17 foot wind turbine of 'OP'

[hvirtane]

I've been reading with

a really great interest

the story of the

'17 foot diameter 3kW wind turbine'

by 'Otherpower'.

It seems to be working

very well and

in my opinion these big

scale machines

need further development.

Maybe it is possible to scale up this

general design layout even bigger...

I don't see yet any size limit

for this great design

idea by Hugh Piggott.

---

Do you have now after some experience

more general comments about the design

as used for this big scale machine?

Any problems you had?

Now I'm thinking that we should make

a rough copy of that one.

---

I wanted to know

some more details

of the construction.

1) First about the main chassis.

a) What is the distance of the generator

axle from the center of the yaw bearing?

b) What is the distance of the tail

bearing tube from the generator

axle?

c) Are the generator axle and the

tail bearing tube on the same plane;

so that there is only that 18 deg

angle of the tail bearing tube

on the same plane as the generator

disks? (No other angle out

of that plane?)

2) About the tail.

The furling system with the machine

seems to be quite perfect.

So the details of the tail

are also important.

a) What is the weight

of the tail boom?

b) What is the weight of the tail?  

3) About the stator brackets.

a) Did you use stainless steel for

the stator brakets?

b) What is the thickness of

the stator brackets?

4) About the main bearing.

a) What is the thickness of the spindle?

b) The dimensions of the bearing(s)?

In Germany and in Finland the thumb

rule is that

the axle thickness should

be at minimum 1/100 of the

wind rotor diameter. So that

for 5 m wind rotor the axle

thickness should be at minimum

5 cm (= 0,05 m).

But that thumb rule is made

for normal axle steel, not

for special car or trailer

wheel axles.

---

This much at this time.

Further questions will

probably follow later.

- Hannu

[hvirtane]

About the magnets.

Are the magnets you have used

comparable to the magnets

'Windstuff Ed' is selling here?

'Very Large Neodymium Ring magnet sections'

www.windstuffnow.com/main/builders_corner.htm

So that with a set of 32 magnets

by Ed you could get the same power?

Or are the magnets, which

you have used still stronger?

- Hannu

[DanB]

Hi Hannu - most of the stuff is on those webpages I think, but Ill try to fill in some of the blanks.

"a) What is the distance of the generator

axle from the center of the yaw bearing?"

About 9" if I recall.

"b) What is the distance of the tail

bearing tube from the generator

axle?"

I never really checked that, and it's not terribly important.  But the tail bracket which holds the tail pivot is about 4" wide at the top, and it's angled at 18 deg.  To do it over, I would make the tail bracket such that the tail pivot was closer to the yaw bearing so that it was stronger.

"a) What is the weight

of the tail boom? "

Im afraid I wasnt that scientific when I designed that thing.  I made the tail boom from fairly heavy sched 80 1.25" pipe (because that was all I had on hand at the time).  If I recall, the whole tail boom with the bearing and the bracket for the wooden vane came in around 40 pounds.  To do it over, I'd build the tail boom from larger diameter thinner walled pipe, it'd be stronger that way.  As it is I think its fine though.

"b) What is the weight of the tail? "

Never weighed that.  Its roughly 15 square feet of 1/4" baltic birch plywood.  It's lightweight, and it furls quite early.

"3) About the stator brackets."

They are of 3/16" X 1" bar stock if I recall.  To do it over again I'd make them a bit stiffer somehow.  It works fine so far, but I do worry about them, you can move the stator by hand.  they should be more rigid.

"a) Did you use stainless steel for

the stator brakets?"

No - thats not necessary.  They are behind the magnet rotors and there's really no flux to speak of there.  We should use stainless studs and hardware to  mount the stator though.

"a) What is the thickness of the spindle?"

1.25", its made for a trailer.  I would use larger next time, this was what I had on hand.  Itll be fun to see how long the bearing lasts.  So far it's been fine... I believe its a bit on the light duty side though, it would be quite easy to make this stronger.

"b) The dimensions of the bearing(s)?"

To quote a famous US president...  "I dont recall".. ;-)

"In Germany and in Finland the thumb

rule is that

the axle thickness should

be at minimum 1/100 of the

wind rotor diameter. So that

for 5 m wind rotor the axle

thickness should be at minimum

5 cm (= 0,05 m). "

There would be no harm in that for sure...  although to me the loads even on this fairly small spindle/hub seem quite small when compared with the abuse they'd see on a loaded trailer.  On a trailer it would suffer much heavier loads and much higher rpm.  Imagin the forces on these bearings when hitting pot holes and going 'round corners and such.  to do it over again, I would definitely use larger stuff here and I suggested that on the web page, but I expect what I have here will hold together for a while.  It should be fun to see!

