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Backyard Death Ray

Use an old satellite dish to make the ultimate weapon
  (+16, -4)(+16, -4)
(+16, -4)
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Take an old 12 ft. analog satellite dish, cover it with aluminum foil and mount a mirror and a concave lens near the focal point. The mirror and lens can be turned different ways. Purpose of the mirror is to direct the light and the concave lens forms a beam that can be focused. Used eyeglasses can be used for the concave lens.

Use this to burn things at a great distance. Satellites, cars, trees, whatever you feel like. Make sure to adjust the glasses so the light is focused.

jmvw, Jul 06 2006

Looks like it really is that simple http://xenotechresearch.com/solvari1.htm
[fridge duck, Jul 06 2006]

Mythbusters http://dsc.discover...ode/episode_02.html
Episodes 46 and 16 [tatmkr, Jul 07 2006]

Electroplating guide and supplies http://www.lacywest.com/t_pguide.htm
Not that tricky as far as I remember. [wagster, Jul 07 2006]

Mythbusters Death Ray http://web.mit.edu/...usters.html#details
[jmvw, Jul 07 2006]

Solar Concentrator http://jacksontechs.../solarconcentrator/
A solar concentrator that I made from a DirectTV dish. I'm burning a hole in a leaf. Behold this terrible destrruction! [jmvw, Sep 12 2006, last modified Sep 13 2006]

Diagram http://jacksontechs.../destructiveray.png
Shows arrangement of optical elements [jmvw, Sep 14 2006]

telescope for burning http://www.youtube....watch?v=vUcWqgbn7fA
[fishboner, Apr 25 2009]

[link]






       Great idea - but I can't help thinking if it was that simple we'll all be making them.....
monojohnny, Jul 06 2006
  

       Only one way to find out.... *packs for expedition to Ace Hardware*
shapu, Jul 06 2006
  

       instead of tinfoil, i'd suggest highly reflective paint. that way it won't tear or crinkle, and it would be easier to make uniform.   

       the lense needs to be placed in a bracket that has an easy way to adjust its focal length. it would be more precise than holding the lense up, and would allow for quick adjustments.
tcarson, Jul 06 2006
  

       tracking the sun would be the hard part.
xaviergisz, Jul 06 2006
  

       That link is nifty. I really like the use of pressurized air to change the curvature of the disc. On Mythbusters when they made a giant sun reflector he did it with a bunch of flat mirrors mounted on a disc. The mylar approach would be much better.
bungston, Jul 07 2006
  

       Concave? Shouldn't it be convex?
ldischler, Jul 07 2006
  

       Either convex (bulging) or concave (hollow) lenses would do. You could use either place a concave lens between the mirror and it's focal point (where the "rays" are converging), or a convex lens beyond its focal point (where the "rays" are diverging).   

       I was thinking of using the concave lens from glasses for nearsightedness, but you could go to the supermarket and buy convex reading glasses.   

       Either way, you probably want very clean glasses made out of actual glass and not polycarbonate, because of heat.
jmvw, Jul 07 2006
  

       //Use this to burn things at a great distance.//
How would you direct this at anything but the sun?
ldischler, Jul 07 2006
  

       The mirror takes care of that.
jmvw, Jul 07 2006
  

       Well somebody find out, I don't have time to make one.   

       I think it would be a blast to find out. Even just melting reading glasses would be fun. How much light does glass absorb? In my area the power with a 12' dish would be roughly 1900 Watts, 2.5 times the power of the fresnel lens at xenotechresearch.com that can boil steel. I'm looking on Craigslist for old TVRO dishes.
jmvw, Jul 07 2006
  

       What about this idea is original enough to warrant bunnage? They're obviously baked, and in fact there was an episode of Mythbusters devoted to making these. Maybe I'm just missing one little thing that is new in this idea.
Laimak, Jul 07 2006
  

       Not sure.. mirrors and eyeglasses? Recycled components? what matters, concept or technology?
jmvw, Jul 07 2006
  

       It's cool so it gets bunned. Widely -known-to-exist is sufficient grounds for an [m-f-d] but baked by the odd nutcase here and there is not.   

