Make your own electromagnet and electric motor, and have fun learning about the fundamentals of electromagnetism.
Build Time: An afternoon
Skill Level: Beginner
Electromagnets and their close relative, the electric motor, are all around us in daily life. From the speakers in your devices, to your air conditioner, to induction cooktops and electronic door locks, much of today’s technology depends on these two devices somewhere, in some form.
However, building very simple versions of them can help us understand how they work. That’s exactly what we’re going to do this month: We’re going to build an electromagnet and a basic electric motor. Neither will move the world, but they will hopefully shift your understanding further up the scale. You’ll also have a bit of fun at the same time!
This project uses rare earth or neodymium magnets. These are hazardous to small children of any age who like to put things in their mouths, especially under 3yrs old. Keep these magnets out of a child's reach when in use and storage. Additionally, these magnets attract each other strongly and can pinch skin when they snap together. Any of them can shatter if allowed to slam together, and the fragments can be very sharp. Exercise lots and lots of caution when handling any rare earth magnets.
ADVICE AND INSTRUCTIONS
We encourage you to read all the way to the end of the article before you build. Not only will you then have a better feel for the overall picture as you build, but we sometimes discuss options or alternatives that you will need to have decided on. You will need some basic hand tools for most builds. Small long-nosed pliers and flush-cut side cutters meant for electronics are the main ones. Materials like tape or glue are mentioned in the steps, too. We always produce a tools materials list if you have to go shopping, but anything that is lying around in most homes is just stated in the steps.
As always with Kids' Basics, we avoid soldering to make the build more accessible to more people, but having an adult around can still be helpful. You won't need any particular skills besides being able to identify components at a basic level, and even then, we help as you go along.
|TOOLS & MATERIALS (See Text for details):|
|Paperclips, bare metal not plastic coated|
|Fine file or sandpaper|
TOOLS & MATERIALS (See Text for details):
|1 x 2m 0.5mm Enamelled Copper Wire *||WW4016||W0405||-|
|1 x 1 x (3mm x 10mm) diameter Neodymium Magnets *||LM1622||T1466||ADA9|
|2 x Crocodile Clip Leads *||WC6010||P0415||ADA1008|
|1 x 2AA Battery Pack||PH9202||S5042||-|
|2 x AA Batteries||SB2424||S4955B *||-|
* Quantity required, may only be sold in rolls or packs.
While we say to use a nail for the first part of this build, any rod of the right metal will work. Generally, plain iron and mild steel are the go. Other metals won’t carry the magnetic field and other iron-containing metal alloys (combinations of metals) like stainless steel don’t do it well enough. However, that should be easy enough for most makers. Big nails, 75mm and larger, are the best but found items like 6mm reinforcing rod would be fine, as would anything made of tool steel, such as a screwdriver. Just be careful that you aren’t using stainless steel.
You will also need a round object to form your motor coil. This should be between around 2cm to 4cm in diameter, and could be a marker, a big enough battery, the lid of a drink bottle, or anything else of the right size. We used a whiteboard marker.
The motor is mounted on a piece of foam-cored cardboard in the build photos, because we have quite a bit around the workshop and studio. You can use any cardboard that holds its shape. A mailing box or box from an appliance are perfect sources for this. You’ll only need a big enough bit to hold the motor.
In terms of the Enamelled Copper Wire (ECW) used for this build, it comes in many colours, sizes, and lengths. ECW is copper wire with a thin resin coating on the outside. It’s so thin you can’t feel its thickness and it has to be sanded or filed off, not cut and pulled like plastic insulation. Most ECW meant for electronics use is covered by brown, red, or clear enamel. The clear version is becoming very common but was once unheard of. However, getting bare, uncoated copper wire is now quite hard, so chances are if you have a roll of copper-coloured wire, it’s still ECW. ECW meant for craft and jewellery use often comes in an array of colours. If in doubt, touching the probes of a multimeter set to continuity or resistance should show ‘open circuit’ when touching the outside of ECW. The amount needed for this project will depend on the size of the nail or rod used for the magnet and the size of the tube used to form the motor coil.
The Electronics Build:
The build will take place in continuous steps, with the motor following straight on from the electromagnet. They will be tested and used at the end of the build. The electromagnet and motor both use the same power supply, which we will construct at the end of the magnet and reuse for the motor.
Lay the end of a roll of enamelled copper wire (ECW) against the nail so that it is at least 10cm longer than the nail. Tape both ends.
From the end still attached to the roll, start winding coils around the nail, carefully so that they stay close together.
Continue until you get to the end of the nail with the free wire end, tape the coil end, then go back the other way.
When you get to the end of the second layer, tape the end then start a third layer. Go all the way back to the end with the free wire, and tape the coil here.
