My Mini Prop for my Mini Mill

[xeroid]

It's been just over five years since I last posted on this board.  WOW! How things have changed and how the site has grown!  Congratulations to the Dans, and greetings to Charged, Old F, Ungrounded Lightning Rod, Rob D (if you're still out there), Tom W and to all you who have joined along the way.

I thought I would post some pictures of the little tiny prop that I have carved for my little model wind generator.  I live in the city, so there is not much A/E opportunity for me these days I'm afraid, so I am somewhat relegated to what I can fit in my back yard.

Thus, my mini-mill sits on an old camera tri-pod with the new 60cm 2 blade prop installed on it that I recently finished fiddling with over my vacation.  It's tricky to get time and $$$ for things like this with 2 little ones and a full time office job, but I hope some of you will enjoy the photo diary I'll be posting here to show the process as I went along.

I've always liked pictures, so let me try to post a few... Let's start with Step 1:  Drawing the guide lines, evenly spaced on the 2" X 4" that I started with...

Basically, I drew on the "stations" and used the spreadsheet downloadable from ScoraigWind (Hugh Piggott's site) to mark out the "width" dots.  Then I connected the dots with curves in order to get the rough wing shape.

Next, I used a jig-saw to cut out the rough shape...


Then I re-drew the guidelines onto the area that I had cut away, and took the measurements from the spreadsheet to draw the "drop" dots, and connected them with a curving line.


Next, I used a drawknife to rough out the drop on the front face of the blades.  If you don't have a draw knife, GET ONE.  They're fantastic to work with.  I got mine as a birthday gift from my Dad from Lee Valley Tools.


Okay, next, I used my stationary belt sander to smooth out the deep scoop near the root.  I got a little over ambitious (and lack skill - to say the least, as I've never really used the thing for much, being an "office dude") and it went a little deeper and a little less evenly than I would have liked, but hey, how else am I going to learn?


I then marked the "thickness" of the blade from the measurements from the spreadsheet, marked them out and carved out the back side of the blade.  I had to jump ahead a few pictures here as I can only put 10 in a post.  Suffice to say, I used the drawknife for the roughing out and the belt sander again for the smoothing and levelling of the blades.  I then drew the "Thickest Point" dots on the back faces of the blades by using 35% of the overall width at each station.  I connected those dots to get a line to show me the thickest part of the wing shape in the currently flat blades...


I then carved the triangular wing shape by carving down everything from the thickest point on the back of the blades to the leading edge of the face and from the trailing edge of the face to the thickest point for each of the two blades.  I then used my smaller stationary sander to sand off the triangular "thickest point" and round it to the wing shape.  It's tricky to see in this shot, but you get the sense of the wing shape.


Here you can see the final sanded blade...


And here it is on the model...


Last Pic.  Here you can see the 2 LED lights that I attached in reversing directions from one another.  When the electricity goes through 1 way, the RED LED lights up, and when the electricity goes the other way, the GREEN LED lights up.  It's a great visual way to explain Alternating Current to the kids, as long as you explain that LED's are like a one way valve for electricity.  It clearly shows how the polarity in the alternator is forever going back and forth, to create alternating current.


I still need to touch up the balance on the blade as it was a little off after I painted it.  Still, it spins up easily and it is faster than the former 3 blader I had on there (until I tipped it over when moving the tri-pod and BROKE one of the blades - ugh).  I have a small diode bridge in there to allow it to charge up to 4 "AA" batteries.

I got the bearings and shafts out of scrap printers that repair technicians gave to me.  (I work for Xerox, so as long as I can stay chummy with some repair guys, I should be able to get plenty of those!)

It has been a fun project.  Thanks for letting me share it with you folks.

Regards,

Xeroid.

[jlt]

That's a very nice little mill you have built. Do you have any more of the alternator ,also how many led's will it run.

[ghurd]

I would like more info about the alternator too.

Cool project.
G-

[xeroid]

Hi jlt and Ghurd.

