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  • Inverse rotor

    I mentioned in the 'Had a good day thread that I had an inverse rotor to repair.
    They are quite common over here, don't know about the US?, used mainly for fan motors.
    The stator on these is mounted on the fixed end plate and carries two bearings.
    The rotor is then on the outside and carries the shaft that runs on the bearings and this whole assembly rotates.

    Pic of the opposite end to the fixed end showing one bearing location.



    Pic of the opposite end showing the bearing location buried round down inside, plus the fixing pads



    As you can see no matter which end you need to bore and sleeve there is nothing to hold on.

    Enter the El Stevo MKI expanding collet, custom made at great expense.



    Just a bar turned down to 32mm, the size of the bearing, drilled, tapped and counterbored to a diameter less than a cap screw.
    4 slits down with a hacksaw by eye, nothing special and a cap screw with the head tapered.
    Stuffed up the spout and tightened via an allen key it will grip tight enough to allow it to be spun in the lathe.



    Cables are held back with duct tape, that's what the white is on the stator as this one has already been sleeved one end.

    This post isn't about doing an inverse rotor as chances are no one will ever see one, let alone having to work on one.

    This post is about thinking outside the box and remembering ideas to be used on other projects.

    .
    .

    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.




  • #2
    Originally posted by John Stevenson
    Just a bar turned down to 32mm, the size of the bearing, drilled, tapped and counterbored to a diameter less than a cap screw.
    4 slits down with a hacksaw by eye, nothing special and a cap screw with the head tapered. Stuffed up the spout and tightened via an allen key it will grip tight enough to allow it to be spun in the lathe.
    But is it accurate to 2 microns?

    Nice job John. I've made one-off expanding mandrels like that with a slitting saw and 1/8" male NPT tap for the expanding taper bit.
    "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

    Comment


    • #3
      Great idea on the expanding collect.
      Are you using soft jaws?

      See many motors in my shop but not one like that yet...
      Bet the next ship that comes here from Europe will have one
      please visit my webpage:
      http://motorworks88.webs.com/

      Comment


      • #4
        Originally posted by motorworks
        See many motors in my shop but not one like that yet...
        We have them in the 'States too -- they're called "outrunner" motors. Outrunners have a rotating magnet-lined bell, spinning around a wire-wound fixed stator. They're generally used for low RPM high torque applications.
        "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

        Comment


        • #5
          Most of the motors I see come from shrimp/crab processing type equipment.
          Most are TIFC and we also see a lot at of "metric" motors .

          Not to steal the post, but along the line of motors and repair
          I find the motor that were made in Europe much easier to work on.
          If you have to bore an end bell they are almost always very easy to do.
          The chinese are the Shiqs to set up.
          e
          please visit my webpage:
          http://motorworks88.webs.com/

          Comment


          • #6
            Yup, soft jaws, use them a lot, allows you to split microns to a thou or two

            I get a lot or weird stuff because the small run of the mill motors are cheaper to replace than repair.

            A lot of my work is on DC motors and old slip ring AC motors as these are just too expensive or too hard to replace.
            .

            Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



            Comment


            • #7
              Those soft jaws are not the usual top jaws, but are one piece. Are they also a Stevenson special? If so how did you machine the threads on the back side?
              Jim H.

              Comment


              • #8
                No just bought in items, we used to have a firm about 25 miles away that used to specialist in making soft jaws for all types of chucks.
                A lot were two piece Kitagawa type for production machines but he also did standard types as well.

                Quite cheap, unfortunately although the web page is still up it looks like they have ceased trading.

                http://www.emnet.co.uk/mtm/softjaw.html

                There have been a couple of articles in MEW about laying out the scroll on the backs of the jaws. Not as simple as it first sounds, if you look at a set from the rear not only are they crescent shaped they are also off centre.
                Interesting article on why this is.

                .
                .

                Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



                Comment


                • #9
                  Originally posted by JCHannum
                  Those soft jaws are not the usual top jaws, but are one piece. Are they also a Stevenson special? If so how did you machine the threads on the back side?
                  Jim, there's a brilliant article by Ivan Law in last month's Model Engineering Workshop about how to cut the weird off-center pinion teeth on the back of scroll chuck jaws.

                  Shoot me a PM if you're interested...
                  "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                  Comment


                  • #10
                    Well Done!

                    I really like that idea of the tapered cap screw. Any I have seen - chiefly in Model Engineers' Workshop - uses tapered pipe thread & suitable plug.

                    Never tried to machine one b4 (and I have not done a whole lot ofr machining) as I believe that they are hardened.

                    Would appreciate somne how to? Hss bit, carbide or?

                    Thanks

                    Comment


                    • #11
                      Thanks Robert, no real desire to make any, just curious if John had undertaken to make them. I know there is a lot more to them than a casual look would indicate.

                      The heads of most SHCS are soft enough to machine with HSS. If not, you can put enough of a taper on them for this application by grinding on the bench grinder.
                      Jim H.

                      Comment


                      • #12
                        What is an inverse rotor?

                        John,

                        I looked in google and did not really understand what the inversse rotor is.

                        Any pointers to other site would be appreciated.

                        TIA,

                        David


                        Originally posted by John Stevenson
                        I mentioned in the 'Had a good day thread that I had an inverse rotor to repair.
                        They are quite common over here, don't know about the US?, used mainly for fan motors.
                        The stator on these is mounted on the fixed end plate and carries two bearings.
                        The rotor is then on the outside and carries the shaft that runs on the bearings and this whole assembly rotates.

                        Pic of the opposite end to the fixed end showing one bearing location.



                        Pic of the opposite end showing the bearing location buried round down inside, plus the fixing pads



                        As you can see no matter which end you need to bore and sleeve there is nothing to hold on.

                        Enter the El Stevo MKI expanding collet, custom made at great expense.



                        Just a bar turned down to 32mm, the size of the bearing, drilled, tapped and counterbored to a diameter less than a cap screw.
                        4 slits down with a hacksaw by eye, nothing special and a cap screw with the head tapered.
                        Stuffed up the spout and tightened via an allen key it will grip tight enough to allow it to be spun in the lathe.



                        Cables are held back with duct tape, that's what the white is on the stator as this one has already been sleeved one end.

                        This post isn't about doing an inverse rotor as chances are no one will ever see one, let alone having to work on one.

                        This post is about thinking outside the box and remembering ideas to be used on other projects.

                        .

                        Comment


                        • #13
                          Hacking away

                          Dunc.

                          They are readily machined - use your normal HSS or TC - what-ever. Just take it a bit slower, higher feed rates and cutting oil/fluid.

                          They are easily cut to length with a HSS or bi-metal (hand) hack-saw.

                          They are just another high-tensile bolt.

                          Comment


                          • #14
                            inverse rotor = external rotor

                            As in a lot of smaller size servo-motors.

                            Comment


                            • #15
                              Originally posted by davidfe
                              John,

                              I looked in google and did not really understand what the inversse rotor is.


                              David
                              Sounds like an analogy would be an internal combustion engine where the crankshaft is held stationary while the engine block and heads, et al rotate around it.

                              I think some acft radial engines worked that way.
                              Lynn (Huntsville, AL)

                              Comment

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