Cereal-box Benesh-like squared-off VAWT for the DIY-inept?

[DamonHD]

Hi,

I realise that one of the skills that I don't have (nor have the tools nor possibly the patience for) is making curved things.

So I'm trying a tiny prototype on the following lines, but I'm interested in pros and cons, since the air is dead still here again at the moment.

Basic idea:

Take one large strong flatish box, eg big cardboard breakfast cereal box.

Cut a vertical strip out of the face of the largest side of the box at one edge, say the left, maybe 1/3rd the width of the box.

Rotate the box 180* and do the same on the rear of the box (so the cut-out strips are diagonally opposite).

You then end up with something that looks like a squared-off Benesh/Savonius.

To ensure that this won't get stuck edge on to the wind, join an identically-hacked box on top of the first, but rotated 90*.

For a real working system, if the idea works, it might be possible to use sheet plastic or metal or even (say) marine ply, or hack the strips from an existing sturdy box.

Construction could hardly be simpler IMHO, and even I might be able to manage it.

Now, I assume that the non-aerodynamic square corners will hurt performance somewhat, but how much?

Is my design a goer?

Rgds

Damon

[DamonHD]

Picture here:

http://gallery.hd.org/_c/mechanoids/_more2007/_more10/turbine-wind-tiny-VAWT-Savonius-Benesh-squared
-off-prototype-made-from-cardboard-cereal-box-and-garden-stake-and-drawing-pin-thumbtack-2-DHD.jpg.h
tml

[ghurd]

Now that is a cool concept!  Thinking Inside the box?

Might try an anti-freeze bottle?

Curved ends. Sort of.

Could use the cut part to get closer to the proper proper profile.

And water-proof.

Looks fun.  I might try it with a stepper.

Certainly won't get VF's $100, but it beats raking leaves!

G-

[DamonHD]

OK, big flat plastic bottle with rounded corners is an excellent idea (and I can attach them by the lids probably)!

Any idea how the square corners will hurt me until I can find such a beast though?

Rgds

Damon

[gotwind2]

Damon.

You are quite mad

Personally I applaud it - You are your Fathers son indeed...

Do you enjoy cycling also?

Ben.

[ghurd]

"Any idea how the square corners will hurt..."

Nope.  I'm not that smart.

Modus operandi? I make about 25 and see what works best.

Cheap fun.  (hot glue and stepper motors)

When it actually WORKS, believe me, I am the one most surprised.

My bet is the square corners won't hurt much for your conditions.

The wind isn't stable, straight or consistent.  A PMA suited for that is crappy anyway.  Etc.

So why sweat a 50% difference in efficiency?  It works or it doesn't.

It's not like you were expecting to spend £10 to go off grid with a cereal box.

Like Ed says "Have Fun!"

[tecker]

 Hmmm you need to cut a 45 on the up wind aproach fom the center . "Power to the inept " here here .

[Norm]

Cut a Pringles can in half lengthwise and put

them in place of the square corners fasten in

place with tape....Duct tape of course!

    Have fun !

           ( :>) Norm.

[DamonHD]

I have a bike rotting in my shed that I haven't been on in years: meanwhile he had all his nicked, so does that make us equal?

Rgds

Damon

[DamonHD]

OK, £11 to go off-grid with the cereal box: you caught me out!

I'm not at home today, but I'm hoping that I might get a breeze to test it in at the weekend, and I think I will fasten the 90*-rotated box on to to prevent stall, though it might be a smaller box (the aim being to get it through stall, not make power).

Rgds

Damon

[DamonHD]

I'm too stupid to understand!

Can you draw me a sketch?

Rgds

Damon

[DamonHD]

Yes, that's definitely a possibility, though I think that if I was going to try to get more aerodynamic and indeed get lift I would need a much shallower profile IIRC from the last paper I read.

But yes, your idea is good, thanks!

Rgds

Damon

[tecker]

Gota start somewhere I said nothing about stupid or inept You did .Gamble a little on your good sense  .  I'll make one but I have to find something to put the cereal in I am inept at organizing  at which you probably excel .

