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Simple DC Motor

September 14, 2009
Ok, so there must be a gazillion sites out there which depict a Simple DC motor like this one, so I figured there would be no harm in adding another. There are plans all over the Internet for such devices and mine is not all that unique. This page describes my take on a very simple project involving the creation of an incredibly simple DC motor.  I made mine out of materials which were readily available to me but there are all kinds of ways you could make one like this yourself. My goal was to make one which was kind-of like a "paper-weight" or desk tchotchke that I could leave out. Anyway it's kind of fun to have around and my son likes to play with it now and then as well. At first look its not quite obvious how it works. It seems to mysteriously rotate about its axis. However after observing it operate a bit and recalling the Right-Hand Rule you'll quickly figure it out. I was inspired to make this device after reading the book Empires of Light: Edison, Tesla, Westinghouse, and the Race to Electrify the World by Jill Jones. In particular Chapter Two was quite interesting. This chapter was an excellent survey of the history of electricity and magnetism and what led us to have practical electric generators and motors today. Another bit of interesting reading is about the inventor of the Brushed DC (Commutated) Motor, Thomas Davenport. As for this simple motor described on this web page, you can search for "Simple DC Motors" and you'll get plenty of results with all kinds of variations. Some which are particularly good are listed below. My design combines a lot of the ideas from these sites linked below. 
It seems like anyone who has built one of these has their own take on it, which makes it kind of fun. Here's a list of what you'll need to make one like I did;
  • Approximately 9" piece of 1x4 lumber (any kind, I used Walnut)
  • A 12" piece of 1/8 " brass wire
  • A Dual "D" cell battery holder (Radio-Shack #270-386)
  • Two-"D" cell batteries
  • Two Alligator Clips (Black & Red)
  • #22 AWG Magnet Wire (Radio-Shack #278-1345)
  • Rectangular household/refrigerator magnet
I started by cross cutting the board into two pieces. One piece was approximately 6" long (base) and another 2-1/2" long ("U" shaped coil support). Once I had the base cut, I marked off where I wanted to put a recessed pocket for the rectangular magnet. To cut the recessed pocket I used a forstner bit to bore out two 3/4" holes the width of the magnet. I bored out the pocket just a little shallower than the thickness of the magnet to allow me to easily remove the magnet if I needed to. This results in the magnet being slightly raised above the surface of the base. I squared up the rest of the rectangular pocket with a 1/4" drill bit and small chisel. The pocket holds the magnet snugly in place without any adhesive.
To make the "U" shape holder I first drilled two 3/8" holes at the bottom inside corners about 1/2" from the bottom edge and 3/4" in from each side. Then I marked off and cut out the inside piece using my band saw. The holes in each of the two corners helped me get inside and cut the corners clean. I also drilled a few 1/8" holes vertically along each end to allow for the brass wire to be inserted. Multiple holes allowed me to raise or lower the brass rods but found the middle position to be the best. Lastly I drilled two counter bored holes in the bottom of the "U" so it could be fastened to the base with wood screws.
With all the pieces cut, I routed a small radius along all the edges to give a more finished look. Then I was ready to assemble the base. Be sure to place the "U" shaped holder in a position which allows free rotation of your coil above the magnet as well as room for the "D" cell battery holder in the back. The coil when standing vertically in the holder should be directly above and centered with the magnet below it. I sanded smooth the Walnut parts, assembled it and finished with a light coat of Danish Oil.
To make the two brass holders (commutators) I cut the 12" piece in half and bent each 6" piece into a shape which allowed the rods to be held above the magnet at the same height they are positioned in the "U" shaped holder. To do this I made a bending jig from some scrap wood and nails. I constructed the jig so that I could bend the brass wire around nails I placed in the board with their heads sticking up. Using a jig helped me to bend each of two pieces approximately the same way making the motor overall a bit easier to balance. Plus it just looks better. The holes drilled in the "U" shaped holder are approximately 1/8" to accommodate the brass rods.
Lastly I wound the #22 AWG wire 10 times around a "D" cell battery allowing about 1-2" extend from each side. Why 10 times? I don't know its just what I tried and it seemed to work fine. You can try experimenting with another number or even the shape of the coil itself. However be as careful as possible when winding the coil. The neater you wind the coil the better your motor will run. Try to keep the coil symmetrical about the extended leads and as round as possible. Neatness counts and will help your motor be as stable as possible. Wrap the ends around the coil itself after winding to help keep the individual windings together. As you can see I also experimented with #26 AWG wire but it just seemed too light and flimsy and it had trouble staying put as it rotated.
Once you have the coil wound and two ends 180-degrees apart and as straight as possible, place it in the base suspended by the brass rods. Let the coil rest freely and adjust as necessary. This is the "rest" position. Note where the coils ends and the brass rods(commutators) touch. You might even want to mark the spot with a marker. Now gently remove the coil from the base remembering where it touched and scrape, file or otherwise remove the varnish from the coil at and around that location across the length of each 'arm'. Choosing the right place to scrape the varnish off the coil will help the motor start spinning even at rest without having to "flick" it and give it a kick-start.
Now all that remains is to attach the "D" cell battery holder to the base with a few screws. Also attach alligator clips to each of the red and black leads to make it easy to attach to the brass rods. Insert a couple of fresh "D" cell batteries into the holder and attach the alligator clips to the commutators. Lastly, insert the magnet into the pocket.
Once that's done your ready to place the coil onto the brass rods and watch it spin.
Here's a close-up of the Motor spinning at full speed.

Simple DC Motor Free Running

Here's an example how removing the varnish from the bottom of the coil arms allows the motor to spin immediately when voltage is applied.

Simple DC Motor Self Starting

I haven't measured the speed of the motor yet but I expect it to be in the upper 800-1000 RPM range.
The DC-load of the coil at 3V is about 3 amps or so. That means if you leave the coil accross the supports without it rotating for too long the coil gets very hot! Plus your batteries wont last very long either. While spinning, the motor pulls about 250-400ma but its hard to measure with a DVM since it's bouncing around all over the place.
Have fun!

Simple DC Motor