Embedded Files
Day 1
Summary of This Lesson
This lesson will introduce members to inductors, which is basically a coiled wire that creates a magnetic field when current runs through it. In-person members will get to create an electromagnet to learn about inductors. Unfortunately, members online will just have to follow along, as it can't be done in Tinkercad. Some elements in this lesson can be used in Tinkercad however, so online members won't be completely left out.
Lessons for Electrical Training on the website requires a Tinkercad account at www.Tinkercad.com, so if you haven't already, make an account on that website. Also, you can press the "Try Circuits" button in the circuits tab of Tinkercad to get an introduction of how to use Tinkercad's circuit simulation feature.
Electromagnets in Action
Let's see what happens when we power a coil of wire that is wrapped around an iron nail or bolt. If we move it close to a metal object, it can attract it, as seen in the video below. The in-person people will get to create an electromagnet to attract different metal objects. For the people online, you can watch the video below to see how a solenoid works (which is similar to an electromagnet, in that it can be used to pull metal objects toward its center).
Here's what the circuit would look like for the in-person people.
Magnetism? What is it?
Magnetism essentially results from the movement of electrons. Sound familiar? That is what electricity is, the movement of electrons. It can also result from the intrinsic nature of electrons, in that they are like tiny magnets (we don't know why it is like that, we only know that is how the universe works). To keep things simple, when there is a current in a direction (electricity), there are magnetic field lines that go around it, meaning that the movement of electrons creates a magnetic field. There is a direction to the field lines, so how do we determine it? There is a simple trick called the right hand rule, and here's a picture below for you. Now what about the intrinsic nature part? When the electrons', or tiny magnets', magnetic fields in an atom face the same way, they don't cancel each other out. This makes the whole atom with those electrons have a magnetic field. When all the other atoms with a magnetic field also face the same way, similar to how the electrons in those atoms face the same way, you get an object that is magnetic. To clarify, a magnetic field is an area or space that would be affected by magnetism, meaning if you had a compass inside of an area affected by magnetism (magnetic field), it would point in the direction of the magnetic field lines. Magnetic field lines go in the direction of north to south, like on a magnet, and are used to show the forces created in a magnetic field, which is why a compass points in the direction of the magnetic field lines.
The Movement of Electrons Creates Magnetic Fields
This picture shows how current (in the picture, it is the blue line with the letter "I" next to it, and it is conventional current, so it is the protons moving from positive to negative) can create a circular magnetic field line, which are the red lines with arrows on it. The right hand rule as shown in the right picture uses the thumb which follows the direction of conventional current, and the four fingers wrapping around the wire as if grabbing it to show the direction of the magnetic field lines. Magnetic field lines are also seen in electromagnets which are wires wound in a coil (it could also just be a wire, but it won't be as strong, and you'll see why later), which have electrons move in a circle many times, similar to the picture to the left.
Why do Moving Electrons Create Magnetic Fields?
Now you might ask why moving electrons can make magnetic fields, like a magnet could. There is a great video below (the left one) that explains how the perspective of the charges in an atom using special relativity (sounds intimidating, but the video explains it in simple terms) can create two different outcomes, one seeing it as an electric field, the other seeing it as a magnetic field. You'll see once you watch the left video below.
What about in Permanent Magnets?
