APL's DIY axial-flux motor

[APL]

Good to know about the bearings,.. thanks. I never got to do any preload adjusting yet, theres to much trouble going
on with the stator. But I'm definitely going to do that, along with tightening everything up that I can find that can be
possibly loose.

The aluminum stock for the spacers came today, so I can start machining those. That will take care of one half of the
equation hopefully. Not going to be easy though, I'll figure it out.

I'm also working on a cad drawing to see if Dui,ni shuo de dui's adaptor idea will fit with the room that's there, and still
have a thick enough axle flange. If I can both bolt, and bond it, I think it will have the bast chance of working.

I think theres enough plan B's in place now to get this thing working, but it's going to take a little work.

 

[APL]

The new spacers are coming along. I need to spin them in the lathe yet, and carve out the insides for the coil clearance.

I don't think it's going to push those around, they certainly look beefy enough, but it leaves little room for cooling. Such as
it is, maybe I can machine some holes in them later on.

 

[APL]

Obligations,.. but now I can get back to biz. The 80 year old lathe was at it's limits, but managed to pull off a sweet
turn on the spacers. I milled them to length, .5mm longer on each side for some wiggle room, or 1.5mm air gaps.



Everything turned out perfectly flat and it feels super strong, definitely a step up!


Now it's on to the axle and stator fix.

 

[InterestedinEVs]

Looking great, sir!

 

[APL]

Thanks!

I turned a short ledge on the axle, to remove the minimum amount of material, and spun up a big fat 15mm thick
washer to fit it.



I kept the tolerance tight, so it's definitely a press fit,.. or in this shop, a hammer fit. Now I have to get the right
flat head screws for it, smear some glue around, and screw it together for the last time. Looks and feels like it's going
to be solid as a rock.



Still have a lot of fine tuning to do, screwing the two washers together, and getting the rotors spaced and bolted, but
trial #2 should be coming up soon.



It's all up to the fiberglass now, and hopefully, with a little luck, I won't have to go that far back on this build.

 

[InterestedinEVs]

That last one is a dang good shot! You care if I throw it on my instagram?

 

[APL]

Feel free, I'd be honored, it's mostly your eye candy! :thumb:

 

[fechter]

Looks really nice! 15mm aluminum is not going to deflect much for sure. Let's hope the fiberglass is stiff enough. Using a larger gap will reduce the forces on it too.

 

[Dui ni shuo de dui]

That looks totally awesome, really hope it'll work!!

 

[APL]

Thanks for the idea! It's working really good. I have the washer bonded and bolted now, and the only way it's
coming off, is to machine it off! :thumb:

Things are moving along,.. but theres so many little operations that it's taking forever. I have the rotors bolted in
place on the axle without the stator, preloaded, and spinning straight.

Looks like the air gap is going to be closer to 2mm for starts, but I'm going to go for it anyway, in the interest of
getting the dang thing going. That gives me .5mm to 1mm of material to mill off the spacers, and get it spaced
just right, after the first trial.

Next is to bolt the stator back on, and hook the phase wires back up. Then it's time to put it back together and
hold my breath. Maybe burn some copper wire, or short a battery out, as a sacrifice to the motor spirits first. :wink:
Going to need a little luck here.

 

[larsb]

I see a too high kV for you in my crystal ball but you're getting a from me either way it goes, keep up the energy to finish the motor!

 

[APL]

Today was the big day. I was just as excited as I was fearful at how it might turn out. As I started the assembly the
first hurdle was the spacer and coil clearance, which passed with flying colors. Then it was on to the Popsicle stick
gap spacers, and finally the rotors. It was a good sign that the sticks were loose when it snapped together.
Finally, the darn thing turned without rubbing. Whew! :thumb:

A little Kapton tape on the spacers for looks.


But it's not perfect yet, theres still a little bending, or something isn't straight somewhere. It will take a lot of
assembly's and disassembly's to get to the bottom of it. Maybe it's the fiberglass, maybe it's adjustments.
It's not much, but it's very annoying.

Either way, I threw it in the test stand and powered it up, and it took right off! I can't tell you what a good sound that
is, and a sight for sore eyes! No-load speed is 730 rpm, at 40.8v.
And I might add,.. it never got even warm to the touch, which is a very good sign.



But the air gaps are way to wide, so the higher rpm is to be expected. I can barely feel the magnets when I turn it by
hand. I'll take a Kv read as well, but it to will be a bit useless too, until I get the gaps dialed in. (if I can)

So, the sweet nectar of success, and a little foreboding. At least I can sleep at night. The next thing I'm going to do is
toss it in the bike and ride it like I stole it! Then I'll take it all apart and try to get to the bottom of the alignment
problem, and close the air gaps some more.

A pat on the back, and a good hand shake to everyone for getting this build to this point, thank you so much for your
help and suggestions!

 

[fechter]

Awesome! Looks great.

If you close the gaps the speed will drop somewhat. I don’t remember what your target rpm was.

 

[InterestedinEVs]

Fantastic sir!! Looks awesome! Congrats on the first spin!

