Halbach Axial Flux Motor

safe

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Halbach Axial Flux Motor

http://www.launchpnt.com/capabilities/electric-motor-design.html

LaunchPoint has completed optimization and initial prototyping for a high efficiency, high power density, Halbach array electric motor. With a total weight of only 1.4 pounds, this motor produces 7 horsepower at 8400 rpm with 95 percent efficiency. At 5 horsepower per pound, this motor has a higher power density than any other motor on the market. The brushless, axial flux permanent magnet design is highly tolerant of temperature and centrifugal effects, and the ironless rotor and stator eliminate iron eddy current and hysteresis losses.

http://www.geminielectricmotor.com/A Solution for the Future.htm



http://goldeneye.ethz.ch/motoren/electric/inrunner/index_EN/



 
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safe

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http://www.matchrockets.com/images/circhalbach.jpg

Apparently this is a (relatvely) new way to order the magnets so that you do not need an iron core.

This brings up an idea... :unsure:

What if you created a bicycle chainring that held the Halbach array attached to them and then mount onto the frame the coils to create the magnetic field. Then by applying multiphase (three or more) you can control the chainring like a motor... the chainring in effect "becomes" the motor.

No geardowns.

No extra chains.

Very high power to weight ratio.

...the only thing I'm not sure about is the torque at low rpms.

(will require some more study)

Will require multiphase controller.
 
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safe

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Halbach Torque and Power

This is very good news...

The AC Induction motor has behavior that does not cut out abruptly at increasing rpm (frequency) because the slip of the rotor is without cogging. An AC Induction motors iron rotor has no orientation to it's magnetism.

The Halbach motor design is actually in some ways like an AC Induction motor because it too has no cogging. The Halbach array has a flat magnetic field on one side and nothing on the other. The Halbach motor then is set to motion entirely by the frequency of the magnetic coils.... so just like the AC Induction motor the behavior is that of:

"Field Weakening"

...this almost feels like finding the "Holy Grail". :cool:

This seems to have all the advantages of the brushless permanent magnet motor (lightweight) AND the AC induction motor (wide powerband).

The real genius of this motor design is that you eliminate the core since it's no longer a part of how magnetic fields are created. The motor uses a sort of "closed loop" from coil to coil... so many of the issues of other motors sort of vanish.

I'm somewhat stunned.... :eek:

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Drop the idea about a chainring mounted motor, the needed rpm looks to be too low (100 rpm) for that to be efficient. However, at 500 rpm (multiple pole design) a simple geardown using the chain would be enough. It should be possible to rig something up that uses the stock bicycle chain. (11 tooth motor, 55 tooth chainring, ~30 tooth rear wheel sprocket)

http://eprints.whiterose.ac.uk/868/1/zhuzq10.pdf
 

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AussieJester

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Still trolling threads at Endless Sphere i see Safe... If CNCAdict from ES gets interested we will see some on ebikes within 6 months. That said he has been AWOL for awhile was meant to have the RC motor design concept ramped up for ebike use and in production by now...Tiz definately an interesting motor though.

I like the size too



KiM
 

safe

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It's A Huge Breakthrough !!! (no joke)

Don't you realize the significance of this?

What this means is that you can get the lightweight high power-to-weight performance of the standard permanent magnet motor and also get the field weakening of the AC induction motor.

You can literally get it all and not just parts in one motor.

PLUS....

There is no core to these things so you have no cogging, no hysteresis, no eddy currents to deal with.

This was really only invented at Lawrence Livermore Labs just recently (1980's), which explains why it's not known about much by the rest of the world. Most people will continue to use the standard permanent magnet motor configuration until they wake up to this idea.

What is surprising is how relatively simply the invention is...

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Not only that, but since there are no return paths for the magnetic flux lines you can INCREASE the pole count significantly without suffering the magnitude of losses that an AC induction motor endures. This means that you can get LOW RPM motors to work well... which means the "Holy Grail" of motors that do not require complex geardowns is possible.

If the base speed of a 60 Hz 2 Pole motor is 3600 rpm,

then the base speed of a 60 Hz 8 Pole motor is 3600 / 4 = 900 rpm,

and the the base speed of a 60 Hz 12 Pole motor is 3600 / 6 = 600 rpm. :D

 
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safe

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Harmonics "Need Not Apply"

It becomes obvious that using Harmonics like the Third Harmonic Injection for AC Induction motors becomes no longer necessary or even desired.

