Electric Generator for School Labs

(Credits go to Tim Station - thank you for inspiring me to make this project.)

(This introduction is very long. If you're not interested, jump below.)

There's one hallmark high school experience you must be familiar with: listening to your physics teacher ramble about something excessively theoretical that you don't understand. In my Physics 2 class last year, that was what I was most frustrated with: as a person with a healthy dose of skepticism, my first instinct is always to doubt the theory that's thrown at me. But why does it have to be that way? Why must our teachers abandon physical, tangible labs if they're teaching electricity and magnetism instead of acceleration and momentum? With my frustration over a lab science gone theoretical, I set out on a mission to prove to myself - and my classmates - that electromagnetism is real.

What's electromagnetism, you ask? Put simply, it's the interactions that magnets have with electrons and the electricity we are all familiar with. It's all around us, in our electric motors, power grids, and more, but these devices are too complicated to easily understand. I wanted to prove something simpler - that with magnets, clever design, and sheer willpower, you can make electricity with your own two hands.

My project was a generator that could be operated manually. By placing magnets of alternating polarities inside a disc and spinning it really fast, the changing flux (magnetic field) can create an electrical current inside a loop of wire. Connect this wire to any old LED, and you'll see it turn on! Mechanical energy to electrical energy. Simple, right?

That's what I thought at first. Alas, it's not quite so simple. One joke I like to make is, "when I started this project, I predicted it would only take a week or two." That was in June. Now it's November. Because this was my first project, I was idealistic, opting for aesthetics over function and neglecting to do any proofs of concept. This would bite me very, very badly later on. You can see in IMG2 that it looked great, but it had many issues in reality: glue did not interface well, the wheel hit the casing often and wobbled a lot, and the coil holders were too small and unadaptable for new designs. And this wasn't my first design, it was the third!

Having learnt my lesson, I spent the next 2 months constantly prototyping - switching the unstable plastic base for wood, adding gears to increase speed, and experimenting with various ways to mount the coils closer to the magnets (IMG3). I went through more than 4 prototypes (IMG4). During this phase, I got a lot of inspiration from my dad, who gave me design ideas he had learned from fixing our Toyota cars in the garage. For example, he suggested I taper the holes for the bearings, which allowed me to fasten them without the use of glue and reuse parts. He had simpler ideas, too: for example, we changed from a vertical to horizontal layout to improve wheel stability.

By September, we had made our first workable prototype (again, IMG3) and began experimenting with the amount of electricity it could generate. Unfortunately, it was not that much - one coil alone generated 0.15V at max speed, nowhere near the 0.7V needed to light an LED. It was back to the drawing board. By this point, I was discouraged due to my overconfidence, but my physics teachers encouraged me to keep going!

The next step was to increase the amount of electricity that could be generated. There are essentially 3 ways to do this: increase the spin speed, find stronger magnets, or add more coils in series. I did all three. As you can see in IMG5, I added a second gear, opted for stronger rectangular magnets, and increased the number of coils (hidden under) to 5. Did it work? While it did turn the LEDs turn on, the wheel hit the coil, severing the cable ties and allowing the magnets to fly all over my garage. Clearly, more redesigning was needed. (See the failure here.)

I realized that the bearings were not completely fixed with the wheels, allowing the gears to deviate and hit things (it's very apparent on the wheel I'm spinning in the video I linked). With some final modifications, including fasteners to keep the bearing in place and a better coil-holding mechanism, it was done! I could safely generate electricity with my own 2 hands (IMG6) :)

I'll be presenting my experiment in physics class this December. Stay tuned!

You'll need some slicing software and a 3D printer. I used PLA for my prints, but PETG can work too. I used Fusion360 for modeling and BambuStudio for slicing.

I labelled all unique parts with P# (for part #) so there is no ambiguity. You can find all files below.

