Going bigger

[(unknown)]

Just starting on a 18' dia prop.  I'm going a completely different route on costruction of the blades.  I built a kind of CNC machine using 3 old dot matrix printers a small dc motor and a dremel cutting bit.  Got a cheap USB intefacew and had my friend write me a program to use the machine.  I'm cutting the blades out of 2" styrofoam, the kind you can buy at a home improvement store.  The center hub will also be cut out of a few layers of styrofoam glued together.  The entire blade and hub assembly will be glued together, wrapped in mylar, and fiberglassed.  I have seen ultralight aircraft wings made this way and are very sturdy.  I am hoping that the ultra light prop will cut in at lower wind speeds.  My first altenator design was very close to the 17' wind gen on the front page.  I am now considering a 3 rotor, 2 stator design.  Stators and center rotor will be machined alluminum discs.

Would like some input from the seniors.  This will be Wind gen #3 for me.

Will post pics of my homebrew CNC soon...

[Flux]

The fibreglass rotor will be interesting but you will get no more output by reducing the weight.

I don't see how you can make stators from machined aluminium without producing an eddy current brake.

Flux

[hvirtane]

Hello,

your method to make blades sounds

really interesting.

You've got any

pictures about it?

Also I wanted to know more about

your home made CNC!

- Hannu

[1000101]

Pictures are coming soon, my digicam up 'n died.

The Homebrew CNC that I built is designed for extremely soft materials, mostely styrofoam.  It is basically the track and stepper motor systmes out of 3 dot matrix printers.  The vertical has about 12" range in approx 1/64" steps, the horizontal came from a 36" wide printer (a little harder to come by) also 1/64" steps.  The other horizontal that travels the length is mounted to a custom table (plywood & 2x4) is 10' long and 4' wide.  I had to make my own track (10' long dot matrix printers don't exist, darn the luck!) The track is a 10' peice of aluminum C-channel on both sides of the table with nylon slides, it moves using a cable & pully system to push and pull on both sides of the jig.  The cutting head is a 7.2 Volt motor from and old RC car with a slightly modified dremel cutting bit attached to the end.

You can use the parrallel port on a computer but you have to make a kind of demultiplexing circuit and write your software around it, this slows the operating speed of the machine ALLOT!  You can buy online or at allot of hobby shops that do robotics a USB to binary output for about $15 to $100, depending on howmany bits you need to output.  I am fortunate enough to have a master programmer friend who wrote up a nice CAD like program that does all the work.  I will try to make directions / schematics of the machine and put the software on the web eventually.

I think this machine is going to very usefull for many projects.  

[1000101]

Info on Step motors:
http://www.doc.ic.ac.uk/~ih/doc/stepper/control2/connect.html

Exapmle of USB interface http://www.devasys.com/usbi2cio.htm (There are do it yourself versions out there that I would not recommend for the electronically challenged, and it's not really worth the effort for a buck or two)

If you decide to use parallel port, learn or brush up on the old TTL, The easiest way is a handful of "AND" IC's, use 3 pins to act as the select for the 3 motors, 4 pins for the data, and the remaining pin for cutting motor on/off.  IF you know how to program the parallel port is port 888.  

[kitno455]

flux is right. at my old job they had a big horseshoe electromagnet. you could pass an aluminum plate thru it slowly no problem. but try to swing that plate with any speed, and you would swear there was some sort of solid inside the open space. the aluminum stopped dead.

do not use conductive materials to make stator.

allan

[Ungrounded Lightning Rod]

Since you have no feedback you have to be SURE the stepping motors never slip.  Compute your cutting paths accordingly, so they don't make the blade hang up rather than cutting.

[cr8zy1van]

I am also thinking of making fiberglass props, and have spent a lot of time
thinking about how I could manufacture them. I have a friend that builds RC
hobby planes (1/6th scale) and he thinks that it should be pretty easy once I
get the original carved. I would make a simple cast/mold and use closed cell
expandable foam (you can buy it cheap at taxidermy shops with the right
density) and then cover it with glass. I am however having trouble carving my
original, but once that is done would be able to mass produce more blades.


The foam I am planning on using can be found here:
http://www.vandykestaxidermy.com/product/01352499/

Keep in mind that the area to pay special attention to would be the base and at the
back of the prop.

[wgatenson04]

Sounds like what I am doing preaty closely, except not going with 3 disks.  I used that foam from the hardware store, and it melts when you fiberglass it.  It disolves if there is nothing between it and the resin, and it melts if there is plastic between the foam and the resin.  Need the higher density foam.  Very interested to see the CNC machine you built.  Also, are you building the blades with spar caps, or just using a mono-thickness design.  What kinds of cloths are you using? Have you worked up the lay-up schedule yet?  Very interested in your project.

[1000101]

The first time I ever tried to fiberglass styrofoam for a pedal boat I had the same problem of the foam melting.  Wrapping the foam in mylar (available though most home improvement stores for radiant barriers) and useing a heat gun to shrink it down a bit for a tighter fit works great.  You can also use alluminum foil, I would suggest using a WATER BASED contact cement on the foam and foil to keep it from sliding around.  Make sure it is water based, other contact cement will eat the foam too.

I have no schedual, I am working on too many other projects right now.

Having a few alignment issues with the CNC, switching the cable system out to a chain.  The rotory cutting head is "climbing" into the foam, working on some solutions for that too.

[solarone]

I'm the American distributor for Kestrel Windturbines from South Africa. So what, you may ask?

Kestrels all have multi-pole, axial flux, poly-phase alternators; that includes the 600,800, 1000 and 2500 Watt models, plus a hydro set we're working on. The 800 and up all have variable-pitch rotors for speed control and all have hollow fiberglass blades; the 2500 has an internal reenforcing "beam" (also hollow FG) built-in as a stiffener.

All of the Kestrels use totally non-conductive materials for their rotor discs (twin for the 2500) since aluminum is an excellent conductor, not suitable for use in an axial-flux alternator. This makes building the appropriate rotors somewhat tricky to fabricate considering the required close tolerances and high strength.

Building a foam/FG blade set might also be a little trickier than one might think, since all WT blades are subjected to endless fluctuations along their length, which will tend to (eventually) separate the skin from the core.

Forget the idea of using aluminum foil as an internal skin, unless you and all your neighbors can live with a huge amount of EMF and/or RF noise in your TVs and radios. Ugh!

Someone mentioned a triple disc; does that mean two stators as well? (How else could you do it!) What is your rated output on this machine?

[1000101]

Yes, Triple rotor - Dual stator.

Nice thought on EMF from foil - mostly cable and satalite in my nieghborhood.

I haven't got any specs on the genny yet, it's not built, I work too much.  

Also for the CNC, I ran across a homebrew machine I'm considering, a Hot Wire CNC foam cutter.  I'nm not sure if it would do well with a 10' long wire though.

http://www.8linx.com/cnc/cnc.htm

[ve7khz]

Hi Flynn,

Interesting thread.

Where are you in the process? PLease give us an update on this 18 footer. I am considering building one of the larger ones as well, minimum 14' and maybe the 17'.

Cheers

Paul