Halbach Axial Flux Motor

[safe]

Which way will the pole faces point? Towards the sky/road, or towards the left/right?

Sky / road like in the picture.

The double sized Halbach field faces outward from the rear wheels axle.

The minimized Halbach field faces inwards towards the rear wheels axle.

The stator is in an outer ring (larger) than the rotor. (and mounted to the frame)

(there is no need to add any bearings like most motors need)

...pretty much the same as the picture.

---------------------------------

Unless you have a better suggestion?

The idea is to build something that is roughly of the same size as a large disc brake rotor.

One of the nice things about these motors is that since they naturally prefer being spread out you can get much better air cooling. With the typical tightly compressed motors you have a hard time getting air into them... but with the big flat disc they should have excellent cooling abilities.

I'm somewhat surprised at how FEW turns these motors seem to need. The solar racer talks about using either four turns or two sets of two for each pole. I guess the leverage is so extreme that you just don't need much.

Kind of amazing... (the whole idea is still sort of blowing my mind )

--------------------------------

This even sort of brings back the idea of doing something like KERS for ebikes.

With these big disc "rotors for motors" you could put them on the front wheel too and do regen.

 

[safe]

Concentrated Coils?

Here's a thought....

Rather than having a stator that stretches all the way around the rotor disc (which can be quite large) what if you concentrated the stator coils into a single area so that the interface is about the same size as what is needed to straddle three phase poles. You then focus on making really large magnetic fields in just one area.

These Halbach motors are not like regular motors and don't need circular flux paths through anything in the middle of the disc, so you can comparmentalize things and not have any losses.

Good idea?

 

[johnrobholmes]

If you used just a partial stator area, you would get partial power compared to a full stator. Could be interesting though. Would be pretty cool to have a motor that mounted to a disc brake flange.

 

[safe]

There is no iron core, so no iron core saturation to worry about. As far as the equations are concerned I can't see any reason why you couldn't concentrate the magnetic forces into one spot as opposed to spreading it out.

It looks to be a "linear system"... you put in energy in the form of current and you get back 90%+ in the form of propulsive or regenerative power. The Halbach concept began with maglev trains and they only get near the levitation rail at a few points, if the trains can get away with limited area, then why not this?

See what I mean?

Crazy... maybe... but it would be great if you could build a disc brake rotor that was actually a motor. Maybe it could double as both? Have most of the acceleration and braking done with the motor / generator and then have mechanical in a "just in case" manner.

Brakes become "regen brakes" + a little extra.

------------------------------

What would need to happen is a manufacturing process where the disc rotors were built so that the Halbach array was formed inside the rotor. That way you could use abrasive pads on the rotor and still use the same part as the motors magnet array.

Sort of like the process at the top of the last page. (see first posting, last page)

Or just go directly to it:

http://www.greencarcongress.com/2009/10/whp-2009029.html

...however, while this would be a great idea it might not be possible from a manufacturing standpoint to do. The magnet material may not have the ability to withstand the frictional forces (and heat) of a brake.

 

[johnrobholmes]

If you increased copper on the one section to equal that of the normal design, a concentrated section would have as much power. The next issue would be force imbalances. Similar to a maglev, I like that analogy.

 

[safe]

The next issue would be force imbalances.

My mind does not fully comprehend all the magnetic forces at play, but I would think you could find a way to wrap the "force zone" around the rotor in a way similiar to how a disc brake caliper wraps around the disc.

It might be possible to amplify and concentrate the fields yet one more level because of the wrap around shape.

(what the heck.... it's worth trying to figure out)

The thing to do is study how the "Magnet Boys" are doing fusion research... they know all the tricks in focusing the magnetic fields because that's how they compress the plasma.

-------------------------------

It's kind of a case of "Forrest Gump" situation but I was actually working at Lawrence Livermore Lab as a silly administrative assistant type during the period when the Halbach stuff was invented. The "Laser Boys" and the "Magnet Boys" were in a competition to see who could get fusion to happen first... we're still waiting....

They had this one magnet that filled a three story room. (a huge globe shape)

 

[AussieJester]

Can you sketch up a design you have in mind please safe, in pencil and scanned (or a digital photo of drawing tiz all i do) is fine just so i (and others) have a better idea of the design your planing ...cheers

KiM

 

[safe]

Sketch

The sketch shows a double sided disc hub that allows you to get "direct drive" strength from the rotor disc. (holding little green magnets) You then need to build an adaptor that will also bolt to the disc (6 bolts) and will have the freewheel threads on it. For $5 you can get a steel rear hub and just chop it and weld it to get the threads. That's how you get a freewheel attached.

Just like you need to adjust your disc brake alignment you would also have to get your rotor-to-stator alignment right too. I figure that the stator should have AT LEAST six poles (two sets of three phase) in order to be sure to get enough "grab" on the rotor.

Since these Halbach produce power based on electrical input (and not much else) you would want to build this stator as having many turns to compensate for the fact it's applying itself to a smaller area.

The stator mounting might be different too... chain clearance is an issue...

 

[safe]

Mental Imagery

Here's a thought...

Think of the Halbach array (disc) as a sinusoidal form... much like teeth on a sprocket.

The stator then needs to have enough "bite" in the teeth of the magnetic Halbach array to be able to make it move, but just like with a chain and sprocket you don't need to have the chain go ALL the way around.

The stator in essense "moves the chain" on the rotor and makes the rotor move. The imaginary chain is moved because you are generating an AC waveform, but without the Three Phases the movement is more like the chain bobbing up and down rather than creating a forward moving wave.

(I think I'm finally seeing this in my mind)

It might be a good idea to build a lightweight rotor guard to keep metal objects from jumping up into the rotor... maybe something out of fiberglass. (sort of like those disc brake dust guards) However, this is actually an argument for using a full stator rather than a partial one because then you have a built in dust guard. (but it means assembly is more work)

 

[safe]

Torque = Force * Radius

With no iron cores with their magnetic flux lines to worry about the size of the disc can grow as big as you want it to be. Since Torque = Force * Radius if you increase the radius of the disc you can decrease the magnetic force needed to achieve the same result.

So the logic goes...

Many small magnets on a big disc is better than fewer big magnets on a small disc.

...this should also help to allow the use of fiberglass resin in a more relaxed manner because the stress levels for each magnet are lower. The leverage of the disc itself does the "work" rather than forcing all the stress into a small area.

http://cgi.ebay.com/100-Neodymium-M...emQQptZLH_DefaultDomain_0?hash=item4ceb543056

100 Neodymium 1/4" cubes, N42, $30

The added bonus is that more magnets means you have a higher pole count and that effectively lowers the gear ratio. A lower gear ratio means that the pulses in the AC waveform act for a shorter time (you are always at a higher frequency) and that means less overheating at low speed. It's not hard to increase the frequency to whatever you need it to be for the higher speeds. So the small magnet solution makes low end power easier to make happen. (as with all things the optimal performance will be somewhere in the middle of various extremes)