1. 25 3D printed parts, including:
2. 88-tooth wheel with holes for handle (x1) (P1)
3. 80-tooth wheel (x1) (P2)
4. Magnet-holding wheel (x1) (P3)
5. Magnet wheel covers (x2) (P4)
6. Handle base, sheath, and center (P5, P6, P7 respectively)
7. Bottom and top casing for 88-tooth wheel (P8, P9 respectively)
8. Ordinary bearing covers for the other 2 wheels (x2) (P10)
9. 10-tooth wheels (x2) (P11)
10. Coil holder (P12)
11. Coil, bottom piece (x5) (P13)
12. Coil, top piece (x5) (P14)
13. Woodworking: mostly simple.
14. A thin piece of plywood, any size works as long as it can feel all axles
15. Saw for cutting off excess and making protective walls (optional)
16. Drill for making holes of roughly 5/16" diameter
17. Hardware:
18. Magnets (x16): I used rectangular magnets of dimensions 20x10x3cm; you can buy the exact ones off Amazon here. You can use other magnets and modify the design, but from my experience, traditional kitchen magnets are not strong enough (my first designs used these and generated little electricity.)
19. Bolts: 5/16" (try to get various lengths; they're cheap from Home Depot/Lowes, lengths depend on if you want the shaft to stick out or not. Bolts serve as the axle for the wheels)
20. Nuts and washers: 5/16" (used as spacers for the wheels and also to fasten/straighten the wheels so they don't wobble)
21. Zip ties
22. Bolts & nuts: these are optional if you're not using zipties. All holes use M3 hole dimensions. Be sure to get shorter bolts, or they'll hit the adjacent wheels and blow up.
23. Screws: #6 wood screws are used on the handle and coil holder
24. Bearings: 608RS bearings (yes, the ones for skateboards!)
25. Tools:
26. Screwdriver
27. Ruler/pencil for drawing dimensions on plywood
28. Pliers, for cutting zip ties/miscellaneous uses
29. Tape, for miscellaneous uses
30. Super glue
31. Match/lighter for removing copper wire insulation
32. Swiss knife can be useful for trimming 3D prints
33. Some wide clothes clips - optional, but useful for assembly
34. Electronics:
35. Voltmeter/ohmmeter
36. Oscillator - optional, but will make your life much easier
37. Copper wire (any gauge works, but thinner = more turns per area = more electricity)
38. Alligator clips, useful for testing
39. Breadboard/LEDs/wires, for testing/demonstration
40. If you want to make it fancy, a soldering kit and some wires can replace the alligator clips

Make sure you have all the equipment and materials above. Print and process all of the 3D-printed parts you need. You'll want a clean workspace during assembly.

For the handle center, you'll want to print it horizontally. This way, the layer lines are perpendicular to the force, and your handle will snap less easily!

The gears have module 1.75. The pitch diameters are 154cm (88 tooth), 140cm (80 tooth), and 26.25cm (10 tooth).

The axles of the magnet wheel and 80-tooth intermediate wheel should have a separation distance of (140+26.25)/2=83.125cm. The axles of the driving 88-tooth wheel and the intermediate 80-tooth wheel should have a separation distance of (154+26.25)/2=90.125cm. Mark these points on plywood. You can orient the gears however you'd like, as long as they have the proper separation distance and don't hit each other. Take your parts and experiment!

You'll also want to mark where the screws for your coil holder will go. Again, do this experimentally with your parts. The outer curve of the holder should line up with that of the magnet wheel.

Having wheels mounted will make drilling challenging, so it's a good idea to drill all your holes now. The holes have dimension 5/16". For the intermediate and driving wheels, it'll be a good idea to create a "slit" whose length is radial to the adjacent wheel of interest. This way, you can adjust distance between the gears and bolts, which will be necessary due to human error/printing tolerance. Often, you'll find later in the process that the gears interface too tightly or loosely.

It's time to put the magnets into our wheel. On P3, look for the 16 rectangular-shaped cavities with a smaller rectangular opening on one side. Insert the magnets, making sure they have alternating polarities.

Tip 1: get the magnets in a stack, push the bottom of the stack into the indent, and slide sideways while holding down the magnet you want to stay inside. This way, you never have to tediously separate all the magnets.

Tip 2: using the stack method, put in every other magnet first. If you try to do both polarities at once, you'll have a difficult time, and you're more likely to mess up. If you do one polarity at a time, it's much easier, since by using the same "side" of the stack each time, it will have the same polarity.

Tip 3: use thick clothes clips to hold each magnet in place after you have put it in. From experience, the magnets are very strong and will try to jump out. With clips, assembly is hassle-free.

Tip 4: do both polarities on one half of the wheel first. With the clips holding magnets in place, use your "stack" to check that the polarities are correct: move it along the wheel and confirm that magnets alternately attract and repel.

Once you've finished and verified one half, install that side's covering. Ensure the circular holes for the zipties all line up! You can ziptie this side first, or keep it in place with clips and do the other side first.

Once you've finished, install the 8 zip ties. The fastening scheme is a bit hard to explain, so you can see the image above.

