I was going through a large box of random motors I got at a yard sale. I was sorting them for use in later projects when I came across a motor I couldn't classify. Long story short, the magic smoke left so I figured I would open it up.

What I found didn't seem to make sense to me. There are two separate stator coils, which I had predicted from my multimeter. But they run around the rotor, not up and down it. The only thing I can liken it to is a solenoid, so I'm confused how this would work as a motor. Also I couldn't find anything with the motor's part number aside from some eBay listings which don't help.

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  • \$\begingroup\$ Your picture looks very much like some stepper motors that I have. However, I've never disassembled any of my motors, so I can't compare them to what you describe. \$\endgroup\$ – Dwayne Reid Jul 16 '20 at 19:13
  • \$\begingroup\$ One unlikely possibility is that it is an electric brake. \$\endgroup\$ – Dwayne Reid Jul 16 '20 at 19:14
  • \$\begingroup\$ Epoch mostly make stepper motors, and a pair of coils makes sense for that. So I guess it is a stepper, but with a slightly odd geometry. Is there a metal core between the coils, and if so what does it look like? \$\endgroup\$ – Jack B Jul 16 '20 at 19:30
  • \$\begingroup\$ I guess it is a 4 wire bipolar stepping motor. I once opened a couple of motors and yours look like the little stepper 28byj48. Here is a picture of the opened 28nyj48 motor.: (1) i.imgur.com/2iu8dxQ.jpeg. You can use a muti-meter to check out the wiring. More references if you are interested: (2) 28BYJ-48 - 5V Stepper Motor - Components 101 2018mar05 components101.com/motors/28byj-48-stepper-motor (3) Controlling 28byj48 bipolar convert with l293d ic raspberrypi.stackexchange.com/questions/97975/…. Cheers. \$\endgroup\$ – tlfong01 Jul 17 '20 at 2:12

It is a motor

A shame it's toast. I found a couple of places selling them - over $80US in both places.

It's a stepper motor, but apparently no longer in production - the manufacturer doesn't list it anymore. Epoch homepage.

At a guess, I'd say yours is much like the others listed on the Epoch page: Two phase bipolar stepper.

As to how it can be a stepper motor, it would appear to be common to have the two winding coils of a bipolar stepper in a kind of "stacked pancake" setup.

This page shows the construction of a bipolar two phase stepper motor:

enter image description here

The windings clearly run around the motor like the ones in your motor.

The second photo you've added shows how it works.

The rotor will have "stripes" of north and south poles around it. Like you'd put a bunch of bar magnets in a cicle, north ends to south ends around the circle.

These "stripes" will be about as wide as the "teeth" around the inside of each coil.

You have just two coils, but many pole pieces against many magnets. Each pulse will only rotate the motor the width of one "tooth."

  • \$\begingroup\$ Wow thanks a lot! That looks just like it. I guess my only question now is, how does this motor generate torque with this coil configuration? \$\endgroup\$ – RonGerals Jul 16 '20 at 19:45
  • \$\begingroup\$ Very cool, thanks again \$\endgroup\$ – RonGerals Jul 16 '20 at 19:58
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    \$\begingroup\$ Many (most?) stepper motors are switched-reluctance motors, are you sure this one has a magnetized rotor? \$\endgroup\$ – Hearth Jul 16 '20 at 20:04
  • \$\begingroup\$ @Hearth: Most of the steppers that I saw on the Epoch site seemed to be permanent magnet motors. \$\endgroup\$ – JRE Jul 16 '20 at 20:05
  • \$\begingroup\$ Now with the correct keywords, I was able to find out that this particular setup makes this a can-stack stepper motor \$\endgroup\$ – RonGerals Jul 17 '20 at 0:32

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