Rotor to column connection

[brandnewb]

Rather than highjacking @MBouwers thread I think it is better to just publicly explain my situation.

I am looking for a way to connect a 1.32m diameter disk perfectly level (perpendicular) to its central column.

I have found things like this

But I can't push the column through without machining skills as these are meant to serve as a foot rather than somewhere arbitrary along the column.

To give some context I have a few images I'd like to share.
I have ready and waiting 192 N45 60x10x5 neodymium magnets waiting to be installed  in a 1.32m diameter like this;


I am figuring out how many winds I need, and thus how thick my coil wires can become with a 1/48 segment of coils consisting as of yet of 6 x 300 winds (600 turns) @ 0.4mm enameled copper wire.

These coils will be installed in series as to end up with a 3 phase double coil test setup.

I will include an animated gif of the turbine spinning even though I have like a million things to change about it. Like replacing the column, making the blades and arms farrr lighter yet bigger and stuff like that.


Now to the question at hand.

What is the best way to attach rather large rotor to the central column. Especially when the column becomes of serious diameter.

BTW, I am very much open to constructive criticism and questions on why I am going this particular route.

[brandnewb]

Also I will ask one final time @MagentJuice.

You told me once that 96 of these magnets had a 1.2 KW potential or something to that effect.
I asked you in a PM what you meant and you describes more of a gut feeling as far as I was able to understand.

Would you please elaborate a bit more? Especially now that there are 192 of these magnets.

[brandnewb]

I will also add an image to motivate why I came up with a coil height of 38mm.
It was not arbitrarily chosen but measured with a tesla meter.

[Adriaan Kragten]

Rather than highjacking @MBouwers thread I think it is better to just publicly explain my situation.

I am looking for a way to connect a 1.32m diameter disk perfectly level (perpendicular) to its central column.

I have found things like this
(Attachment Link)
But I can't push the column through without machining skills as these are meant to serve as a foot rather than somewhere arbitrary along the column.

To give some context I have a few images I'd like to share.
I have ready and waiting 192 N45 60x10x5 neodymium magnets waiting to be installed  in a 1.32m diameter like this;
(Attachment Link)

I am figuring out how many winds I need, and thus how thick my coil wires can become with a 1/48 segment of coils consisting as of yet of 6 x 300 winds (600 turns) @ 0.4mm enameled copper wire.
(Attachment Link)
These coils will be installed in series as to end up with a 3 phase double coil test setup.

I will include an animated gif of the turbine spinning even though I have like a million things to change about it. Like replacing the column, making the blades and arms farrr lighter yet bigger and stuff like that.
(Attachment Link)

Now to the question at hand.

What is the best way to attach rather large rotor to the central column. Especially when the column becomes of serious diameter.

BTW, I am very much open to constructive criticism and questions on why I am going this particular route.

The wind turbine in your video is a pure drag machine. A pure drag machine makes use of the worst methode to extract energy from the wind. The maximum power coefficient Cp is only about 0.05 compared to 0.45 for a well designed HAWT. This is proven in my public report KD 416 which can be copied for free from my website: www.kdwindturbines.nl. Another disadvantage is that the optimum design tip speed ratio is very low and about 0.15 (see figure 2 KD 416) which means, that for a large rotor diameter, you get a very low rotational speed, even at moderate wind speeds. So you need a big, very expensive generator if it is direct drive. To generate a certain amount of energy, you need an amount of material which is very much larger than the amount of material needed for a well designed HAWT which generates the same power at the same wind speed. So the development of drag machines is a waste of time and money.

[brandnewb]

Yes my Mentor. Thank you Adriaan for your comment.

I am well aware of this pure drag style system. And the subpar performance. But in the end of the day this is what I think I need. As for me this seems the safest option I have because I am looking to keep the rotation speed low.

I do not want to have a game of lawn darts around my house.

I am not looking for optimum efficiency. I will repeat myself again. BIG turbine, some "worthwhile" output.

Even though I just lack the ability to wade through your technical publications I am still very much thankful you publish them.

If I ever grow confident enough to go back to a lift type system them I already think I know how to auto start them.

But Andriaan, can you please, or anyone else for that matter, advise on the question at hand?

[brandnewb]

Also Adriaan?

If you are not impressed by my coils then I am not sure if I ever can offer something new to the table of this forum.

What is your opinion?

maximum respect.

