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Solar Scorcher
March 24, 2013 8:56 AM   Subscribe

Backyard Solar Death Ray. Melt pennies in seconds with a fresnel lens repurposed from an old large screen television. Grant Thompson has other fun and liability lawyer unapproved projects such as melting metal, making solid rocket fuel and making a compressed air rocket launcher. (via homunculus and his post on Monkeyfilter)
posted by caddis (30 comments total) 29 users marked this as a favorite

 
In the rocket launcher video he uses PVC, which shatters into a billion sharp shards when it fails, under half its rated pressure (280 PSI for 2-inch schedule 40) and holding it near his face while not wearing eye protection. Yes I realize it probably won't explode on any given day but if it ever does he'll wish he had sprung for ABS instead.
posted by localroger at 9:12 AM on March 24, 2013


Brb, going to achieve world domination.
posted by Sarcasm at 9:16 AM on March 24, 2013 [2 favorites]


I saw this the other day and was trying to think of any practical applications and came up with none. Now, I am not a practical guy by any means, but if I am going to go through the effort of making such a think I have to consider, "What am I going to do with it?" Unfortunately the answer here is nothing, so I'm not going to make one, but I do love the fact he's done it for me. Now I especially don't need one.
posted by cjorgensen at 9:28 AM on March 24, 2013 [1 favorite]


It would be neat to see if this could somehow be used for blacksmithing. I'm picturing a Dobson-type telescope stand.

...but the pointless destruction of food is sad, having kids standing around giant lenses worries me, letting kids eating eggs off a surface that you've been melting other shit on seems kinda dumb and pouring gas straight out of the full container onto a super hot surface is the sort of dumb shit that I only expect to see in drunk camping videos.
posted by bonobothegreat at 9:49 AM on March 24, 2013 [7 favorites]


I can't believe after melting coins he thought it was a good idea to pour gasoline on the concrete tile. STRAIGHT FROM THE CAN. This guy has a death wish.
posted by Roger Dodger at 10:09 AM on March 24, 2013 [3 favorites]


Anyone doing any kind of science on the internet or anywhere else where aspiring scientists might see it should be wearing safety gear, pretty much no matter how safe it is. What this guy's doing is cool and very irresponsible.
posted by Huck500 at 10:32 AM on March 24, 2013


This guy has a death wish.

This guy has the dumb.
posted by pracowity at 10:56 AM on March 24, 2013


His enthusiasm is infectious. And boom goes the dynamite.
posted by Sys Rq at 11:03 AM on March 24, 2013 [1 favorite]


Are there any modifications you could make to use a smaller lens for a solar oven? One that would get to 350-400F?
posted by 1066 at 11:04 AM on March 24, 2013


Hmm. A steam engine, using a tungsten-jacketed boiler (so that it won't melt under the focused light) could be made, while a simple Solar PV Tracker could be modified to not only control the solar panel that powers the actuator, but also keeps the lens pointed at the boiler.

With enough lenses in an array, one could make a quite powerful steam engine, capable of powering all sorts of things, like generators to store electricity in batteries, water pumps, bellows, mechanical reciprocating saws, you name it.

Looks like I'm going to be the one running Barter Town now.
posted by chambers at 11:09 AM on March 24, 2013 [6 favorites]


Sure, if you just move the oven closer to the lens, then you'll have a wider beam of light and thus less concentrated heat. The trouble is that you'd need to keep adjusting the lens to keep it perpendicular to the sun. You could motorize it and put a tracker on it.

But really, the amount of energy that you can capture from the sun is the constant per unit area, so you are better off just building an oven with large reflectors.
posted by ssg at 11:15 AM on March 24, 2013 [1 favorite]


Are there any modifications you could make to use a smaller lens for a solar oven?

Just use a smaller lens. Light gathering power increases as a square of the lens diameter. Fresnel lenses are not quite the same as a glass lens but should be in the same range.

Or use several small lenses. You can buy cheap 10x7in fresnel lenses, they're used as magnifying lenses for reading. Or cannibalize some overhead projectors. I'm not sure what the focal length is, it might be hard to make a solar oven without the lenses melting from being too close to the focal point.
posted by charlie don't surf at 11:18 AM on March 24, 2013 [1 favorite]


I used to play with a handheld 12 inch square Fresnel lens when I was in middle school. It would melt the zinc-copper-clad pennies minted after 1981 but copper pennies from before that point laughed at it. I would do most of the stuff this guy's rig does just on a smaller scale -- the temperature is determined by the light concentration, which was about the same, but the smaller collector meant less heat so it would only melt smaller objects.

And I didn't try pouring gasoline on the heated surface.
posted by localroger at 11:24 AM on March 24, 2013


I've toyed with the idea of using something like this -- I have a north-side sidewalk that never gets enough sun to melt snow and ice and I have to do a lot of ice melt/chop/scrape operations. (I can never get to projects like this because I have stuff like that to do!)