So we've just went over how moving electrons can create a magnetic field, but what about in permanent magnets? Do they have current running through them? Technically, they do. Electrons do move, except instead of through a wire, it is around the atom. So if an electron moves in a circle, the magnetic field looks similar to the left picture above. However, in an atom, electrons can go in opposite directions. This means that two things cancel out. First, it's the current. Current is overall canceled out when two electrons move in opposite directions, which happens in an atom. Second, magnetic fields from the movement of electrons are canceled. You can see why the magnetic field gets canceled by either seeing how current is gone which is needed for magnetic fields, or how when you use the right hand rule for two electrons moving in a circle in opposite directions, the directions of the fingers (magnetic field lines) also go in opposing directions, canceling each other out. In reality, electrons go around the atom randomly, so not exactly opposite, but that randomness can also prevent the uniform movement of electrons in a single direction, which is needed for a magnetic field from that method. So why can permanent magnets still have magnetic fields if the movement of electrons is not the answer? Well, we've discovered that electrons are magnets in of itself. I know, it may seem a little lazy to just say that a permanent magnet is a magnet because there are tinier magnets inside (the electrons), but that is how the universe works. We just don't know why that is, we only know that is how it is. Essentially, the tiny magnets' (the electrons) magnetic fields align, or face the same way, so they don't cancel each other out. This makes the atom with those electrons/tiny magnets have a magnetic field. Aligning other atoms with magnetic fields in the same direction gives you an object that is a permanent magnet. You can watch the video to the right to get a better understanding of permanent magnets.
Summing it up
To sum everything above, magnetic fields can be created either by moving electrons, or by the intrinsic nature of electrons that can basically be tiny magnets. In a wire, electrons can flow mainly in one direction, so magnetic fields can be created through the movement of electrons (reasoned with the theory of special relativity, explained in the left video above). In an atom however, the movement of electrons go in opposite directions, canceling the magnetic fields due to the movement of electrons and the current out, so in order for atoms to be magnetic, the electrons need to be unpaired in order for their intrinsic magnetic fields to not be canceled out, creating a bigger magnetic field which encapsulates the atom that the electrons go around, and eventually creating a magnetic field around the object with all of those atoms. In the right video, it also stated that a metal object like a rock of iron could not be magnetic due to the atoms' magnetic fields inside of it not aligning, but could become magnetic with an external magnetic field that makes those atoms' magnetic fields to align.
That's all great and Stuff, but How is it Used and How does it Move Stuff?
Now that we've learned how magnetic fields exist, now we can go to how it actually is used, and how it moves stuff.
If you've played with magnets, you'll know that the north pole of a magnet attracts the south pole of another, and if you try and pair two like poles together, they force each other away.
Why does it do that? Let's take a look at the magnetic field of a magnet in the picture to the right. What you are seeing is basically three pictures showing the same concept in three different ways. The arrows of the lines of the magnetic field (created by the "tiny magnets" which are the electrons) go from north to south. If you were to imagine bringing the north side of one magnet to the south side of another magnet, you'll notice that the arrows from the north side of the first magnet point generally into the south side of the second magnet. This means that there are some magnetic field lines that go from the north side of the first magnet into the south side of the second magnet. Here's a picture below to help you see what that means.
What do the direction of the arrows mean you say? It shows the direction of the force caused by the magnetic fields. So in the picture above, if you look at the top middle, we see magnetic field lines that point from the north of one magnet, to the south of the other. You can imagine these arrows indicating a pulling together of the north and south pole, so they attract. When the two magnets come together, they create a bigger magnet, which is basically what happens when the magnetic fields of atoms align with each other, they become a bigger magnet (multiple atoms), from smaller magnets (the atoms, with the magnetic fields of their electrons aligning). What about if there are two like poles coming together? If you look at the last two pictures, we see that the magnetic field lines, or forces, do not join together. Those forces from the magnetic fields of both the magnets do not work together when the same poles are pointed at each other because in terms of the horizontal direction in this picture, the forces are opposing.
So now you know about magnetic fields, how they exist, and how it can be used to move stuff due to the invisible forces caused by those magnetic fields. There is one more thing, but don't worry, it is basically the same as what you just look at with magnets.
