The Halbach Disc Motor Ebike Project

safe

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The Halbach Disc Motor Ebike Project

http://www.motoredbikes.com/showthread.php?t=23955

The theory was developed on the other thread and now I'm going to begin the actual "build" process of the Halbach Disc Motor idea. (after about two months of motor research)

This will NOT be an axial motor.... the magnets will extend their magnetism radially away from the rear wheels hub center. Just want to be sure that people understand the concept because most of the Halbach disc-like motors that are standalone (not built into the rear wheel) make use of the axial design and two parallel discs surrounding the third which is the rotor that holds the copper magnet wires.

In this design there is just ONE DISC and it has a Halbach array facing radially outwards from it's circumference and the magnet wires will be on a stationary device that will resemble something like a brake disc caliper.

Here are the components that I will begin with:





...looks like tomorrow might be warm enough to do some work on this.
 

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Darrell_H

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I just looked through several of the 143 posts on the Halbach Axial Flux Motor thread and several red flags came up. I didn't have time to read all 143 but, since the I saw the same assumptions in post #143 as post #1 I have to wonder if any sanity check on this "theory" has been performed.
Safe, can you address these issues:
1. The 2nd photo on post number 1 shows what looks like copper coils around air, no iron. For a fixed Gauss level (current times turns) the flux in air will be thousands of time less than the flux in iron, so the flux coupled to the magnets will be much less for a given amount of current. Is there iron inside these coils?
2. The article about Halbach states that all experts and CAD models are all wrong. This raises a big red flag because it sounds just like new-age logic. All CAD is incorrect....yet you use what looks like a CAD model in post #7. Contrary to this idea that all CAD is wrong, most 3D CAD analysis I have worked with shows field lines around a bar magnet very close to those seen in real life when you sprinkle iron filings around it. What is this CAD which is all wrong? Who are these "experts" who are all wrong?
3. Also about post #7, what I first noticed in the picture is that the vertical field lines on the top and bottom of the vertical magnets are not mirror images of each other. What material do you have in your model besides air which would cause this? What is the "backing" material made of? What is the purpose of the horizontal magnets in the Halbach scheme. They don't seem to bend the field in any usable direction.
3. Throughout the posts I see several times the phrase, "only copper losses". Copper losses contribute a huge portion of the total loss in motors. Why use the word, "only"?
4. One picture (I forget which post number) shows a 3 phase stator which is surrounded by an array of magnets (looks like a typical wash machine PM configuration). The author shows all coils to have a North field pointing outward, then he goes on to diss that motor. This is simply not how 3 phase waveforms work. What gives with that picture?

You're obviously very interested and working hard to experiment with this Halbach motor but, I'm worried that you'll spend a lot of time guided by this Halbach article which has a lot of misleading guesses which borders on pseudo-science. Some real 3D CAD analysis before spending days with trial and error could save a lot of time.
 

spad4me

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I just looked through several of the 143 posts on the Halbach Axial Flux Motor thread and several red flags came up. I didn't have time to read all 143 but, since the I saw the same assumptions in post #143 as post #1 I have to wonder if any sanity check on this "theory" has been performed.
Safe, can you address these issues:
1. The 2nd photo on post number 1 shows what looks like copper coils around air, no iron. For a fixed Gauss level (current times turns) the flux in air will be thousands of time less than the flux in iron, so the flux coupled to the magnets will be much less for a given amount of current. Is there iron inside these coils?
2. The article about Halbach states that all experts and CAD models are all wrong. This raises a big red flag because it sounds just like new-age logic. All CAD is incorrect....yet you use what looks like a CAD model in post #7. Contrary to this idea that all CAD is wrong, most 3D CAD analysis I have worked with shows field lines around a bar magnet very close to those seen in real life when you sprinkle iron filings around it. What is this CAD which is all wrong? Who are these "experts" who are all wrong?
3. Also about post #7, what I first noticed in the picture is that the vertical field lines on the top and bottom of the vertical magnets are not mirror images of each other. What material do you have in your model besides air which would cause this? What is the "backing" material made of? What is the purpose of the horizontal magnets in the Halbach scheme. They don't seem to bend the field in any usable direction.
3. Throughout the posts I see several times the phrase, "only copper losses". Copper losses contribute a huge portion of the total loss in motors. Why use the word, "only"?
4. One picture (I forget which post number) shows a 3 phase stator which is surrounded by an array of magnets (looks like a typical wash machine PM configuration). The author shows all coils to have a North field pointing outward, then he goes on to diss that motor. This is simply not how 3 phase waveforms work. What gives with that picture?

