Make a Brushless DC Motor

This video instructable will show you how to build a brushless DC motor with minimal tools and materials. It can be done in an afternoon or less, and costs almost nothing (the materials are things that are on the edge of being garbage or not garbage if you have them laying around). The wiring may look confusing at first glance but you will be fine, it is not a terribly difficult project.

The video shows it pretty well, I don't think there is much to write out. The materials you will need include:

-A small plastic jar

-4 magnets

-A metal rod (or a nail)

-12 small steel screws

-A small piece of square wood scrap

-Enamel coated copper wire (easy to salvage if you don't want to buy some)

These pictures are shown in the video as an animation but you may want to look at them for a minute if you are thinking about how this motor operates. It is a repeating 6 step cycle, each 6 steps complete half a revolution of the 4-magnet rotor:

Step 1) A+ B+

Step 2) B+ C+

Step 3) C+ A-

Step 4) A- B-

Step 5) B- C-

Step 6) C- A+

For example A+ B+ means we have "+" power supply connected to the A+ wire and the B+ wire, and "-" power supply connected to the A- and B- wires. This is what I referred to in the video as "forward" current. An "A-" step would mean "reverse" current in the "A" set of coils ( "-" power to the A+ wire, "+" power to the A- wire). The coil sets share a common junction (A-, B+, and C- wires are soldered together).

There are several possible ways you could configure the current to run, that are not needed for this motor. Noticing what those are is helpful for understanding why each wire is connected where it is.

Do not ever need:

A+ B-

A+ C+

B+ C-

B- C+

A- C-

A- B+

So we connect the A- B+ and C- wires together... At every point in the cycle we will have 2 coil sets powered on in series with each other. For example: anytime the "A" is getting forward current (an A+ step) you will definitely also need either B+ or C- current. Imagine "+" signal comes in the A+ wire and flows through the A coil series and out the A- wire to the junction of the 3 wires soldered together (A- B+ and C- wire ends). If it is on the A+ B+ step then the B- wire gets the "-" power signal, allowing the "+" signal to now continue from the junction into the B+ wire, through the B coils, and out the B- wire to the "-" power source.

I hope that makes sense. You can look at the pictures and imagine each step, and track the magnetic poles as they are represented in the drawings.

Once you have made a simpler motor you may want to take your skill further with more thinking, reading, and experimenting. Then you would be able to make custom motors for whatever application you have. The pictures in this step show how I made a brushless outrunner motor.

After making the plastic one shown in the video, I made a steel-construction outrunner motor. The outrunner design has the stator with the coils in the center and a rotor bell around that with the magnets on the inside surface of the rotor. This particular one uses 12 coils and 16 permanent magnets in a ring around the coils.

The permanent magnets are north-south-north-south every other magnet all the way around. The bell the magnets mount inside of is a piece cut from an empty spray paint can. The coils are in 3 sets (A, B, and C) like before but all coils are wound the same direction this time (all clockwise). So the winding order is A+ B+ C+ A+ B+ C+ ... for all 12 coils. The core that I wound the coils on is made from a stack of fender washers epoxied together. There are ball bearings in the center of the washers for the axle to spin in. I welded a large hexagon nut onto one of the washers to give a good mounting frame to the motor (so it can attach to something). The hexagon nut made it easy to eyeball the position of the 12 cuts that needed to be made into the washers to form the individual cores for the coils.

Thank you for viewing this Instructable and I hope it is useful to you!