Dual rotor, changes for larger sizes?

[nothing to lose]

I loved the post on the new 22" dual rotor and other works.

They are getting BIG.

I think design changes might need to be made soon to acomadate the larger sizes as these are growing very fast.

For my 48" dual rotor machine am planing to use a 1/2" thick plate steel 48"dia and a ring 48" outer dia 42" inner dia. Mount mags to solid plate and to ring as a normal daul rotor would be done, but then use a spacer between solid front rotor and back ring and bolt the 3 pieces together using stainless bolts. This would cut weight and material dramatically while still providing a rigid outer dia. dual rotor with basically only one actaul solid rotor. There will be no reall pulling force against most of the solid rotor, only at the outer area where the ring is located. The only real force is a gyro effect when yawing and perhaps cutting sections out to provide a sort of spoked wheel will work well and further reduce weight. Unlike a regular daul rotor where there are 2 seperate rotors acting on thier own, the outer ring area is actually re-inforced with the addition of the spacer and back ring. I may actaully for this reason use a 1/4" or 3/8" plate for the front rotor and also add in a 1/4" thick ring for extra support if needed or if leaking flux through the thinner plate.

Such a build should make for a very light but strong daul rotor type machine.

 The only problem I actually see is a lack of airgap adjustment perhaps.

 Build spacer for stator thickness and best geuss any extra. If further adjustment is needed removing rear ring and adding shim rings would be about the only way. Actaully I will most likely mount the second ring to the front where such removel would not require any other disassembly of the unit.

Since standard sheets are 48" wide I think, then 48" is the pratical limit to size, though there are various ways perhaps to exeed that limit.

Although my 48" mill is a joke (maybe) I am serious about building a large daul rotor gennie as stated with a ring and spacer instead of 2 full disks. If such a methode works well, you have the ring for the large mill and you also have the center you just cut out. So thinking about a 22" here, ring of 22" outer dia. and 16" inner dia. you would have a 16" disk for a rotor from the center cutout section of the ring.

Since you guys are getting into such large sizes I thought I would pass on my plans here in case you like the idea too. The spacer section could be made of many different materials and various ways. My plan is to make a plywood ring, cut into exactly 4 equal sections for a patern, then cast 4 aluminum curved sections to make a  spacer ring whatever thickness I need. The size of the ring of course will vary with the mills size. For my 48" I would probably cast a ring of 42" inner dia. and outer would depend on the length of mags used, 2" long mags spacer would be maybe 45" outer dia.

 Just something I plan to try out and think will work well so I pass it along.

[Waterfront]

48''!!! Wow, that's quite a beast...

How many magnets would you put on a monster like that? hehe... You'd also need a gigantic prop, and the strongest of towers...

I think your idea might work well, although I think 48'' is starting to get a bit large for a homebrew project, hehe...

Let us know if you do try it, it would make for some very interesting postings!!

[kitno455]

there recently was an exercise bike gen made this way here on the board, it seemed safer since the outside was smooth (they put spacer at outside)

i wonder if you could use a really big aluminum hub that was centered axially between two rings instead, a bit like a split-rim heavy truck wheel.

i would build it a bit like a wagon wheel. central hub, independently balanced spokes, thru-bolt at outer end, with two rings....

allan

[windstuffnow]

  Ok let's see.... divided by... sqrt of... carry the one... count my fingers... a 48" steel disc 1/2" thick would weigh 256.35 lbs so a dual rotor version ( just the steel discs ) would be a total of 512.7 lbs.  I'm thinking My 3ft prop would have a hard time turning it, although once you got it up to 100 rpm it would be darn hard to stop!  ;o)

.

[monte350c]

Hi NTL,

Good idea.

You know, if you alternate your bolts that attach the outer ring to the main 48" disk with threaded holes you could have a dozen or so "jack screws".

Then if you need to shim out the front magnet ring, loosen but don't remove the main attach bolts, turn the jack screws in the required amount, install some shims, and re-tighten the main attach bolts.

This sounds like a pretty neat project.

I am currently working on a dual rotor steel core toroid type machine. The prototype is sitting on my workbench with a single 10 turn test coil in it. It's small (only 17" diameter) - I'm shooting for 2 KW. We'll see.

Once I finish up the windings, and test I'll post a few pics.

Good luck on your project!

Ted.

[Flux]

Let us know how the torus works out Ted. I have a small toroidal transformer core I intend to try if I ever get the time. It seems a good idea but good core material is expensive.

