Dual rotor axial flux motor design

[Miles]

The other possibility is an opposed pair of spindle bearings. You can get 15 deg. or 25 deg. contact angle in the small sizes.

[Kingfish]

Timken makes a single-taper bearing that goes down to 8mm, though I think you are wise to upsize the axle for more common product as it is bound to be less expensive

If weight is an issue, you could make use of hollow shaft stock. Just an idea...

~KF

[Miles]

So they do: http://www.timken.com/EN-US/products/be ... up%29.aspx

[Miles]

Crikey!

Core cross-sectional area has gone up 1.375x

Volume of copper has gone up 1.45x

Number of turns down from 6t to 4t

2 phases length down to 3 metres.

[fechter]

36W of wasted heat will barely get warm. And that's at full power. Who needs cooling?

[Miles]

Who needs cooling?

Quite.

You have to add the parasitic losses to the 36W but if I use G-O steel and 0.178mm laminations, they should be pretty low.

[Miles]

If we don't need the through venting, we can pack more copper in and get:

[Miles]

Km would then be 1.21

Weight has crept up to 1.4kg because of the additional material, so specific Km is 0.87

Scorpion S-5545 10t Delta: http://www.scorpionsystem.com/catalog/m ... 545-150KV/

Weight 1.026 Kg

Kv 150 rpm/V

Kt 0.0637 Nm/A

Rm 0.03 ohms

Km is 0.0637 / SqRt 0.03 = 0.37

[ 0.37 / 1.026 = 0.36 ]


Astro 3210 8t Wye: http://www.astroflight.com/pdfs/3210WEB.pdf

Weight 1.0 kg

Kv 169 rpm/V

Kt 0.0565 Nm/A

Rm 0.08 ohms

Km is 0.0565 / SqRt 0.08 = 0.20


Ok, the Scorpion is in the lead....

It's not now...

[bearing]

Number of turns down from 6t to 4t

2 phases length down to 3 metres.

With the same kV?

[Miles]

Yes, that was the assumption. There's quite a lot more iron, now...... We'll see.....

[Miles]

Just came across this one:

Design of an axial flux machine
for an in-wheel motor application
Masters thesis by Christian Du-Bar.

[Miles]

Arnold Magnetics Thin Gauge chart:

[fechter]

What about asymmetrical pole pieces?

I realize this is way 'outside the box', but there could be some benefit at high loads. Normally the 'teeth' are centered on the windings. The teeth need to be there to maximize the active area and still have room for copper. Everybody always centers them. I guess if the motor needs to behave exactly the same in both directions, this may be the right thing to do. Most of us run the motor one way or the other most of the time and rarely need to reverse it.

When the iron starts to saturate at high loads, it will be almost like it 'shrinks' or has reduced active area. By offsetting the teeth, this effect can be minimized. The iron in the attracting side of the tooth will saturate first, so shift the tooth over so more of it is on the repelling side. You'll still have the same room for copper, but instead of an "I" shaped cross section, it would be more "C" shaped. At light loads where the iron is not close to saturation, the change won't make much difference, but at high loads the active area should 'shrink' less.

One disadvantage is you need to build the motor for a particular rotation direction and reversing it would require flipping the stator around.

I think this may have more benefit on a radial motor than an axial one, as the teeth get really skinny at the tips.

Maybe not worth the gain, but an interesting idea.
I don't expect MFEA models to accurately reflect this concept.

[Miles]

That's a cunning idea.... It's a pity that it doesn't fit in with my 2 speed retro-direct gearbox concept, which does require the motor to operate in both directions.....

[Miles]

Carpenter Hiperco 50A losses graph:

[kenkad]

fechter,
Your comment about the tooth offset for single direction rotation is interesting. Some two years ago, I had asked Shane Colton (when he was deep into dual rotor axial flux design) about this type of thing and if a better solution might be to 'skew' the offset of the dual rotors a small amount (maybe somehere between 1-3 degrees). He was going to try that to see if it also minimized cogging, but, I do not think it finally worked into his efforts. At least he never indicated that there was any noticable effect. I personally believe that it would be more noticable as a minimization of cogging. Since I am not a motor designer, this may be way off base. This is on my list (rotor skewing) of things I want to test as well as magnet orientation of the adjacent magnets on the rotor (not the typical N/S in/out orientation). Isn't learning fun?
kenkad

[Kingfish]

Some months back someone posted an induction motor that had renderings, photos, or animations of a C-shaped (as opposed to skewed) laminated stator by some big-named company (possibly GM or Honda). The stator had big single-copper wire turns. My understanding was the skewing and C-shape is designed to reduce torque ripple, although I find the affect upon saturation interesting and appealing. Unfortunately most of us do not have advanced-level modeling software and full-time researchers figuring out the proper mechanical offsets per each lamination.

Checking my lotto numbers, KF

[Miles]

Just looking at the Sineton dual stator radial design (below, top left):
http://www.sineton.com/web/index-10.html

[Miles]

N.B.
"Core losses are substantially reduced with the use of a grain oriented silicon steel."
http://www.sineton.com/web/index-33.html

It's not clear how they take advantage of GO steel with the above topology...

[Miles]

Latest version:

[Miles]

OD increased from 92mm to 100mm
Electrical loading increased. Rm is now circa 4 milliohms.
Kv <150 rpm/V
Nominal speed 4000rpm
Flux frequency at nominal speed 533 Hz
Core volume 8.5222E4 cubic mm
Core mass 0.672 kg

[fechter]

You might need some kind of housing to connect the two end plates together. Lamination stacks are not very rigid. There could be some eddy currents in the screws holding the lams together, but it should be fairly minimal. Normally they try to avoid having the fasteners in the teeth. It would be a lot of work, but it might be worth using some kind of adhesive between the laminations.

[Miles]

It would be a lot of work, but it might be worth using some kind of adhesive between the laminations.

I definitely want to bond the laminations together. At the moment, the plan is to get the 75+ different lamination profiles laser cut and bonded into core modules. Haven't had a quote yet, though

[Miles]

Can I get a very rough approximation of the iron losses from the Watts per lb value given in the electrical steel specifications?

For Arnolds thin gauge GO 6mil (0.15mm) @ 15kG (1.5T); 400 Hz the losses are 9 Watts per lb.

My core weighs 1.48lbs. So, that's 13.5 Watts @ 1.5T; 400 Hz.

Say, 21 Watts at 533 Hz 1.5T.

Increase that to 25 Watts to allow for the greater flux density.

Increase again to 30 Watts to allow for stray, windage and bearing losses...

[Miles]

This is what the above figures look like in Drive Calc......