Scratch-built Motor Uses A Clever Design

[Lou] is on a hot streak when it comes to interesting builds. This time around he made his own motor using wood, PVC, some fasteners, and a bunch of enameled wire.

His method of building a commutator is intriguing. He first builds a rotor by cutting two opposing sides off of a PVC four-way connector and pushing a short galvanized pipe through what’s left. After adding two PVC nubs with caps and nails as pivot points he wraps the PVC and metal pipe with a continuous length of enameled wire. The enamel is then sanded off the windings around the PVC, and half is covered with electrical tape. The spinning rotor will cause the brushes to contact the bare wire during half of the rotation, and be insulated by the tape during the other half. The video after the break shows the motor in action, then walks you through each step of the build.

If you liked this video you should check out [Lou’s] water bottle rocket launcher, or his automated Ping Pong table topper which stores the game in the ceiling.

17 thoughts on “Scratch-built Motor Uses A Clever Design

  1. Hang on, you would get better performance if your magnets were mounted on the OTHER side of the angle brackets. I know the reason you mount them on that side is to stop them flying off, but the metal in the angle brackets will divert a lot of the magnetic flux through the metal and around the magnet instead of into the region where the rotor is spinning, where it can generate torque.

    You can check this by tapping the angle bracket side of with something metallic, you will find the attraction much weaker on that side compared to the side without the angle bracket

  2. I was about to write the same as Mike. I’d put the magnets on the other side. However, this motor is running at no load and it is quite clear that it spins quite fast, putting the magnets on this side of the metal plate is like wasting the magnets but I guess if you put them on the other side this thing would spin even faster and perhaps too fast… but then you could lower the voltage to prevent it spinning too fast which isn’t a big deal.

    Anyway great build and great video. Definitely worth watching.

    1. There is a commutator, only half the enamel is sanded off from one side, that is the commutator. Also, because of that, the motors are usually not self starting. They rely on momentum to spin it past the dead time.

      We made these in school. Real easy to do.

      1. Nope. That is not it. Notice, in the video, that the rotor is made completely of plastic coated wire, that has no enamel. Both sides are bare copper. There is no commutator. Build it yourself and you will see, amazingly, it works fine without one. Any other guesses? I used to carefully sand enamel or remove plastic from one side too, until I realized there was no need.

  3. Look closely when it spins, I think one side or the other is bouncing off of its contact when the rotor reaches the side that is repulsed by the magnet. The coil is light enough that the repulsion pushes it up, breaking the circuit. Rotational inertia carries it around, it falls back on the contact, the circuit is made again, and the attraction starts to pull it around again. To verify this, hold the magnet over the top of the motor, I bet it won’t run then…

    1. Macona and Llyod are thinking the same thing I am. The leads must lift off the holder at some point. I imagine the builder can’t help but bow the rotor a little, causing it to naturally hang with one side downward, when the power is off. If this downward side is North, and the permanent magnet is also North, the rotor would flip, but also lift up a little, breaking contact. By the time it comes back in contact, the momentum has carried it around to face North-North again. I think the same thing could happen with a manget above, as the rotor would get lifted a little by a North-South pull. In any case, it is much easier to build, when you don’t have to sand half of a wire :) Just be ready with some explanation when your kid says, “Hey, There is no commutator!”

  4. The commutator is an up-scaled design shown to us by the famous science geek, Mr. Wizard (Donald Herbert Kemske). That said, and memory serving, it wasn’t even his design. I remember rather clearly because I tried to replicate it as a kid, but lacked the proper parts.

  5. I have two question for the first scratch built motor:
    1. Can the motor run with only one 6-volt lantern battery?
    2. Can the motor run in 4 positions when holding it by hand: upside-down, upward, sideways?
    I want to make sure if this design runs on only one 6-volt lantern battery and in 4 positions before starting. Thank you!

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