The alternator is fairly simple.  It has 6 magnets.  They are the OLD item # 40 curved magnets that I got from the OtherPower.com site YEARS ago.  Sorry, they're not even available anymore.  I used to have 8 (which would form a complete circle, about 3 inches inner diameter), but 1 broke and then I couldn't get one of the polarity that I needed to replace it, so I was down to 6.  I spaced the magnets out a bit using a small piece of wooden dowel between them to get even spacing.  I had a piece of sheet metal that had come from some old powder coated metal shelving that was once for storing records files.  I used a strip of that around the outside of the 3/8" plywood disk and glued the magnets spaced by the dowels to that, after polishing off the powder coat on the side that was to take the glue.

The coil set is held by a 3/8" plywood frame.  I just notched out the spaces for the wires on the magnets and put my coils on there with hot glue.  I had glued the coils into solid little cubes using the cyanoacrylate glue and accelerator, also from Otherpower.com.  Great stuff that!

Anyways, it will only produce about 3 maybe  4 volts at top speed, so I expect that it will charge up my little "AA" batteries with relative safety.  I don't actually recall the exact amount of milliamps it puts out, but I left room on my little battery holder for 4 "AA" batteries, so I must have done enough math at the time to figure that it would produce enough to charge that number of batteries.

I am working on a slightly larger mill, with 12 magnetic poles 1 and 1/4" long and by 3/16" thick, by 9/16" wide, stacked 2 magnets high at each pole (so total of 24 magnets, but in 12 positions).  I am anticipating about 9v through an air coil, but I am hoping to put in some kind of of a laminate in there for more efficiency.  Stay tuned...

Regards,

Xeroid.

[DragonFly III]

I made an alt similar to yours but mine but i expected too much from it.  It would get 12-14v in a strong gust but ussually was around 6- 7v.  It was 6 mags.  The ones I used on the car alt conversion on the hydro section.  They are 5/16 thick, 1" on bottom 1 3/8" on top.  Oh they are wedge mags from a few old hard drives.  I didn't know any better then so it was a 6 coil wired in series.  I mounted them on a piece of plywood that I made a grove for a transformer laminate ring.  Even when it was producing 3-4v it would fry a LED with a 1k ohm resister.  Not sure of the exact power output.  I wish I would have seen your blades before.  I used a box fan blade that I modified.  the blades were really wide so i cut them thinner and used the cut sections to make them longer.

Man those are cool looking blades.

[xeroid]

Thanks Dragonfly III.  That reminds me, the stator (coil set) is wired in single phase.

For tips on 3 phase wiring (which will lower the voltage, while boosting the amperage of your alt - but you probably knew that) go to Edwin Lenz's site:
http://www.windstuffnow.com/main/3_phase_basics.htm and read the whole thing.  It will take you a few minutes, but I found it made it crystal clear.

Then, check out the idea he has for a switch that will switch your mill between 3 phase star and 3 phase delta wiring.

I suspect that if you just change the wiring configuration to 3 phase star, you may be able to drop the volts and up the amps to a decent "AA" battery charging mill.  If that doesn't do it, you can drop the volts and boost the amps more by going to 3 phase "wye" (aka Delta) wiring.

The switch I mentioned is detailed and diagrammed at the bottom of a project Edwin did at this link:
http://www.windstuffnow.com/main/alt_from_scratch.htm

With a little tinkering with the existing ends of the wires on your alt, you should be able to get it to charge up your batteries.

Thanks for the compliment on the look of the blades.  The carving wasn't perfectly accurate, but I am reasonably happy with the results.

Regards,

Xeroid.

[DragonFly III]

Well that mill has been dismantled and all parts salveged for other projects.  I have a larger alt now, (28 mags, 21 coils)  3 phase Star with 7 coils per phase.
I don't think I'll ever build a single phase machine because of the advantages of 3 phase.  I will certainly be checking into the star/ delta switch if I can ever get my mill into decent wind.