 

[SlowCo]

Must be great to see it running after all the work that you put into it. Beautiful :thumb:

 

[APL]

Thanks! It does feel good, and I'm sleeping better, but mostly it's good to finally move on to the next phase's of the
build, instead of being stuck in one spot for so long.

I'll get a Kv reading, and then put it in the bike and ride it for a few days, to see if there's any other issues that pop
up before I tare it apart again. The last motor had a rub that came on at high power, and that could happen here too.
I'm interested in seeing what kind of heat develops as well. One of the main test of this motor is the SMC cores that
were using.

The predicted rpm was a little over 400rpm. And I have no doubt that it will get close to that once the air gaps are
reduced. As I said, there's hardly any cogging at the moment. It will be interesting to see how much power it has with
such a large air gap. While it was test running, I used a glove and a rag to try to slow it down, and it didn't have much
effect.

Once it's going down the road, I'll get some speed and watt readings, and we can track how much of an effect reducing
the air gaps has.

 

[SRFirefox]

Congrats! I look forward to seeing it mounted on a bike!

 

[fechter]

If the gaps are too big, the maximum torque will be less at core saturation. The torque density will be lower too. But the iron losses will be reduced so it may actually be more efficient. You could potentially compensate for the higher rpm by changing the gearing and get back some of that torque.

It will be real interesting to see how it feels on a bike. Top cruising speed vs. no load speed will tell you a lot.

 

[APL]

This weekend is busy, but I was able to get a voltage reading of the phase wires.

439rpm - 18.10v - G/B
438rpm - 17.80v - G/Y
437rpm - 17.60v - B/Y

Probably could average it out to 18v @ 439rpm. Using the Bavaria calculator, that comes out to 18Kv.

Looking back to page 44, I think we were predicting 10.4Kv at 550 rpm. So either Kv comes down with a smaller
air gap, or it does have a higher Kv than we predicted.

 

[Dui ni shuo de dui]

Finally, the darn thing turned without rubbing. Whew! :thumb:

That's awesome news, I'm so happy for you!
During those past months your thread is the one that got me checking ES every day for updates, so I'm really super happy to see your motor finally move on its own!
Congratulation on your perseverance and your really clean work, this motor looks amazing and I'm sure it will be super powerful with a bit of tuning.

Bravo!

 

[APL]

Thanks Dui, ni, shuo, de dui, your input has helped a lot,.. as well as all the other folks in the club house, I couldn't
have made it this far without you.

Experimenting with motors is more treacherous than I thought, and axial's, as it's turning out, are even worse. But
we've come a long way, and I think theres still a long way to go.

It's good to know that this thread can be a bright spot in someones day, it makes it all worth it, and I hope that future-
folks will be able to use some of the info within these pages as well.

 

[APL]

I was able to get the motor in the bike today, and take it for a test spin. I have good news and bad news, (of course).

The good news is that it goes down the road just fine, drawing about 130 watts at 25mph, it was 130 degrees after
two miles. I took another ride for four miles, and on the way back I gave it more throttle on a slight down hill, and it
hit 30.5mph in high gear, at a little under 200 watts. It was 150 degrees at the coils when I got back.



The throttle is soggy though, and you can tell that the wide air gap isn't letting it develop much power.

The bad news is that it rubs at about 200 watts. Evidently the fiberglass is still not strong enough, and bends under
power. Bummer. I just spent six months making a 200 watt motor! :lol:

Well, were going to have to fix that.

Need a stronger carrier, this fiberglass isn't cutting it. Everything else works fine though, so it's one more hurdle to jump.
I think it's time to brake out the carbon fiber.

It's also possible that this fiberglass isn't laid up in different angles, and has a weak side and a strong side to it. I did
notice that it always bends in the same spots.
After all, it's made for made for insulation of electronics more than it's made for strength purposes. Just a thought.

Kevlar, carbon, slotted aluminum or stainless? What are the options?

 

[Dui ni shuo de dui]

Oh, bummer.... I'd say start with aluminum, it'll be very easy for you to manufature and it's a good way to keep it cheap while making a few tests, you can always upgrade to carbon later if aluminum proved to solve your issue.

 

[fechter]

The best material I can think of would be titanium, but that's probably too expensive. Titanium is a very poor conductor so would minimize losses compared to aluminum. Any kind of metal is going to need a slot to break the loop around the cores. 300 series stainless steel (non-magnetic) would also not be too bad and much cheaper than titanium. I don't know how conductive carbon fiber would be in this kind of application but would also probably work well.

I'm pretty surprised the fiberglass was too flexible, but one of those things you find out from testing.

Anyway, a huge accomplishment to get it on the bike and actually ride it. Sounds like it will be awesome if you can get past the flexing issue.

 

[stan.distortion]

Congrats on the first spin! Would moulding something from fibreglass fibre and resin work? 3d printing is really good for mould making, a simple shell would probably be enough but waxes and water soluble filaments are available and apparently some are very easy to print. Fibreglass seems like pretty much the ideal material, it might be possible to 3d print a hefty carrier but I'd be wary of the temperatures. Still not sure about carbon fibre, I know it has some properties in magnetic fields, it's from the electrical conductivity of carbon iirc but not sure, would suggest plenty of reading up before going that route.