special motors, patents, fuel consumption reductionFlat brushless motor for velomobile

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Teach
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Flat brushless motor for velomobile

Unread Messageby Teach » 05/09/20, 11:38

As part of a velomobile project, I am working on the design of a flat brushless motor, with axial flux (magnetic field parallel to the axis of rotation) in the style of this example. Incorporating a flat motor into a bicycle wheel is much easier to imagine and a flat motor has more torque at lower revs, as a bicycle does.
The stator is central and carries the windings, which facilitates the fixing and the exit of the wires in the case of a wheel (windings, Hall sensors).
The (double) rotor carries the permanent magnets and is integral with the rim.
There is a strong interest in using a arrangement by Halbach for permanent magnets, insofar as this configuration eliminates the need for a ferrous support to "loop" the field lines behind the magnets: these are fixed on a composite plate for example, hence the gain weight...
I'm not good (euphemism!) At magnetism, my lessons are (very) far, but I know how to model, so if anyone can give me some clues based on the first sketches to know what power we can - at first glance - expect such a thing, I'm a taker ^^
Some 3D outputs:
the stator (before inclusion of the windings in the resin ...:
stator.png

statorDetail.png

one of the rotors, with the poles of the magnets in red / gray:
rotor.png

rotorDetail.png
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izentrop
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Re: Flat brushless motor for velomobile

Unread Messageby izentrop » 05/09/20, 14:53

Hello,
Not easy to find trapezoidal magnets. The reels must also follow this shape. The magnetic circuit does not seem complete either. Air gap too large for a correct performance it seems to me?

The most optimized and widely used flat motor technique is this:
Image
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Teach
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Re: Flat brushless motor for velomobile

Unread Messageby Teach » 05/09/20, 17:29

Hello Izentrop,

your photo represents a flux motor radial 'classic', very complex to achieve, in any case too much for me!
On this engine, the arrangement is not of the Halbach type, hence the need for the steel ring around, and it is heavy!
I have seen some of this type, but there is then a small square magnet between each rectangle, and the effect should probably be less ...
I must be able to find if you want to see this ...

On my project, the magnets are not trapezoidal: they are in contact on the inside diameter but slightly apart at the outside diameter. It is certainly a stopgap, but it is within my reach at a bearable cost! Exist in 20x5x5 with direction of magnetization on 5mm and not 20 as conventionally, and it is the basis of the project. The magnets of each rotor face each other SN obviously.

What do you mean by 'the magnetic circuit does not seem complete'? The peculiarity of the Halbach arrangement is that it repels the field lines on one side (roughly speaking, this is the role of magnets whose orientation of polarity is parallel to the plane).
For the air gap, in my case, the magnets are +/- 1mm from the wires, the stator support is 2mm thick: this is again what seems to me to be within my reach in terms of realization ... we'll see if better is possible ^^

The winding is carried out by going up on one side / going down on the other with an offset corresponding to the distance between the poles: for example a red goes up opposite a pole magnet S (itself facing an N of the other side of the stator) to descend in front of an N pole, and if I am not mistaken (3-finger rule!) the force is always tangent in the same direction, hence the drive. In my case there is a loss in the internal and external diameters, but this type of engine has a very high efficiency, it should pass ... By the way, the efficiency is also very good in generator, which is interesting in electric propulsion! It is this type of engine that equips the 2 wheels of 'energetic' competition.

On the link provided as an example, the wires go up and down at an angle, which simplifies the winding, but the force generated is suddenly oblique and the wires pass at an angle on the field generated by the magnets, it is not great either more. In any case his engine runs honorably ;-)
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Re: Flat brushless motor for velomobile

Unread Messageby izentrop » 05/09/20, 18:17

Téach wrote:What do you mean by 'the magnetic circuit does not seem complete'?
to channel the magnetic flux with the least possible loss as in commercial motors.
My lessons are far away, a document that may be able to help you https://hal.archives-ouvertes.fr/hal-01 ... spanet.pdf

In the link cited, the guy does not seem to have been at the end of the project, so we do not know the power or the performance? ... that one either http://scolton.blogspot.com/search/label/LEAF
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circuitMagnetic.jpg
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"The details make perfection and perfection is not a detail" Leonardo da Vinci
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Re: Flat brushless motor for velomobile

Unread Messageby Teach » 05/09/20, 19:35

This motor is "classic" with x coils which create a magnetic field in their ferromagnetic core, the coils do not (or very little) undergo the inter-iron field. The drive is between the magnets (permanent at the periphery, electro on the stator) which attract / repel.

