my inrunner build ? go ahead and laugh

[enoob]

BUT

im not done this is just to flush out whats in my head and learn. i know its crude but it was arts and crafts time with my boys when the light went off on how to solve a problem .
http://i251.photobucket.com/albums/gg30 ... runner.jpg
based on these magnets x 24
http://www.kjmagnetics.com/proddetail.asp?prod=D8X0DIA

the black rods would be epoxy'd to the top the yellow to the bottom . once pressed on the shaft they produce the halbach.

if its feasible what would be the best material to machine the disks out of ?

i have to visit the shop and clean up the motor i want to run it in . i should have shots of that in a day or so

if anyone has cad skills but no shop or $ for bits and wants to trade for machined copys of what i do id love to talk .

[johnrobholmes]

Those magnets have axial flux, it wouldn't work for typical inrunner style.


edit: Doh, those are diametrically done, would work fine.

[enoob]

) not alot of diametric rods out there . thought id seen some 2" long versions but these get the point across. im leaning towards rotor plates that are 3/4" thick trapping more than 1/2" of magnet at each end with a 2" magnet that leaves 1 inch in the middle fully exposed on roughly a 6" od rotor. my hope is it will make it easier to properly orient the magnets so that once both halves are pressed together they produce an external halbach.

at this point ima try and hack some cad work together and see if i can figure out the od of 24 of those magnets and then work the 2 disks from there. carbon fibre for the disks ? just so happens theres this guy i know...

lol

no else has yet so i did

edit- found these , cheaper not sure about the hole in the middle shown with the penny . think id prefer the magnet density over an easier method of trapping them.
http://www.emovendo.net/magnet/12-x-1-d ... lnder.html

[Thud]

enoob,
are you settled on the size? the 3/8 dia. here:
http://www.magnet4less.com/product_info ... cts_id=115
seem much more experimenter friendly on the check book.
For the cad work-what are you looking for specificly?
just a simple array with the dimensions like this?

the devil is in the details.

[enoob]

lol . yup thats what im lookin fer. now ill mic the id of that stator and see but i had intended on useing what ive seen here to take a shot at fabing one up . we'll see .
also makes building a jig easy peasy.
thank you

not stuck on size at all so i may even run with what you post there . did find these though
http://www.magnet4sale.com/Neodymium-Ma ... tized.html
with that said i just spent the last 6 hours reading and bookmarking everything i could find on neo magnets and they are not all built the same . seems establishing a gauss rating is important.
that said it will be easier to watch only 50 bucks grenade on the bench . or melt through the concrete floor.

ill pick up that motor in the mornin and see what shakes. be a good time to visit the farm , been stormy here.

[Jeremy Harris]

Interesting ideas, thanks. A few thoughts on making a big inrunner:

1. The use of round magnets that are diametrically polarised has the major advantage of allowing a perfectly aligned Halbach array to be formed from off-the-shelf magnets that aren't too expensive. The disadvantage may be slight distortion of the flux field due to the variation in air gap, but this could be minimised by using small diameter magnets (relative the the diameter of the rotor).

2. Round magnets lend themselves to being more easily fitted to an ironless rotor. I'm no expert in magnetics, but I wonder what the impact on performance would be for a rotor machined from a big diameter solid bar of something like Delrin, with peripheral holes CNC bored right at the outer edge to take the magnets, revolver-style? Maybe a very thin wind of carbon fibre tow around the outside would hold the whole thing together at high rpm?

3. Winding flat, overlapping inrunner coils should be fairly straightforward, these could then be wrapped around a slightly oversize dummy rotor mould, then encapsulated. Ideally the windings could, perhaps, be bonded to a iron outer ring at the same time, to enhance thermal conductivity as well as complete the magnetic circuit. I can't see an obvious way to make a motor without an outer iron can, without the added complication of having an outer ring on the rotor, with another Halbach array.

I rather like the idea of a very big inrunner, as it has the potential to give high torque and dissipate heat a bit more effectively than an outrunner. It would be pretty easy to fit fins to the outer case to enhance it's thermal properties, something that's hard to do with the other configurations. Although high efficiency is very desirable, I think lot's of us would accept an efficiency loss if the resulting motor was affordable and easy to build, perhaps from a kit of CNC'd components.

Jeremy

[enoob]

I'm no expert in magnetics, but I wonder what the impact on performance would be for a rotor machined from a big diameter solid bar of something like Delrin, with peripheral holes CNC bored right at the outer edge to take the magnets, revolver-style? Maybe a very thin wind of carbon fibre tow around the outside would hold the whole thing together at high rpm?

this is what i have floating in my head . ill hopefully see dave at performance fiberglass tomorrow and see if hes willing to take a shot at a carbon fibre core. i had thought derlin , ill see if i can find info on how it reacts to heat .