(Yes, all 8 zip ties are necessary. In my first iteration, the strong magnets slipped out from under the covers. Better safe than sorry!)

Finally, put in your 608RS bearing. It should slide and tighten in the central hole, going in from the bottom (the side with the covers is the top.) Then, install a bearing cover (P10) from the bottom; the indented region should tighten with the bearing. Make sure the 3 holes are aligned with the 3 slits on the main magnet wheel. Also make sure that the bearing sits level with the top of the magnet wheel when you hold the bottom fastener in place and try to push down on the bearing.

Install a bolt, then a washer for the magnet wheel. Ensure the axle is perpendicular to the plywood. The coil holder will sit on the wood, so stack nuts and washers as spacers until the wheel rests just above coils. Note that the magnet field weakens with distance, so try to get it as close as you (safely) can.

Once you're sure of distances, place your magnet wheel onto the bolt and tighten it with another nut. Then, as the "top fastener", put in the 10-tooth wheel (P11). Make sure the 3 holes/slits from the top fastener, center wheel, and bottom fastener are all aligned. Then, you can install 3 zipties and fasten everything together.

(Bolts and nuts are also fine. M3 will work, but it will be challenging to install because the wheel is solid, and thus it's difficult to get a nut on the bottom.)

Note: the top nut is hidden by the top gear. You MUST install the top nut before attaching the top gear/fastener. This applies for the intermediate wheel too.

The process goes similarly. Insert your bolt, make it perpendicular with washers, and begin spacing with nuts and washers until the intermediate gear can interface with the 10-tooth gear of the magnet wheel. Make sure to test that the engagement isn't too tight or loose - if it is, loosen your bolt and slide it along the slit to adjust it to perfection.

When you're ready, push the bearing into the wheel from the bottom, followed by the bottom fastener (P10). Place the assembly onto the bolt and tighten with a nut on top. Place the top gear (P11), making sure the zip tie holes for all 3 parts are aligned. When you're ready, put in 3 zip ties and tighten.

Congratulations, you're almost done with the main assembly! Now, when you spin the intermediate wheel, both wheels should spin smoothly.

Finally, install the last wheel. The process is similar.

Install the bolt, make it perpendicular with a washer, and stack nuts/bolts until the driver wheel can interface with the 10-tooth gear above the intermediate wheel.

Before installing the wheel, put in the bearing from the bottom, followed by the top fastener (it should tighten with the wheel) and bottom fastener. (Technically, this wheel has no "top" or "bottom", so any orientation works.) The top fastener is part P8 and taller, while the bottom fastener is P9 and flat. Align the zip tie holes and install the zip ties to constrain the bearing. Finally, place the wheel onto the bolt and tighten with a nut.

To install the handle, locate the 3 holes forming a triangle on the perimeter of the wheel. Slide the sheath (P6) onto the center piece (P7); the sheath move freely without being restricted by the center. Then, align the + shape with the corresponding shape on the base (P5) and push it in; you may need to apply super glue. Finally, align the base holes with those on the wheel. Screw in three #6 wooden screws to attach the handle to the wheel.

When the wheels have wobbling or deviation, that's never a good sign. In fact, the failure you saw in the YouTube video from the introduction occurred because the wheels were free to wobble, allowing the magnet wheels to hit the coil. Manually spin the wheels and ensure they have minimal wobbling. If the wobbling is significant, here are some possible reasons:

1. The bolt is not perpendicular. Ensure you are using a washer and make sure the bolt is perpendicular to the plywood looking at it from all sides.
2. The bearing can wobble on the bolt. Make sure your top nut is tightened and the surface of the bottom nut is flat. Sometimes, if the bearing is fastened too tightly or loosely by the nuts, the bearing will be pushed into a slanted position; this is especially an issue if you're using locking nuts. Thus, adjust your tightness as necessary.
3. The bearing is not level with the wheel. If you suspect this is issue, cut the center zip ties and examine the fasteners. Holding the bottom fastener in place against the wheel and removing the top, the bearing should sit level with the wheel, and it should not be able to go down past that. Likewise, holding the top fastener in place against the wheel and removing the bottom, the bearing should extend slightly beyond the wheel, and not be able to be pushed further in. (Note that the design for the driving wheel is different - the bearing and wheel should be level on both sides.)
4. If your wheels are interfacing too tightly, one may push the other sideways. To fix this, loosen the nuts on the bolt and move it around until the gears interface perfectly.
5. Sometimes, if you do not tighten all 3 cable ties on the 10-tooth wheel simultaneously (i.e. you tighten one completely before moving on to the others), there may be issues. To fix this, redo the cable ties, tightening each one incrementally in turn until all 3 are tight.

