APL's DIY axial-flux motor

[APL]

edit: this thread has been split-off from the "Appel Electric Cruiser" thread, which can be found here: https://endless-sphere.com/forums/viewtopic.php?f=6&t=95745

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Thanks Chalo,.. and it's good to know about the 7075-7050 series aluminum. Sounds like the right stuff!

It looks like we've got options for the axle ends, the proof is in the pudd'n, as they say. I'll just have to give one a try and see what gives.
Amber ironed out the wire route, and we've dialed in the axle size. So I think it's time to move on to an even more complicated mess.

The simple bar magnets are a loose end,.. in the fact that I haven't actually wound one to see how much room it will take up. :?
I chose this design because of the simplicity to remove, rewind an expand the size. The motor is made with experimenting in
mind, and a low tech approach.

How many strands, winds and wire size is up to you and me. As well as the 3 phase wiring configuration.

I thought I'd start out with about the same wire mass as the motor I have now, same size and winds.

The Crystalyte has 51 poles, and this has 48, so only 3 poles short. Although, they are positioned much more closer to the axle.
I imagine this will result in more speed, and less torque. (Comparatively)
As long as I can get 750 watts out of it, I'm good.
And I imagine that has to do more with with wire size, and heat, and how much current you can pump in to it.

The amount of steel in the bar is relatively the same as the two sides of a standard hub motor,..or, the U shape straightened out.
So it will have the same amount of wire on the bar as both sides of the U shape Crystalyte core.
However, the wire can be wrapped more closely for a tighter copper mass density.

I know I'm going to get beat up on this,..but does anyone see any red flags here? Any thoughts?

Keep in mind that cogging is not really an issue here, because it's a mid drive, and the rear wheel coasts, plus, the air gap is
adjustable, so you can dial in whatever you want.


View attachment 1

 

[APL]

 

[APL]

Well, after reading some more about motors, I see my concept of cogging is wrong. My bad. It has more to do with
motor start up, and not magnetic drag. Sorry. I'm learning mostly about how much I don't know about motors.

But a person can drive a car without knowing whats under the hood, and I still think I can build a motor without knowing
exactly how it works.

The next step is to wind a magnet, and see how much space it actually takes up.

Since it's an experiment, i really don't feel like making 2000 laminations for the cores, only to find that something has to
change, and dump them in the trash in a week.

So I'm thinking of making some ferrite cores for starters. Once the thing is spinning, I can invest in laminations. More
flux density loss to add to the rest of my losses, I know,.. but it's unknown what that really means, in actual performance.

I found this info, and link, on the subject.
"This paper presents an analysis of the stator core losses in two kinds of 3-phase 32-pole brushless DC motors. One stator is manufactured by ferrite and the other is steel laminations. The losses are evaluated by performing time-stepped finite-element analysis and the results are used to evaluate the suitability of the models. The theoretical analysis and experimental results derived from the inverter-controlled BLDC motor drives are presented for confirmation. Experimental results show that the motor with ferrite stator has higher maximum speed and efficiency than those of steel laminations. On the other hand, the motor with steel laminations produces higher torque than that of ferrite material. Based upon these comparison results, ferrite core stator is very promising for low-torque and high-speed applications."
https://ieeexplore.ieee.org/document/4460318


The main focus is to get the thing off the ground first.

There doesn't seem to be a lot of interest here, on this project. I should drag it over into the Motor Tech section, but I'm
not that comfortable with it, and would rather have something that at least works before I do that.

So, I'll just go about making it at my leisure, and give some updates here from time to time, as things get done.

In the mean time, I finally got a big fatty tire out back on the cruiser bike, and she's looking better! Sometimes style wins.







Next up,.. some bigger batteries, and holder. Milwaukee just came out with a new 12ah drill pack, and although they're
a bit large, (6" x 3-3/4" x 3-1/4"), I'm hoping to get at least four of them on there,..for 40v at 24ah, and a lot more on demand
watts to draw from. Stay tuned.

 

[wturber]

There doesn't seem to be a lot of interest here, on this project. I should drag it over into the Motor Tech section, but I'm
not that comfortable with it, and would rather have something that at least works before I do that.

Be careful about judging interest based on interaction. I simply have very little to add by way of suggestions or information.
Note the number of views that your sketches have for a better indication.

 

[Wolfeman]

Regarding the lack of interest, your bike is super high on the scientifically verified ISB scale (Incredibly Super Bitchin). I think it is just so well put together that a lot of us just don't have anything to suggest to make it better. We just sit in front of our screens, slack jawed and wistful, wishing we could build something that cool. Just my two cents.

