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Miniature Switched Reluctance Motor (SRM)

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  • Miniature Switched Reluctance Motor (SRM)

    I've decided to go ahead with a small SRM as a metalworking project as well as an adventure in electronics. In the thread on making a punch and die for motor laminations I showed a concept for a small motor using steel washers for the rotor and the stator. I finally made some chips!

    It's pretty rough, but my workshop is unheated and after an hour or so I just wanted to "git 'er done" and get out of there back to the relative warmth of the house. I had problems trying to mill the slots on the stator, so I just used a hacksaw and a file. Same with the rotor. After drilling the four holes I just sawed the slots and touched up a bit with a file. I think the pole pieces should be about the same size so as to get good magnetic coupling, but the torque is applied when they are not aligned. So when one set of poles become aligned, the next set of stator poles is energized and causes rotation. I will need a sensor or encoder to determine the rotor position.

    Here are a few more shots of the rough metalwork:

    Somehow the LCD of the calipers did not show up, but the stator is 2.75" OD and the rotor is 1.25" OD. These were made from USS plain steel washers, USS 1-1/8 and USS 7/16.

    Now I need to add a shaft for the rotor and a housing for the stator, and then add some windings. I think I will touch up the metalwork a bit more, make all the edges smooth, and add a layer of tape before the windings. I'm not sure how many turns or what size wire, but probably about 100 turns of #28 to start with. This is basically an electromagnet, so the magnetic force will be determined by ampere-turns. I will need to use PWM or other means of current limiting at low speeds, and then apply more voltage at higher speeds where the inductance will limit the peak current before the next pole is energized.
    Paul , P S Technology, Inc. and MrTibbs
    USA Maryland 21030