7 RC sensorless controllers running 1 very neat DIY motor.

[Thud]

BigMoose,
Excelent link. I have been looking at the CSIRO motor photo's in the video trying to determine if the aluminum plate with the boring on it is for the halbauch configuration. If so it seems at that scale the halbauch is very benificial. I have found a few attemtps on the rc motor sites with no real gains represented.
Thanks.

enoob:
You can never go wrong getting the kids involved.
Regarding building plywood motors:
I will caution anyone attempting it should do the math regarding the flywheel forces generated. A stout retainer ring must be utilized on the magents, no wants a hole in their roof or head if proper practice is not observed.
Have fun, making stuff with my dad are some of my best memories.
I didn't know a shop could be cleaned.... :lol: my work spaces all look teribly clutterd I need some time fix that.

12K GULP! thats a lot of batteries.

 

[bigmoose]

Thud, look back above at my post. I edited it... I found the design paper for the CISRO Motor!

 

[317537]

impecable layout. Using wood like that is great for protypes and using it for a prop would create plenty of air flow however applied to a ground vehicle may generate some heat.

This is a reversed engineered vawt generator with chunky coils so the sensorless could be run through coupled diodes from the coil input and a simple fet array using back emf. To kick start would takle a little more finesse.

Oh and I forgot those big ass inductors too.

 

[enoob]

Thud, look back above at my post. I edited it... I found the design paper for the CISRO Motor!

well that document just drove home how much i dont know .
something tells me ill be doing more copying than creating when it comes time to build the real thing.

as for the plywood thud i hear ya. ill be waiting for them to explode and be prepared for it . should make good video

ill be surprised if i can actually make one spin at all in the first few trys at it.

 

[Miles]

Just in case anyone missed Thud's thread on AF motors.... :wink:
http://www.endless-sphere.com/forums/viewtopic.php?f=28&t=13957

 

[Thud]

bigmoose,
Thank you! Those links are fantastic.
After a few exchanges with luke, I now see the parallels to the luanchpoint design.
I especialy like the video's in the "myownhybred" link. Thouse will help everyone understand the flux patterns developed & our attempt to manipulate them to do our bidding. There are several in additon to the Halbauch series.
I have a ton of work today but am looking foward to reading the rest in detail starting on my lunch break.
where is that "Buy bigmoose an internet beer" button?

To the general population: don't be intimidated by the tech-talk stuff I get so excited about. Just go back to the OP & drink in that hand built motor. I never attended collage & never did a trig equation untill I was 25 years old. I wish my HS math teacher haddn't passed before I could apollogise for all the crap I gave him....

Big, I don't know how closely you have been following this or the parralell design threads. Do you see any obviouse flaws in the thought proccesses on some of the designs presented or discussed? I would value your input greatly if you have time to offer your observations. Thanks again. T

 

[bigmoose]

I had a nice chat with Luke Saturday morning on some of these issues. Know that I am not an expert on ironless motor design... so your thought processes and critical assessments are likely as relevant as mine...

The salient feature I shared with Luke was that as I read the technical papers of folks developing their first axial flux machines; almost all had high hopes, but their prototypes tested out between 50% to 75% efficiency. The motors "worked" but not at stellar levels of performance.

My approach would be to learn as much about the successful designs that are documented in the open. There appears to be as much "secret sauce" with axial ironless motors as with valve guitar amps... (btw I am dabbling in a 12AX7, EL84 class A for a friend...)

Take the above info and redesign for simplicity and low cost. The fear is that the "secret sauce" may be overlooked in the redesign.

The CISRO folks said they had custom magnetics made with magnetization vectors at 30 degrees and 60 degrees. They even show it in an illustrative figure. At this point I would say that is a key "secret sauce" ingredient to the high efficiency. At best we are only going to find 90 degree orientation magnets off the shelf. So what is the NRE (Non Recurrent Engineering) to get the first batch of custom magnets made? Is it a showstopper? How did CISRO overcome this obstacle? Also the use of litz wire to cut down on eddy current losses in the copper. The design equations for figuring the optimal wire gauge are in that paper also. 2nd "secret sauce" ingredient.

Remember you can make a motor of this type in your home shop spin; but if the critical component of success for you is greater than 95% efficiency, then you have to run with the best of the best or find another game ... or bend the laws of physics!

 

[Miles]

Here's a model I made to a drawing of a coreless AF from Thud:

I haven't connected up the coils yet....

 

[Miles]

Here's a model I made to a drawing of a coreless AF from Thud:

Perhaps the strip coils would work for a slower speed motor?

I guess a Litz wire coil would be much better for faster shaft speeds, though....

 

[rhitee05]

I'm a little late to the party, but I thought I'd toss in a couple cents' worth for those who seem interested. I spent some while reading up on the subject after this thread got started late last week (one of the benefits of academia, an all-you-can-eat subscription to IEEE Xplore). Lots of technical papers written on the subject. Wish I could post them on here, but a few tidbits I learned.

