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

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

    The miniature working scale models of internal combustion engines being built by Brian got me wondering if the same thing could be done for an AC induction motor, particularly three phase. The only thing I have been able to find so far is this project:

    http://chestofbooks.com/crafts/popul...l#.UsRrRJ0o7IU

    It's hard to read the dimensions, but it looks to be several inches square. My idea is to make one that is about 2" long and 1.25" diameter. Here is the concept:



    The rotor as shown is made from a stack of 1/4" SAE washers, with eight holes drilled through each and small slits to form the magnetic gaps, and then copper bars (actually about #10 AWG solid wire) is fed through the holes for the "squirrel cage", and then copper end plates are attached to complete the circuit. These washers are 0.625" OD and 0.281" ID.

    The stator as shown was to be made from a 1.5" length of 1.125" steel rod, but it would probably be much easier and better to use a stack of washers for this as well. I show a USS 9/16" washer which has 0.625" ID which is a good fit for the 0.625" OD of the 1/4" washers with a little bit of machining. The OD of the 9/16" washer is 1.468" which is larger than what I show, but that may be OK. Or I could use an SAE 1/2" washer with an ID of 0.531" and OD of 1.062", or a 5/8" washer with an ID of 0.656" and OD of 1.312". The SAE is also thinner, which is good.

    I would also need to drill 12 holes in the stator washers and add slots. Then I would need to fill the slots with magnet wire of an appropriate size, and this could be a real challenge on something this small. And the slots would need to be completely deburred and then coated with some sort of insulation, or use thin strips of Mylar or Kapton or other insulating film, to avoid scratching the varnish.

    The rest of the design, such as the bearings and end caps, should be rather straightforward.

    I'm not sure how to figure the number of turns needed for a practical voltage. I have a feeling that I might be able to use something like 20 turns of fairly fine wire like #30 (0.010). It will probably work out to be perhaps 5 or 10 volts and maybe 200 mA, which means a motor rating of one or two watts. Too low for HP rating (0.002), so maybe it should be in mousepower.

    I don't know if I'll actually build this thing or not. But if it's something that's never been done before, it might be worth it to try. I think the relatively thick washers may not be very efficient, and ideally something like this would be made from very thin silicon steel stamping or laser cut parts. And also I may need to make a tiny VFD, but that's easier for me than the mechanical aspects of this thing.
    http://pauleschoen.com/pix/PM08_P76_P54.png
    Paul , P S Technology, Inc. and MrTibbs
    USA Maryland 21030

  • #2
    It can be done. You should varnish the core washers.
    If you look for an old IBM disc type typewriter, the motor that spins the type disc is a 3 phase motor, used as a stepper. It runs quite well on a 3 phase 12V transformer. Normal stepper motors can run as regular single phase motors with just a small capacitor and low voltage ac.
    Helder Ferreira
    Setubal, Portugal

    Comment


    • #3
      Another thing. The rotor must have one more or less slot for the motor to work properly. Before soldering the rotor bars, the rotor stack should also be twisted.
      Helder Ferreira
      Setubal, Portugal

      Comment


      • #4
        I have seen some references for the ideal numbers of rotor and stator slots, as well as the degree of rotor skew. Some links:

        http://maintenanceforums.com/eve/for...2/m/8621030173
        http://www.reliance.com/mtr/pcrssmn.htm
        http://ac-induction-motor-reviews.bl...tor-noise.html
        http://www.ijest.info/docs/IJEST12-04-06-032.pdf

        Actually I am more interested in making a switched reluctance motor (SRM), and I have a thread in another forum that discusses it:

        http://www.diyelectriccar.com/forums...tor-77483.html
        http://pauleschoen.com/pix/PM08_P76_P54.png
        Paul , P S Technology, Inc. and MrTibbs
        USA Maryland 21030

        Comment


        • #5
          There are way smaller three phase induction motors than that. I have seen them in little gyroscopes and fans in military equipment. If you consider three phase brushless, even tinier.

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          • #6
            Yes,Arc Systems in one supplier,they make them down to a 15/16" OD case diameter.And there is a Japanese company that goes even smaller IIRC-

            http://www.arcsystemsinc.com/categor...on-Motors.html
            I just need one more tool,just one!

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            • #7
              Originally posted by macona View Post
              There are way smaller three phase induction motors than that. I have seen them in little gyroscopes and fans in military equipment. If you consider three phase brushless, even tinier.
              Absolutely..... Don't want to dump on the idea, but the size proposed was made reasonably commonly 50 years ago. I have a servo rotor that is 0.875 diameter, and may be from the 1940s
              CNC machines only go through the motions

              Comment


              • #8
                I do not know how well a solid steel stator core would function. A-C motors normally have thin lamination's for both the stator and rotor. They should be painted for insulation purposes before assembly. Check out junk electronic equipment and you will find small motors of many styles.