The principle that I would like to apply is different insofar as it is the current which passes through the wire, itself subjected to the field generated by the permanent magnets, which causes a force perpendicular to the current (and therefore to the wire) and to the field , force which here is +/- tangent to the mean radius. The wire being fixed, it is the field (in this case it is the permanent magnets) which moves ...
A very simple example here, without finishing on the placement of magnets!
I very humbly admit that I took a long time to understand how it works and what was the interest of Halbach in general, and applied here in particular!

And thank you for the link to the article, but by far I do not have the doctorate level ^^
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Re: Flat brushless motor for velomobile

Unread Messageby izentrop » 05/09/20, 22:39

Simpler wind turbine generator with axial flow and permanent magnets like that of the piggott https://heliciel.com/helice/eolienne%20 ... lienne.htm

Used as a motor here http://www.amazingdiyprojects.com/electric_motor.html. You have to buy a book to find out more.

I still have doubts about the powers announced :?:
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Re: Flat brushless motor for velomobile

Unread Messageby Teach » 06/09/20, 08:12

Even if it means making a flat engine and as light as possible, as much to ensure that in addition it has a good performance, even very good ...
These wind turbine generators cap, I fear, around 75% if they are well built (the wind is free, we can discuss the merits of the output ...), and the wheel motor of your first photo at 85% if it is good. I obviously do not expect the 95% or more in amateur construction, but it is this type of return that we can obtain, it is in any case what is announced.
I will undoubtedly appear stubborn, persevering in the flat motor with axial flux and permanent magnets in Halbach :D
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Re: Flat brushless motor for velomobile

Unread Messageby thibr » 06/09/20, 10:37

for performance Barnabé shared some findings : Mrgreen:

but the outputs of the piggott, with closure of the static magnetic flux and without any metal part other than the coils in the rotating magnetic field, must not be bad, even if the power density is not very good but it is not a pb for wind power application : Wink:
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Re: Flat brushless motor for velomobile

Unread Messageby izentrop » 06/09/20, 12:34

Hello,
You'll have to do as well as them if you want to compete in terms of performance. Square section wires, optimized magnets on both sides, grain oriented electric steel ....
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Re: Flat brushless motor for velomobile

Unread Messageby Teach » 06/09/20, 13:06

to Thibr:
Barnabé does not mention efficiency, just power produced ... it would take a torque sensor on the propeller shaft (before the generator) to be able to calculate something. The shape of the blades does not suggest a good wind power output. Which in no way detracts from the achievement or the didactic effort : Wink:

in Izentrop:
: Mrgreen: competing with them (> 97%!) is not the goal, but doing better than a basic bicycle motor (75 to 80% at best) to be able to integrate it into the wheel, yes, and all the more with a very torquey engine from low revs!
On the other hand I have no metal in my configuration, it is the interest of the Halbach, and the weight gains a serious blow!
Son of Litz, it's possible, I used a D0.6mm thread available, the square sections are unaffordable (and very difficult to work) for the average péquin that I am!
Optimized magnets, on the Magnax I don't know how they did it, but the arrangement of Halbach on either side could be classified under the category 'optimized': is this the case with them, I have nothing seen, the doc is very evasive!

For info, Bernard Cauquil, reference in solar bike which accumulates the daily kms (7000km in 25 days, respect!), explores the all-electric transmission, and it seems to me an extraordinary path, which becomes extremely interesting if the engine / generator outputs are improved: silence, flexibility, weight, ease of installation ...
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