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Thread: Brushless DC Motor for High Torque Experiments

  1. #11
    I have all of the prints before me and it looks like some changes to the design are in order. There will need to be an increase in the width to each of the parts where the shot will be placed to build on integrity. At the current diameter (6"), that would mean a reduction of stator poles from 24 to 12.

    I am going to be switching from AutoCad 2014 to Fusion 360 shortly. My hopes are that this can become more of a coordinated effort among others.

    I am still pushing forward with a modified version of the original build file and will post my results. My biggest hurdle right know is removing the mass of steel shot/resin from the mold. I am having to build a jig to fit in a vice to see if I can push it out without damaging the 50 hour 3d print. If all else fails, even if I have to cut it out I should still have a piece to test core saturations.

    * The take-away from this. Design a casting mold where the piece can be removed more easily.

    Input is welcome.

    DougIMG_20170703_140213_158.jpg

  2. #12
    Okay...The vice idea did not work...neither did the cut to remove. So, it is back to the drawing board altogether. If you were to ask "What did work"? The Bondo brand fiberglass resin worked great to adhere the steel shot. Coating the masking tape to the inside then rubbing petroleum jelly over it worked good. The areas that just had petroleum jelly did not work as well. I used pla filament for my first bout and it actually held up great. The heat caused by the reaction of the 2-part epoxy did not distort the plastic a bit. It was conveyed to me to try splitting up the print more to make it easier to remove so that is what I am going to work on. I am open to other suggestions.

    Thanks
    Doug

  3. #13
    For the new design the total outer diameter should be set to 8". This should accommodate the added thickness of the workpiece and still allow for a 4" diameter rotor (for torque). I think that the outer wall should be printed in 4 parts and printed separate from the rest of the print. Tabs for those parts should be made to bolt those parts together. Removable spacers would have to be printed to ensure the inner wall is lined up correctly in this case. Here is a picture (X2) of an example of 1/4 of the 8" outer wall. IMG_20170703_202524_419.jpgIMG_20170703_203535_694.jpg

    This is a start. It was tough getting back on this horse.

  4. #14
    And here is a new proposed inner portion of the stator. It is in a puzzle piece design. There are twelve pieces.
    IMG_20170703_224630_131.jpgIMG_20170703_225853_875.jpg

  5. #15
    Update: The new prints are coming along beautifully. I should be able to have another go at the resin tomorrow. The 10" mdf that it is sitting on will serve as the mounting base. It will be painted and have the mounting bolts installed through the bottom. IMG_20170705_070348_678.jpg

  6. #16
    Successful Casting!!? One leg of this project is complete. The casting turned out great with only a minimum amount of finish work to do. Here are three videos with some step by step detailing of the process. There is still a great deal of testing to do, but one thing you can take from this so far is that you CAN do successful casting of parts with 3D printed molds. I have not seen a lot of public information for this subject on the internet. Take note that at least one product here is being used outside of the parameter of the manufacturer's suggested use (Bondo). There has been no testing yet on this project so experiment at your own risk. I am excited about this. If it works as described there is the potential for many circuits and motor/generator setups to be experimented with. I do have to say that this is not an easy project. It lays somewhere between intermediate and advanced.

    https://www.youtube.com/watch?v=LzC5SP4e_uA
    https://www.youtube.com/watch?v=aPIIT2ObSvc
    https://www.youtube.com/watch?v=3uz2U-aGob4

  7. #17
    I sent Tom with Teslagenx the new files if anyone needs them or wants them printed. Going forward it will be up to you to design your own motor housing, bearing holders, motor/generator rotor, and what wiring & circuit you use. I will post my results as I complete experiments. The outer dimension of the stator is 7.75". The inner diameter is 4.0625". The depth is 2.125". I did include a 12 pole rotor file if anyone wants to do a basic pulse motor/energizer (Bedini SSG or reed/hall switch) or use it as a generator. The axle diameter for that is 3/4" and the two set screws are 1/8". The magnets are 2" X 1/2" X 1/8".

    Enjoy
    Doug

  8. #18
    Doug this is really great work! Thanks for sharing your method with so much clarity.