3. Winding flat, overlapping inrunner coils should be fairly straightforward, these could then be wrapped around a slightly oversize dummy rotor mould, then encapsulated. Ideally the windings could, perhaps, be bonded to a iron outer ring at the same time, to enhance thermal conductivity as well as complete the magnetic circuit. I can't see an obvious way to make a motor without an outer iron can, without the added complication of having an outer ring on the rotor, with another Halbach array.

although i like the idea of dual halbach array ill keep it as easy as i can for now. the slightly oversized dummy rotor as a form for windings is precisely what i had in mind . dug the wood lathe out of the corner for that task, sacrificial mould . i was thinking of wrapping the od of the windings with a long thin gauge iron sheet untill that wrap was the same thickness as the windings ?

I rather like the idea of a very big inrunner, as it has the potential to give high torque and dissipate heat a bit more effectively than an outrunner. It would be pretty easy to fit fins to the outer case to enhance it's thermal properties, something that's hard to do with the other configurations. Although high efficiency is very desirable, I think lot's of us would accept an efficiency loss if the resulting motor was affordable and easy to build, perhaps from a kit of CNC'd components.

by no means do i expect to see any efficiency numbers i can brag about but may be rather neat if it makes decent power and i can assemble it for less than $100 . i spend $100 a month on beer so this can take a step up the priority ladder for a week or so.

[AussieJester]

i had thought derlin , ill see if i can find info on how it reacts to heat .

.

Polyethylene might also be a possibility...

Heres a fact sheet on Delerin for you good thing about this is you could turn it in a wood lathe!
Has a melting point of 347 too

KiM

[enoob]

indeedee doo . starting to like the derlin idea . i think i can get it locally in 1" thick sheets and it looks like the magnets would give up before the derlin would. interesting.

[dontsendbubbamail]

indeedee doo . starting to like the derlin idea . i think i can get it locally in 1" thick sheets and it looks like the magnets would give up before the derlin would. interesting.

Derlin was developed to replace Aluminum during one of the wars. It machines well, but is a bit expensive. One square foot of 1" will go for about $100 USD.

Bubba

[enoob]

) ya found its not cheap . local outfit quoted me 75psf and they have offcuts cheaper for cash . black or white even

[rhitee05]

I don't want to rain on your parade, but I think you'll be disappointed by the performance of a Halbach array made of cylindrical magnets. It's a very ingenious idea to make use of off-the-shelf products, but the resulting airgaps between magnets will really reduce the effectiveness. I actually tried to model this up using FEM to make sure my intuition wasn't leading me wrong. Here is a comparison for cylindrical vs. square:

Inrunner Halbach - Round.jpg

Halbach array made of cylindrical magnets

(76.73 KiB) Downloaded 91 times

Inrunner Halbach - Square.jpg

Halback array made of square magnets

(66.2 KiB) Downloaded 76 times

This assumes 1cm diameter/width magnets with a 1cm airgap to a 1cm thick piece of steel/iron. Choice of magnet strength, etc. is arbitrary but the same between the two figures. These depict one cycle of the 0/45/90/135/180/225/270/315 Halbach array. I made the figures so the color-coding and scales are the same in both figures. Blue represents the lowest flux, trending upward with color to red at the highest flux.

In the square array, note how the fields are very concentrated within the magnets (on the bottom) and the steel on the top. The fields are also very consistent across the two resulting poles over the 3rd and 7th magnets.

In the round array, note how much weaker the flux is within the magnets and steel. The flux entering/exiting the array's poles are still fairly consistent, but weaker than the fields from the square array. The airgaps between magnets reduce the flux amplification in the array. The effect is analogous to adding extra resistance to an electrical circuit, less current will flow.

You could solve a lot of this problem if you had a machined piece of steel or iron that filled in the gaps between magnets, but that takes away a lot of the easy-to-build advantages of this design.

[Miles]

You could solve a lot of this problem if you had a machined piece of steel or iron that filled in the gaps between magnets, but that takes away a lot of the easy-to-build advantages of this design.

Stacked plates? I guess it could be much thicker plates than are needed for a stator as there'd be no need to minimise Eddy currents.... This technique might be more applicable to a large inrunner?

[rhitee05]

Stacked plates? I guess it could be much thicker plates than are needed for a stator as there'd be no need to minimise Eddy currents.... This technique might be more applicable to a large inrunner?

Yeah, something like that is what I had in mind. I agree that you don't need to worry about eddy currents here, so thicker plates could be used and they wouldn't have to insulated, so a solid machined block should work as well. I ran another model to see what the effect would be:

Inrunner Halbach - Round with Steel.jpg

Round Magnets with Steel Structure

(52.99 KiB) Downloaded 50 times

It's not quite as good as with square magnets, but most of that is due to the reduced magnet volume. Better than just round magnets alone, and having that steel would also provide structural benefits for the rotor.

[Miles]

Interesting. Thanks, Eric.

Would there be any advantage in using a 30 deg. sequence, do you think?

Eric's pics:

[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.