The Halbach Disc Motor Ebike Project

It is nice to see you are back posting in this forum.
I am building some more motorized bikes.
I loose track of time.
Staton sells a lefty freewheel as well as a righty and lefty hub, 24 inch only.

My battery life is terrible. the heat really affects(drains) the life from a pack.
In my opinion a recompense style geardown with a suitable motor is the only to fly.
This is my opinion only.








A 'first' on this site possibly but not 'first' to do it, using the bottom bracket bearing housing for the freewheels is an old trick matey seen it done many a time on various forums, you can use the left hand threaded one with a SouthPaw freewheel on the left hand side of the rim too (check my worklog i have done exactly that on my cruiser) Interestingly, the left hand threaded bottom bracket housing must come in various thread pitches as i tried 4 before i found one that would screw in successfully!

Safe often is the 'first' to do many things though...according too himself anywayz LoL

Where you been Spad4me anywayz haven't seen you about for ages?

KiM
 
http://www.youtube.com/watch?v=Md4gikM9Ezs
The North and South poles that pulse, just use ND Magnets pointed sideways to prevent having to have the iron in your coils.
See Video and imagine the following setup:
> coil < coil >

I didn't look at the video, but since the coils need to produce an alternating current the magnets would be correct half of the time and incorrect the other half. I don't think that would work.
 
The Fiberglass Option

One way to build the Halbach Disc is to use the aluminum chainring I just bought as the base. I had started with the idea of going with a radial design since at the time I was unable to imagine that axial would be possible.

Now I'm kind of leaning back again to the axial idea...

Also, I'm wondering if the whole disc could just as easily be built as one solid fiberglass unit with the ends split into a "Y" shape so that the magnets could be epoxied inside. Going to have to think some more about how to actually do that from a fabrication standpoint.

Much of the time with these projects you spend a lot of effort just figuring out how you will fabricate the item. This will likely require some special tools. I already created a special tool for spinning the disc that will fit into my drill and has a standard 6 bolt mounting pattern to it.

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The Halbach Disc with an axial design offers significantly better focus on the fields and is the way that the CSIRO solar racer is set up. It would be more likely that I would get close to the 95%-97% efficiency if I simply imitate what they did.

As they say... "Imitation is the most sincere form of flattery."

So in the simulation program I made this axial flux example using my 1/4" magnets and a 1/4" air gap. Visually you can see why this is the superior design. All the magnetic flux is focused where you want it and there is nothing outside of the disc. This makes more sense for a bicycle because it will not tend to attract stuff to the disc. (it will remain cleaner)

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Widening the Gap

One of the questions I've had is wondering what effect the air gap has on the shape and intensity of the magnetic flux.

If you double the gap between the arrays the result is that the magnetic flux lines get smoother and more symmetrical. The strength is less but from a cogging perspective it's "more pure" with some ideal gap size. (it appears) Seems like when the magnets are "too close" that they start to interact with their opposing magnet on the other side and this is likely a negative effect.

Anyway... notice how the flux changes with increased air gap:

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By doubling the air gap it should be possible to have LOWER PRECISION in the fabrication. That's a big issue for me because I don't have access to any fancy tools so everything I do an ordinary person could do in their own garage. The idea of this project is that once the knowledge of how to do it is understood (from a practical standpoint) then others could imitate the techniques until someone actually starts to manufacture them as a real product.

The radial design would gain all it's efficiency by having a very small air gap and that's hard to do with crude tools.

Another factor is that with the axial design the coils would get 100% utilization instead of the 25% that the radial design would achieve. While that only means the loss of a few percent in overall efficiency it's still a needless loss.

Axial is just better all the way around. :cool:
 

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In my opinion a recompense style geardown with a suitable motor is the only way to fly.

Yeah, well for me that's "Old School" thinking. I already have one bike that uses geardowns and gearing and have put 7,250 miles on it.

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The whole idea of this project is to create something that isn't already out there... the whole idea is to think of something NEW and not just rehash the old stuff.
 
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Double Block... Double Gap

I love this simulation program because you can try out all sorts of ideas and see how the magnetic flux lines are effected.

