Building a Reed Switch Brushless DC (BLDC) Motor

Today was one great fall day. The morning temperature was in the 40s and gradually it warmed up to the high 60s. After reading the Bible, cutting the grass, raking the leaves and doing some other honey-do work around the home, it was time to build a Reed Contact Motor from Kelvin Educational products. This kit can be ordered from Kelvin also has many other interesting science and robotic kits that you or your parents might be interested in ordering for a birthday, Christmas, or to provide something for you to do during a spring or fall break.

Although this instruction manual said it came from Farmingdale, New York, the parts list was written in millimeters (mm) and the dimensions were provided as if the kit was designed in the United Kingdom using 52,0 mm vs. 52.0 mm as seen in the United States. The reason I mention this is the author of the instruction manual used terms I was not familiar with like Mignon cell batteries, PMMA, Pillar drill, etc. A clever youngster can read the instructions and figure out how to measure and diagram the parts for drilling and sawing, but some of the above terms might through you off – that is why you might need an adult nearby.

Here are the main pieces that come in the plastic pouch that was shipped to me:

1 kelvin reed contact dc motor contents

Kelvin Electronics Reed Contact Motor

This above photo shows the instruction manual, the plywood base, the copper wire, the acrylic side brackets, the reed contact, the pine coil holder/magnet rotor, battery holder, and various sundry items like the magnets, brass nails, and the set screw that you use to make the electromagnet.

The first few pages of the instruction manual give you the dimensions that are required to build the motor. Here is an photo of the components I put on the three main components.

2 reed switch motor pieces marked

The three pieces that need to be dimensioned prior to cutting

In order to build this kit you have to provide two different saws (one to cut the acrylic and one to cut the wooden base, rotor, and coil holder), two needle-nosed pliers, glue, masking tape, soldering iron and solder, and a AA battery. It took me about 2-1/2 hours to cut out the side supports (acrylic), the base, the rotor, the coil holder, glue the magnets to the rotor, and wrap the 30 feet of wire to make the electromagnet. Here are a couple of photos of the finished product before testing.


3 closeup of reed switch assembly

Close-up of the reed switch (note how the reed switch was soldered to the brass nails)

5 top view of reed switch motor

Top view of the completed motor (note how the reed switch is lined up with the magnet)


4 side view reed swith complete start testing

Side view of the completed motor

Once the motor was complete and pictures taken, the next step was to insert the battery to see if the motor would start. I carefully put the battery into the battery holder and … nothing happened. What went wrong? I had checked to be sure the polarity of the magnets were correct before I glued them onto the rotor. Once again I checked to be sure I had wired it all correctly. As I started looking at the rotor and moved the motor slightly it started to run! Immediately, I knew what had happened. In order to make this motor run you have to have the magnets be a little off center in order to pull onc part of the reed switch away from the other part of the reed switch. Since I had a little “give” in how the rotor lined up, it was easy for it to automatically move to the right spot on its own. That is what is nice about most DC motor kits – most of the time you don’t have to make them perfect to have them run.

Here is a photo of the rotor spinning merrily along.


6 reed switch motor complete and workingReed Switch Brushless DC motor working!

Here is the video of the motor as well:

I get a lot of enjoyment making these DC motor kits and hope you do as well. This BLDC kit cost around $7.95 plus I had ordered additional motor kits to save on postage. Now that it is getting colder it would be a good time to start making a few DC motors for Boy Scouts, Girl Scouts, science clubs or even enter the next Science Fair at your school. Again, it was a great fall day!

Quote for the Day: “Do what you love and what you love will reward you.” — Dave Martin


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