On the main subject I have also had similar thoughts on using one disc with a ring on the outside. The spacers could be steel but something lighter would be a good idea.

Even with 2 discs it would be a good idea to have support to take the load of the magnet pull. Could make the supports act as a fan as well. Not that I shall make anything that big.

Flux

[nothing to lose]

"a 48" steel disc 1/2" thick would weigh 256.35 lbs so a dual rotor version ( just the steel discs ) would be a total of 512.7 lbs.  I'm thinking My 3ft prop would have a hard time turning it"

Sorry Ed, I think it would weigh more like 350lbs maybe 400lbs, the second rotor would have no center becuse it's just an outer ring, but we have to add some for bolts and spacer also.

I figure the Lenz2 I build might turn it ok, 8' Dia 4'tall?

Just kidding.

Actually I have put alot of thought into some of these BIG ones. I found some OLD tractor wheels, spoked steel wheels, broken cast iron hubs. The outer rim was like a ring of channel iron probably around 6'dia.

I did not buy those then, no way to haul them, but it got me thinking on this really big stuff.

48" dia? Shucks they are almost half way there now at 22", what will be be seeing them build in June or July, 36" so this time next year (or sooner) they may hit that size.

[nothing to lose]

I have many thoughts on the design and I will be building it but not 48", much smaller.

There could be bennifits to putting the space ring on the outside, preventing water/ice from entering. And with just a ring the stator could be mounted differently, like directly to the axle instead of using mounting brackets. I have many different ways in mind to do this, including the way the stator is made.

[nothing to lose]

That's a good idea on the jack screws and shims. And small holes could also be drilled so that if shims are needed after installing them they could be bolted so no chance for them to slip back out latter.

[nothing to lose]

Ya, I probably would never actually make that big of one either. But I will build a smaller one this way, maybe a 16" and see how it works at that size. I can handle 16" in my lathe. If that works and when I figure a few more things out, I will build a larger one using the same design.

And as Ed said, over 250lbs for one 48" rotor, I could not work that very well myself alone, and I do not have anyone around me interested in such things or willing to help out. So I am limited to what I can do by myself and with the help I get from all the great folks here.

Merry Christmas and may the Winds be with you throughout the season.

[BigBreaker]

I would stagger stainless steel bolts around the outer rim to separate the rotor plate from the rotor ring.  The inside bolts would be 5 inches from the outside edges and the outside bolts would be one inch from the outside edge.  This provides a longer lever arm against the pulling force of the mags.  Alternatively you could use steel bar stock spokes as a more external braces and save weight.  You might even use two rings inside of a plate and a ring.  Spokes would not be very strong against the yaw forces though...  Is that the wagon wheel concept?

The precessional torques (the gyro forces) would be tremendous on a machine like this.  I would consider installing 45 degree angled braces from the outer edge of the rotor plate to the shaft bearing.  I would then fill the empty space between the braces with foam and make that whole area into a cone for aerodynamic efficiency - maybe cover in fiberglass too.  Balance everything before and after.  Bracing like that would allow you to make bigger cutouts in the rotor plate.

At some point gearing just starts to make too much sense...  faster spinning mags can be so much lighter.

[monte350c]

Hi,

I made a post back in the dark ages (well maybe not quite that long ago) on something similar:

http://www.fieldlines.com/story/2003/10/27/83959/494

I know it's not exactly the same, but if you could find a good center...

Like if you only needed 17 to 20" then perhaps an aluminum wheel from a car or truck, combine with a lathe, and a parting tool...

Ted.

[nothing to lose]

Actually I am watching for semi wheels, have not found any yet though.

If an aluminum wheel will steer a fully loaded semi down the road at 70MPH....

Well I think that would be safe enough in my book to stick in the woods on a tower, somewhat modified of course

But they seem to be rare, I have found lots of steel ones, but I am not looking for those!

[windstuffnow]

  When I go into town ( small as it may be to be considered a town )  I drive by a house with an 8ft spoked wheel leaning against the tree in his front yard... many times I've been tempted to stop and ask if it might be for sale.   All steel, don't know what it was for originally.   I'd bet it weighs about 700+ lbs.   A friend that keeps his plane in my back hanger has a punch machine outside the building which has a clutch driven flywheel on it of about 40 inches in diameter... that one most likely weighs in at around a ton.  I can lift around 1500 lbs with my loader but all it did was moan when I tried to help him move it... had to have a semi-truck tow vehicle come in to move it... I have no idea how he's planning on assembling the thing.   I believe if you get that up to around 50 rpm an put something in its way it will plow right on through.   I forget what size punch press it is ( tonnage ) but it would take a fair sized piece of metal to stop it.   I have a project for either of those flywheels... I may end up having some 4ft sheet sectons cut and assemble them on the machine, just need about 1000 lbs of metal spinning at 50 to 75 rpm.   One of those long term projects that keeps haunting me.