Why did we want harmonics?

Well, because the iron rotor in an AC Induction machine creates this constant "echo chamber" as the magnetic flux passes through it. It's like shouting in a cave.... the sounds echo back and forth within the rotor of the AC Induction motor until they do something. The concept of harmonics is that you send specific waves into the rotor so that they bounce out at just the right time to cause torque at a lower rpm than the fundamental.

http://www.matchrockets.com/images/halbachflux.jpg

With the Halbach configuration the permanent magnetic field is "flat". Also, the magnetic field lines now go in circles between the field coils so there is no core to go through and no possible reason for using harmonics.

So a simple Sine wave controller (Three Phase) would be all you need for this... and that means you can use less expensive components.

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Note: RC motor controllers (ESC) should not work with these motors because there wouldn't be any kind of backEMF pulses to watch. As I understand it the RC ESC's in effect watch for the cogging behavior of the standard permanent magnet design and do their timing based on that. The Halbach design needs a controller more like the AC Induction motor because there is no cogging. However... many of the AC Induction motor controllers use sophisticated algorithms that figure out what is going on inside the iron rotors and you DON'T WANT THAT, so you might have to take a step back to regular Voltage vs Frequency control. It also might be possible to think up some new and better controller schemes for the Halbach motor.

The controller will be another interesting thing to watch evolve.

However, it also might just be as simple as Voltage vs Frequency with some kind of current control thrown in. From what I can tell these motors have very, very simple mathematics to them. This is actually making things less complicated and "better".

Obviously I'm very excited about this.... it's like searching for something knowing that the right answer has not been found and then finally finding it. At last we (the ebike community) might have found what we needed from the beginning.
 
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AussieJester

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No safe im a total idiot i don't understand anything about it .... :: shakes head :: Im surprised you can though, took you long enough to discover brush tension and electric motor timing :p

No Safe, i simply don't get a hard on and feel the need to make a dozen unanswered posts expressing how great electric motors are...When they are available off the shelf for a reasonable price ill consider getting one, until then im more than happy Like 95% of the other people in this world will be, to use what is available now. Do carry on though what ever floats your boat...


KiM
 

safe

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AC Induction Motor Project "Cancelled"

Had I rushed forward into the AC Induction motor project without thinking about it very much (just buying a bunch of stuff) it's very likely that I would not have had the freedom to cancel the AC Induction motor project because I would have had an investment to protect. So far I've only invested some time (drilling the stator) and a little money ($20) for an old dishwasher motor.

Unless something emerges that says the Halbach design does not live up to their performance charts (unlikely) it only makes sense to switch to this design over the other.

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What do we know, what have we learned?

:D The journey began with permanent magnet motors of the brushed and brushless kind. They have in effect a couple of design flaws. The first flaw is that they have a fixed speed that they can attain before the backEMF (caused by cogging) prevents more rpms. This means in practice that you need to use multispeed gearing to get useful performance. The second flaw is just with the brushed motors and that is that the brush/commutators tend to fail if you push them too hard.

:D The "next step" was to realize (by watching the Tesla roadster and others) that with the AC Induction motor you can expand the powerband indefinitely. This is because the iron rotor has fields created in them and they are "smooth" in the sense that there is no cogging behavior. No cogging, no speed limits.

:D Finally... with the Halbach... we eliminate the cogging and even throw away the iron core itself dropping the weight of the motor significantly. You now have effectively an AC Induction motor in that the movement has no cogging elements to it and yet you use permanent magnets.

The Halbach makes the permanent magnet motor "appear" like an AC Induction motor.

...and the controllers will be more AC Induction than Brushless motor in logic.
 
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safe

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Do carry on though what ever floats your boat...
It vindicates my intuition about the direction of ebike motors.

The whole permanent magnet motor thing with it's geardowns and multispeed complexity was just...... wrong.... in my opinion. The maintenance on all that stuff was going to make operating these things a nightmare.

You are trying to be "Mr Practical" and all... and I get that... but have some excitement that the answer has been found.... "finally".

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All these Halbach motors are placing efficiency numbers in the middle to upper 90% range... that's simply incredible !!!

If I'm going to build a motor from scratch I might as well do this type.
 
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