Inductors and Solenoids/Electromagnets
The picture to the right is called an inductor. It can technically also be a solenoid/electromagnet too. What is an inductor and a solenoid? Well, they both use magnetic fields which are created by electrons flowing through a wire, and magnified by the coils, but for different purposes. Passing current through an inductor creates a magnetic field that at first allows very little current through it, but over time, the current increases gradually. That inductor's magnetic field can store energy, and transform it back into electrical energy by creating current when there is no external supply of current. A solenoid also creates a magnetic field when passing current through it, and also has current that slowly increases as time goes on due to the magnetic field it creates, but the main purpose is for it to create a magnetic field to move a piece of metal, not to gradually increase current, though it does still do that. All in all, an inductor and solenoid are basically the same thing physically, meaning they are both coils of wire. It's just that a solenoid is all of what an inductor is, but it is used to move a piece of metal. Since both create magnetic fields, and permanent magnets also have magnetic fields, they can attract each other if their magnetic fields are strong enough! A inductor/solenoid has a north and a south pole, which is determined with the right hand rule, where the north side has magnetic field lines going out of it, and the south side has magnetic field lines going into it, just like a permanent magnet.
Inductors, Solenoids/Electromagnets in terms of Electricity
Now that you know that passing current through a coiled wire makes a magnetic field, let's see what happens in terms of electricity for an inductor/coiled wire. Well, it's quite simple. A coiled wire is just a wire, that's well, coiled. Wouldn't this mean that a lot of current passes through it? If enough time is given for it to do so, yes. What this means is that when you pass current through an inductor, the current gradually (gradually in terms of electricity is actually really fast in human terms, but compared to the current rising in a wire, it is pretty slow) rises until it hits its maximum current. When current moves through the coil, it makes a magnetic field, which you now know how that happens. That magnetic field can actually cause the electrons to not pass as freely through it at first, but then it will gradually allow electrons to flow freely with enough time. Now what happens when there is a lot of current through a normal wire? It generates a lot of heat and can burn up, if there is no other resistance. The coiled wire that had current running through it will allow a lot more current to flow through it later, which can generate a lot of heat, just like a normal wire with a lot of current would. So in short, an inductor with current through it will gradually increase the current, which can increase the heat going through it. You might wonder why you are learning this, and the reason is because this will be needed to understand how motors work, which will always be used on robots.
I really suggest watching these videos to understand how these coils of wire work, they've certainly helped me understand.
That's it for this lesson
I know it was a lot to take in, as it was a combination of magnetism and electricity. Trust me, I had a hard time learning all of this, but with time, and perhaps multiple youtube videos, along with simulations or your imagination, it will make more sense.
Day 2
Summary of This Lesson
This lesson will go over motors, which is related to inductors, since motors have coils of wire in them. Now, we can see how inductors, or simply, coils of wire, are able to make things spin. Members in-person will get to play around with motors, make their own mini motor with coiled wire, a battery, and a permanent magnet (which are basically the essentials for a motor to spin). Members will discover how current changes as the motor's load changes, and how it gets hotter as the load changes. Members will get to see how increasing the voltage can increase the speed that the motor spins, thanks to an increase in power due to the voltage increase.
Lessons for Electrical Training on the website requires a Tinkercad account at www.Tinkercad.com, so if you haven't already, make an account on that website. Also, you can press the "Try Circuits" button in the circuits tab of Tinkercad to get an introduction of how to use Tinkercad's circuit simulation feature.
Make it Spin
The in-person people will get to tinker around with real motors and power them to see what happens. They will use smaller batteries to power a small 5V motor with a breadboard to represent using the PDP in FRC, and will use larger batteries to power larger motors, such as ones used in FRC. In Tinkercad, you can still use a simulated motor to see how the change in voltage can increase the motor speed, but you won't be able to see/feel the affects of a motor under a load unfortunately. For the members online, here's a simple simulation for a motor. You've used motors in some other places, so you might already know what the affects of more voltage would be for a motor, but try it out anyway. When simulating, you'll see the letters "rpm" on the motor, which stands for rotations per minute. That is a unit used to measure how fast something is rotating, and in this case, it measures how many times the motor's shaft makes a full rotation, every minute.