For an ironless stator, apparently the optimum coil shape is actually a rhomboid. Pie-shaped coils aren't optimal because the straight runs on the top and bottom are useless copper that adds resistance but doesn't contribute to torque. They claim a rhomboid is the best compromise.

View attachment Coil Shape.JPG

Also allows a nice trick for water cooling, if you layer the coils together at a slant:

View attachment Layered Rhom Coils.JPG

I know these are just sketches, but re: the drawings posted by LFP and Miles, you really want the coils to be larger relative to the magnets. Think of it this way: assuming that the magnetic flux is even across the entire face of the magnet, only the flux that goes through the center of the coil "sees" the entire number of coils. Flux that passes partway through the windings will only "see" the number of coils outside that point. Ideally, you'd want the opening of your coil to be the same size as the magnet. Notice the Ro and Ri markings in the coil picture above - those would mark the extend of the magnets. The end windings can be outside the flux since they don't contribute.

I think the flat wound coils LFP suggested are a fantastic idea. Dense copper fill and low resistance, plus the wide part of the copper is parallel to the flux so eddy losses are small. That's exactly how the coils in the machine from this paper are constructed.

You might also consider spacing the magnets out more from each other to minimize the flux leakage. I think a good rule of thumb is the same spacing as the width of the airgap. If they're closer than that, some of the edge flux will tend to couple directly to the magnet next door instead of crossing the airgap to do useful work.

One final note on the multistage idea. There's a lot written about that and the scaling seems to be pretty much linear - 2 stages gives 2x torque, etc. But it seems like torque density (by weight or by volume) is better if you just make the diameter larger. The consensus seems to be make the diameter as large as possible (or practical), then go multistage if you still need more power.

Finally, I'll leave you with this picture from the paper. The machine they designed was a dual-rotor single stator, ironless machine similar to those discussed here. It's rated for 70 kW in a package about 40cm x 5 cm. It's intended as an alternator, but the design is fully reversible.

View attachment Axial Generator.JPG

Here's the citation, for those with the interest and means:
Caricchi, F. et al., "Performance of Coreless-Winding Axial-Flux Permanent-Magnet Generator With Power Output at 400 Hz, 3000 r/min," IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 34, NO. 6, NOVEMBER/DECEMBER 1998, pp. 1263-1269.

 

[Miles]

Here's a 3D PDF of the model illustrated above, in its present state.

[Click on the image to activate the model]

 

[Miles]

Here's the citation, for those with the interest and means:
Caricchi, F. et al., "Performance of Coreless-Winding Axial-Flux Permanent-Magnet Generator With Power Output at 400 Hz, 3000 r/min," IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 34, NO. 6, NOVEMBER/DECEMBER 1998, pp. 1263-1269.

5.5 Nm/kg 8)

 

[Miles]

For an ironless stator, apparently the optimum coil shape is actually a rhomboid. Pie-shaped coils aren't optimal because the straight runs on the top and bottom are useless copper that adds resistance but doesn't contribute to torque. They claim a rhomboid is the best compromise.

Maybe a mandorla shape would be even better?

 

[Thud]

Bigmoose,
I have no illusions regarding the efficancys of a home built motor. I am hopeing to get near 90% with a motor that fits the bicycle application a little more neatly. A lot of the rc-motors post big e-numbers but we have a tough time operating them in their range.
I just want enough torque to satify the requirment (with a grin)& a Kv rating that gets us away from the muti-reductions required. Luke is far more ambitious in that regard.

I love the secret sauce analogy. Even if we only get 7 out of 10 herbs, it might be some great tasting chicken

I am amazed you would bring up guitar Amps, I dont build them, but I used to abuse them. Sold off all my vintage stuff in the late 80's while raising a family. still have 1 old kalamazoo that prolly needs re-tubing.(haven't pluged it in it 12 years) been achustic for awhile now.
Thanks again for the input.

 

[Thud]

Thanks miles,
Now we are getting to the meat on the requirments.

Thanks rhitee05,
That is valable information that prolly gets taught in HS physics, But since I never took HS physics I am learning on the fly. looks like another name on the credits page is due.

That current model is a quick & dirty sketch for a corless axial design after some exchanges with luke, I added the iron flux rings to the magnet rotors as I doubted a halbauch array into the confines of 5"diameter with off the shelf magnets was doable, I may need to revisit that. the issue I see right now with diy halbauch is the wide spacing you get between magnetic poles.
The big motor guys seem to be using additional phases in the "super" motors. I belive the csiro is 4 phase, maybe more. Is the launchpoint more than 3 phase.(need a re-read)
It may be simple programming on the controller but my tiny brain is decidedly 3 phase & standard controllers ATM.
going back to work now. keep that info flowing.