[MattM]

Most people on that style will brace the top by running a beam over it.  You may want a cross-brace.  While solid beams are generally very sturdy, your diameter is at the point you might want three poles and run guy wires from the poles to a top mounting that floats above your central column / device.

[Adriaan Kragten]

Also Adriaan?

If you are not impressed by my coils then I am not sure if I ever can offer something new to the table of this forum.

What is your opinion?

maximum respect.

It is difficult for me to give comment on the photo of your coils because the optimum shape of the coils depends on the orientation of the coils with respect to the magnets. In chapter 9 of my public report KD 341, I have given the optimum coil shape for a 1-layer, 8-pole winding of an axial flux PM-generator. In the top picture of figure 5, you see that six coils are used for an 8-pole armature. So there are two coils for each phase. A coil has two legs. Look at the coils U1 and U2. The coil geometry is chosen such that if the left leg of a coil is opposite to the heart of a north pole, the right leg of a coil is opposite to the heart of a south pole. The voltage generated in the left leg will then be in phase to the voltage generated in the right leg and the total voltage will then be maximal. It can be proven that there is a phase angle of 120° in between the voltages generated in the coils U, V and W and so the given winding is a 3-phase winding. If the generator has more than 8 poles, the number of coils has to be increased by the same factor. So if you have for instance 24 poles, you need totally 18 coils.

So figure 5 gives the coil figuration for a 1-layer winding of an 8-pole generator. The advantage of a 1-layer winding is that all six coils are laying in one plane and that there are no crossing coils heads. The disadvantage of a 1-layer winding is that only half of the possible positions for the coil legs are used. It is possible to add six more coils in a second layer. The six coils of the second layer must be rotated 90° with respect to the six coils of the first layer for an 8-pole generator. But now all coils heads of the first layer are crossing the coil heads of the second layer. At the crossing points, the coil bundle becomes thicker than the thickness of one layer but this should be no problem if the crossing points are laying outside the path of the magnets. So for a 2-layers, 3-phase winding of an 8-pole generator there are totally 12 coils and so four coils per phase.

A way to solve the problem of crossing coil heads is to pile the coils like tiles. It looks like you have done this in your photo of a part of your winding. This is also sometimes done for windings of big 3-phase asynchronous motors. The disadvantage is that it is no longer possible to first lay all coils of one phase. So all coils of the three phases have to be laid simultaniously but for a big winding, this can be done. So your winding might be okay but this is only the case if the pitch in between the left and the right left leg of a coil is the same as the pitch in between the heart of a north pole and the heart of a south pole and if the sequence of adjacent coils is U, V, W.

[Adriaan Kragten]

I have looked at your winding again and now I think that it is wrong if it is a 3-phase winding. Assume that the grooves are numbered 1, 2, 3, 4, 5, 6, 7, 9, 10 and so one. The pitch in between grooves 1 and 4 is equal to the pitch in between the heart of a north pole and the heart of a south pole. The coils of the phase U, V and W are using the following grooves:
Coil U1, groove 1 and 4
Coil V1, groove 3 and 6
Coil W1, groove 5 and 8
Coil U2, groove 7 and 10
Coil V2, groove 9 and 12
Coil W2, groove 11 and 14
and so on

So all odd groove numbers contain the high left leg of a coil and all even groove numbers contain the low right leg of a coil. In your photo, adjacent grooves make use of the high left leg of a coil and this is incorrect. I also expect that you are using one groove for a high left leg and for a low right leg which is also incorrect. One groove should contain only the leg of one coil. Once all coils are laid, the high left legs of a coil are pushed down in the groove as much as possible and all grooves must be closed by a closing strip. So then you still get crossing coil heads but the crossing points are lying outside the area swept by the magnets.

Next assume that you have a 24-pole generator. This means that you need a stator with 3 * 24 = 72 grooves. 36 coils can be laid in 72 grooves and so 12 coils are of phase U, 12 coils are of phase V and 12 coils are of phase W. A problem with coil W12 is that the right leg of coil W12 must be shifted under the left leg of coil U1. So the left leg of coil U1 must be lifted out of groove 1 to mount the right leg of coil W12 in groove 2.

[brandnewb]

Yes Adriaan,

My coils as like you describe in where one magnet pair is over one leg of a coil and the other magnet pair is over the other leg of the coil. It's all rather carefully measured out if I am not making a huge blunder somewhere.

Also the coil wire ends are now sticking out at the inner of the test piece but they will be wound one more to stick out of the outer part.