You're obviously very interested and working hard to experiment with this Halbach motor but, I'm worried that you'll spend a lot of time guided by this Halbach article which has a lot of misleading guesses which borders on pseudo-science. Some real 3D CAD analysis before spending days with trial and error could save a lot of time.
Sanity Check he don't need no stinking Sanity Check.

You missed the sixty plus pages on rewiring a brushed motor.
The misleading article on a dishwasher motor.
There are thousands of page's of odd pictures , that safe has authored.
No real information just advertising on someone else's threads when he can.
 

safe

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Halbach Uses No Iron

I too was amazed when I learned of this because it seems to contradict everything we have thought "normal" about electric motors.

Start with Wikipedia:

http://en.wikipedia.org/wiki/Halbach_array

A Halbach array is a special arrangement of permanent magnets that augments the magnetic field on one side of the array while cancelling the field to near zero on the other side. In the diagram, the magnetic field is enhanced on the bottom side and cancelled on the top side (a one-sided flux).



In order to visualize what the flux lines look like I found a pdf that had these images that represent the two options.

First there is a "standard motor" with alternating poles:



Now with the Halbach motor the alternating poles also have the rotated magnets that cancel the magnetic force on one side and increase it on the other. The effect acts like a "short circuit" of the magnetic flux lines and this allows you to design without the need for iron. The only reason that iron rotors and stators are used is because the flux lines of a "standard motor" are so spread out that you need to "assist" them with the iron because iron holds magnetic flux many times better than air:



...there still is the issue of the "air gap" and just like with "standard motors" if the gap is too large it effects performance negatively.

Can you see how those flux lines are different?

The intensity of the flux lines are much greater (darker) with the Halbach and there is no need to "loop around" through some iron backing plate. The flux loops become small rather than large.
 
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spad4me

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I believe a halbach array doubles the flux in AIR on one side and reduces the flux in AIR on the other side.
Proper selection of a laminated steel core concentrates the flux..
Lots of people have tried to make an efficient halbach motor.
You safe could be the first.
 

safe

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Lots of people have tried to make an efficient halbach motor.
You safe could be the first.
No, I won't be the first... the solar racers in Australia use Halbach motors to get 95% - 98% efficiency already.

However, I might be the first to develop a "practical" implementation of a theory that has already been used to win contests. Ebikes need a practical design... so that's what I'm doing... being practical.

The winning solar racers use Halbach (axial, not radial) motors:

http://www.myfen.com.au/Article/Nine-solar-racers-choose-CSIRO-advantage/77236.aspx

...or read more about the CSIRO Halbach motor. (pdf)
 

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safe

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1. The 2nd photo on post number 1 shows what looks like copper coils around air, no iron. For a fixed Gauss level (current times turns) the flux in air will be thousands of time less than the flux in iron, so the flux coupled to the magnets will be much less for a given amount of current. Is there iron inside these coils?
In a "standard motor" the magnetic flux needs to follow a very long looping path before it finally returns to the other end of the magnet. Having to travel so far (in distance) means that the field strength will drop even with iron there to assist in keeping the flux strength high.

With the Halbach motor they solve the flux strength problem by making the path shorter. The flux only needs to loop as deeply as the magnets themselves and then come right back.

