3-phase Motor Design (small model)

Topics include, Machine Tools & Tooling, Precision Measuring, Materials and their Properties, Electrical discussions related to machine tools, setups, fixtures and jigs and other general discussion related to amateur machining.

Moderators: Harold_V, websterz, GlennW

Post Reply
User avatar
ctwo
Posts: 2705
Joined: Tue Mar 27, 2012 12:37 pm
Location: Silly Cone Valley

3-phase Motor Design (small model)

Post by ctwo » Fri May 11, 2018 3:30 pm

I picked up a lot of very small disc magnets. They stack like coins (0.062" x 0.033").

I had an idea to make an electric motor with them - I was going to make something that looks like a 9 cylinder radial engine. 12 magnets would form the rotor and I would wind wire coils as the 9 cylinders.

I machined a steel flanged diameter of 0.227" and parted it off ~0.035". I had planned on setting the disc magnets tangent to the circumference of the rotor so that all N or all S poles face to the center, but I'm wondering if that will work. I was then wondering if I should alternate N/S to pointing to the center, or if all that is nonsense and the N/S poles should all be facing each other to make a ring of magnets, like a doughnut cut into wedges.

The design is not for any functional purpose, but it should be able to spin when applying a 3-phase square wave signal to the coil sets.
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...

John Hasler
Posts: 903
Joined: Tue Dec 06, 2016 4:05 pm
Location: Elmwood, Wisconsin

Re: 3-phase Motor Design (small model)

Post by John Hasler » Fri May 11, 2018 3:52 pm

You have to alternate them and there must be an even number poles on the rotor.

https://en.wikipedia.org/wiki/AC_motor# ... nous_motor

whateg0
Posts: 491
Joined: Sat Mar 28, 2009 3:54 pm
Location: Wichita, KS

Re: 3-phase Motor Design (small model)

Post by whateg0 » Fri May 11, 2018 4:25 pm

My son made a model of a motor a few weeks ago for his science class. Just DC, but had a commutator of sorts, no fixed magnets. I'll be watching this to see how your motor turns out. Sounds like a fun project.

Would it work better to use a non-ferrous material for the rotor? Or does it matter? I've never given that much thought before, so I don't know what the flux would look like.

Dave

User avatar
ctwo
Posts: 2705
Joined: Tue Mar 27, 2012 12:37 pm
Location: Silly Cone Valley

Re: 3-phase Motor Design (small model)

Post by ctwo » Fri May 11, 2018 5:26 pm

My first rotor was aluminum, but I made it for 10 magnets for an unknown reason.
Attachments
small-rotor-20180509_152944.jpg
motor-3ph.png
motor-3ph.png (22.25 KiB) Viewed 1148 times
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...

User avatar
ctwo
Posts: 2705
Joined: Tue Mar 27, 2012 12:37 pm
Location: Silly Cone Valley

Re: 3-phase Motor Design (small model)

Post by ctwo » Mon May 14, 2018 2:27 pm

I started to orient the magnets the other way. I thought about cutting a disc for the rotor and then making 12 notches to accept the magnets. My first attempt at eyeballing my lathe chuck jaws level and vertical were not very good, and neither was the height adjustment of my "shaping" tool... the worst was that my tool was a bit too narrow and the magnets will not fit into the slots...I shall start anew and employ the rotary table on my mill to "shape" the slots, hopefully the correct thickness this time

(and I measure my magnets at 0.33" thick and my tool measured 0.035" - HSS blank ground as a parting tool)

I added a dime for relative sizing...
Attachments
motor03.png
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...

whateg0
Posts: 491
Joined: Sat Mar 28, 2009 3:54 pm
Location: Wichita, KS

Re: 3-phase Motor Design (small model)

Post by whateg0 » Mon May 14, 2018 3:44 pm

I have been watching videos of people taking automotive alternators and converting them to motors. Until recently, I didn't know they were actually turning them into 3ph motors and driving them with what amounts to a VFD, in the form of some RC drive. Last night I saw a video of a motor that some guy built that's water cooled. I can't imagine winding the stator on that thing! Oops, it was a DC motor. Still, that's a lot of wire winding!

https://www.youtube.com/watch?v=2LNfDI3QUpQ

Dave

User avatar
ctwo
Posts: 2705
Joined: Tue Mar 27, 2012 12:37 pm
Location: Silly Cone Valley

Re: 3-phase Motor Design (small model)

Post by ctwo » Mon May 14, 2018 4:23 pm

That would take some time. I'm just goofing off with scrap, but would someday like to build an electric motorcycle, including a motor like the one in the video.
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...