The big failure with this machine was the blades hitting the tower a few weeks after I raised it.  It needs the alternator tipped back a good 5 deg to be safe I think.  I would also use a larger wheel hub/spindle/bearing assembly.  I would use stronger stator brackets.  I would use larger diameter pipe with thinner walls for the tail boom.  I would probably go to 18" diameter steel rotors for the alternator - probably necessary if we increase the hub diameter, and that would also get us a touch more power so we could probably run a slightly larger blade set.  Larger rotors on the alternator would put a bit more space between the magnets which would be nice...

All that said though, except for blades hitting the tower back in Feb, (which was an easy fix) - it's been a fine machine so far for me.  I frequently see it hit over 3KW (at which point my meter is pegged) and its doing really nicely in low winds.  Time will tell though...

[DanB]

No Hannu - the magnets I used are much larger.  This machine has nearly 25 pounds of magnets in it overall, the magnets are 3" long, 1.5" wide, and 3/4" thick.  I didnt feel comfortable with a 1/2" thick stator this large in diameter, so I felt I needed a larger airgap which made thicker magnets seem like a good idea.

Im not sure of their exact size, but I expect Ed's magnets are perhaps 1.5" wide at the top, about 1" at the bottom, and about 3/16" thick.  Ed can correct me on this - but the bottom line is... the 17' machine requires a LOT of magnets.

When we consider that when we double blade diameter, we have 4X the power at half the rpm, then it makes sense to me that if we double blade diameter, we should expect to need about 8X the overall weight in magnet.  10' machines I build have about 5 - 6 pounds of magnetic material in them.  This one has about 25.  I expect the 24 magnets in Ed's 6' diameter kit wind turbine weigh in around 2 - 3 pounds (rough guess).  

[DanB]

Just some further thoughts on all this... kind of a fun topic that doesnt get discussed too much is the ratio between qty of magnet in a wind turbine vs blade diameter.

I figure the 10' machines I build have 24 cubic inches of magnet in them.

The 17' machine has about 108 cubic inches.

Hugh Piggott's 16' dia 'Nirvana' machine has 58 if I recall.

Hughs machine makes better use of its magnets I expect, the stator and airgap on his is thinner, and he used much larger rotors so that his doesnt suffer from the close crowding between the magnets that my 17' machine does.

The main reason I used 16" diameter rotors on my 17' machine was this...  16" diameter rotor is the largest I can go so that my small milling/drilling machine could work at the center of the disk.  As it turned out, I had all that work done in town with a CNC water jet cutter so I could've gone larger and probably squeezed a bit more power from these magnets.  I expect with all those large magnets I used, done right - one could probably build a 20' machine.

[hvirtane]

I'm really happy to hear that

you haven't had any other

problems with the machine so far,

besides blades hitting the mast.

Do you have any idea about

the total energy generated

in a month? What about the

wind speeds at that time?

---

"this fairly small spindle/hub

seems quite small when

compared with the abuse

they'd see on a loaded trailer.

On a trailer it would suffer

much heavier loads and

much higher rpm.

Imagine the forces

on these bearings

when hitting pot holes

and going 'round corners'

and such."

---

One German specialist, Prof Crome

is telling that slower the

wheel is rotating on the axle

with the same loads, the thicker

the axle should be. Now I cannot recall his

thumb rule for the rotation speeds, but

in principle I think that he is right.

The high speed means a big gyroscopic force,

which is resisting the rotating wheel

to bend the axle sideways?

But trailer spindles are probably

made of very good steel qualities.

---

Concerning the distance of the

axle from the yaw bearing your

construction seems to be quite near

Hugh's thumb rules. I checked

the dimensions of the 2,4 m

machine of Hugh, and there the distance is

said to be 12,5 cm. If you'll double

the diameter of the wind rotor, it

would be good to double

that distance, too?

---

I calculated roughly

dimensions of the

magnets, which Ed is selling.

they seem to be 1,7" wide

at the widest point. But probably

they are thin. If Ed is reading this

thread, could you, Ed please specify?

Your magnet set prices are quite good...

=

At least one question remains:

Did you lean the pivot for

the tail boom also at

an angle backwards (behind)

the yaw bearing? Or is that 18

degree the only angle with that pivot

compared to the yaw bearing tube?

- Hannu

[hvirtane]

I wrote earlier:

At least one question remains:

Did you lean the pivot for

the tail boom also at

an angle backwards (behind)

the yaw bearing? Or is that 18

degree the only angle with that pivot

compared to the yaw bearing tube?

I'm trying to clarify it with a picture

here below. This picture is showing

the angles how Hugh is suggesting to

make the angles.

