Halbach Axial Flux Motor

[AussieJester]

There is also another fella planing to building a Halbach inrunner style moor on ES now too Safe...Looking at Delerin for possible material for endplates. He has a Lathe to turn them though so prolly not alot of us to you i guess...

KiM

EDIT: Possible Magnets http://www.kjmagnetics.com/proddetail.asp?prod=D8X0DIA
http://www.magnet4less.com/product_info.php?cPath=1_11&products_id=115

 

[Email]

At above 20 hp the Induction motor has very high efficiency. (Tesla's Motor)

You misunderstand me. This is a Tesla Tubine, and it has nothing to do with electrical induction. In order to combine low temps and high pressure, think dry ice & H2O. Lots of info about people building their own, etc. And the low temp stuff is just to keep your magnets working (that is if you put them inside the tubine in a Halbach array). And the more reading you do on the Tesla Turbine this winter the more you'll learn that his discs were not perfectly flat and needed some washers to add turbulance (perfect for adding in magnets). I'll be reading up more on the Halbach array and see what info I can squeeze out if it. I believe the two techs could be a match made in heaven.

 

[safe]

This is why we value the Halbach array.

Normally a magnet creates a field that is like this:

...and if you trace the path of the flux lines they need to go in WIDE CIRCLES.

The Halbach array effectively "short circuits" the flux paths and reroutes them back outward on just one side. This is the essential reason that the Halbach is of any value because it eliminates the big looping flux paths.

Big looping flux paths normally need to be dealt with using lot's of iron everywhere. You needed iron in the rotor and iron in the stator. Basically the standard motor designs were just one massive chunk of iron channeling flux paths around in big wide circles. All that channeling of flux paths would produce losses. (hysteresis, eddy currents, I2R losses, and saturation)

The axial (pancake) shape is not the only type of Halbach motor possible. You can also build them facing inwards and get a motor that would be of a more standardized shape:

...so it's not about "shape" but the lack of iron that we are interested in the Halbach design. We are left with just the copper wires and as far as losses all we have is the copper loss. So if you use plenty of copper in your design (Litz) then you (by definition) will have high efficiency. These motors tend to be in the 90% and up range as far as overall efficiency.

Just want to make sure you are following what it really of value here.

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Note: My parts arrived yesterday, so I'll be starting the project thread soon.

 

[safe]

EDIT: Possible Magnets http://www.kjmagnetics.com/proddetail.asp?prod=D8X0DIA

It will be interesting to see how he secures the magnets. Square shapes have the advantage that once glued with epoxy their shape will inhibit them rotating. With cylinders there will be a strong force trying to rotate them to all line up together and at 22-29 lb pull force that's going to be tough to handle.

Probably will need more than just epoxy for those magnets:

Dimensions: 1/2" dia. x 1" thick
Tolerances: ±0.002" x ±0.002"
Material: NdFeB, Grade N42
Plating/Coating: Ni-Cu-Ni (Nickel)
Magnetization Direction: Diametrical
Weight: 0.851 oz. (24.1 g)
Pull Force, Case 1: 22.33 lbs
Pull Force, Case 2: 29.34 lbs
Surface Field: 7157 Gauss
Max Operating Temp: 176ºF (80ºC)
Brmax: 13,200 Gauss
BHmax: 42 MGOe

...my small cubes have a pull force of only 5 lbs.

 

[safe]

Simulation Program

Now I know where some of these Simulations are coming from:

http://www.femm.info/wiki/HomePage

...and I made up an example of a Halbach in case anyone wants to play around with the program.

 

[safe]

Halbach Axial Disc Motor (for ebikes)

It just dawned on me this morning how you would build an Axial flux Halbach motor using two Halbach discs for an ebike. You go with the idea I'm presently using for the radial design (chainring, magnets on the circumference) but you would build two discs instead of one and orient the magnets facing inwards. Now you build the stator so that it "inserts" itself between the air gap.

This would give all the benefits of the dual Halbach discs and also make it possible to do it without adding much in the way of weight. (unlike a hub motor the discs need not have iron in them)

...with very little stray magnetism to worry about (Halbach orientation means the outside of the discs have no magnetism) this design would tend to not gather a lot of road material. With a thin plastic cover to prevent stuff from being drawn into the gap you could completely eliminate any worries about gunk getting inside. This would probably be a better option for something like a mouintain bike because it would keep the mud out. (not a big problem with road racing)

 

[safe]

Improved Design

Why use two discs?

Save some weight and just use one and then on the circumference you split the disc into two sides and place the magnets inside. This will make the disc physically stronger because the gap is supported nearer to the actual magnets.

This might even be LIGHTER than a standard axial flux motor design.

Amazing...

 

[AussieJester]

You could get tricky and incorporate this into a hubless wheel like thus couldnt you...make for a futuristic looking ride, (i woulnt mind making this exact bike from aluminium...)

KiM

 

[safe]

Well my main goal is practicality... how well can we realistically adapt ideas to the ebike.

The idea of actually doing a full axial design Halbach disc motor is actually pretty good. It increases the efficiency to equal the CSIRO solar racer.

The radial design might only be 90% efficient because you lose a little because of the air gap and you also waste energy with the coils because 3/4 of the copper is not really being useful.

 

[KeepOnKeepnOn]

I was really looking forward to this being a build thread. Now its all mucked up with 15 pages of bantering, graphs, photographs of magnets, magnetic fields, tribute to maste Halbach etc, etc, etc. Build it, I want to see this thing moving a bike.