       The dish in the link has a catenery curve, so it won't focus that well. The dish described in the idea is parabolic, but covered in crinkly foil so also won't focus well. [tcarson]'s idea of using reflective paint won't work because the paint will scatter light like crickly foil will. You might try painting it with metallic paint which could then become the cathode for plating it with silver (link). A quick polish and you'll hopefully have a half decent large parabolic mirror.
wagster, Jul 07 2006
  

       very baked- they made this on the television show Mythbusters on the discovery channel...the purpose was to dispel the myth that ancient greece had a "death ray" using this concept of focusing light with mirrors.
tatmkr, Jul 07 2006
  

       They didn't use a satellite dish. To dispel the myth that it is the same as the Backyard Death Ray, their puny "death ray" uses 300 flat mirrors, so it only amplifies the power of sunlight 300 times. If the Backyard Death Ray can focus on an area of 1 square centimeter (which it might, with wagsters help), it will amplify the power of the sun 105200 times. It could cut their boat in two. And their mirrors took 10 minutes to focus, a problem that the Backyard Death Ray doesn't have.
jmvw, Jul 07 2006
  

       //The mirror takes care of that.//
Once you point at something, It becomes an off-axis parabolic, not so easy to make work, even if you fiddle with the optical elements.
ldischler, Jul 07 2006
  

       So you'll get the best results with narrow angles to the sun. Burn things to the east in the morning and things to the west in the afternoon. Will the coma be bad enough to stop the device from being effective at larger angles? We're not trying to project a pretty image of the sun. If the projection looks like a mushroom, that's fine, as long as it works.
jmvw, Jul 07 2006
  

       instead of coating it, why not strip the paint off the dish and polish the existing metal? it might not be as shiny as a silver coat, but you could skip adding conductive paint if you want to silver coat it at a later step.
tcarson, Jul 07 2006
  

       Old satellite dishes are around, supplanted by the new little ones. I think they are usually fiberglass, so not amenable to polishing. The mylar/vacuum pump approach to focus should work with a satellite dish, though I bet it will not remain airtight for long. Without that ability, though, your death ray will only be useful against boats at a certain given distance from the dish, and any Roman warships will figure out how to avoid those waters pretty fast.   

       The idea of fine tuning the focus by putting lenses is the way might work, but you would definitely want some way of turing the dish on and off while you fiddle with that. A window blind to pull across the center might serve.
bungston, Jul 07 2006
  

       I wonder if this could be made on the supercheap by stretching a sheet of mylar between two uprights - say 2 4x4s planted in the sand. You would then have a tall mirror. If the 4x4s were inclined slightly forward, this would produce a bright square on the sand: sunlight x2. If strings were mounted on the back (for example, tied to plastic squares hotglued onto the mylar) one could carefully tug on these, maybe hooking them to tent pegs at the proper distances behind your upright mirror. Each tug would deform the bright square in the front. One large square in the center could be enough, when pulled to produce a convexity adequate to focus. One could gradually tug the square of sunlight x2 into a bright point. If it worked, the next step would be to mount your tall mirror on something where the angle of inclination could be easily changed.
bungston, Jul 07 2006
  

       //The dish in the link has a catenery curve// So they claim, without any explanation. I'd have thought a uniform membrane experiencing a pressure difference would approximate a spherical, rather than catenary, curve, for small deviations from flatness. Still, the same argument holds - it will produce an image of the sun convoluted with a caustic curve.   

       I envision an arrangement of lenses and mirror much like that on an overhead projector - the lenses produce a nearly parallel beam, which is then directed by rotating the assembly and adjusting the mirror's angle.   

       The other arrangement would be a hyperbolic mirror that produces a near-parallel beam back towards the mirror. And this wouldn't be the only hyperbole. Ultimate weapon indeed! Make one that focusses the light from supernovae at other star systems, and it might start to be worthy of the name.   

       I know of an unused *enormous* (I didn't measure it, but I think it's about 5m diameter) parabolic dish not 100km from where I live. I'm now even more tempted to make an offer for it.
spidermother, Jul 07 2006
  

       //They didn't use a satellite dish.//   

       Actually they did. There were quite a few different models featured on the episode. Personally, I thought the most effective was a parabola of perfect mirror, but it didn't have variable focus and was only effective at a specific distance.
Laimak, Jul 07 2006
  

       Perhaps the flat mirror idea isn't so bad. Computerize the thing. Make the mirrors as small as your target spot, say 1 cm^2. Mount each mirror on top of a small biaxial actuator and build a big grid of these things. The grid wouldn't have to be flat, you could, say, cover a large wooden horse with it. Software controls the aim of each mirror. Add a triangulation gizmo that uses visible laser for autofocus (or visible doppler laser) and a sight for aiming as well as a joystick (a digital one, not the old jittery analog PC kind that uses 555 timers). LCD shutters over the mirrors could turn the thing on and off, or you could have the software "unfocus" for off state. A biaxial actuators could look like two squares separated by a ball joint and four coil springs and with copper spools to tilt them one direction or another. After you burn something, you could have the system do a disco ball effect in victory.   