.

[dinges]

You're probably talking about my bike genny.

It has the bolts on the outside of the rotorplates, to mount them together.

It's basically an upscaled version of my tiny genny (10W/.8m turbine diameter). My system gives slightly bigger rotordiameters, but you get more room in the center where you need it most.

However, with my bike genny I was already running into scalability problems; the system works, but for anything larger I'd go to the standard Volvo-hub method (rotorplates connected in the center).

With my method, your rotordiameter increases because you need extra room (bigger diameter of the rotorplates than the statorplate. At larger sizes, these few extra cm's make for much extra weight and 'perceived' size, whereas at smaller diameters it's hardly noticeable.

I thought I said in the thread of the bike genny that for larger sizes the standard layout might work better. Just wanted to repeat the point here.

However, for the 'back' rotorplate (the one furthest from the prop), my method gives a big hole in the center, with the magnets mounted on a small 'rim'. This saves a bit of weight. Still, I think I'd go with the system of the Dans rather than mine.

You might try to 'skeletonize' your rotorplates, or drill holes to reduce weight & better cooling/ventilation to the stator? It would reduce strength only very little.

Looking forward to your updates,

Peter,

The Netherlands.

[hvirtane]

We are planning to use

a Mercedes car aluminum wheel

with a Mercedes car wheel hub.

The steel magnet rotors bolted

on that aluminum wheel

(, which has to be machined somewhat).

An advantage is that the main

things are machined ready

in the German car factory

to fit well together.

That aluminum wheel will

be somewhat lighter than

using two all steel disks.

The planned diameter of

the generator is 50 cm.

The plan is not completely

ready yet.

One problem in my mind

is to find out, how

big a prop and a generator

that Mercedes car wheel

axle can stand...

We are planning for

6 m - 7,5 m diameter.

So far the biggest used

is only 4,5 m.

- Hannu

[nothing to lose]

I don't remember off hand seeing anything quite like I am thinking. I'll look at your bike gennie, maybe it's similar.

[nothing to lose]

"One problem in my mind

is to find out, how

big a prop and a generator

that Mercedes car wheel

axle can stand..."

Don't forget the bearings too. I bet the wheel and axle will handle more than the bearing will. Is that Mercedes a big car?

My rule of thumb is sort of figure weight of car, divide by 4, add a whole lot more

Old heavy cars 4,000+ pounds, is over 1,000 pounds per wheel :O

My 67 olds was 4,400lbs without people or cargo!

The wheels not only have to carry the weight, but at 70-95 MPH they have more spinning forces trying to rip them apart also. Then  take a sharp turn at 60MPH and if the tires don't skid there is all that weight and other forces trying to break them in half sideways. Add to that POT HOLES they smash into at highway speeds.

Is it really posible to over load the axle, wheel, bearings ec.. with a low rpm heavy genny yawing in hard winds??? Would your tower support 1/2 a car?

I really don't know that answer so play it safe!

 And not all cars are built the same, some barely will go 60MPH and don't weigh much either, smaller less solid wheels etc.. so what your working with will change in what it can handle.

[hvirtane]

It is from a normal

(big) Mercedes Benz

as they made them in 90's.

Mercedes Benz parts are nowadays

cheap here, because those

cars are really common.

A new bearing set

costs only 15 euro.

One problem is that car

wheels are spinning fast

and the axles have got

easier life because of that.

With the wind rotor the

rotation speeds are slow and

the gyroscopic forces are

not that big. When the direction

of the wind changes, the rotor

turns rapidly.

An old thumb rule is that

the axle thickness should be

1/100 of the wind rotor diameter.

For a 5 m rotor a 5 cm axle.

- Hannu

[SmoggyTurnip]

Another problem that no one has metioned yet is the play in the bearings. If the bearing had .6 degree movement that would translate to .25" inch movement at the edge of a 48" dia disk which would cause your magnets to crash into the stator.

[hvirtane]

The bearing play is a real problem.

I've thought about it. But

at least with car wheel hubs it

shouldn't be a big issue. Normally

the bearings with car wheel hubs are

adjusted that way that you don't

really feel the play

by rocking the road wheel.

- Hannu