It's time to prepare our coils. Each coil is split into a top/bottom piece to avoid printing supports, so you should have 10 pieces in total (P13 x5 and P14 x5).

For each coil:

1. Apply a bit of super glue to the inner piece (P14). Then, slide the inner and outer pieces together and wait for the glue to dry.
2. On each side of the coil, you will find 2 tiny holes; you will only need 2 of the 4 total holes (pick your side). With your coil of copper wire, stick the end through one hole from the inside to the outside. Tape the end of the wire to the outside of the coil. You'll want to leave at least 5cm of excess, since we'll be connecting the wires together.
3. Begin wounding the wire around the coil. Keep the wire roughly parallel to the side of the coil. Don't wound all your wire on one side of the coil; make sure it's equally distributed across the width of the coil, from one side to the other. Wound as much wire as you can without blocking the 4 tiny holes; more loops = more electricity!
4. Tip: You can put a screwdriver, dowel, string, or something else through the center hole of the coil to make it easier to spin. You can even use a power drill to spin the coil and wound the wire automatically.
5. When you're done with the wire, cut it off with pliers (making sure to leave at least 5cm of excess) and stick it through the other hole. You can tape this end to the coil too if you'd like.
6. Copper wire is wrapped in orange-ish insulation to prevent adjacent wires from conducting. However, we will need to connect the wires, so we need to remove it. Using a lighter, expose the ends of the coil wire to the flame for a few seconds. Afterwards, use a paper towel to wipe off the insulation; the wire should appear silver.
7. Tip: Connect an ohmmeter to the ends of each coil and check the resistance. If you burned off the insulation properly and didn't accidentally snap the wire while wounding the coil, the resistance should be a few tens of ohms (from experience.) If something is wrong, this resistance may be many hundred kΩ or MΩ. In this case, troubleshoot (ensuring you have removed enough insulation is a good place to start.)

Repeat this process for all 5 coils.

Place your completed coils into the 5 slots of the holder. They should slide in and snap in place. Make sure the ends of each coil are still accessible; just pull them out from the front. (You may need to remove the wire ends from their holes - this is a personal choice.)

We need to connect the coils in series so their voltages add. You can think of each coil as a battery: if we connect the + end of one to the - end of the other, they add. Conversely, if we connect ends of the same polarity, like + to +, their effects cancel out. If we wire them in parallel, they can produce more current at the same voltage (for our purposes, we will wire them in series for more voltage.)

Here, we are not trying to determine which side of the coil is "positive" or "negative". When the magnetic field generated by the spinning magnets "oscillates" in each coil, the current in the wire oscillates too, creating an AC sine wave. If we want our voltages to add, we want to make sure the waveforms created by each sinewave add - that is, all waves reach their peaks and troughs at the same time.

Warning: you cannot test the coils without putting them in the holder first. The relative phase shift between the coils changes depending on their locations along the wheel; the holder is designed so that they are exactly in or out of phase.

Warning: you can also not test each coil individually to find polarity. Because of how the coils are placed on the holder, adjacent coils will actually experience opposite polarity fields at the same time. To compensate for this, we should test two coils of interest simultaneously with the spinning wheel.

For oscilloscope:

The easiest way to do this is with an oscilloscope. If your oscilloscope has at least 2 channels, hook each to one of the coils, with ground connected to one end and the main clip to the other end (does not matter which is which, since that is what we're trying to find out.) Then, slide your coils while they are inside the holder under the wheel and spin it slowly (if you spin it too quickly, it can be a safety hazard.) On your oscilloscope, zoom in and observe each coil's waveform. We'll use an arbitrary "first" coil as the reference to which we tune all other coils. If the coils are perfectly out of phase (one's peak aligns with the other's troughs), switch the oscilloscope legs on the second coil and ensure the new waveforms are in phase. Then, mark the "positive" ends of each coil (the one connected to the main clip of the oscilloscope probes) with tape. Repeat this process and mark every coil's "positive" end; it's better to compare each coil to the first coil rather than its adjacent coil, so that if you make one mistake, it doesn't mess up everything.

