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World's smallest working model three phase AC induction motor project

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  • #16
    Here's a representation.
    Each color represents a phase. When the level is high, the dc is on. Only one phase is on at any time. Because the power comes from a dc source, the voltage only goes from zero to a maximum- it doesn't go negative. That's a simplification of the whole thing. This diagram shows gate voltages on an electronic controller for brushless motors. The actual voltages on the windings that are controlled by the gate voltages through the power mosfets will be more complicated than this.
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


    • #17
      The two types of PM motors with 3 stator windings that are physically practically identical, are AC sinusoidal, fed by 3ph as its name implies.

      And BLDC, Brushless DC due to the fact that only two windings are energized at any one time, and they represent a DC brushed motor turned inside out.


      • #18
        I do have some transformer lamination material I could use, but I have no easy way to cut it to the shapes required. There is no real practical application for this motor, so the efficiency is not critical, and I will be happy if it just runs. The challenge will be the machining of the small components, and I also like the idea of using commonly available parts like the standard washers. I was aware of some of the small 400 Hz 3 phase induction motors and I can see that my model is probably nowhere near "the world's smallest". There are some distinctions between a true induction motor and a BLDC or stepping motor, which is primarily the lack of permanent magnets. And then there are motors which use slip rings to connect to the wound rotor, and these are synchronous AC machines which may be motors or generators (or alternators).

        I do have an idea for a rather different sort of motor in which a magnetic field is applied to the rotor through the shaft and bearings, and then the rotor would have windings and rectifiers and perhaps other electronics to create the DC and magnetic poles. The applied magnetic field could be at a rather high frequency so that a minimal amount of iron would be needed, and perhaps the frequency could be high enough to use powdered iron or ferrite. Once the magnetic poles are established in the rotor, the stator may be energized with a rotating field using three (or more) phases. Perhaps that would be a more interesting, unique, and potentially useful device.

        I also have some ideas for a SRM, as mentioned earlier, and that is another technology that has seen some resurgence in the past 10 years or so since the electronic circuitry needed has become much less expensive and readily available. An SRM relies on the magnetic force of the iron and is essentially a switched DC phenomenon rather than AC induction, so eddy currents are not so significant. An SRM rotor can be built from a solid block of iron or with iron pole pieces held in a rotor made of non-magnetic material, even plastic or ceramic. The stator may need to use laminated iron for better efficiency, especially at higher frequency and RPM, but might also be made from powdered iron or ferrite. I envision a motor with a large circumference, such as a bicycle wheel, with many pole pieces on the periphery of the rotor and along the stator, so that a high frequency can be used for a relatively low RPM. It might even be possible to have a short stator which interacts with only a portion of the rotor, housed in something like the fender of a motorcycle. It may present some challenges because of exposure to the elements of water and debris, but the magnetic components could be sealed in a smooth protective covering.

        For the project as proposed here, I may use larger washers so as to make the machining easier. Or I might just move on to something else. I find most of the pleasure in the initial design and plans, while the actual implementation becomes a bit of a chore.
        Paul , P S Technology, Inc. and MrTibbs
        USA Maryland 21030


        • #19
          I have found some possibilities for thin steel discs. You can get shim washers as thin as 0.001":

          But they are about $0.35 to $0.50 each for 10 mil, and for a 1" long motor you would need 100 of them, or about $35-$50. Then they would need to be coated, pressed together, and machined. Perhaps a sheet metal punch would be the way to go, using the steel lamination material I have. A set of punches for thin metal from 1/8" to 3/4" is about $160, and large diameter from 7/8" to 1.25" for $385.

          This is a pretty inexpensive alternative:

          I also found a company that sells plain steel discs from 1" to 3" diameter at reasonable prices, but they are 16 gauge (about 0.065") which is about the same as USS or SAE washers, and too thick.

