Author Topic: Making a parabolic mirror  (Read 9554 times)

Paul L

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Re: Making a parabolic mirror
« Reply #15 on: May 02, 2013, 06:20:54 AM »
Hey Samd,

    Using square aluminum tubing is a great idea - it should give you a nice clean edge without too much fuss.  You'll probably have to use some kind of filler for the joints around the corners though if you want a really nice finish.
    I'm not sure if duct tape is the best way to go - I would imagine that it'll be hard to get the kind of tension you'd want in exactly the right place to remove the wrinkles when you're using tape that wide.  The stuff I was using was roughly 3/4" wide and it was still hard at times to get out the smaller wrinkles.  But there's not harm in trying, and if it works, would be a lot faster than using the tape I did - it too me roughly an hour to finish my large mirror.  You're going to have to have patience when doing this, and expect a sore thumb the next day!  As far as the hair dryer is concerned, it didn't do a thing to remove wrinkles from my mylar.  I'm guessing that different types of mylar will react to heat differently, so you could give it a go anyways.  The heat gun is just a nice final clean-up for the super-small wrinkles and creases, but if you don't have a gun, stretch it out first and take a look at it.  You might find that it isn't necessary at all!  Good luck and let us know how it goes!           
   
« Last Edit: May 02, 2013, 06:24:27 AM by Paul L »


samd

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Re: Making a parabolic mirror
« Reply #16 on: May 02, 2013, 09:34:43 PM »
Our local hardware store sells these plastic corners - about a buck each. I could always 3d print some custom ones to fit my current aluminium bars that radiate outward from my 3d printed mechanism. They seal up nice with a bit of silicone.
http://www.rcr.com.au/metalmate/connect-it-ideas/

If the heat gun 'de-wrinkling' doesn't work I might have to fit a corflute backing and apply very slight vacuum.
I was also toying with making a magnetic mount in the center of the lightweight reflector, and adding a second rope - like a surfboard legrope. In really strong wind gusts the reflector could dislodge, and hopefully drop to the ground where windspeed is very low, instead of being carried off to a neighbours' yard.

I guess if I hit my target cost then having a few wrinkles mightn't decrease the watts per dollar too much...



WendellHerrera

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Re: Making a parabolic mirror
« Reply #17 on: January 29, 2014, 03:40:45 AM »
Yeah, I've heard of people doing that before too.

I recently just finished a project from this last semester which "evolved" a parabolic shape using a genetic algorithm. (There is a good example program of a genetic algorithm which finds the best car for the given terrain at this link http://boxcar2d.com.) Basically, it was about the most convoluted way of finding a parabola that would give the desired focal point as you could imagine, but I plan on using much of the code for more practical projects in the future. For example, there is one neat example of a solar green house someone built where the back of it is parabolic. This way much of the light that hits the back of the greenhouse is focused into a tank of water to store excess heat. Maybe a genetic algorithm could be used to optimize either the same or similar ideas.


Thanks for explaining parabolic mirror in right manner.. I was bit confused but the now I got the right information.

trevorb

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Re: Making a parabolic mirror
« Reply #18 on: February 02, 2014, 12:42:09 PM »
Paul L,
 Your mirror looks exceptional!  Regarding the catenary versus parabola shape for focusing, a rotating bath of fluid will define a parabola.  An acquaintance of mine had envisioned a manufacturing operation where he would cast large parabolic mirrors by spinning them as they cured.  He thought he would do this by using a truck rear axle half buried in the ground.  The exposed wheel would be used as the casting platform and a driveshaft would be driven by a motor until the casting had cured.  This was never tried, but seemed possible in theory.
http://en.wikipedia.org/wiki/Free_surface