If you switch from a Single Block Halbach array (the standard type) to a Double Block Halbach array where you double up the magnets for each rotation in polarity the effect is to double the field where the magnets are doubled. Normally... normally... this produces a strong cogging effect. However, if you use the Double Block Halbach on each side of an axial design and then also double the air gap you now stabilize the field again.

That's awesome. :D

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What does this mean?

It means that you can use BOTH a wider air gap AND also double up on the magnets so that you space things out more. Both of these things produce a situation where more slop in the design is acceptable. For the crude tools that a homebuilder is going to have this higher tolerance for imprecision means it's easier to build.

Using 1/4" magnets you could have an air gap as large as 3/4" of an inch...
 

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Fabrication Flash

It just dawned on me how to fabricate this...

Start with a simple disc which either could have the aluminum as it's base or not. (it's not all that important either way) Now once you get the disc covered with fiberglass and smoothed on both sides (by using the drill tool attachment that has the 6 bolts) you have something to attach the magnets to.

You now have the "base".

Now you go about epoxying the magnets on either side of the fiberglass and once they are all in place you seal everything with a thick layer of fiberglass and reinforcing cloth.

You now have a solid fiberglass disc with embedded magnets, but no air gap.

Here's the tricky part... with the thick and solid disc which holds the magnets embedded inside you spin the disc with the drill while carving out the air gap using the grinder. The air gap is literally ground out of the solid fiberglass and so it will end up with a perfectly (good enough) made shape. The magnets are deeply embedded in the disc already so they do not need any additional work. Fiberglass does not produce much heat when ground, so the magnets will not be overheated in the process. (much less than metals like steel)

This makes things easier because the air gap is done LAST rather than trying to build the two sides as separate pieces and then having to put them together. Trying to get any kind of precision doing it that way is beyond the home builders abilities. This also provides the separation between the magnets during assemble so that they don't mess each other up.

Hmmmmmm.... now all I need is to buy more magnets and for spring to come... :sick:
 
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...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....
One thing you might want to consider is the possibility of using a heat pipe for cooling.

A heat pipe is a simple device - start with a tube. Add a wick down the center, toss in enough alcohol to dampen the wick material, then seal up the tubing.

When you add heat anywhere along the tube, some of the liquid alcohol changes state from liquid to gas, and as such it carries the heat of evaporation with it. Since the gas molecules require much greater spacing than the liquid, it is under pressure, and it flows to equalize the pressure. Where the temperature is cool enough, the gas will condense back to a liquid, (reducing the pressure, and maintaining the gas flow,) and the latent heat originally required to evaporate the gas is released on condensation, where it can radiate/conduct away. The liquid alcohol now seeps back through the wick, using capillary action, to where the wick is drier, closing the loop.

Typically, the 'cool' end of such a heat pipe would be terminated inside a finned heat sink.

A well designed heat pipe acts like a heat conductor with an extremely high coefficient of heat conduction - about 500 times that of copper...
 
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One thing you might want to consider is the possibility of using a heat pipe for cooling.

That was one of the big advantages of "Going Radial" (not to be confused with "Going Rogue") because I could do a better job cooling the stator. Now I'm starting to gravitate to the idea of using an axial design and that's going to mean that the space I have to play with is really cramped.

Everything is a tradeoff... the axial design has better efficiency, but it might be possible to use a radial design and some serious cooling techniques and get more peak power. (with a loss in efficiency in the process)

It's just exciting for me to be learning of all these potential options... sometimes it just seems like people repeat the same ideas over and over and never really think outside the box. The Halbach is really "out there" as an idea, so it's a fun process.

I appreciate your suggestion. :cool:
 
That was one of the big advantages of "Going Radial" (not to be confused with "Going Rogue") because I could do a better job cooling the stator. Now I'm starting to gravitate to the idea of using an axial design and that's going to mean that the space I have to play with is really cramped.

Everything is a tradeoff... the axial design has better efficiency, but it might be possible to use a radial design and some serious cooling techniques and get more peak power. (with a loss in efficiency in the process)

It's just exciting for me to be learning of all these potential options... sometimes it just seems like people repeat the same ideas over and over and never really think outside the box. The Halbach is really "out there" as an idea, so it's a fun process.

I appreciate your suggestion. :cool:

You mean Going Rouge don't you.
 
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