Cut the wire off the roll so that the two ends are the same length, then file or sand the enamel from about 1cm of both wires. Make sure you get all the enamel off. If it’s a clear coat, you might like to colour it with marker, as we did.
Clip a red crocodile clip lead onto the red lead of the 2AA battery pack, and tape over any exposed metal. Do the same for the black side. Install two AA batteries.
Attach the red wire to one wire of the electromagnet, and tape over exposed metal with masking tape. Clip on the black lead, but do not tape this one. Hold the tip of the nail near some paper clips to make sure the magnet works, then remove the black clip.
Lay a length of ECW so that it sticks out at least 5cm from the end of a round object to form (wind) a coil on. Hold it firmly down with a finger.
Wind twenty turns of ECW, but unlike the electromagnet, they can go over each other and should not spread out.
Hold the coil carefully and slide it off the former. Our former was slightly tapered (smaller at one end) so our coil would only slide off in one direction.
Being careful not to let the coil unwind, wrap one end of the wire around the coil three times then straighten the rest out to the side. Do the same with the other side but make sure they are directly opposite each other, dividing the circle in half.
With a file or sandpaper, remove all the enamel from the wire sticking out from one side of the coil. On the other side, remove ONLY HALF along the entire length. The easiest way to do this is to hold the coil upright at the edge of the table, with the wire on the table, and sand or file only the top half - do not turn the coil over.
Take a paperclip, and bend the smaller, inner piece out slightly, just enough to get pliers on it. Grip it well and twist so that a small loop is formed, with the rest of the clip sticking out behind. Lastly, bend the end of the larger section so that it sits out to the left of the clip. Check the photo carefully.
Repeat the previous step for another paperclip, but this time make the larger section bend to the right. Use masking tape to secure them both to a cardboard base, about 1cm further apart than the width of the coil.
Slide one end of the coil into one of the small loops in the paperclips. Gently bend the other wire so it can slide through the other loop. Use pliers if needed to straighten the wires so the coil sits evenly and straight. You may also need to bend the paperclips slightly to get the height even.
Place a 10mm x 3mm Neodymium magnet under the coil, between the paperclips. You may need to lift it with small pieces of cardboard. Tape it securely in place so that it has about 5mm clearance underneath the coil.
Disconnect the red wire and tape from the electromagnet, being gentle in removing the tape so that the wire is not pulled and the coil is not damaged. Clip the lead to one of the paperclips.
Clip the black lead to the other paperclip, then use one finger to just catch the edge of the coil to make it spin. Watch its behaviour carefully. It should spin, but it may slow down and stop. If so, spin it the other way.
USING THE BUILDS
The electromagnet should pick up or stick to anything ‘ferrous’, which means iron bearing metals. This means it can ‘sort’ different metal objects into ‘ferrous’ and ‘non-ferrous’ categories. You can explore its strength by seeing how heavy an object is before the magnet can no longer pick it up.
Another experiment is to see how many paperclips you can chain together with only the first one stuck to the magnet. Keep the red crocodile clip lead with tape over the metal parts so that it cannot touch the black lead and short-circuit, but not so much or so tightly that it’s hard to swap the battery pack to the motor.
In terms of the motor, its use is mainly as a demonstration. It isn’t powerful enough to drive a load. However, it does demonstrate the basic principle of a motor well, which we’ll look at now.
HOW IT WORKS
Any current flowing through a conductor produces a magnetic field around it. There is a rule that describes this, and it goes by several names. It is often called Maxwell’s Right Hand Rule, but it is similar to some others, so be careful if you do further reading. If you place your right hand around a straight conductor, with your thumb pointing in the direction of current flow (from + to -), then your fingers curl in the direction of the magnetic field.
However, when you start wrapping the wire into a coil, that magnetic field overlaps. Also, ferrous metals like iron will act as carriers for the magnetic field, shaping it. The effect of this is to create an electromagnet. The more turns there are in a small space, the more magnetic field lines interact with the core.
The strength of the magnetic field depends on the amount of current flowing through it. The more current flowing, the stronger the field. However, something else is going on. All wire has resistance. The more turns you place on a coil, the more resistance it has because the wire is longer. This isn’t very much resistance, however. In a coil, there is an interaction between the magnetic field and the current that created it, and this interaction actually opposes, or pushes back against, the current that created it. Exactly how is another discussion for another time, but this limits the current flowing through the coil.