 

[spinningmagnets]

The threads that get the most comments are the ones where someone is asking how to do something. Projects like this are incredibly inspirational, but most readers feel that you are more advanced than them, and they are reluctant to comment. So far (as of today) your article has 1,234 views.

The home-page link has a thumbnail pic, so the readers knew what it was before they clicked on it. About 600 views a month.

 

[APL]

Thanks guys for the awesome support! I'm a bit of a nubee. Faith has been restored , and I'll plod along on this project,
complete with all the failings and drama that it incurs.

Labousky designed, built, and put his motor on a bike and rode it,..very impressive. Hopefully, I can do the same,..with a little help from my friends.

 

[kerim]

I love this project and keep coming back here in order to check how you are getting on. Keep on posting!

 

[APL]

I forgot to edit Lebowski's name before I submitted the last post, sorry, my bad.

Lebowski Axial motor build, check it out.
https://endless-sphere.com/forums/viewtopic.php?f=30&t=46476

Way smarter than me, and my inspiration for this build.

 

[APL]

I suppose I should give a motor 101, on whats going on here, for those who aren't sure yet how this works.
Otherwise,.. if this is old hat for you, or to boring, then page down.
This is just my view, or interpretation,.. so far, and trying not to get to technical.

When you wrap a coil of wire around an air core, and put some power to it, you get a magnet. We all know that.
It creates a field,..but the field isn't concentrated yet, it's wide.

When you place a piece of steel into it, it concentrates the filed. Hundreds, even thousands of times, towards each end.
Each face of the core now has the strongest magnetic flux point, and that gives the motor a solid place to grab and push from.
Thats why virtually every motor uses steel cores. Real power is made from using strong, concentrated flux points.

Steel is magnetic. That is one thing,.. but it's also a conductor, and thats is another.

All 'metals' are conductors because they contain within their structure, billions of 'free electrons'. Free electrons are extra
electrons that don't belong any place in particular. They just hang out.
Electricity uses them to 'move' with, a lot like water in a hose.

But 'magnets', can also move electrons in metals,.. if you get them close enough.
'Induction' is the act of the magnet moving the free electrons around in the metal.
'Induction heat', is the result of moving them super fast.

Moving a magnet across any metal, is like moving your finger through water. Theres a slight pressure on the front of your finger,
and a swirl on the back side. If you move it fast enough through the water, as if you were water skiing, then there would be a lot
of pressure, and a lot of heat.

This pressure and swirling of fields, and electrons, is what we call 'eddy current', It's not so bad at low levels, but at motor
speeds it will become a problem. It creates a drag, and ultimately, .. heat.

Big motors,.. big heat problem.

A great deal of thought over the ages has gone into trying to figure out how to keep this from happening.

The most common technique is to use thin laminations of steel bundled together. The thinner, the better. The long thin shape of
the steel, when placed in the right direction, prevents, or reduces the swirling eddy effect.
The steel also has silicone in it, which helps reduce the affect even further.


Another way to do it, is to use a 'ferrite core'. Ferrite is a form of powdered iron that is glued, or bonded together. The idea is
that all the millions of individual little pieces of steel each contain and reduce the eddy currents within itself. It works quite well,
except that there is a reduction in the magnetic flux power, because there is a reduction in the amount of steel, taken up by the
glue,.. and, a loss because of the space in between the particles.

There are many kinds of ferrite core materials. Some are very Hi Tech, and contain metal spheres that have layers inside, in specific ways to reduce eddy currents.
There are many different types of ferrite 'metal mixes', each designed for a specific electronic purpose.

The drawback to ferrite cores for motors, is the magnetic reduction, and the strength of the material. Ferrite is brittle, and cracks, whereas laminations are very strong.
Motors and big power transformers use laminations, and small transformers and high frequency electronics use ferrite.

Making a core from laminations is hard. You have to make many, many pieces and each one has to be exactly like the next,
usually requiring laser cutting, or a punch press.

Ferrite cores are easier to manufacture, precisley bonded and heated under pressure, the cores can be cast, in large numbers,
for most applications.

But it can also be made at home, in a little cruder form. :?

Thats what I'm hopping to do here, (famous last words), ..make the cores, (which could turn out to be a complete failure).

I need to devise a way to measure the difference in magnetic strength between the two types of cores. To see how much I've lost.
A Gauss meter, which measures magnetic fields, would make that easy, but are typically to pricy, for just one motor.

OK, hope that wasn't to painful,.. enough of this talk!
Time to make something!

 

[wturber]

I need to devise a way to measure the difference in magnetic strength between the two types of cores. To see how much I've lost.
A Gauss meter, which measures magnetic fields, would make that easy, but are typically to pricy, for just one motor.