As you increase the voltage, you will also see the reading for current under it to increase as well. As Ohm's law suggests, we know that I = V/R, so as voltage goes up with the same amount of resistance, the current also rises. There is another circuit, except with a resistor. As you may know, resistors decrease the current, since I = V/R, so as resistance goes up, current decreases. This decrease in current makes the motor spin slower. If you were to set the voltage output of both power supplies to the same amount, the motor hooked up to a resistor will spin slower than the motor not hooked up to a resistor.
Now, the motor spins one way with this setup. The positive from the power supply connect to the positive of the motor, with a similar situation happening between the motor's negative and power supply's negative. Try and guess what happens if you switch the connections. What happens is that the motor spins in the opposite direction. Go ahead and try it! Connect the positive of the power supply to the negative of the motor, and negative of the power supply to the positive of the motor. You might ask why this happens. From the last lesson, you might know that switching the direction of current in an inductor/solenoid/electromagnet, whatever you want, would switch the direction of the magnetic field lines, or put simply, the north and south poles switch sides. This is essentially what happens in a motor.
So cool, we have seen what a motor does when current passes through it due to voltage creating the current, as well as what happens when you switch the direction of current, but how does it really work? What's inside? Here is a great video explaining how a DC motor works. The in-person people will also get to make a homemade (or I guess schoolmade) motor after learning how a motor uses the magnetic fields of inductors (simply just coiled wire) to rotate a shaft.
Alright, so we've gotten motors to spin, and know how it works, but of course, things need to be attached to the end of it to make other things spin to be able to do things like lift something up, pull things, or just whack stuff with it. This means that there is a load being put on the motor, because we are attaching more weight onto the end of the motor, making it work harder to rotate its shaft compared to not having that load there. We can simulate this in real life by simply squeezing the end of the motor. In-person people will get to do this and feel the motor getting warmer. They will also get to see the current rising with a multimeter as more squeezing is done.
Why does the current rise and why does it get warmer? Well let's answer the getting warmer question. We know that more current means more electrons flowing through the circuit. Since there is current, there needs to be voltage in the first place so that the electrons can move through the circuit. This voltage gives each electron energy depending on the amount of voltage. The more current means more electrons per second, and since each electron means carries some energy, that means that more current means more energy per second going through the circuit. This is what power is which was covered a few lessons ago, but is good to review here. All the energy from the electrons gets dissipated by the time it gets to the end of the circuit, so that power from the amount of energy per electron and electrons per second gets dissipated as either mechanical energy (the spinning of the motor), or heat. So that explains why heat increases, because of current. But why does the current increase? From the video above, you know that a motor has multiple coiled wires (or inductors) that take turns being an electromagnet (an inductor/coiled wire could be used as an electromagnet). So what does the coiled wires taking turns being an electromagnet have to do with more current? The speed of rotation, or the rpm is what we are looking at here. Imagine a motor spinning fast, freely, without a load. The coils are also spinning fast with it as well, so the brushes switch contacts with different commutators. The brushes are the contacts the press up against the metal pieces at the end of each coiled wire, which are called the commutators. Anyway, this means that each coil gets current for only a short amount of time before not receiving it anymore. From the last lesson, you read about how an inductor (coiled wire) increases in current "gradually", and when the inductor reaches its max current after some time, it releases a lot of heat. So, if we think of the opposite situation, where the motor spins slowly or even completely stops because of a load, each coil in the motor has current running through it for a much longer amount of time, meaning current has a chance to really increase, causing a lot of heat. That is why increasing the load increases the current, and so, the heat with it, because the coils have a longer exposure to current.
Making a mini motor!
The in-person people will get to make their own motors! They will get to make a coil of wire, similar to the coils inside of a motor, attach it to a stand which allows current to flow through the coil, use a battery to power it, and use a permanent magnet to continue the spin, similar to how a real motor works.
Here is an imbedded link to the same project with more specific instructions for the people at home, and also in the meeting.
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