                Comment


                • #9
                  If this is being done strictly as a model, a scaled down version of something, then your choice of materials won't matter so much. If there's a use involved, then at these sizes you would want to use a magnetic material that's suitable- that means very thin laminations, and preferably in a high flux density capable material. At the least you would want to use existing transformer lamination material- maybe scrounge from a transformer. For a large enough width to make the stator, you might look at a microwave oven transformer, or find a toroidal transformer where the length of the core is enough for your widest pieces. It's likely that considerable work would be required to separate the laminations, particularly if the whole core has been vacuum dipped, and where there are weld seams across the lamination stack- common on microwave transformers. Best would be to obtain a roll of amorphous ribbon steel to make the laminations from. Good luck getting any of that-

                  One of my hobbies is playing around with electric motors of all types. I have built a few of my own, but usually use an existing armature. I have some ideas in mind that will require me to make my own lamination stack, and that looks like it means punching them out. It will require a custom punch and die set, two of them actually, and a clamping setup to hold the thin material and allow for indexing. It's not a highly technical set of jigs to make, but those would certainly be a project in themselves, and would only be suitable for one particular design. Being a hobby though, maybe one day I'll find some joy in embarking on this project.

                  I'm leaning more towards permanent magnet brushless designs, so I'm not creating a replica of anything. That's an interesting concept though. I'm not aware of anyone at all that has an interest in doing that, in the same vein that a modeller would replicate an IC engine in scale. Where is the big block holley double pumper fuel injected and blown version electric motor worthy of modelling?
                  I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                  Comment


                  • #10
                    Those little computer fans have 3-phase motors in them, or at least that's what they appear to be. Built-in DC->3-phase inverters, too.

                    Comment


                    • #11
                      Originally posted by jdunmyer View Post
                      Those little computer fans have 3-phase motors in them, or at least that's what they appear to be. Built-in DC->3-phase inverters, too.
                      They are 3 phase brushless DC. They use a simple driver and hall effect sensors to drive the ring magnet in the hub of the fan. There are now sensor less vector ICs for driving motors too that dont need hall effects for feedback.

                      Also look at the motors that are being used in RC and quadcopters. Tiny brushless motors and motor drives to go with it.

                      Comment


                      • #12
                        Yup, those RC brushless motors are all 3 phase. Check out the power to weight ratio on those- and the rpms too.
                        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                        Comment


                        • #13
                          Bokers makes washers in a wide variety of sizes and materials. They may be able to supply washers in a suitable material and thickness. I am sure that you are not the first one who has needed motor or transformer laminations. They also do custom stampings, but that may get expensive in small quantities.


                          Originally posted by darryl View Post
                          If this is being done strictly as a model, a scaled down version of something, then your choice of materials won't matter so much. If there's a use involved, then at these sizes you would want to use a magnetic material that's suitable- that means very thin laminations, and preferably in a high flux density capable material. At the least you would want to use existing transformer lamination material- maybe scrounge from a transformer. For a large enough width to make the stator, you might look at a microwave oven transformer, or find a toroidal transformer where the length of the core is enough for your widest pieces. It's likely that considerable work would be required to separate the laminations, particularly if the whole core has been vacuum dipped, and where there are weld seams across the lamination stack- common on microwave transformers. Best would be to obtain a roll of amorphous ribbon steel to make the laminations from. Good luck getting any of that-

                          One of my hobbies is playing around with electric motors of all types. I have built a few of my own, but usually use an existing armature. I have some ideas in mind that will require me to make my own lamination stack, and that looks like it means punching them out. It will require a custom punch and die set, two of them actually, and a clamping setup to hold the thin material and allow for indexing. It's not a highly technical set of jigs to make, but those would certainly be a project in themselves, and would only be suitable for one particular design. Being a hobby though, maybe one day I'll find some joy in embarking on this project.

                          I'm leaning more towards permanent magnet brushless designs, so I'm not creating a replica of anything. That's an interesting concept though. I'm not aware of anyone at all that has an interest in doing that, in the same vein that a modeller would replicate an IC engine in scale. Where is the big block holley double pumper fuel injected and blown version electric motor worthy of modelling?
                          Paul A.
                          SE Texas

                          And if you look REAL close at an analog signal,
                          You will find that it has discrete steps.

                          Comment


                          • #14
                            I recall black stove pipe being suggested as a magnetic material. It would seem that it's soft enough, and maybe that would still be a good choice today. There are materials these days capable of much higher flux density before saturation, so you should consider whether your project would need that. You wouldn't want to use galvanized, and probably not chromed either, since the goal is to prevent as much conduction as possible within the material. You would still want to insulate the individual lams from each other. For one of my projects, I laid out all the laminations on a piece of cardboard and gave them all a coat of lacquer. It doesn't take much, since the voltage levels between laminations is so small that almost any coating would suffice.

                            Bokors- never heard of it, I'll look it up.
                            Last edited by darryl; 01-02-2014, 03:41 AM.
                            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                            Comment


                            • #15
                              what does three phase dc current look like?

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