So the answer is that there is less "work" that needs to be done, so it's not as high a priority to increase the magnetic strength with iron cores. The CSIRO motor only uses four turns of wire to achieve what they need. (it's amazing)

Also, once you start to reintroduce the iron you then have to deal with the losses associated with the iron and those are unnecessary losses. If you need more magnetic strength you just use more copper in the windings.



The "Bottom Line"

The Halbach motor "exists", has proven itself in competition and comes out on top. Whether I can achieve equal results is more a statement about my own fabrication capabilities in my garage than the theory itself. It would be nice to have machine tools and access to high tech manufacturing, but for now it's being done on a shoestring budget. If things go well in the first version then I'll try another and another...
 
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safe

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Halbach Disc Mounting

The first thing I've done (other than lace up the double sided disc hub to the rim) is to create this chainring "spider" that attaches to the six bolt hub.

The magnets will be attached to the chainring (eventually) in a Halbach pattern where the magnetic forces are directed outwards. (radially) Then outside the chainring will be the actual magnet wires (coils) in a sort of disc brake caliper configuration covering only about 1/4 of the chainring. The idea is that it's easier to use lots of magnets in a big chainring and get the leverage advantage that way than to use a full wrapping around set of coils on a smaller disc. However, if the power turns out far less than I'm hoping for I might end up having to do the full wrap. (so future upgrades are likely)

This was about a 3-4 hour project for the mount... not too bad...



...tomorrow I'll be grinding down a steel rear hub so that I can extract the threaded portion for a freewheel attachment. It looks like it's going to work out really easily. (easier than I thought)
 

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safe

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...the vertical field lines on the top and bottom of the vertical magnets are not mirror images of each other. What material do you have in your model besides air which would cause this? What is the "backing" material made of?
I'm kind of pondering this issue myself...

The Halbach magnets take care of just one side of the flux path problem. The other side of the flux path is the magnet wires (coils) and the presence of the Halbach array on one side does not do anything to help on the other. The dual Halbach axial flux motor designs concentrate everything into the center and then the rotor (which holds the coils) only has to pass through the center of the magnetic field that is already there. The dual Halbach is the superior design choice if you can do it.

In my design the chainring will hold the Halbach array and it will face outwards in the radial direction. However, the magnet wires (coils) have no iron core backing to them, so they might not be very efficient. In a sense I'm going backwards in the design for practical reasons and that might mean that I'll have to reintroduce a small amount of iron into the magnet wire (coils) in order to get decent performance.

So in a sense this might NOT actually end up without iron... :beta1:

(I'm just hoping to minimize it as much as possible or maybe add excess copper as a substitute)
 
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safe

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Good Enough For NASA?

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080013147_2008011124.pdf

In a rather large (8 mb) pdf file from NASA they go into the use of Halbach motors and it looks like I've found the preferred way to do the windings:



...this looks to be the proper way to do the winding. (no mention of iron)

Technically speaking I think this is a "magnetic bearing" so it might not be right for this application.

Rotating the coils the other way (like in the first motor I saw) doesn't look to be the optimal way to go, but I'd like to get a Simulation of all this before I finalize on the design. (it might be some time before I get to the coils anyway, so no hurry) I'm pretty sure about the magnet design for the chainring, but this magnet wire coil stator is still being thought out as I go.

What would be pretty interesting is to have the center of this stator hollow for either air cooling or even water cooling. Being able to pass water past the coils (which is the only source of heat) would allow me to experiment with overloading the motor to see how powerful I can go with it. At this point I have no idea how much power will be possible with this motor.

Of course this is all assuming that the idea is correct... :geek:

Just by observation it's pretty obvious that 3/4 of the copper in the coils is wasted because the only part that is going to produce a "useful" magnetic field is next to the magnets. The loop is closed (so that's good) but it means there's some wasted copper. A little wasted copper seems a tradeoff that you have to make in order to avoid the use of iron.
 

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