Custom Electric Motor

I think it was my sophomore year in high school, I decided I wanted to build a generator. I knew the basic princple that I needed to move a magnet through a coil of wire, and that is about it. So I took a cardboard toilet paper roll, wrapped some rubber coated wire around it once, and made a rig to hold a ceramic magnet that I could fasten to a drill motor. After fussing with it for about an hour, I gave up and did something else.

Now a few years later, I have about finished my bachelors of electrical engineering degree, and I understand the design a little better. I was reading through a book I had recently acquired "The Inventions, Researches, and Writings of Nikola Tesla," and some of the first sketches of an AC motor inspired me of my short lived high school ambition. Now of course at this point, I realize that an electric motor and generator are in fact one in the same.

Tesla's patent sketches of the AC Motor (Photo credit Wikipedia.org)

So I decided it would be a fun weekend project to try and make my version of the electric machine! I wanted it to be as simple as possible in terms of construction, and also as cheap as possible. So I decided the frame should be 3D printed (as if I would have chosen any other option), and the cores of the coils would be roofing nails that I had sitting around. The magnets were picked up for $6.00 at a local craft store, they are neodymium and measure 2561 Gauss. Most of these dimensions were arbitrarily designed as this was more of a hobbyist weekend project than a technical engineering project. The motor stator and rotor was designed in SketchUp 2015. I designed for the bearing (a skateboard bearing I keep on stock) to be press fit, knowing that once it was 3D printed, it would fit tight, and could be sanded down.

The designed 3D Model of the motor

 

I printed the rotor first, and it turned out well. The magnets press fit into the slots well; this is a handy feature for later experimentation (plus glue is messy, so I like to avoid it). I printed with 40% in-fill, and it feels pretty sturdy. My only mistake was making the hole too big for the screw, because it caused difficulty when lining everything up.

The motor rotor

 

Next, the stator body was printed. I designed it with mounting holes so it could potentially be fastened to a piece of wood, along with the control electronics. It should be noted that I purposefully left the motor open faced, because it serves as a good motor demonstration piece. I had to sand our the bearing socket with my Dremel on the lowest setting, and then lightly hammered it in with a block of wood.

The motor stator body

 

Next I cut the ends off of my roofing nails, and began winding my magnet wire. I wound them by hand, and did not wind to a precise value. I stopped winding when the coil was about as wide as the nail head. The first stator body was broken when I tried to press one of the coils into the stator hole. I quickly printed another body, and drilled out the holes a bit. This time I went a little to big, and had to wrap some of the nails in Teflon tape, to get a tight fit. Once the coils were all installed, I lined up the rotor by eye, and fastened everything together.

The finished motor

 

Now I have not started designing a controller for this motor yet, so I have no information on it running in motor mode. However, I did hook up some of the coils to my oscilloscope, and did some testing in generator mode. Just spinning the motor by hand, I got about a 5 mV peak output.

The output from a single coil on the motor

As usual, if you want any of the models, or have any questions or comments, please comment below, I'd be happy to talk to you about the design!