Once you've marked all coils, connect them together. Starting from the leftmost coil, connect its negative end to the positive end (with tape) of the coil on its right. You can "connect" them by twisting the ends of the wires together. A more robust way would be to solder, but don't do this until you're sure you've connected everything correctly. Repeat this for all 5 coils (4 connections). You can tuck the twisted bits under the coil so it doesn't hit the magnet wheel during operation.

For voltmeter:

The voltmeter process is more frustrating and needs more trial and error, as it's difficult to tell whether the phases align.

To start, turn your voltmeter to AC voltage. Put 1 coil under the magnet wheel, spin the wheel a bit (not too fast to avoid safety hazards), and make a mental note of how much voltage it makes along with how fast the wheel is spinning. This is an important observation for later.

Between 2 adjacent coils, guess their polarities and twist one end from each coil together. Place it under the magnet wheel, spin it a bit, and observe its voltage response on the voltmeter. If you are reaching a higher voltage with the same spin speed, or it is easier to reach higher voltages, then you wired things correctly! If the voltage appears lower or the same, you will need to connect the other leg for one (and only one) of the coils.

Repeat this process, comparing the voltage response of 2 to 3 coils, 3 to 4 coils, and so on. If the voltages are adding, you will be able to reach a certain voltage at lower spin speeds, or a higher voltage for a given speed.

Troubleshooting:

Sometimes, you will see no response. Here are a few reasons why:

1. Your voltmeter is on DC voltage, not AC voltage. No, seriously. As a rookie, I made this mistake and was perplexed. After a day of frustration and troubleshooting, I realized my voltmeter had been on DC mode the entire time!
2. You didn't burn the insulation properly. As I mentioned in step 8, insulation prevents wires in contact from establishing an electrical connection. The best way to test this is to hook up an ohmmeter on the free ends of 2 connected coils and observe the resistance; anything above a few tens of ohms means there is no connection. To fix this, try burning more insulation from the connected and free ends and wiping it off. The wire should be visibly gray instead of orange, and the resistance should drop. Sometimes, the way you connect your clips to the coils will also affect the perceived resistance (connect it at the very ends of the wires.)

Conclusion:

When you have finished connecting coils, it should look something like the first image above. You should tuck the connections under the coil so they don't hit the magnet wheel. You can also solder the connections together to reduce resistance (optional).

We're basically done! Place your coil holder with the coils under the magnet wheel. Fasten it to the plywood with two #6 wooden screws, using the screw holes on the coil holder and your pre-drilled holes in the plywood. It doesn't matter which holes you chose; I chose the outer 2 holes on the holder. Then, we're ready to test!

Big warning: because of the substantial gear ratio, the wheels can spin very, very quickly. NEVER put your fingers anywhere near the wheels while they are spinning, especially not where the gears meet. You will get seriously injured. Also make sure your clothing and hair does not get caught in the wheels.

As you saw in the failure video from the intro, if anything hits the wheels during operation, they can burst out and pose a hazard. Before you operate the wheel at a serious speed, spin the wheels slightly and make sure the wheels have little to no deviation, and that the coils won't hit the wheels or vice versa. Make sure the wheels operate smoothly and without obstruction.

Now's a good time to hook up our electronics. Hook one free end of the coil array to the breadboard's positive end and another to the negative end. Across the positive/negative strips of the breadboard, place an LED, making sure the longer leg goes into the positive side. You can add a resistor in series if you're scared of the LED blowing, or a second LED in the opposite direction if you like fun. (While the LED is a diode, it can operate with AC currents of high enough frequency; this is essentially PWM.)

1. Tip: to get the copper wire securely in the breadboard, you can jam it into the same hole as another wire.

Now, get ready and give the generator some speed. Once you break the forward voltage threshold of the LED, you should see it flicker to life. Congratulations!

Would you like a video demonstration? Click here.

If you're a teacher who wants to use this in their classroom, it's better to operate it yourself than to let your students do so. They may abuse the machine and break it, or inflict self injury. If your students would like to operate it, make sure they understand the dangers and risks.

I took a step towards making this safer by adding a short wooden wall around the contraption, as you can see in the first image. You can also make students wear gloves and/or goggles as a precaution.

The fact that the wheels spin straight and do not wobble is an important safety feature. If you notice that wheels begin wobbling or deviating, it should be your top priority to repair it and stop the wobbling. As we've seen from the intro video, wobbling wheels can hit things they shouldn't, break cable ties, and cause magnets to fly out.

To the builder, thank you for making it this far! I hope you found this project fun and/or useful!

Brian