my inrunner build ? go ahead and laugh

[Miles]

Better than just round magnets alone, and having that steel would also provide structural benefits for the rotor.

For an inrunner, it would solve the problem of restraining the magnets, too. Keeping them at the right orientation might be a challenge, though......

[rhitee05]

I assume, Miles, you're referring to the 30/60 arrangement used in the CSIRO motor discussed recently? Here's a model of that:

Inrunner Halbach - Round 30deg.jpg

Round Magnets in CSIRO-style Halbach Array with Steel Structure

(55.74 KiB) Downloaded 54 times

To within the limited accuracy of my model, this seems roughly the same as the 45/90 degree array. They seemed to think there was some advantage, though, so maybe a more rigorous model would show that. I only have a free version of the software I'm using (QuickField), so it's limited in the number of points I can model. I had to cut a few corners to get this model small enough, so I can't expand it to show any more detail without finding another tool.

One interesting note, though. My model is showing really high flux densities in the pieces of steel between the magnets. I think my model is actually seeing saturation in those regions, and that's with my model using magnets of strength roughly equivalent to AlNiCo. Presumably that would be worse with strong Neo magnets. I'm not sure offhand what the implications of this are to real-world implementation.

[Miles]

Thanks. That only seem to have a very slight advantage, if any.

[Thud]

rhitee,
Those are nice models, thank you for posting them.
9 magnets seem to be a recuring theam in the halbauch array. Are there any other configurations?
If I am interpreting the graphics correctly the 9 will unite to make 1 pole.

Origanly I assumed it was the lower pole count that was detrimental at the scale some of us are working at or
perhapes it is just weaker magnets, very small magnets assembled to create the H.A.
Either way, I apreciate the visuals. please keep contributing.

[rolf_w]

...I ran another model to see what the effect would be:

Inrunner Halbach - Round with Steel.jpg

nice models and it shows: having the magnets embedded in iron prevents the magnetic flux from crossing the airgap - this is where you want it as this is where your current conducting coils are!

[enoob]

thanks a heap for the info guys your kinda dragging me into the deep end of the pool and i no swim so well yet but im getting what your laying down.

im in the process of jigging up so i can mock this out of mdf then ill show you what im about to say BUT i had intended on no air gap between the round magnets . what ever material i end up using in the rotor i hope to have a total thickness that is more than the magnets are long. if the magnets are 1" long and i use 2 plates of 3/4" derlin my hope is that once pressed on the shaft there is no gap between magnets and each one is held in by the slim fingers of derlin hopefully trapping them by the od. still looking for some adhesive that will work affectively at bonding derlin to derlin and to the magnets.

block or square magnets seem to be a tad more difficult to trap in an inrunner. that said i found some info that states neo magnets can be machined with carbide with the alarmingly inherent danger of the dust and powder spontaneously combusting . but the threat of imminent danger and poisonous airborne particals is present with the mdf so i can see how to dovetail some blocks into an inrunner. still leaves me with a question mark as to how the magnet will react ? brittle enough that i can see myself shattering them or causing fractures that hurt performance.

i was also kind of hoping that with the round profile i can get the air gap from stator to magnetic pole down to an optimum ? ive begun to see magnetic flux as something that flows like water but can be compressed and squished ? if so the round profile leaves alot of room.

other wise it had occured to me that some schedule 40 pipe in a 4" od to hold the magnets and something non magnetic bonded in the id may do the job.

[Miles]

It's not just whether there's point contact between magnets, or not - it's also the area of contact........ Reluctance of the air is about 1000x that of steel......

[enoob]

rhitee,
Those are nice models, thank you for posting them.
9 magnets seem to be a recuring theam in the halbauch array. Are there any other configurations?
If I am interpreting the graphics correctly the 9 will unite to make 1 pole.