In the picture in the side view

the angle is 20 degrees

and in the top view

the angle is 35 degrees.

Did you do it the same way

in the principle?

- Hannu

[hvirtane]

Dan wrote:

- the magnets I used

are much larger.  

This machine has nearly

25 pounds of magnets in it overall,

the magnets are 3" long,

1.5" wide, and 3/4" thick.  

I didn't feel comfortable

with a 1/2" thick stator

this large in diameter,

so I felt I needed a larger

airgap which made thicker

magnets seem like a good idea.

I'm not sure of their

exact size, but I

expect Ed's magnets

are perhaps 1.5" wide

at the top, about 1"

at the bottom, and

about 3/16" thick.  

Ed can correct me on this

- but the bottom line is...

the 17' machine requires

a LOT of magnets.

---

Hannu:

Now one thing is that

your stator is quite thick,

5/8" and so the airgap is large, too.

What about, if we would use Ed's

magnets and make the machine

12 V? Then we wouldn't need

so many turns with the coils

(maybe exactly 1/4?).

If we would use with Ed's magnets

exactly the same dimensions

for the disks but managed to reduce

the airgap into about the half

of that of yours, let's say

our stator would be only 3/8...

Do you think that

we could get almost

the same power?

So, if we could get about

the same power this way,

in my opinion this means that

sometimes with designing the

machine to be a 12 V machine,

we could actually achieve

a better power out of it?

- Hannu

[hvirtane]

One more question:

The magnets, which you Dan used,

are they available from

'Wondermagnet.com'?

If they are, how much

is the price for the

same set you have used?

- Hannu

[DanB]

Hi Hannu -

"If we would use with Ed's magnets

exactly the same dimensions

for the disks but managed to reduce

the airgap into about the half

of that of yours, let's say

our stator would be only 3/8..."

I think the stator would be too thin and too flexible considering it's size.  Even if it were not though... we'd fit much less copper in there, the magnets are still much smaller, especially in their longest dimension, and I expect we'd still have less flux through the coils.  Consider the 10' machines we build from magnets which are 1" X 2" X 1/2" - we use 12 per rotor.  Even those magnets are much larger than the wedges Ed sells, I expect for a 10' machine you'd want perhaps 16 of those wedges per rotor.  For a 17' machine you'd need lots more yet.  For wide airgaps we need thick magnets.

"Do you think that

we could get almost

the same power?"

No - not even close if we used 16 of those per rotor.  No matter what we do here, we need lots of magnet in the machine.  If we had larger steel rotors I think we could save a bit in magnet cost/weight.

"So, if we could get about

the same power this way,

in my opinion this means that

sometimes with designing the

machine to be a 12 V machine,

we could actually achieve

a better power out of it?"

The voltage of the machine is not really an issue - power out should be about the same.  But...  12 volts becomes unreasonable for machines this large.  I'd have had to wind the coils with incredibly thick wire and the rest of the wiring down stream (line down the tower etc...) would have to be massive.  The 17' machine would at times produce 300  amps as a 12V unit.  This was the main reason I changed my entire system to 48 Volts.

[DanB]

Yes, basicly its that very same arrangement.

[DanB]

Hi Hannu -

I never really got enough to resell, though I could.  As it is now they around $18 ea, perhaps slightly less.  I may have a load brought to me soon by boat which would save a great deal of shipping cost, then they could cost somewhat less though Im not sure how much yet.  

Perhaps a more economical design would be something along the lines of Hugh Piggott's 'Nirvana' alternator, which uses 56 of the 1" X 2" X 1/2" blocks (or something close to that).  We sell those for about $6.00 ea.  With big magnets it really boils down to their volume.  1" x 2" X 1/2" blocks have 1 cubic inch of material in them.  The ones I used for the 17' machine have about 3.3 cubic inches of material in them.  I expect Ed's wedge magnets have about .5 cubic inches of material in them.  The machine would cost less to build if we used larger rotors and made better use of the magnetic material in it but the tradeoff is in size/weight.  As it is, the machine comes close to 300 pounds overall.  I expect if we used 18" rotors on it the weight would go up a good bit when we consider the additional weight of rotors, stator brackets, stator etc..

[hvirtane]

Dan:

The voltage of the machine

is not really an issue

- power out should be

about the same.  

Hannu:

My idea was, that

we would get a thinner

stator, because we

needed less turns

for the coils.  

Dan:

But...  

12 volts becomes

unreasonable for

machines this large.  

I'd have had to wind

the coils with incredibly

thick wire and

the rest of the wiring

down stream (line down

the tower etc...)

would have to be massive.  

The 17' machine would

at times produce 300  

amps as a 12V unit.  

This was the main reason

I changed my entire system

to 48 Volts.