OK, hope that wasn't to painful,.. enough of this talk!
Time to make something!

They may not be accurate enough or not appropriate in some other way, but there are Gauss meter apps available for smart phones.

https://play.google.com/store/apps/details?id=com.keuwl.gaussmeter&hl=en_US

 

[APL]

Busted! :| Now I have to eat crow.

Good call wtuber, that might just be the ticket. Gauss meter might not be what I'm looking for,.. seems to have more to do with
EMF,than magnetism,..as I learn more.

But theres a magnetic field density app as well, so either way, it's all good.

Will these apps work on an I pad as well? They must be using a hall sensor in the circuit.
https://play.google.com/store/apps/details?id=com.techercity.magneticfielddetector&hl=en_US

 

[wturber]

Busted! :| Now I have to eat crow.

Good call wtuber, that might just be the ticket. Gauss meter might not be what I'm looking for,.. seems to have more to do with
EMF,than magnetism,..as I learn more.

But theres a magnetic field density app as well, so either way, it's all good.

Will these apps work on an I pad as well? They must be using a hall sensor in the circuit.
https://play.google.com/store/apps/details?id=com.techercity.magneticfielddetector&hl=en_US

I'm not very familiar with Apple products. If it has a compass, then it can probably act as a magnetometer. I have Physics Toolbox Pro on my Moto G5 Plus and it will log data and export as CSV.

This is the company and they make iOS apps as well.
https://www.vieyrasoftware.net/

 

[APL]

Some core progress. Decided to make a solid core out of some soft steel, to wind some wire around for a size test.

I can also use it as a mould core, for the ferrite,.. and for the flux strength, and induction test, to see what solid steel
will act like.


View attachment 2


Its like making a little I beam.

A thin wrap of some Kapton tape and it's done, except for some plastic coil ends,.. those will be next.


View attachment 1


10 strands of 24awg wire, wrapped 12 times around the core. Same as the H series motor I have, and equals
out to 6 turns around each tooth of one magnet.

Heres what 10 strands of 24awg wire looks like. 12 turns take about 3 feet of wire, so I cut 4' pieces.
About 40 feet of wire.

 

[APL]

I was surprised to see how easy it was to wind. Takes up a lot less space than I had expected. I made the coil ends way to big,
and may not even need them.






Came out to 98 grams as you see it, ..so, 24 coils. ..make it an even 100 grams, X 24, is 2400 grams, or 5- 1/4 LBS
For solid steel.

Looks like the coils will have no problem fitting in a 24 coil pattern. And there will be plenty of room for air to be drawn past
them, by the spacer/fan's.


View attachment 1



So at least that part will work so far. Also, there will be no problem changing to larger wire, you could go as large as #8 if you want!

I've had this idea for a while of using small copper tubing for a wire,.. the idea being that it could be water cooled, and you could
use large amounts of current and lower voltage, and still not get hot. The fewer batteries you have to use for voltage, the more
batteries you have for current.

Could there be a water cooled Axial in the future? How about a giant water-cooled 3.2 volt, three pole motor?
Every battery would be in parallel.






Ferrite powder came in the mail, 99% pure so they say. I'm still trying to decide on a binder for it. I'm thinking of polyester resin.
There are many ways to bond this stuff, most of the good ones require high heat, glowing orange type heat.

A more DIY approach would be to just glue it, try it, and see what happens, so thats what I'm going to do. Winding these things
is easy, and you can wind and unwind all day, so making or changing new cores is no big deal.

 

[APL]

Wire comes off easy and can be saved for later, a nice plus.





I like using the silicon casting media for molds, but it has to be used up within a few months, or it hardens inside
the container, , lesson learned,.. only buy a small amount, if you can. I had half a quart of each part left, and it was 'hard'
when I opened it. What a waste.

I've made quite a few 'fiberglass' resin molds in the past, so I'll try that here this time, it's a simple way to make single parts.
And it's rigid when dry, so the parts come out fairly exact. Things tend to stick together though, so precautions must be taken.

Find a fairly stiff 'small' container, to reduce waste. Pour water into it, to see how much resin to use, then transfer that to a
mixing cup, and mark the level, slightly higher than you'll need. You want to make sure you don't have to remix, midway,
as the two parts will have different cure rates.





I like to use Solo brand drinking cups, (any food store), as they are not affected by thinners, paint, or resins. Test your mixing
cups with lacquer thinner first, to make sure they won't melt.

PVA is a water based, non toxic coating to dip, or spray on the parts or 'plug', you are casting.
This is absolutely needed to make sure the part doesn't get stuck inside the mold.
Very thin, so use at least a couple of coats.
If you choose to spray it, then do so outside, because it dries in thin air, and turns into fluff, that will get into paint jobs later.
Use as low a air pressure as you can to spray it. I usually use an air brush, at 15-20 lbs of air pressure.
It dissolves in hot water, to get it off.





