commutator ring. They are stationary. Well, if they are stationary, even the plane switch would work better than brushes, obviously. Like we have this electricity switch which turns on the lights. So we can always do this type of arrangement. But much more than that. With advances in electronics, we can do electronic switch. So we have plus and minus main contacts going here from the battery. And this will be my electronic switch which will switch based on certain timing or whatever else, will switch the contacts between them. I am not talking right now about electronics inside it, but there is a way to do it. All we need to do, we need the position of the magnet. So we need to detect when it's really in this horizontal position. Well, we might have some kind of a marker. I don't know. Maybe light, maybe electric contact or something. I don't really know. There are many ways of doing this without actually electrical contact. For instance, you have a light which goes through this position and when it's crossing the light, you have some contact closed. Or some other maybe electromagnetic type. There are many different ways of doing it. And again, I'm not talking about how. But it's a solved problem and it's really relatively easy. When we will talk about electronics, we might actually discuss this. Not right now. Right now we are talking about electricity and DC motors. So there is some kind of a sensor which senses the position of this magnet. Signal goes to this switch and switch turns to this position by actually connecting differently the direction of electricity in these two frames. And basically, that's it for this particular design. So again, it's better because we have a stationary contact to be switched between. They're not rotating. And we can use electronics to do it which means there is no mechanical movement except only one movement of this magnet which is the source of the rotation and that's exactly what we want. So we can put on this axis, we can put anything we want. Electric drill or whatever. Okay. Now we will talk about improvements to this design which are kind of obvious. And that would actually lead us to a real DC motor as we use it right now. Okay. My first improvement is instead of wire frames we will use coils. Coils are basically frames but repeated many, many times. And obviously the more turns the wire does the stronger magnetic field is created and the stronger magnetic field is created the more power we can get from the motor. Obviously. So these are coils. Also, for obvious reason we can put iron core inside. So that's the real electromagnets. So you know that if you put iron core inside the coil it's increasing the magnetic properties of this electromagnet. Why? Because iron has temporary magnetism properties. So whenever you have the current going into the coil around it the atoms are arranging inside the iron in such a way that they are pointing to the same direction which basically is the source of magnetism. If you remember when we were talking about what is basically magnetism. Permanent magnets have this the same orientation of all the axis of the atoms. Well, at least important atoms. And again, the iron has temporary magnetism so whenever you switch the direction of the current the atoms of iron are reorienting immediately and that produces the magnetic field in a different direction. North and south change to south and north and that's what we need. So we are making our stator stronger. Stronger electromagnets. Okay, that's number one. Number two, which is also very important. I mean, look at the movement of this magnet. When it's in this position the rotation moment is strongest. So the force which turns it the stronger in this case because there is a bigger radius from the top to the middle because it's actually the top which we are rotating. So it's a stronger momentum. Now, as we are moving to this direction momentum is very weak because actually these two forces are kind of stretching this magnet so they're working against each other. Here they're helping each other to turn it. In this case they're actually not very much helping but we are passing the dead point a little bit but still this particular perpendicular to the radius is very actually small in this case because that's what happens. So if force goes this way and this way we have to multiply force by this distance to get momentum. So they're working kind of against each other but in this position momentum is greater because we multiply by this length. So how can we overcome this problem? You see, if we will just leave it as is it will not be a uniform rotation. It will be kind of stronger and then weaker, stronger than weaker so it will just move like this which is not really good. Well, here is the idea. Let's put another pair of magnets here and here. What we will do I mean we can do with switches anything we want right now using electronics. We will use these two whenever our magnet is in this position but at this position we will switch these off and we will use these two as the source of magnetic field. So we will use four instead of two and the rotation will be smoother. So instead of just going stronger and then weaker and then stronger in this position we will have stronger, weaker from these but stronger from these so that would make much smoother rotation. So the magnetic field would be actually stretched along these lines and then as my magnet is turning at some point I'm switching about 45 degrees we are switching these off and switching these on and it will continue turning. It's smoother. So instead of two strong and two soft spots we will have four strong and four weak spots and the weaks will not be as weak those strong will be really stronger. That is kind of a rotating magnetic field and that's the key to arranging more and more uniform rotation because instead of four I can put six electromagnets and turn them sequentially on to make even smoother and the more electromagnets I put the smoother rotation will be because the smoother magnetic field would rotate. So all I have to do is to understand how to switch from one to another to another to another. Let's say if you have six then every 60 degrees I'll turn, I have to switch something switch something on and something off in whatever direction we need and that can be accomplished through electronics. It's a lot of wiring obviously. These are all coils and the coils should be connected somehow etc. but it's all done once and then there are no movements basically everything is done electronically switching. All I have to do is some kind of a sensor which is basically senses the position of this magnet this way or this way or this way. Okay. That's a very important improvement. We are creating a rotating magnetic field. That's what it is. Rotating magnetic field. Now in practical case we don't have to switch off immediately as we are leaving for instance this particular direction. We don't have to switch it off here and on here. We can continue switching on for instance this and this if it's in this position this and this can be on and this and this so it will be turning because this is still helping right so we don't have to switch it off because this magnet is still helping when we are in this position. So anyway it can be arranged. The idea is the most important rotating magnetic field and one more improvement which is actually also very important instead of having this bar magnet in the very beginning in the very center of this circular arrangement of electromagnets what I can do I can have a ring magnet. What is a ring magnet? Well if you have a one magnet and another magnet and then you bend them so that they are connected here and here well here you have a ring magnet right it also has north and south but it's a ring. Why is this is better? Well if this is my ring magnet it actually is much smoother rotating than the bar obviously because it's all symmetrical and since the radius is larger it has more inertia and the more inertia you have again the more uniform your rotation will be so this is actually the design of contemporary DC motors you have a magnetic ring inside you have a certain number you can have 6, you have 9, you have 12 all you need is electronics which are switching the electricity in these electromagnets on and off properly and that would actually suffice well that's it the most important part actually about DC motors is that using some electronics some smart electronics which we are not really talking about how we can arrange on and off of different contacts and then arranging circular arrangement of these electromagnets we are creating a rotating magnetic field rotating magnetic field causes this magnet, permanent magnet which is in the form of a ring to rotate and then you can obviously install some kind of whatever we need to install on it fan or whatever propeller well that's it I would suggest you again go to the physics 14 course on unison.com these are I think it's electromagnetism part of the course and the particular topic is electromagnetic properties of the current of DC current, direct current and in there you will find this lecture about DC motors I suggest you to read it there are nice pictures over there which might help you and again the main idea of this particular lecture is that we are creating a rotating magnetic field just remember it's really very helpful and it will help us with alternating current thanks very much and good luck