In my musings, ideally this would be an automated system, perhaps with a Raspberry Pi somehow rigged to help it track the sun and gradually move down the sidewalk. Of course, it couldn't be 2000° in that case; there are, uh, pedestrians.

So, yeah, I was wondering things like "when his kids are going after the eggs, where is the light focused?" and "how does he know when he picks it up and faces the camera that he isn't going to end up with a stripe of boiling flesh across his face?"
posted by dhartung at 11:57 AM on March 24, 2013


I have a one square foot Fresnel lens that will light asphalt on fire instantly and melt brown beer bottle glass to make beads. It pretty fun but after a few minutes of use you end up with spots in your vision.

The previous owner of my house left a 53" projection TV behind and last summer it failed. I took the lens out of it just like this guy and have even bought some wood to make a frame to hold the lens stiff. I haven't got around to actually doing anything with it all yet though.

I saw this guys videos recently and was pleased that he had actually made a frame like I was planning and that it worked well.
posted by Confess, Fletch at 12:01 PM on March 24, 2013


I wish he'd aimed it at a giant ant.
posted by JimInLoganSquare at 12:24 PM on March 24, 2013 [1 favorite]


Thanks ssg and charlie don't surf!
posted by 1066 at 12:29 PM on March 24, 2013


Shit's cool.

His presentation is fairly professional, so I'm surprised he isn't wearing proper safety gear.
posted by nrobertson at 12:32 PM on March 24, 2013


"Well we cheated death again and destroyed a lot of metal doing it."
posted by nrobertson at 12:39 PM on March 24, 2013


I saw this the other day and was trying to think of any practical applications and came up with none.

I've seen folks using these at craft fairs to make jewelry.
posted by hades at 12:56 PM on March 24, 2013 [1 favorite]


It pretty fun but after a few minutes of use you end up with spots in your vision.

It is like staring at the sun. It can cause permanent damage. They guy should be wearing dark sunglasses. There's a reason welders wear these things.

I do like the way he experimented with all these different formulas to get the best one for his rocket (except for the lack of safety part).
posted by eye of newt at 1:33 PM on March 24, 2013


"I wish he'd aimed it at a giant ant."

Or smaller people
posted by Pinback at 2:35 PM on March 24, 2013 [2 favorites]


Or use several small lenses. You can buy cheap 10x7in fresnel lenses, they're used as magnifying lenses for reading. Or cannibalize some overhead projectors. I'm not sure what the focal length is, it might be hard to make a solar oven without the lenses melting from being too close to the focal point.

I don't know exactly what they were using, but a friend of mine piloted the first high school chapter of Engineers Without Borders at a school in Atlanta, and their summer project was to use plastic reading magnifiers of about that size to make brick solar ovens in … Mozambique, maybe? Somewhere on that part of the continent. Worked very well, from what I understand, though it took several hours of sunlight to hit the desired temperature.
posted by solotoro at 2:58 PM on March 24, 2013


You don't need magnifiers to make a solar oven, just reflectors, an insulated box, and a piece of glass (not plastic) to admit the light. You can even use a styrofoam box for the enclosure; the interior will reach 400F and bake your cake without melting the foam. (You line it with aluminum foil.) Works surprisingly well.
posted by localroger at 3:01 PM on March 24, 2013


Light a Survival Fire With Urine!
posted by homunculus at 3:03 PM on March 24, 2013


You can get 8-3/8 X 11" fresnel lenses for the same price as the 10 X 7" ones, and with the same magnifying power, from American Science & Surplus.
posted by Kirth Gerson at 3:45 PM on March 24, 2013


Ah, homunculus, I've seen that video before. I remember the smarmy voice of the presenter was even more distasteful than the subject matter, though. Still, great finds generally. Also happily surprised Monkeyfilter is still around. It seems the same can't be said of linkfilter or politicalfilter though.
posted by JHarris at 4:10 PM on March 24, 2013


Yup, it's still there. And MonkeyFilter threads never close! You can keep adding links to old threads FOREVER.
posted by homunculus at 4:28 PM on March 24, 2013 [3 favorites]


I made his slime. It actually worked. My kids were stoked. I was stoked. After being let down by so much internet chemistry, this just worked.

I've had a PVC rocket launcher for years, and know other people who've had them for for years. They're one of Make's most popular kits. I've never heard of one having any problems. Extra paranoid? Wrap it in a few layers of duct tape.
posted by obiwanwasabi at 12:50 AM on March 25, 2013


I just yesterday helped facilitate a workshop where we made parabolic solar cookers similar to this out of scrap cardboard and reflective mylar. They will boil water. A friend uses his regularly for making soup.
posted by Cookiebastard at 9:06 AM on March 25, 2013


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