       But it would hardly be a backyard project.
jmvw, Jul 07 2006
  

       /backyard project/ Make it into a backyard project. Coat the satellite dish with plasticine clay or roofing tar. Hand place each mirror. Position the dish so that it is "aimed" at an object suitably far away. You can place the mirrors by watching the round dot it produces on the target, and manipulating it so it is on target. The target spot will get brigter and brighter as more mirrors are added.   

       No focus capability, though.
bungston, Jul 07 2006
  

       A deadly mosaic? Fun, but too much effort.
jmvw, Jul 07 2006
  

       Today we played with a free DirectTV dish that I covered with aluminum foil.   

       The dish is about two feet/75cm in diameter and the antenna is off center. I believe the dish is shaped to have an off center focal point, because it seems that turning the dish so that the sunlight is projected directly onto the antenna/lnb gives the best focus. I glued aluminum foil to the dish surface.   

       Unfortunately the light was not sharply focused. The focal "point" had a diameter of about three inch; somewhat larger then the lnb.   

       I noticed the plastic on the lnb was melting, so we covered that part too with aluminum foil.   

       We held some dry leaves in the focal point and they smoked immediately and burned after a little while. Kind of like a magnifying glass, but over a much larger area.   

       Not exactly a Death Ray.. We'll keep trying.
jmvw, Sep 12 2006
  

       Strong work [jmvw]! I am sure you could produce Death with your ray given enough time. If you can cook some palatable hotdogs that will serve as proof of principle.   

       Please post photos!
bungston, Sep 12 2006
  

       Photo's and video for my friend bungston: see link. I'm still dazzled from working with this thing.
jmvw, Sep 12 2006
  

       Excellent work there jmvw. Nice video of a halfbaker's hand too!

Also, I like bungston's idea of using it as a solar powered barbeque.
DrBob, Sep 12 2006
  

       Sterling work!
fridge duck, Sep 12 2006
  

       Thank you!
jmvw, Sep 14 2006
  

       I just picked up my second free satellite dish, much larger then the last. I've been thinking a little bit about parabolic reflectors. Other cool things could be made with these things, such as an extreme directional microphone or loudspeaker.   

       I figured out how they make these dishes that have off-center focal point: they're just cutouts from a parabolic surface that isn't centered.   

       But more importantly, I realized that this Backyard Death Ray idea can work just as I originally thought it would. I was thrown off by [ldischler]'s comment about the off-axis parabolic and also by what I read about telescopes on Wikipedia.   

       This thing is not a telescope. It does not need to project a pretty image of the sun. It merely needs to produce a parallel light beam that can be aimed.   

       A parabolic mirror focuses the light and then a lens (or concave mirror) produces a parallel narrow beam that is aimed directly at the sun (in the case of a concave mirror directly away from the sun). A mirror placed in this beam can aim the "ray" anywhere we want it (limited by the shadow of the dish).   

       I added a small and clumsy illustration that might help. See link called diagram.   

       It seems to me that if the light rays exiting the lens are parallel, then they will still be parallel after being reflected by a mirror. Perhaps this kind of setup would work even in a telescope.
jmvw, Sep 14 2006
  

       My recent experiment with aluminum foil shows that [wagster] was correct about poor focus. I wonder if these dishes are good enough to focus well even with a smooth reflective coating.
jmvw, Sep 14 2006
  

       WHY did everyone stop talking about the focusing lens? why why why? That was the genius of this thing.   

       There are precious few examples of using light to burn at a distance on the internet. They either use hundreds of mirrors, or other crazy stuff we can't afford. This was a really good halfbake!!! I can find no reason why we can't at least burn things like paper and vinyl at a distance of 30 feet or so.   

       You are onto something with the telescope I think.
fishboner, Apr 25 2009
  

       you could use an everything other than UV filter to make a completely nonvisible UV beam then write things on peoples cars with fadespaint magic ray
beanangel, Nov 29 2011
  

       + I was just thinking of what to do with our satellite dish, as we cancelled over a year ago, but the ugly dish is still there!! (I'd like to send them some *death ray*, as they keep sending us a bill!)
xandram, Jan 26 2017
  

       Hmmm ... with a few modifications, you could gimmick the dish to retransmit the incoming signal in antiphase, which would probably have a noticeable effect on reception quality in the immediate area.
8th of 7, Jan 26 2017
  

       Would it? Why? I mean, the antiphase retransmission wouldn't reach any neighbouring dishes (or would it?).
MaxwellBuchanan, Jan 26 2017
  
      
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