Origanly I assumed it was the lower pole count that was detrimental at the scale some of us are working at or
perhapes it is just weaker magnets, very small magnets assembled to create the H.A.
Either way, I apreciate the visuals. please keep contributing.

nice models indeed . more than i had expected to see on this . kinda thought inrunner was a shunned word here

would the arrangement of the round magnets in a circle contacting each other change much ? or do those models hold even when the magnet array is bent ?

im going to go look at it again thud but i think we get 1 pole every 4 magnets ? ill see if i can find the vid of the guy with a small inrunner halbach that he put under a magnetic viewer. he has large air gaps and an aluminium ring to hold them in but i found it interesting. ah here it is

thanks miles . unless some one says different ill look at making the outer ring of the rotor in steel . shouldnt be to tough, core of alloy and perimeter of steel ?
http://www.youtube.com/watch?v=qv-9IAj_ ... re=related

[Miles]

I think that everything enclosing the magnets needs to be steel.

[enoob]

I think that everything enclosing the magnets needs to be steel.

roger that . if i read things right maxumum potential is reached when the steel is at least the same thickness of the magnets . after that i thought i read that steel through to the rotor shaft can can cause parasitic magnetic loss. is it worth the effort to us a non magnetic material in the very core between the rotor shaft and the steel holding the magnets ?

the bonus is ive got steel and aluminium at the farm that i could work into this. yay i love free.

[Miles]

after that i thought i read that steel through to the rotor shaft can can cause parasitic magnetic loss. is it worth the effort to us a non magnetic material in the very core between the rotor shaft and the steel holding the magnets ?

As long as there's no movement between the magnets and the steel, there'll be no losses, AFAIK.

[Miles]

For connection with the shaft, an aluminium plug at each end of the rotor bore should be fine.

[Miles]

If the magnets were slightly longer than the depth of the steel, you could then grip them to hold them at the correct orientation while they were being bonded in. If the steel part was made up from more than a single layer, then the magnets could be flush.

[enoob]

very good then . this will make it easier as i wont have to deal with such tight tolorances to get all the magnets contacting and in a perfect circle. should also help with the rpm limit i imagine. only down side is ill have to grab some beer and visit an old friend to get him to turn this block of steel for me. havent seen him in a while chit chat will take longer than the turning.

thanks a ton guys . ill make some metal shavings and get back to you.

i stripped down an old alternator last night . rotor is 4"od , shaft would work great good sealed bearings, stator is junk. after stripping it and pressing the claws and winding off the shaft the cast case with rotor shaft is just shy of 3 pounds.
makes me wonder what coreless windings and a new rotor will come in at.
seem like this would make a good frame for a 5" or less od axial flux motor as well with 3 1/4" end to end for plates.

[enoob]

If the magnets were slightly longer than the depth of the steel, you could then grip them to hold them at the correct orientation while they were being bonded in. If the steel part was made up from more than a single layer, then the magnets could be flush.

bingo . i want to use two layers . embed half the magnets in each layer making it easy to orient the magnets so that when i push them together i get my complete rotor in halbach.

[AussieJester]

You could always go 'ghetto' and get a tub of Devcon and spread this between the magnets would also help hold them in place...

KiM

[rhitee05]

9 magnets seem to be a recuring theam in the halbauch array. Are there any other configurations?
If I am interpreting the graphics correctly the 9 will unite to make 1 pole.

It's actually an 8-magnet cycle. I added the 9th magnet to make the model more accurate, since the real array would be a continuous circle.

I'm aware of 3 Halbach configurations. The first one I posted was a 45-degree configuration, where each magnet is rotated 45 degrees from the previous. This is similar to the LaunchPoint motor being discussed here. The second one I posted was a 30/60 configuration, which uses increments of 30 and 60 degrees. This is used in the CSIRO solar car motor. There is also a more simple 90-degree configuration, which only uses a 4-magnet cycle. At a low model resolution, all 3 configurations seem to show roughly the same flux densities. I assume that there are in fact some differences to justify different configurations being used in different applications.

it shows: having the magnets embedded in iron prevents the magnetic flux from crossing the airgap - this is where you want it as this is where your current conducting coils are!