[Norm]

Here's the cerial box or rather cracker box.....



cut tabs up to the curve and bend tabs and tape

curved part on.

and you get this.



a fair weather Benish VAWT.

 It works with a fan but doesn't self start...

couldn't try it in the wind cause as usual...

No Wind.

               ( :>) Norm.

[DamonHD]

Ah cool!

I think that may be harder to do with a more weather-proof plastic box that I am aiming to use, but I'll try with a smaller one.

I think the self-start issue is dealt with by putting another box at 90* on top to catch the wind from all directions, but again, I have to try that myself when there is a breeze to test with!

Thanks

Damon

[DamonHD]

Ah ha!  It turns!

We have very very light winds at the moment, barely enough to make even my most sensitive toy fans turn, and certainly neither of my 1W HAWTs...

But, lumberingly, the cardboard box VAWT is turning (and self-starts).  A bit more observation and then I may scale it up into weatherproof plastic.

Rgds

Damon

[Norm]

  Actually I just used a cereal box to show how

easy rounded corners on a cereal box can be ....

even easier with foamboard hotglue and ducttape.

  the cardboard on the foamboard isn't weatherproof

but some latex exterior paint will

make it so....

  Another idea I had is to make a squirrel cage

VAWT like what was recently posted...smaller

scale. Using foamboard for the top and bottom

blade supports and using plastic mini-blinds for

the blades ?

            ( :>) Norm.

[DamonHD]

Well, another idea that I had from looking at what was cheap in the local shops, was use a large-ish round plastic dustbin / garbage can, and cut suitable slots to make a squirrel cage.  Should be reasonably strong with the lid on, and completely weather-proof.

I'm not sure what the right cut profile would be, and I guess that it is then better to bend the cut flaps in rather than (for example) removing them entirely, but I'm sure I can adapt an existing design.

The effective swept area might be a few square feet, which might do for the ~10W I'm after in lowish winds.

Any comments on this new hare-brained idea?

Anyway, I want to give this box design a bit more of a workout first.  I've got a nice big (scanner) box that I might be able to temporarily mount on my gen for testing.

Rgds

Damon

[Norm]

I've made a Benesh type VAWT...it spins at the

proper rpm ...about 75 but when hooked up to the

stepper motor that it is supposed to drive and

the 2 led light that it is supposed to light

...the windswept area wasn't enough in a light

wind so I figure it would have to be about 6ft.

tall, rather than the 3ft. it is at present.

I'd stick with the box design that you have,

only much larger...use corrugated plastic if you

can get it.

  Getting too late for further comments tonight.

       ( :>) Norm

[DamonHD]

Corrugated plastic is definitely the sort of thing that I'm looking for!

Rgds

Damon

[Norm]

Some signmaking companies use corrugated plastic

for their signs...

Maybe someday corrugated plastic boxes will be in plentiful supply.

....in the meantime since it isn't readily

available I've been thinking of using foamboard

the curves are a little more difficult but I'm

going to try an experiment.

I'll take a piece of foamboard that I am planning

to curve and wet it in warm water and shape it

over a round form and let dry....it should work,

even if it comes unglued, can always reglue it.

If you can find foamboard without the cardboard

covering?  They have a paint for painting plastic.

 anyhow I'll let you know the results of my

foamboard experimenting.

  I've concluded that you are convinced that

there is a place for mini-VAWTs for lighting

just as with solar lights and charging nicads

and such?....me too ! They talk about windfarms

how about the concept of 'Windgardens' ?

         ( :>) Norm.

[DamonHD]

Well, I'm really hoping to provide a few tens of Wh per day to help power my existing off-grid office lighting and partially-off-grid Internet servers...

http://www.earth.org.uk/solar-PV-pilot-summer-2007.html

I'm not trying to power the freezer or the rest of the house, so yes, a small turbine of some sort should, I hope, be useful.

Rgds

Damon

[DamonHD]

Yes, "wind garden" is a nice concept.  I may borrow it!  B^>

Rgds

Damon

[Norm]

I took a piece of foamboard 8inch x  5inch....

soaked it in hot water for a few minutes, then

wrapped around a 2inch pipe wrapped string to

hold in place and dried with a hair dryer.

A success wrinkled a little on the inside curve,

 I believe this would really work.

         ( :>) Norm.

[DamonHD]

Can you put up a pic?

Rgds

Damon

[Norm]

sure....





I assure you it is quite rigid

I'll make a model of foamboard today....large

enough to drive the stepper motor that I mentioned awhile back.

              ( :>) Norm

[DamonHD]

Ah, cool.

Well, I have two tasks to get going:

1. The blades: I have a big cardboard box that will get me through testing.  I'll look at the foam board, if nothing else then to wrap round the outside of my final box to cover corners, for about Mk 3, or as the 90* slave on the top to prevent the box getting stuck edge-on into the wind!  A really good idea within my skill range, thanks!
   
2. Mounting the gen itself.  I'm still not quite sure how best to do it yet...
   
   

Rgds

Damon

[DamonHD]

OK, a little video.

It also has my plastic-bottle S-VAWT in the pic, along with a suitably decorative HAWT yard-art child's fan, which is one of the more sensitive devices that I can observe.  The box VAWT sometimes starts to turn before the 'HAWT'.

Anyway, a brief gust of wind and...

(click on the 'full' link)

http://gallery.hd.org/_c/mechanoids/_more2007/_more10/turbine-wind-tiny-VAWT-Savonius-Benesh-squared
-off-prototype-made-from-cardboard-cereal-box-and-garden-stake-and-drawing-pin-thumbtack-5-DHD.avi.h
tml

Rgds

Damon

[Norm]

Damon,

     I think maybe you'll like this one....

all from one piece of foamboard 27 x 20 inch.

The folds are made by cutting on the fold marks

thru the one layer of cardboard then the other

layer of cardboard folds at the cut, it all folds up just like a

big king size open ended cereal box, only one

joint to fasten with some tape.

  You don't really need a pure curve on the ends

...just a couple of flat sections forming an

almost curve.....what is a curve anyway? just a

bunch of infinite short lines joined together !

 



See what I mean? those 3 flats on the end, Just

cut the top layer of cardboard and about halfway

thru the foam...when you bend it, the foamboad

breaks and the bottom cardboad bends ...

 I was going to take a picture of the foamboard

before I folded it, but it went together so easy

that I forgot.

 These could be stacked one on top of the other,

modules, until it was large enough to suit.

Some clear caulking on the edges to seal against

water...some paint or contact vinyl and it's weather proof.

   ( :>) Norm

[DamonHD]

That's excellent, I shall definitely look to see what my local DIY store has in foamboard!

As you say, if I find the right sort of paint I should be able to keep it weatherproof.

The last question is, then, do you think it will be strong enough to deliver the torque to turn the generator for an extended period?  If not, I can find some way to re-inforce it.

BTW, are you still having problems with self-starting?

Rgds

Damon

[ghurd]

I made a square one a few days ago.  4 corners, 4 openings.  0.5 gallon milk jug. Turned easy, but never turned fast, like it was stalled.  Not good at all.

Made a 'normal' one from shampoo bottle. Looks pretty decent from the top. Considerably better than I expected. Except it was hung on a string and swivel, so when the wind blew harder it tipped over (up?), reducing the swept area, keeping the RPMs in check like it was furled.

Needs to be on a fixed axle.  Not enough wind to tell more than that.

Fun stuff!

G-

[DamonHD]

I suspect that the rotor profile needs to be fairly flat (with a fairly narrow sideways passage/vent) to have the right characteristics to catch the wind and not let it out too easily without absorbing most of its momentum.

Rgds

Damon

[Norm]

  You would probably want a small 2 inch square

of 1/4 inch plywood bolted and glued to the

bottom,Is this a mini-gen like from Ed Lenz's?

  I haven't had enough wind outside to test, to

see if it is self starting but I was planning on

stacking at least one module at 90 degrees on

top of this one, next problem for me would be to

find a small enough alternator that it could

drive.

  As soom as I finish this project, I really

must get back to my swing project which I'm

going to be entering in my diary in a couple

of weeks...

  Ever think of generating enough electricity

in a glider swing to run your reading light and

small Computer? it could be almost effortless.

  ( :>) Norm