Fiberglass resin takes ten drops of hardener for one ounce of resin, in this case four ounces, so 40 drops. Put the drops in a
table spoon, or container first, and then pour that into the resin, to eliminate a possible overdose, or it will get very hot, and crack.





Very slowly pour it in, half way, and let it dry overnight.

 

[izeman]

always funny to see typing erros on products. the layout, the printing, the application of the sticker on the bottle. it has gone through so many hands and noone recognized "alochol"
sounds to super funny because this is how really drunken people would pronounce alcohol in german :lol:

 

[APL]

Ha! That's funny, I've had this stuff for a few years, and never noticed! They say the eye sees one thing, and the brain sees
another. I'm the worlds worst speller, so it all looks right to me.

 

[APL]

This PVA dries up thin, so use several coats if you can. I use an infra-red lamp, or a hot car interior, to speed up drying times.
Nothing more than 120 degrees or so.

After the first pour is dry, clean it with a solvent, or NAPTHA, and re-coat it with more PVA. Maybe use a little oil, or silicone
on top of that as well. Then pour the second half.





The two halves will stick together around the outside edge, so a bit of splitting is necessary to open it.

Resin molds are very brittle, and tend to crack, and chip, so they are only good for a few quick parts. Try using a few less drops of hardener.
Silicone molds are far superior, and can produce many parts. If the ferrite works out, then I'll use silicone for the other cores.
But first I have some testing to do.





Now it's time to actually make the ferrite core.

 

[APL]

I poured about three ounces of resin in a cup and mixed in as much powdered iron as I could.
Mixed it well, and let it set overnight. Then I scraped off the top, and dug out the most packed iron.




It totally acts like Bondo, in fact thats what it is,..Metal Bondo.
About five drops of hardener, and mixed it up well.




Packed it in each side and clamped it together. Hope I don't have to do this over again.





Finally get to move on to testing.

 

[wturber]

I wonder if you could get a bit higher iron density by putting a bunch of neodymium magnets on the bottom of the cup. That should help out gravity a bit. It might even help you drain off the low iron resin.

Note: That is, underneath the cup, not in the bottom along with the resin.

 

[APL]

Yup, I thought of that too, good call wturber,.. makes sense,..so I tried it, and was shot down. The stuff acts like Ferro-Fluid
and gets stiff because all the particles want to line up along flux lines and connect each other! Crap.
So I thought maybe a less powerful refrigerator magnet? But then, I'm magnetizing, and aligning all of the particles in one
direction as well,..and I didn't think that would be a good idea. Am I wrong? Maybe.

I thought about making a press to squeeze it, or a vacuum bag system?

At any rate, I'm thinking that this is why they use high pressure to make this stuff.

I'm not having any high hopes at the moment. The big question in my mind is "can I get 750 watts out of this beast, by using
crap ferrite?" or any ferrite for that matter. My gut feeling is that I'm going to have to use laminations.

At the moment I'm looking for some laminations, to add to the experiment. The weight difference between the three should tell
us something.

I'm also thinking that maybe a bigger ferrite core could compensate?

It's the simple stuff that keeps me awake at night.

 

[APL]

Also, some info. on Fe-Lam. comparison.





View attachment 1





Taken from; https://ieeexplore.ieee.org/document/4460318 More info. better pictures.

 

[wturber]

Centrifuge? Let it sit overnight then spin the crap out of it. :^)

Or maybe work differently and add the resin drop by drop, kneading it like dough?

Also, I wonder what happens if you used the neodymium magnets but inverted the cup and let the resin drain out over some extended period of time - perhaps aided by some slight warming to let the resin flow more easily.

 

[APL]

Thats brilliant wtuber!

Turn it upside down indeed! I'll try that with the few ounces that are left.

I'd like to make another core thats just a straight sided, rounded bar, to add some mass,.. I'm pretty sure ferrite is much lighter.
I'll use the new resin on that. The 'I' beam shape is to reduce the weight of the steel, and provide a place for the coil ends to stop.
But it's not really needed with the ferrite, and a bar will slide through the coil, so there wouldn't be any unwinding needed.


If the ferrite works out, I've been toying with the idea lately of making the stator side plates out of composite too.
Just a thought at this point.

The idea is that I could pour and bond the ferrite cores right into the side plates,.. if I split the centers of the cores.

The two sides would slide into the 'core-less' coils and connect in the center, where the coil's power is the strongest.

A coil set could be changed in 10 minutes. Hmmm....