Quick and dirty parabolic dish solar concentrator design!

I do not have one.       I was hoping YOU could help me make a quick choice!
  Basically I want to go to the store, buy an 8 by 4 corugated plastic sheet, cut it in petals, stick aluminum kitchen  foil to it (as few wrinkles as possible) and have as rigid a parabolic HALF dish as possible.   Then I mount it in my equatorial mount frame and test it.
http://www.youtube.com/watch?v=5OqG2LesnSo
  It gets a bit harder because the dish is not exactly a half. Some extends a bit past the center of the dish.
Here are some of the issues and choices.  Do you cut along the corrugations or across them?
Do you do petals radiating out from the center  or is it better to do the thing with cones? Like in the picture in the link
http://solarcookers.ning.com/photo/cone-size-of-the-4-cones-solar-1?context=latest
Cones might have a problem due to the corrugations not being in line with the shape that I make. so it might warp in strange ways.
Is there an alternative to the corrugated sign plastic sheet?
BUT they might work because I can guesstimate a not perfectly round dish more easily than with petals..
I think that something with a focus about 6 inches wide would be sufficient for me.
It has to be rigid and light as can be too.   What can I use as umbrella splines to make it keep its shape?
Thoughts and suggestions would be greatly appreciated. I might have a day off tomorrow so get those suggestions in quick as you can!
Thanks
Brian

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jerryjaksha6 years ago
I would suggest using a foil faced foam board like the isocyanurate building board insulation board . It will take a concave bend easily if one side is removed , is cheap, and already has a foil face. You can peel off the back paper layer to make the boards bend.

Jerry
gaiatechnician (author) 7 years ago
I think I will use cone segments to make the dish. Only problem is the outer cones are darn long. It would be 5 or 6 cones.
I have been looking for parabolic dish petal calculations on the net and got nowhere. With petals there would be much more cutting but it is easier to arrange them on a flat sheet to get best use from it.
Basically there is probably something where you design your dish, focal point, radius, height, etc and then it spits out the petal size and shapes for 6 petals or 12 petals, etc. Then you just make a template and away you go.
It might be a spreadsheet, in excel or open office or java or javascript
I am sure they are out there.
Just cannot find them.
Thanks
Brian
gaiatechnician (author)  gaiatechnician7 years ago
So, I did the cone thing and it looks great. I got greedy (or mean or cheap) and tried to use as much of the 4 by 8 material as possible.
I will put it in a frame on equatorial mount but any suggestions for tensioning it so that it holds the correct shape without a frame? Because something like this might be a good emergency parabolic dish for disasters. It has 1.5 to 1.6 sq meters of collector area. Which is huge!
Anyway, maybe string for keeping the correct distances in strategic places and plastic irrigation or electric pipes held in front or behind to keep the tension?
I duct taped it together for the moment. But I am thinking velcro for the long term would be ideal.
See the first picture for the amount of waste. Not a lot! And not many cuts either (see the second picture for that and the size. That is a 4 ft level.
I have to thank Magnar on solarcookers (ning) for introducing me to the cone method.
Thanks Brian
IMG_1729.JPGIMG_1735.JPG
Try this
http://graffiti.virgin.net/ljmayes.mal/var/parabola.htm
gaiatechnician (author)  steveastrouk7 years ago
Thanks for finding that.
I will go with the cone method for now, (fewer cuts) and I am 95% done with getting one to fit my frame AND use all the plastic in the 8 by 4 sheet.
I can try the petal method in the next one.
(I have to do a fairly specific parabola for my thing)
It would be very interesting to compare them. Cones are "supposed" to produce a surface bent in one direction. This should mean that when you apply aluminum kitchen foil, you get almost no wrinkles.
The petals are probably more susceptible to bending in 2 directions. But you only need one template and you can cut off lots.
I am using alu foil to mimic 3rd world DIY. They probably do not have reflective mylar. I think mylar would work well with either cone or petal. It does not wrinkle so easily.
Thank you
Brian
gaiatechnician (author) 7 years ago
I have been working on the cone idea and here is what I have so far. I bought a 8 by 4 piece of corrugated plastic and tried to design the cones to concentrate the light on a 6 inch target. The idea is to use as much of the plastic as possible. The following pictures have explanatory image notes in
https://www.instructables.com/id/Dual-Parabolic-Dishes-on-Equatorial-mount-and-the/  but they do not seem to have come through here.
And I am not writing them again!
Please check it out.
Input would be great.
Seems I lucked out because there does not seem to be much waste.
Brian

scan of dish2b1.jpgscan of dish3rightsideup.jpg
Why use corrugated plastic ? The thing will develop intrinsic stiffness as its bent to shape, and it looks like you have a substantial outer frame.

Steve
gaiatechnician (author)  steveastrouk7 years ago
It is all I can find in 8 ft by 4 ft sheets. Sheet aluminium might work but there is a problem with it. If you shine a laser on it the bounce is terrible. It has some sort of surface structure. Perhaps it would disappear if you buff it.
So I will go with alu foil over corrugated plastic.
Or maybe mylar if I buy another roll.
And you reckon you'll get a better mirror from foil on a piece of plastic ????