This project is very hard — you need to be handy to make the commutator part of the rotor. Also, this project tests my electrical engineering skills. If you want an easier motor, I will upload a basic BLDC motor that is much stronger and far easier to wind. Please don't test it with batteries — you cannot control the current; use a lab supply (about €40–50 from AliExpress).

Hello guys, I'm uploading the DC motor that I made. It uses a very basic rotor winding pattern with 3 windings wound in the same direction. The rotor is hollow so you can fill it with iron powder for better permeability. The stator is the same.

How to assemble:

1. Fill the rotor with iron dust, put the caps on and epoxy over the caps so no iron dust can escape.
2. Fill the stator — put a piece of paper underneath, carefully aim for the sides of the stator, fill them up, put the caps on and epoxy the edges. After the epoxy hardens, check for leaks of iron powder; if there are leaks, add more epoxy. Don't leave epoxy puddles above the caps because they will interfere with closing the motor. Work the epoxy into the openings and avoid puddles above the caps.
3. Put the magnets — I've used neodymium magnets 40×10×5 mm N52. You can use a total of 8, but 4 is perfect. They determine the power of the motor; if you only want to show it works, you can use lower-quality magnets (not N52). Place the magnets so that one side has one polarity and the other side the opposite polarity, giving two poles on both sides and a neutral line in the middle. Look at the last picture — there you can see the two poles and the neutral line in the middle. Our brushes sit on the neutral line.
4. Commutator — part 1: put 3 wires through the rotor shaft holes. I used 0.7 mm copper wire, enamelled, but you can use bare wire for easier soldering. After you put them in, on the side of the rotor lift them out of the channel — I used a needle to lift the wire out. Then proceed with the windings.
5. Windings: the windings are very easy — 3 windings in the same direction. I made around 30 turns for every winding with 0.35 mm wire, but 30 was not enough; make 60 or 80 turns (with only 30 turns the magnet cogging holds the rotor and it's very hard to start). Be careful not to fill it too much so the windings rub against the walls of the machine or become hard to solder. After you do 30–80 turns per winding, don't cut the wire — hook it onto the metal wire you bent out of the channel earlier and leave a bit of extra length so removing the enamel in this area is easier. Do this for all 3 windings. One of the windings will have a cut end and you just solder it normally after removing the enamel; be careful not to exceed the ring on the rotor shaft. You need to insulate the windings with electrical tape or similar so they don't short through the bearing.
6. Caps and bearings — you need 608-size bearings. You can 3D print a plastic one or buy real ones. Plastic bearings can withstand tests at idle without load, but you still need to lubricate them. Put one cap on the stator and use at least two M2.6×16 screws in opposite directions. Then put the rotor in and fit the second cap on the other end. Make sure to straighten the wires sticking out of the stator so they can pass through the bearing. After that use at least two screws again and test if the rotor can spin without hearing rubbing noises from inside. Keep in mind if you used iron dust in the rotor there will be cogging steps.
7. Commutator — part 2: if you made it this far, congratulations — this is the hardest part because you need to be handy. You will need spot-weld nickel strips about 8 mm wide, ~25 mm long and ~0.2 mm thick (or the thickness you have). Keep in mind that the bearing on the commutator side becomes “lost” — the shaft with the commutator cannot go through the bearing hole after we solder it. (This design is not ideal, I know, but the point here is to show the commutator and the sparks.) Cut the nickel strip into 3 equal parts. Apply strong epoxy and place each plate under each wire with a gap between plates (basic commutator). Wait until the epoxy hardens and then solder each wire to the plate under it. That's it.

This project is very hard — you need to have experience building at least BLDC motors. It's not the most expensive thing to try, but starting the motor afterwards is not guaranteed. It's very hard to locate errors and the start is a pain: for 7 seconds of spin time I tried for 3 minutes to start the motor with those crocodile clamps. I'm uploading this project so you can see it's possible to make a DC motor out of plastic that resembles store-bought motors. I know there are other 3D-printed contraptions that are technically DC motors, but they look, well, like a contraption :)
Video with sound: