[CNC Darren]

I have cut some of the pink insulation foam(just like the blue stuff) in to a simple delta wing shape for a R/C model. The stuff cuts like butter with a 2 flute carbide bit, I was cutting at 40 ipm. I have nevercut the white foam but have carved it before and that stuff isnt as strong and makes a HUGE mess. As for the fiber galss on the foam it works great and when cured is hard as rock. I do use a vacuum bag for doing glass work tho, that allows you use less resin(less weight) and gives a nic finnish. I have even seen a Hovercraft prop made out of foam and fiberglass for the main thrust prop that was more than strong enough for that application. As far as getting the foam out of the blade, in model airplanes its really more work(alot more) than any weightloss you will get. The thin section of foam just doest really weigh that much.

Darren

[Evodyne]

Darren,

Hi! It's encouraging to know that type of foam can be milled nicely. How was the surface finish? Any problems with melting or bit clogging? I'm wondering if the "white" stuff that we see used for packaging-the large cell, kinda crubly brittle stuff is different from the expanding stuff Terry is talking about. At any rate it's a mute point: the blue/pink is readily available. Terry: your approach would not really require cast foam, would it? If you were to cut slabs of the stuff we are alluding to so that they tightly fit into your wooden box (allowing the blade assembly to be turned over), wouldn't that work just as well? Just a thought. Hey Darren, thanks for the info-good to "hear" from you again!

Sincerely,

Lance

[CNC Darren]

The surface finish wasnt to bad however I was using a straight 1/4" flat end router bit not a ballend. There was some surface roughness as can be expected because of the flat end but it smothed off really nice with a little 120 git sand paper. With a ball end and a low stepover tho this would not have to be done and would probably be as smooth as wood cut the same way. I belive all the foam is EPS (expanded PolyStyrene) but the pink(Dow brand) and blue(owens corning) is extruded and the white is expanded to large blocks and then sliced to thickness. The blue and pink would be better for this application(i think) due to it seems to be stronger and tougher than the white, just my opinion.

Darren

[10bulls]

Ok. Here's my blade making idea...

Brilliant! I was afraid you were going to say cut out about 40 1" profiles and glue them together...your way is very cunning indeed.

Just my tupence...probably not necessary for the way you have described, but an idea just popped into my head for milling wood or foam that may have flappy ends/edges. I wonder if you could sit the already milled side in a tray of wet sand or something (almost like casting), so that it provides a bit of support. Probably a dumb idea and guaranteed to get sand in all your precision linear bits.
I've seen people use wax or low melt alloys to do similar, but these wouldn't work for foam.

Anyway, great stuff Terry. I for one am gonna give it a go as soon as I get a chance.

[MrBean]

The blue / pink foam should be ideal. I'm not sure if I can pick any up locally, but I do have a few cans of the expanding foam, so I was intending to use that. I might phone round some builders merchants and see If I can get some pink or blue foam. I think that would be easier to use.
My wooden box was only to make a block of foam in. I will stick the foam block down to the cutting table with D/S tape. This worked for my wooden blades. The cuting forces on foam will be much lower so tape will be fine.

Thin sections 2-3 mm, could be left accross the width of the thinner blade sections, at full height, on the first machined side. So that when it's flipped over it has support underneath. Then cut them off later.

I don't know when I'll get time to test this idea. One of you guys might beat me to it. In that case. Good luck. I really hope this works.

Regards Terry....

[10bulls]

... I do use a vacuum bag for doing glass work tho,...

I've not come accross vacuum bagging before. Do you know of any good online tutorials? (...at the home bodger end of the skills set )
A bit of googling turned up this link (good overview). www.fibreglast.com
Would something like a fridge pump cut it as a vacuum pump?

[Evodyne]

I've not come accross vacuum bagging before. Do you know of any good online tutorials? (...at the home bodger end of the skills set )
A bit of googling turned up this link (good overview). www.fibreglast.com
Would something like a fridge pump cut it as a vacuum pump?

I'm in the same boat. Bet if we asked in the "Foam Cutting" section we might snag some RC builder who bag their own foam blanks. I thought the idea of supporting the thin sections was actually a good one-but what to use? I'm not in favor of sand-could get ugly. I'm also curious as to how one would bag something if it were being laid into a female mold and were convex. Hmmm.

[CNC Darren]

a fridge compressor work pretty good for a cheap vacuum pump, http://www.berkut13.com/sucker.htm details one used for doing composite work for full size aircraft. I found this site on vac bagging http://www.pilotsguide.com/rc/vacbag.shtml it gives the general idea on how it works. www.joewoodworker.com also has some good vac bagging info.

Darren

[greybeard]

Terry - double sided tape might be a problem with the foam. The adhesive on the tape might soften the foam such that half way through milling it lets go.

[MrBean]

I've started on the blade CAD tutorial for Rhino. The first part is on the site in "The Blades" section. There's more to come but I've run out of time for now. Sorry.
I hope those of you that requested it will find it helpful.

http://www.homemade-wind-turbines.co.uk

Regards Terry.....

[Evodyne]

Terry,

That IS a lovely shade of pink! Nice job.

Regards,

Lance

[skippy]

Just in case some of you are looking for some tech info, here's my collection of vac bagging and composites articles. Some came from here at cnczone and some from other sources. This first one is an amazing website on its own.
http://www.corsair82.com/corsair/vacinfs/
http://www.fibreglast.com/documents/361.pdf
http://www.fibreglast.com/contentpag...enter-286.html
http://www.netcomposites.com/
http://www.webbikeworld.com/t2/carbo...arts/index.htm
http://visionaircraft.com/

skippy

[MrBean]

Thanks for the links Skippy. I'll look at those more closely when I have more time.

I updated the site again. This time I've made the stator. It's not the best, but I'm happy that it came out at all. Soon I'll be able to get the stator on the machine, and bench test it for power output. Hopefully it won't be as crap as the MK1 was.

http://www.homemade-wind-turbines.co.uk

Regards Terry.....

[MrBean]

I just received an email from a guy that makes propeller blades by hand. Although not designed for wind turbines, they really do look nice.
Take a look here:

http://www.nmine.com/handmade.htm

That must be one huge printer he's using.

[Evodyne]

Wow, you guys keep me busy! Skippy-nice links. Like Terry, I'm stretched for time now, but perhaps this weekend. Terry, your stator looks fine. What are the rough dimensions? And the prop link was eeenteresting. Hey, you can't argue with his end result! I wonder, in the case of laminated wood, what the increase in strengh is over a solid wood blank? I still need to get out to interview the owners of the two big turbines by me and see what they actually produce. Again, maybe this weekend. Too much going on on too many fronts to get any one thing done properly. Ugh! Well fellas, keep up the good work. An off topic but related question: any of you have an interest in solar as well as wind? A good deal of this foam fabrication stuff would directly translate to making parabolic dishes or troughs.

Lance

[skippy]

"A good deal of this foam fabrication stuff would directly translate to making parabolic dishes or troughs."
Lance, we're all ears as it sounds interesting. Excuse my ignorance but what's a parabolic dish and a trough in the context of solar energy?
Skippy

[MrBean]

Hi guys. The stator is 13" diameter if you exclude the mounting lugs.
It's 9/16 thick (14mm)

any of you have an interest in solar as well as wind? A good deal of this foam fabrication stuff would directly translate to making parabolic dishes or troughs.

Yes. I'm interested in solar, but mainly the PV type. I found some cells here in the UK for £0.90 / Watt. Not a bad price. You have to make your own panel from the cells tho'.

Excuse my ignorance but what's a parabolic dish and a trough in the context of solar energy?

I'm assuming they are for solar heating. A parabolic dish has a particular curve, to focus light/heat on to a single point, or for a trough, a single thin line. I think the reflector in a car headlight is parabolic (more or less).

Terry...

[Evodyne]

Terry-you ought to be real close now on the alternator, right? What's left?

There have been some developments in photovoltaics as far as efficiency. Stuff ought to be on the market in the near future. Regular amorphous silicone cells are 8%-10% efficient. The single crystal ones which used to be the best were about 12%-15% efficient. You should soon see 18%-20% or better efficiency cells on the market. Likely to be pricey though. There are high temp cells too where you use a fresnel lens to concentrate light onto the cell. Over 30% efficient. But you need sun tracking for that one. Terry-I helped build a 1500 Watt 120 VDC PV array some years back. Just like you said-had to solder leads onto the cells (a major pain in the ass), then from strings of cells with reverse polority protection diodes, then put the strips onto an insulated carbon fiber panel, and finally encapsulate the entire thing is a protective plastic. A lot of work-I think I'd rather buy one already made.

Skippy-with gas prices heading up I'm looking into several things to keep my costs down. Better insulation and windows is one, as is an add-on woodburner to assist the natural gas furnace. Eventually I'd like to replace the furnace with an geothermal heat pump (see here) too. The other avenue is to take advantage of net -metering and sell power back to the utility to lower my bill. Hence the interest in wind turbines. Solar too. Probably passive first-as it's cheap to implement. PV is expensive, but an option. The final approach would be a concentrating (thermal) system. Look at the attached picture, below. The outdoor furnaces heat water and pump it through a heat exchanger in the existing air ductwork. thus you have dual-heat system. But the same approach would work with a dish to heat a working fluid (oil-doesn't freeze) and route it through a heat exchanger. I've got a big, sunny (and windy) yard. Why not take advantage of it, right?

At any rate a parabola has the property of focusing parallel incoming light to a single point. Terry was right on the money: a dish focuses to a point, a trough to a line. That area gets hot-real hot. But they can be a pain to build due to the shape. But (and I'm thinking of the trough) you could cut shaped sections out of foam and glass them for strength. Then apply mirrors. Really no different than shaping a wing from foam and glassing it. The drawbacks of the thermal system are: they need to move to track the sun, they may be suceptible to winds, and you need a pump to move the working fluid. One type heats a Stirling engine which turns a generator-several kW output! Hey, I just though of it-but we are motion control experts too! Just what's needed. Hmmm. My dad's got an old satellite TV dish-a big 9 foot diameter puppy he's not using...

[MrBean]

The stator is on the machine all wired up (for testing only) with one magnet rotor. Seems to be performing OK. It fully lights a 10 Watt car bulb with almost no effort at all, and that's with just the one mag rotor. I was in the dark over how to wire the individual coils in each phase. I was unsure if they should be wired in alternating turn directions for each phase. CW>CCW>CW, or CW>CW>CW. Turns out it's all the same direction CW>CW>CW.
I still have to resin the magnets into the discs to keep them wether proof, and finalize the stator wiring. After that it should be OK for a test run with the basic set of blades.

Here's a really ugly picture of the test wiring. As you can see I left the coil ends long untill I'm happy with how to wire it up.

Oh yeh, and I done some more on the blade tutorial.


Terry.

[Evodyne]

Terry,

You seem to be dangerously close to having a go at it. You know what will happen...you'll get it all erected and the wind won't blow for a month. Ha! It's a shame your restricted by codes from building a biggy. I need to pop over to your site and see the new tutorial stuff. Thanks!

Lance