Hannu:

Now I understand.

You need to use then

so thick wire that the

coils are not at all

thinner and so the

stator also would

be as thick.

My idea was wrong.

- Hannu

[nothing to lose]

Danb,

I have been thinking of various designs and such, doing different things.

 When we get into large steel disks we get into heavy weights, but in reality aren't you using only the outer rim of the disk and the center is empty space? I have been wondering about a spoked type wheel to remove some of that weight and still keep it strong. I geuss in a way think wagon wheel

 Use heavy steel ring for the outer rim where the magnets mount, spokes to center hub.

Maybe make the spokes like short blades even for low winds.

Another thought is to use a steel rim on the back side bolted to the front rim, outer edge beyond the stator. Then mount the stator from the center instead of the outer edge. My thought here is that you remove all the wieght from the center of the back rotor. Bolting the front and rear rims together should hold them true and solid, nice and strong. Might use less resin for the stator also since it would not need to be much larger than the magnet/coil area itself, plus what ever extra for strenght.

 I think it would work for the large stuff as long as it does not twist, warp, flex, etc.. while yawing.

Off topic, but how are Arts blades working for you guys. I bought a set, still not flying them

 Got too busy with other stuff and never ordered a trailer hub, nothing local I could find to buy, farm stuff I found is to large a hub, not sure it was 4" pattern either, just 4 bolt.

 Haven't had time to run up to Springfield, heck I was supposed to pick up stuff at Grizzly store, I hope it is still waiting. Nothing major, couple missing part for my lathe/mill like drill chuck key. Should have had them ship it, but was planning to drive up that weekend anyway, never had time.

Anyway, are those 8' Art blades providing good power on that mill as expected, and how do you think they would work on a daul rotor now that you guys been flying them awhile?

How big a daul rotor you think they will power?

 Can you guys do a post on them, let us know how they are working and your opinions what all they may work well on. That would be nice, thanks.

 I started to mount them on my small genny, made a wood hub and everything. Then they seemed to weigh twice as much put together than all the parts seperate

Decided they were to heavy for that small of shaft and tower, so here they sit.

[hvirtane]

nothing to lose

When we get into large

steel disks we get

into heavy weights,

but in reality aren't

you using only the outer

rim of the disk and

the center is empty space?

I have been wondering

about a spoked type wheel

to remove some of that

weight and still keep

it strong. I geuss in

a way think wagon wheel

Use heavy steel ring for

the outer rim where

the magnets mount,

spokes to center hub.

Maybe make the spokes

like short blades

even for low winds.

Another thought is to

use a steel rim on

the back side bolted

to the front rim,

outer edge beyond

the stator. Then mount

the stator from the

center instead of

the outer edge.

My thought here is

that you remove all

the wieght from

the center of the

back rotor.

Bolting the front

and rear rims together

should hold them

true and solid,

nice and strong.

Might use less resin

for the stator also

since it would not

need to be much larger

than the magnet/coil

area itself, plus what

ever extra for strenght.

Hannu:

I've been thinking sometimes

exactly the same lines.

One of my friends (in India)

complained

that it is impossible to make

true and straight big disks

for magnets. But by making

them like spoked wheels

with rims I think that

you can make them as

big as you want.  

The next thought:

why not making the magnet

rim just on the tips

of the blades...

You would get a really

big magnet rim with

speed for the magnets...

The spokes of the rotor

would be the wind rotor blades...

But then the stator...

Maybe you would fix it

on the tower...

---

Also the idea to fix

the stator on the center

sounds good.

- Hannu  

 

[nothing to lose]

"The next thought:

why not making the magnet

rim just on the tips

of the blades...

You would get a really

big magnet rim with

speed for the magnets...

The spokes of the rotor

would be the wind rotor blades..."

Not sure but I think I have posted something similar idea, at least been thinking it if I never actually posted it. Like helicopter blades with those rims at the tips.

Man if I could get 2 sets of those

Bolt them together so that the blades are offset, if it was 3 blades a set then it would be a 6 blader, 4 blades would be an 8 blader. Maybe get lots of torque that way, then the mags that far out on that rim would have supper speed past coils even at a low rpm. Maybe 4 spokes or so running out from the center to hold the stator in place.

I bet those choper rotors are pretty well ballance to begin with, and bolting 2 together should make them solid so they don't flex.

[benjamindees]

Based on those figures, here's the volume of mags versus the swept area (including specs from a 14' on the otherpower.com page):

10. ft. prop = 0.306 cu. in./sq. ft.
    
14. ft. prop = 0.505 cu. in./sq. ft.
    
16. ft. prop = 0.289 cu. in./sq. ft.
    
17. ft. prop = 0.476 cu. in./sq. ft.