Brushless DC Motor for High Torque Experiments

[DMANN]

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

[DMANN]

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

[BobZilla]

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!

[DMANN]

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

[Gary Hammond]

Hi Doug,

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

.......... 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.

[DMANN]

Thanks Gary. That may be a good option. I completed the file for sample motor end/ bearing holders. This is what I will use on mine. It is for 3/4" X 1 5/8" X 7/16" bearings. The inner bolts are 6-32 X 3/4" and the outer holes will be for 1/8" threaded rod to connect both sides. There will be an inch of room on both sides of the stator for wire to stick out. Pictures are included here. You will need to print or have printed (2) bearing holders and (8) legs (4) for each side. My extruder stepper died during the 1st two leg print, but I was able to check compatibility with the stator. It works beautifully. I sent Tom w/ Teslagenx the files if anyone needs them printed.

Enjoy
Doug

[DMANN]

This first one is wired for a monopole application and not a BLDC. The magnets on the rotor match the number of stator poles (12).

[DMANN]

The magnetic lock with the 12 magnets = the 12 stators was just too strong. I had the coils wound with 3 sets of 4 in series. It took shorting the coils with two 12V lawn batteries in series to even turn it. So I have decided to offset the number of magnets to stator poles. I am currently printing a 10 magnet rotor. I believe that will allow me to turn it with much less power. I will save the 12 magnet rotor for a generator add-on for later. My busy season with work has picked up so this project is going to be slow-go from here to the end of the year.

[DMANN]

These are a couple of resources for those that are interested for wiring and running a true BLDC motor. http://www.bavaria-direct.co.za/scheme/calculator/
I did not know that rc had gotten so powerful until I did some research. Here is a powerful esc at a reasonable price. It auto senses so you can use halls or not. https://www.rcsuperstore.com/Traxxas...shoppingengine

[DMANN]

I posted a outrunner stator mold to Thingiverse if anyone may be interested. It uses the Babcock process with #8 steel shot. It can be used in a generator, a monopole motor, or bldc motor design. https://www.thingiverse.com/thing:2954231

Doug

[DMANN]

Sandwich style bearing hubs added along with wire protector boots to go on slots on 06/26/2018 at 12:43 PM est. Bearing size is 3/4" X 1 5/8" X 7/16". Bolts holes are for 1/4" bolts. You will need to get bolts the length to fit to whatever you are mounting to. The boots are glued to the slots (top and bottom). I am currently working on a sample magnet rotor using a 8" cake pan Pictures are provided at: https://www.thingiverse.com/thing:2954231

Doug

[DMANN]

Drill jig for 8 in. cake pan added on 06/26/2018 at 4:27 PM est. Use a 1/4" drill bit for holes. Once all holes are drilled you can take a step up drill bit to drill the center hole to 3/4" for the shaft. I'm working on the hubs to be posted next. This is the cake pan that I am using (Wilton Bakeware 8" x 2" Performance Cake Pan, Round) 7 dollars from Walmart

Doug

Bearing rotor (cake pan) hubs added at 10:26 PM on 06/26/2018.