We have to be a little careful here about interpretation. Steel between two opposing magnetic poles will cause a magnetic short circuit and divert flux away from the air gap. That's not what's happening in the round w/ steel model, however. In this case, the steel is linking the adjacent parts of the Halbach array (which are not opposing poles) to provide a low-reluctance path. Just like electricity, magnetic flux requires a complete circuit and more flux will flow with lower reluctance. Cylindrical magnets by themselves have basically a zero-area contact patch, so the flux is required to travel through the air and thus a high-reluctance path. Having the steel lowers the reluctance and increases the flux flowing through the airgap. Don't be fooled by the potential lines, the coloration is what indicates flux density. The flux density in the steel opposite the magnets is a good measure of how much flux is actually making the complete circuit and thus doing useful work in the motor.

Eric

[enoob]

You could always go 'ghetto' and get a tub of Devcon and spread this between the magnets would also help hold them in place...

KiM

well thank you . you just showed me my bonding agent for the magnets to the steel
this should make a great adhesive for this with the added bonus of some steel in any of the cavity's between the machined parts and the magnets. beeeeeautiful .
i was looking at adding some kind of ferro fluid to an apoxy for this but me likey your stuff better.

[Miles]

You'll still need a close fit............

[enoob]

and a wing with a prayer.

[AussieJester]

I have used Devcon in the past, for those that haven't i can best describe it as JB Weld on roids, the stuff is the shit, its also a lil pricey but well worth it, you can also get it in many guises ie. with different metal added to it, steel aluminium copper etc etc It will definately have no problem holding magnets in place can guarantee you that.

KiM

[rhitee05]

I think I have to eat my hat a little bit here. I just did some more modeling, trying to do a more quantitative analysis of the different scenarios. All of these look at a partial cycle (6 magnets) of the 30-degree configuration. I changed a few other things, so these results are not directly comparable to the previous models.

- Round magnets only (no steel)
- Round magnets with steel backing, but nothing in front
- Round magnets surrounded by steel level with the magnet faces
- Square magnets with no steel

These plots show flux density in the radial direction across the middle of the airgap (the useful flux). The important bit of data is basically the peak flux density (don't mind the negative sign). The magnets-only case actually shows the highest flux density of the round magnets, with the steel-surround case the lowest. It's worth pointing out that there's only about 10% difference here between best- and worst-case, but that's exactly opposite what I've been saying. Given the rough nature of these simulations, I'm going to call those all roughly equivalent.

But, note the plot for the square magnet array. Using square magnets gives you about a 27% increase in magnet volume over the round ones, but a 100% increase in the flux density.

So, a square-array is still more efficient, but it doesn't look like a round array is as bad as I thought it'd be without some steel. I'd say it's time for enoob to start making some metal shavings to see what happens in the real world.

[enoob]

wow i love the internet . this is to cool.

thanks alot for your time rhitee5 . much appreciated

ok i just shared a beer with my neighbor mechanical contractor who i helped with a french door install over summer and got him keyed up to do some metal machining for me tomorrow as payback.

if not steel back to derlin ? or is aluminum ok for this . got lots of that around that i could work myself as well.

[AussieJester]

or is aluminum ok for this

+1 for aluminium...lighter and easier to work with...

KiM

[paultrafalgar]

So, a square-array is still more efficient, but it doesn't look like a round array is as bad as I thought it'd be without some steel. I'd say it's time for enoob to start making some metal shavings to see what happens in the real world.

Don't want to distract you guys from your excellent thread, but take a moment to look at this video where Cedric Lynch (Godhead) explains why he uses rectangular magnets:
http://www.in.com/videos/watchvideo-ced ... 01603.html
Before you die of laughing at his manner, remember, he makes better electric motors and vehicles than anyone! Enjoy!