However, the less turns there are, the less this effect exists. That means if you put too few turns in your coil, either for the electromagnet or for the motor, you may overheat the battery by drawing too much current. On the other hand, too many turns means a lower current flow, and you may have a weaker magnet. The ideal number of turns depends on a bunch of factors including the wire size, core material, core size, and others. The calculations are not suitable for Kids’ Basics. In fact, they’re probably not suitable for any general audience, belonging mainly to engineering teaching resources or some very senior highschool physics courses. You can, however, experiment.
The motor works in a similar way. The same lines of magnetic field force that surround the electromagnet coils, surround the motor coil. However, we shaped the coil differently and there is no core. Importantly, we added a permanent magnet. The magnetic field of the coil pushes against or is pulled toward that of the permanent magnet because opposite magnetic poles attract each other while two the same repel each other.
In the motor’s case, the action can be explained with another right-hand rule. With your right hand open flat, place your thumb to point in the direction of current travelling through a conductor from positive to negative. Your fingers will point in the direction of the magnetic field while your palm faces the direction of force on the conductor. Having lots of loops of the conductor all arranged the same way means this force adds up.
Again, there are several names for and versions of this rule, and Fleming’s Left Hand rule does the same job but confuses a lot of people. It involves having fingers point in unnatural and uncomfortable arrangements and unless you are already a technical or mathematical thinker, the palm rule is likely easier.
As current passes through the coil, the magnetic field generated pushes or pulls against the permanent magnet. As you might have predicted, as soon as the coil turns through half a rotation, it’s facing the other way and so are its fields and forces. The coil will turn until the permanent magnet is attracting one pole of the motor and repelling the other, and no more rotation will occur.
The answer is to make sure power can only flow for half the rotation. This is why we sanded the enamel from only half of one side of the coil. When the bare metal is in contact with the paperclip carrying the supply current, the coil is energised and is either repelled by or attracted to the magnet. As it gets to this point, however, the part of the wire which still has the enamel on it meets the paperclip, and the current stops flowing.
Now, Newton’s First Law of Motion, which we covered last month in Issue 50 of Kids’ Basics, gets involved. An object at rest will remain at rest, or an object in motion will remain in motion, until acted on by an external force. With the current not flowing, there is no longer any magnetic force involved. While a conductor moving through a magnetic field (which happens as the unpowered coil spins) produces a current, there is no circuit for the current to flow, so it is a non-event.
There are forces of friction from the air the coil moves through and the meeting of the metals where the wires from the coil sit in and rub on the paperclips, but it is not enough to slow the coil very much. It continues to rotate with its built up momentum, until it has gone far enough to have completed a rotation. At this point, the bare section of the coil wire makes contact with the paperclip again, and the motor continues to spin.
Now, that’s very inefficient and not the way practical motors are built. Normally, a set of ‘brushes’, which are slippery but conductive surfaces, are used to transfer power to the ends of the coil. Instead of having the coil conduct for only half its rotation, the coil ends are connected to a ‘commutator’, which is two curved plates with a gap in the middle. As the coil spins, the brushes send current through the coil in one direction. As the coil turns, the gap between the plates passes under the brushes, and then the brushes are touching the opposite plate to before, sending current the other way. Because the coil is now in the other half of its rotation, it is now attracted to the magnet where it was being repelled before, and so the rotation continues.
Note in the diagram the positions A and B being the same parts of the coil at different positions.
This type of motor is much harder to build than the one we have built, but is closer to how a real motor is made. Unfortunately, it’s also hard for some people to follow with just a diagram. Perhaps in a future article, we’ll find a way to build one.
WHERE TO NEXT?
With the electromagnet, you could get scientific about your explorations. Why not draw up a table and record how many paperclips or other objects you can pick up with the electromagnet when you change the number of turns on the nail? You could start with a whole layer and add whole layers one at a time, and record your results.
Alternatively, you could add turns in groups of 20 or so. For a fair test, only one variable can be changed at once. Make this the number of turns, and keep the core, batteries, and size of the pick-up test objects the same.
Also, keep an eye on the condition of the batteries so they don’t run down and alter your results.
If you have younger siblings, a fun experiment is a simple yes/no test to decide whether a metal is ferrous (which will stick to the magnet) or non-ferrous (which will not stick). Children who are too young to deal with the word ‘ferrous’ can still join in, because they just need to know if a metal sticks or not. You can use Post-It notes or similar, and decide on a colour for ferrous and a colour for non-ferrous.
Add an extra dimension by having to decide first whether something is metal or not. For example, painted metal like a fridge door may look like plastic, and some painted plastic looks like metal.
With the motor, you can experiment with the number of turns on the coil. This will give varying results and it would be interesting to find the most ideal number of turns for your magnet and coil diameter.
You could also stack more than one of the 10mm magnets, and see what difference this makes. Just be careful to leave enough clearance under the coil and adjust if necessary!