 

[rhitee05]

Miles,

Never heard of mandorla before, I had to google that. Seems like that shape would be wicked-hard to wind. Unless you're talking about lap winding - overlapping the phases? That's definitely a good idea, it would reduce the Kv of the motor and dramatically increase the copper fill in the stator. A couple more snippets from the paper discussing the rationale for rhomboidal coils:

Therefore, disregarding the case of machines having a very large number of poles and, thereby, very short end windings, the use of trapezoidal coils negatively affects the value of torque produced per unit of , and this is undesirable for machine applications with high power ratings.

In fact, due to the inclined arrangement of the coil active sides, in rhomboidal coils, the end windings are greatly shortened, but with only a small reduction of the coil flux linkage if compared with the conventional trapezoidal-shape coils.

The geometry of rhomboidal coils is characterized by the inclination angle alpha and the ratio Kr between the inner radius and outer radius... With the
values of and related to an optimized design, it is found that the use of rhomboidal coils results in 25%–30% reduction of winding resistance and 10%–12% reduction of EMF, compared to trapezoidal coils.

I haven't read any discussions in the literature so far, but I think circular coils may be even less optimal than rectangular/trapezoidal ones. Only the portion of the winding in the radial direction generates torque, so with a circular winding every part of the coil except the two extremes has a cos(alpha) term. Let me try doing some off-the-cuff math here to work it out.

Assume for a circular coil the height of the coil is pi inches/cm/whatever (for easy math). To find the radial component for one half of the coil, take the integral of sin(x) over 0..pi = 2 inches. So, including both halves, a circular coil of diameter pi has 4 inches' worth of radial component (the torque-producing part). Given a circumference of pi*D=pi^2, let's create an effectiveness ratio of radial length divided by total length. For the circular coil, that would be 40.5%.

Now take a rectangular coil (for easy math I'll ignore the trapezoid). For consistency, we'll assume it's pi inches high and pi inches wide. It'll have 2*pi of radial length (the effective part) and 4*pi of total length, for an effectiveness ratio of 50%.

The paper quotes 60% as roughly an optimal angle for the rhomboid coil. Again, assuming pi inches tall, that's pi/2*sin(60) for each leg, which is ~1.36 effective length. The actual length of each leg is ~1.81. Neglecting bend radius and so forth, that would be a ratio of ~75%. That math is optimistic, but it does seem to back up the conclusion.

Sorry for the really long post. I hope that's a useful explanation.

 

[John in CR]

Luke,

That looks like a winner...70kw with water cooling, 460nm peak torque. Use a carbon fiber composite to replace as much of the metal as possible to get it down near the 20kg range.

 

[Arlo1]

Sold! Where do I sign up?

 

[Miles]

Miles,
Never heard of mandorla before, I had to google that. Seems like that shape would be wicked-hard to wind. Unless you're talking about lap winding - overlapping the phases? That's definitely a good idea, it would reduce the Kv of the motor and dramatically increase the copper fill in the stator.

Eric,

What I meant was something like a wide aspect-ratio ellipse. The mandorla shape, as opposed to the mandorla symbol, refers to the shape of the area enclosed within the overlap between two circles. I guess there'd be no point in the magnets covering the end turns.

 

[rhitee05]

What I meant was something like a wide aspect-ratio ellipse.

Ah, now I see. Yes, that might work reasonably well. Seems like that would be roughly comparable to a rhomboid shape.

 

[amazingdiyprojects]

Hi all!
I believe that it is possible to build very efficient motors with amateur means.
Water cooled version single ESC motor.
I have built motors slightly more efficient than the Turningy motor in picture, also more efficient then some Plettenberg motors.
I have compared the power requirements swinging a certain propeller, (Menz 26/10 in this case if i remember correctly) at same rpm.

Best regards/Axel

 

[Thud]

Axel, very nice aray of designs there,
Are there iron cores in any of your stators? or any type of core material?
your insperation had me clean the shop tonight.
I also roughed out the case for my test mule motor.
need more time.......more time.

 

[amazingdiyprojects]

Yes, time is a major factor....

And speaking of time; i once dismantled a car alternator with the objective to rewind the stator and
build a permanent magnet rotor. After a few test windings around a pair of teeth I realized
how hard that would be an how time consuming it was, so I started to build a axial motor
from scratch, which is allot less frustrating.
That is the nearest i have yet come to build something with an iron core.

The small 20 k rpm motor has wooden cores in the coils....

If it were not for the need of thin lamination of soft iron (compared to massive pieces of iron that would be easy to machine) i would
have built a iron core motor a long time ago since they are capable of delivering so much torque in a small package.
Sooner or later i have to try to build one though, if not else so just for comparison and gaining knowledge and understanding.

/Axel

 

[rhitee05]

I wonder if you could do something like epoxy and iron powder to make a homebrew core? If you make it a pretty dry mix and pack tightly it should have decent magnetic properties. The idea with using powder would be to try and keep the conductivity low to reduce eddy losses. Ferrite powder is non-conductive, so that might work.

 

[Thud]

I have about 20 flyback transformer cores(powderd iron) I could recrush & make some home brew core.
Ya think that would be the ticket? I also could mine about 10 #s of ferrite in short order also.
What do you speculate would be the most effective?