Halbach Axial Flux Motor

[luka69]

Re Magnetic Levitation.
For those interested the following site explains the concept.
www.skytran.net/press/sciam02.htm

 

[luka69]

Flat Halbach arrays
(From Wikipedia)
The diagram shows the field from a strip of ferromagnetic material with alternating magnetization in the y direction (top left) and in the x direction (top right). Note that the field above the plane is in the same direction for both structures, but the field below the plane is in opposite directions. The effect of superimposing both of these structures is shown in the figure at the bottom:

 

[johnrobholmes]

Using a basic hubmotor stator, pole count, and wind would be an excellent start I think. Also, without the iron you wouldn't have to worry about the large inductance increase that happens with the higher pole and slot counts. Higher inductance can cause sensorless commutation problems.

 

[safe]

When you think of bicycle brakes which is the strongest?

Drum brakes or disc brakes?

Typically the disc is stronger because you can increase the rotor size without incurring a weight penalty.

However... from the practicality standpoint I think you are on to something. The hub (drum) style would keep the dust and metallic particles out and produce something more trouble free.

You will need to find specialized magnets that are oriented in the opposite direction to standard.

 

[johnrobholmes]

Rim brakes are strongest, they have the best leverage!

 

[safe]

Formula 1K and Formula 2K Discs

Let's imagine a future where people are racing ebikes at Go Kart tracks. (my dream)

You go out to race in the Formula 1K class and you have just one bike to race with. Now that race is over and you rush back to your pit area and take off the Formula 1K disc (with relatively weak magnets) and swap in your Formula 2K disc with stronger magnets. You swap battery packs. Now you swap out your Formula 1K approved controller chip (limited to 1K power) with the Formula 2K controller chip. (limited to 2K of power) At the starting line there is a quick inspection by the race organizers to make sure you are equipped properly and then the second race is run.

You have used the same bike in two racing classes... :helmet:

This same thinking applies to legal rules for the street... one disc and controller chip combination would be appropriate for each legal category.

 

[safe]

Rim brakes are strongest, they have the best leverage!

Protecting the rim from gathering metallic material would be hard if you installed a Halbach array into the rim. The hub (drum) style makes the most sense when you are concerned about riding in areas that might attract a lot of dirt and grim and other stuff. The disc seems good too if you give it a thin fiberglass or plastic cover to keep out the undersireables. The rim brake is a good idea in that you might even be able to mold it right into the rim, but how you keep it clean would be hard.

However...

If you switch the array so that it faced inwards then surrounded the rim and spokes with something that snugly fit underneath the area where the fork and wheel pass each other (where you normally mount the brakes) then it might be a good idea. Maybe two Halbach arrays on the two inner sides of the rim? The big problem I see is that weight starts to degrade performance when it's on the rim itself.

What if the "Rim is the Motor" ?

I would guess that it would take some very weak (small) magnets to make this work.

Maybe a material process could be invented that embedded small magnetic particles oriented in the correct direction while the process is being formed so that the rim does not add any weight. This is all beyond our capacities... so we might have to leave this to future inventors.

Any idiot can buy magnets and glue them together on a disc... in fact... I'll even prove it...

 

[AussieJester]

Now you swap out your Formula 1K approved controller chip (limited to 1K power) with the Formula 2K controller chip. (limited to 2K of power)

Which class can i be in Safe

Rim brakes are strongest, they have the best leverage!

disk brakes are more resistant too brake fade i think...Get some twinz up front John ChoppersUS for the dual disk front hubs too mate..

KiM

 

[safe]

Note that the field above the plane is in the same direction for both structures, but the field below the plane is in opposite directions.

But what is the real magic is in the magnetic flux lines. Normally the flux lines have to go through a big loop (through the iron cores) before they come back to the other pole. With the Halbach the loops are very small and very intense. There is NO LOSS due to the shape of the motor. This means that big discs are possible where they are not with conventional motors.

In the standard iron core motor you have magnetic flux lines that look like:

...but with the Halbach you can see how much more intense the fields become because the flux lines make smaller loops. The backing of the Halbach array has very little activity.

So the Halbach array does two important things for us. First it creates a field on one side that is twice as strong. Second it allows us to close the loops of the magnetic flux lines so that they are very small and do not need iron cores to try to "extend" the field strength. This second reason is WHY conventional motors tended to be smaller... because it means you used less iron with shorter distances.

The Halbach array frees us from the motor "shapes" we are used to... (discs become possible)

Bigger discs mean you can use smaller (less strong) magnets to achieve the same torque.

 

[safe]

Massive "Old School" Power

Check these out:

http://www.kjmagnetics.com/proddetail.asp?prod=AY0X030-C&cat=168

...a full set is about 2.5 lbs.

Imagine the conventional style motor you could build using 12 of these. They also have the other top-bottom magnetisms so a Halbach array can be done.

These can also be combined with our AY0X030-N and AY0X030-S to form a circular Halbach array.

With 12 slices that's:

12 / 2 (Halbach) = 6

Three Phase means 6 / 3 = 2

...so you end up with a standard Three Phase two pole motor with a speed of 3600 rpm at 60 Hz.

But your losses are going to be only from copper loss, so efficiency would be in the 95-97% range and depending on how you wire it you can drive these to whatever rpm you want.

For those that want "Old School" motors this could do it.

Insane levels of power because each magnet has a pull force of 74 lbs each.

The price sets you back $266 though.