User avatar
ctwo
Posts: 2705
Joined: Tue Mar 27, 2012 12:37 pm
Location: Silly Cone Valley

Re: 3-phase Motor Design (small model)

Post by ctwo » Wed May 16, 2018 10:14 am

Well, I went back to mounting the magnets flat again and increased the rotor size slightly. I have it set to place the magnets and glue, however, I am also thinking of machining a very thin band to go around the circumference. I may also relieve the rotor a bit on each side.

The plan for the body is to slot a piece of round al stock, about 0.1" back from the face. Then bore a hole for the rotor. Then in the rotary table, mill the 9 cylinders.
Attachments
motor-rotor-04-20180514_233642.jpg
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...

mikeehlert
Posts: 109
Joined: Thu May 28, 2015 5:17 pm
Location: Los Alamitos, CA

Re: 3-phase Motor Design (small model)

Post by mikeehlert » Wed May 16, 2018 10:29 am

When that rotor spins thee will be a lot of centripetal force trying to throw those magnets. Just saying.

whateg0
Posts: 491
Joined: Sat Mar 28, 2009 3:54 pm
Location: Wichita, KS

Re: 3-phase Motor Design (small model)

Post by whateg0 » Wed May 16, 2018 3:19 pm

Not sure what you are using to adhere the magnets to the rotor, but I have made a few things with neodymium magnets using CA and it doesn't seem to stay stuck. There just isn't anything for the CA to "grip". I'd at least give the glue enough room to wrap around the upper edge just a little to provide a mechanical capture there.

Dave

Conrad_R_Hoffman
Posts: 379
Joined: Wed May 24, 2006 8:40 am
Location: Canandaigua, NY
Contact:

Re: 3-phase Motor Design (small model)

Post by Conrad_R_Hoffman » Thu May 17, 2018 6:21 am

The rotating part shouldn't rely on adhesive to hold it together, lest it fly apart. You can glue or pot things for location, but the rotor has to mechanically constrain things on its own. I've designed various magnetic assemblies, though not a conventional motor, and the question that always needs to be answered is, how does the magnetic loop close? Anything with significant air gap is going to work poorly. There's a free magnetic simulation tool called femm that can show you what's happening. There are also many examples of how to use it for motor design. The learning curve might be a bit steep if you've never done this sort of thing, but compared to most simulation software, it's pretty easy.
Conrad

1947 Logan 211 Lathe, Grizzly G1006 mill/drill, Clausing DP,
Boyar-Schultz 612H surface grinder, Sunnen hone, import
bandsaw, lots of measurement stuff, cutters, clutter & stuff.


"May the root sum of the squares of the Forces be with you."

User avatar
ctwo
Posts: 2705
Joined: Tue Mar 27, 2012 12:37 pm
Location: Silly Cone Valley

Re: 3-phase Motor Design (small model)

Post by ctwo » Thu May 17, 2018 12:43 pm

I will cut a thin band to press around the circumference, use silicone, and place the magnets and band just before I'm ready to run it in. That way the magnets can settle into a good spot and hopefully provide some balance. I decided to use steel pegs shaped like a T for the cylinders, which will be pressed into the body and come closer to the rotor.

I'm not expecting a particularly strong or fast motor, more of a novelty for this one. Thanks for flemm, I gave it a shot and will need to read some...

I've drawn my interpretation of the fields at the start condition, using three phase square wave. Taking the top coil as #1 and counting clockwise, #1 and #3 are repelling, #2 is attracting, and this repeats for each set of three. I may control the pulse widths for some optimization.
Attachments
motor-fields.png
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...

Post Reply