    Hey I don't want to come across as one of those donkeys that thinks they know something better but I couldn't help but think of one thing as I was watching you fight with the internal part of the mold.

    I'm curious if you have thought of using disolvable filament? Perhaps not for the whole intrenal mold but more as a liner like where your tape is going on now. You could print a very thin skirt that could fit around your main mold that could be dissolved away with water, and there are others that dissolve with limeoline but if the resin wouldn't be harmed by some water that would be easiest.

    Anyway it's fantastic just as you have done it, not doubt about that!

  9. #19
    Quote Originally Posted by BobZilla View Post
    Doug this is really great work! Thanks for sharing your method with so much clarity.

    Hey I don't want to come across as one of those donkeys that thinks they know something better but I couldn't help but think of one thing as I was watching you fight with the internal part of the mold.

    I'm curious if you have thought of using disolvable filament? Perhaps not for the whole intrenal mold but more as a liner like where your tape is going on now. You could print a very thin skirt that could fit around your main mold that could be dissolved away with water, and there are others that dissolve with limeoline but if the resin wouldn't be harmed by some water that would be easiest.

    Anyway it's fantastic just as you have done it, not doubt about that!
    Hey Bob. The problem that you would run into with the dissolvable part would be having to reprint it each time, but that probably would not matter unless someone was wanting to get into manufacturing. What I ran into was the resin slightly ran over the inside in a few locations. It also barely seeped under the inside in two locations. If that could be controlled better then that problem should be nulled. It would probably be a good idea to work with a partner on this. I am somewhat satisfied that I only lost 4 of 12 of the inside puzzle pieces.

    Finishing Process: One other issue that I want to address here is the fact that you may have some small areas on your workpiece that need some additional adhesive added. This should be revealed when you pull the tape from it. You can mix some more resin and patch those areas. Or you can just use superglue or gorilla glue to patch them. I like gorilla glue because of the 3 - 4 times expansion and it can be sanded. Remember that you will need to clean the vaseline from the piece before you do that with some alcohol. This problem too can probably be mostly nulled by better control of the resin/ steel shot application process.
    If you wanted added durability you can also coat the stator with fiberglass or carbon fiber.

    There are many things to explore with the casting process itself. I'm sure there are many resin or polyurethane products that one could test. I am sure that there are some high heat products out there too. I think the max you can go on the constant heat with the Bondo brand resin is 180 - 200 degrees F before it starts to become malleable. That product was just easily available at the local "big box" store. For durability it may be possible to add strands of fiberglass and carbon fiber in the actual workpiece as resin and ss is being added.

    So far, I am really satisfied with it. I'm continuing to design and print as I type this. I'm exploring options for bearing holders and motor end-caps. I think I've settled in on a design for my motor. I just need to finish printing it and put it all together. I want it to look nice but also be more than just a glitter coated piece of turd.

    Thanks,
    Doug

  10. #20
    Hi Doug,

    I've been following your work and admiring your ingenuity and workmanship skills!

    Quote Originally Posted by DMANN View Post
    .......... I'm sure there are many resin or polyurethane products that one could test. I am sure that there are some high heat products out there too. I think the max you can go on the constant heat with the Bondo brand resin is 180 - 200 degrees F before it starts to become malleable. That product was just easily available at the local "big box" store. For durability it may be possible to add strands of fiberglass and carbon fiber in the actual workpiece as resin and ss is being added. ..............
    I used Devcon Plastic Steel Liquid B, mixed with steel shot, to pour into both a thin plastic tube and some PVC pipe fittings to make a coil core for a switched reluctance generator I fabricated a while back.

    This Devcon product has enough powdered steel filler that it will attract a magnet but doesn't conduct electricity. It seems to have about the same magnetic attraction by itself as a ferrite core. With the steel shot added it's attraction seems to fall somewhere between ferrite and welding rods as a core material. It's rated for up to 250 deg F. and cures harder than body putty, but is easily machinable. The only problem I had was that I filled the tube with the steel shot first and then tried to pour the Devcon through it. Even though it flows, it's too viscous to pour through the shot. It has to be mixed together with the shot before it's poured into the mold.
    Last edited by Gary Hammond; 07-08-2017 at 09:01 AM.
    Gary Hammond,

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