Ironless axial flux Halbach project - 170mm, 36 pole, 44mm bcd disc brake mounting

[pedalless]

For Australia with the 200 watt input limit and the speed limits you are going to want to get as much current to flow as possible, so your design criteria is probably different.
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Australia hasnt got this 200 input limit you keep saying we have 200watt maximum motor out put Safe. The is a guy in Sydney court now who has to prove his motor is 200watt output he has already been fined 1000 dollar case adjourned to get evidence of 200watt output this case is listed on this forum safe go read, you are wrong about this input rule we must have 200watt maximum ut motor. There was talk of law change but this didnt happen it was going to be 200watt output rear wheel, law wasn't passed at this stage remains 200watt maximum motor output. Thankyou.

 

[AussieSteve]

No speed limits, either, except the posted ones.

 

[madact]

I've checked the PCB router at work, which they're willing to let me use - turns out it has some pretty decent capabilities in terms of thick copper and fine cuts. Should be able to cut 0.5mm channels in 1.2mm copper without too much trouble. After some careful consideration of the laser cutting option, my current thinking is that getting perfect alignment of pre-cut layers would be a very tricky addition to the already complicated process of lamination; if I were to get the alignment wrong, it's game over, start again - there's no good way to un-glue what's been glued. The epoxy I'm thinking of using does re-flow at 80C before final cure at 200C, but that isn't practical for re-positioning.

 

[safe]

This stuff is really high tech. Actually, the fact that non-professional fabricators like us are even trying is either adventurous or foolhearty. My strategy is to build and then rebuild until you get where you want to go. Sometimes the first attempts allow you to learn something that you can improve upon in the next iteration.

The university mindset tends to want things to be perfect the first time out and that can get you into a paralysis situation, but if you think of people like Thomas Edison who developed the lightbulb he actually made it a sort of assembly line process where he tried all sorts ideas until he got close to the answer.

So I'd say just "go for it" and make a few mistakes that need to be done over. There is no shame in first attempts that aren't perfect. And you never know, you might get lucky and glue it successfully the first time through...

(of course if the process is expensive, then you shouldn't rush in)

 

[madact]

My approach at the moment is to go for a fully milled version first, then if the glueing process is hassle free and the motor works reasonably well, I'll try laser cutting the radial lines and just milling the inner and outer 'ends' of the conductors, which should reduce resistive losses 20%-30% over the milled rotor and give a correspondingly higher current limit, due to the difference in track width...

 

[safe]

I really don't think you have to worry about heat too much. At 250 watts (200 watts... or whatever you need to do) there is just not enough heat to be a big worry. Efficiency and heat are directly related, so the argument for better efficiency is there, but thermal stresses aren't going to be a problem. I've done some pretty insane things with these little motors pushing ten times as much power through them and the failure tends to be in other places than the fiberglass resin that holds it together. But it is funny sometimes how much "one" obsesses about little ways to improve things before you start. My experience has been that I've often gone far out of my way to make some little improvement only to have some other problem crop up later that nullifies the added work.

The best approach (in my opinion) is to get a prototype up and running and then gradually refine the next iteration. It's "research" (the education part) and "development" (the iterative refinement part) that gets you where you want to go.

"R" without "D" usually doesn't deliver...

(the "work" part is the iterations... 1% inspiration... 99% perspiration)

 

[clarkfeng]

Aluminum base is the right choice

I agree with Safe.

Steel base will damage magnetic line in halbach array

You should try the same simulation, but change the backing material from steel (brake disc) to aluminum or anything else that is inert. You will find that steel backing actually doesn't help much and in fact can even slightly reduce the magnetic flux.

Have you done the math on a 36 pole motor?

Will the stator cover 100% of the disc?

My design is to use about 44% coverage and a wider gap and add some core material back in to enhance the performance a little. (at the expense of cogging)

I like the fact that others are experimenting with the Halbach Design.

Also... another thing... I just got done cutting the steel disc out of my project and replaced it with a smaller more rigid base. For a disc motor you really don't want the flex that these discs allow. It's pretty easy to just cut and drill a flat plate and use it instead. I'm doing mine in fiberglass, but carbon fiber would be better.

How much power are you planning to run?

And I'm still not completely clear on how you are going to mount everything. The stator mounts to the frame right? The disc carries the magnets and turns right? Or no?