          Seeing how that $55 hole punch is made, I wonder how difficult it would be to make a punch with all of the holes and slots I need? They are mostly round holes, so I should be able to drill them as needed in two blocks of steel, and then get drill rod or hardened steel rods to fit the holes well. I could also make the slots using thin pieces of hard steel perhaps in another jig. It should work well enough in an arbor press and probably wouldn't take too much force. And it may even be possible to use the round center portion punched from the stator to make the rotor. It should be very close in size and by the time a final machining operation were done it should result in a reasonable size gap.

          I'm in very unfamiliar territory on this idea, so any suggestions would be welcome. I'd also be happy to farm it out at a reasonable price but it would probably be a valuable learning project for me to try. I don't have an arbor press but I have a HF 12 ton shop press that I've never even assembled. Probably way overkill, and a small arbor press would be a useful addition to my toolset.
          Last edited by PStechPaul; 01-02-2014, 02:30 PM.

          Paul , P S Technology, Inc. and MrTibbs
          USA Maryland 21030


          • #20
            I admit that this suggestion is "off the wall," but could you build an EDM unit and prepare both a die and punch in the required shape? The unit might have to be a fair size, but it can take a while to chew out each electrode, and they can be made of pre-hardened steel. Once you have the die set, the rest is just cranking a handle!
            If anyone else is interested, I also have a bunch of transformer laminations. I think that they are 3"x51/2" and 3"x11". They are free, but shipping can be hell. For anyone in the states, I could probably drive to Ogdensburg NY, and mail a flat rate box. In Canada, no such luck!
            Duffy, Gatineau, Quebec


            • #21
              Such a motor would run on ac or dc, but the source would still have to be switched to coincide with the rotor position. If powering from dc, the rotor could be a solid piece, since it doesn't experience large changes in the magnetic flux, which means there is little in the way of eddy currents. The stator should still be of laminated structure since the polarity of the magnetic field would be changing as the rotor turns and the switching of the power sequences. If powering from ac, both components should be of laminated construction since both would see a changing magnetic field.

              For highest torque, you would want to maximize the area of material in the flux pathways, and minimize the length of the flux pathways. At the same time you would minimize the air gap to allow the highest possible flux density. These are generalizations, as you could optimize factors to decrease drag, etc. I mention this because in many if not most demonstrations of experimenter-built apparatus, there is little to no closure of the magnetic pathways. The air gap is basically huge, inches in many cases, and the potential to achieve a good measure of output and efficiency is thrown away. And yet great claims are made for these things-

              One area where I see this in in wind turbine alternators. People go to great lengths and cost to produce power levels that are but a fraction of what the potential would be, given the number of magnets and the size of the packages.

              About laminations- it seems to me that one of the daunting tasks is in punching out the slots in equally spaced degrees, while preventing damage to the thin material itself. I'd think it almost mandatory to have a 'compression plate' come down and pinch the disc while the punching is taking place. Without a lot of pressure, you couldn't punch all the slots in a disc at once, so some form of indexing would be needed. I don't see this as being a difficult part. The punch could be an integral part of the compression plate, which would itself be keyed to the die with rods or something, external to the disc being punched.

              You would likely need to hole the discs previous to punching, as you would need some way to set the radius for the slots. To be somewhat practical, an apparatus could be made to hold the discs, set the radius, clamp down on it, and guide the punch. This apparatus might then be fixtured in a press which would supply the punching force.

              The above descriptions work best where the slots are to be made around the periphery of a disc. For stator slots, the idea would be altered to suit.

              On the subject of stator laminations- these could be round, square, or have any other outer shape, but most likely would be round in any project that I might do. I have envisioned pivoting the blanks using a central hole, then using a rotary shear to blank them out. If they are of any appreciable diameter, it would be less possible for a home shop guy to punch them out due to the need for suitable equipment.
              Last edited by darryl; 01-04-2014, 02:55 AM.
              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


              • #22
                Originally posted by darryl View Post

                About laminations- it seems to me that one of the daunting tasks is in punching out the slots in equally spaced degrees, while preventing damage to the thin material itself.
                The laminations do not need to be punched , they can be machined electrolytically using similar masking methods to home shop pcb prodution.

                Bruce Simpson used electrolytic machining to produce intricate reed valves for one of his pulse jets.