[Adriaan Kragten]

Yes Adriaan,

My coils as like you describe in where one magnet pair is over one leg of a coil and the other magnet pair is over the other leg of the coil. It's all rather carefully measured out if I am not making a huge blunder somewhere.

Also the coil wire ends are now sticking out at the inner of the test piece but they will be wound one more to stick out of the outer part.

(Attachment Link)

Your stator has a different construction as the one which I assumed in my previous post. I now see that you have grooves at both sides of the stator. It might be possible to use such a stator but you must be very alert about which coils are connected in series and about the direction of the current in each coil. The direction of the voltage at a certain postition is the same for the upper and the lower groove. For a 3-phase winding, there must be a phase angle of 120° in between the phases. You get this phase angle if there is a distance of two grooves in between the left legs of phase U and V and of two grooves in between the left legs of phase V and W. But what I see in your photo is that there is a distance of only one groove in between the left leg of different phases and this means that the phase angle is only 60°. A positive phase angle of 60° can be changed into a negative phase angle of 120° if the direction of the current in one coil is changed. But if coils of different phases are connected to the 3-phase rectifier in the wrong way, the resulting DC-voltage can be much too low. It is not possible for me to judge only from this photo if you have made the correct winding because I can't see how the coils are connected to each other and how the coils are connected to the rectifier.

There is another point. Assume that the upper and the lower groove at a certain position have the same groove number. So coil U1 uses lower groove 1 and upper groove 4. Coil U2 uses lower groove 4 and upper groove 7. If these two coils are connected in series, it must be done such that the direction of the current in both coils is different! If the direction of the current would be the same, the voltage generated in coil U1 would be completely neutralised by the voltage generated in coil U2.

Rectification of a 3-phase current is explained in report KD 340. The voltage fluctuation of the three phase is shown in figure 3 of this report and in this figure it can be seen that the phase angle is 120°. A phase angle of 120° corresponds to the angle of rotation of the armature in between two north poles.

[brandnewb]

yes sir, I have gotten the coil details rather figured out already but thank you for notifying me none the less.

I am mostly concerned in this thread with how to connect a rotor to the column

But the coils, assuming they will work, are cool yes? I for one am impressed. No intimidated even by them. hahah

[Adriaan Kragten]

yes sir, I have gotten the coil details rather figured out already but thank you for notifying me none the less.

I am mostly concerned in this thread with how to connect a rotor to the column

But the coils, assuming they will work, are cool yes? I for one am impressed. No intimidated even by them. hahah

For an axial flux generator it is important that the distance in between both armature disks is constant and that the stator disk with coils is just in the middle of both armature disks. A slight bending of the shaft will make that the armature disks are no longer in parallel and so the air gap changes. This effect is especially important if the armature disks are very large. So I think that it is not allowed to use a stiff coupling in between the generator shaft and the shaft of the wind turbine especially if a VAWT has no support at the top. Bending of the generator shaft is prevented if both the rotor shaft and the generator shaft have its own bearings and if an elastic coupling is used in between both shafts. But such a construction is rather expensive.

[MattM]

Maybe he can use a splined shaft connection, like borrowing the strut off of an automobile.  This would allow for play in the rotor while keeping the part hooked to the generator in the same spot.

[brandnewb]

interesting idea this splined shaft

[Adriaan Kragten]

The stator construction with a synthetic disk with grooves at the upper and the lower side has some important disadvantages. I assume that the stator disk is a ring which is connected to the shaft by spokes and that the lower end of the shaft is hollow to guide the phase wires coming from the winding. So the shaft of the wind turbine must be connected to the rotating housing of the generator and not to the stationary shaft.

The coils of an axial flux PM-generator are normally wound outside the generator and all coils are connected to the stator disk from one side or cast in epoxy as a stator disk. But if the stator disk has grooves at the upper and at the lower side, the coils must be wound directly at the stator. This is a lot of work as for every turn, the total wire length of one coil must be pushed through the central hole in the disk. I would never do it this way. It seems much easier to make the grooves only at one side of the disk as then a complete coil can be mounted from one side and no central hole is required. So I believe that the coil configuration which I have given in my previous post is a better solution.

[joestue]

regardless how the coils are wound, the goal is to maximize the effective cross sectional area of copper between the magnets (assuming an air core).

a 3 d printed jig to hold a 2 layer coil, followed by pressing and cast epoxy may be worth the effort.

2 layer coils should be at least 1.5 times as effective as a single layer coil.