Get our free book (in Spanish or English) on rainwater now - To Catch the Rain.

Changes

Jump to navigation Jump to search

Papasan Chair Solar Cooker

880 bytes added, 18:11, 5 May 2008
===Reflector===
*To cut your reflector from a sheet of anodized aluminum, you will want to first measure the radius of the chair, from the center point to the rim. It is important that the measurement of the radius includes the 3-dimensionality of the curve of the chair. Use this measurement to make triangles with 2 of the sides the length of the radius plus one inch and the 3rd side around 8 inches long. Take care to draw an extra space [Image:PCSC - parabolic sheet.jpg|thumb| This shows a material-saving layout for cutting the sections. Note that the triangles don't terminate at the a point of the triangle , so that a 1/4" mounting bolt will fit through it.]  [mirror_measure.jpg] This shows a material-saving layout for cutting the sections. You may want to measure how many times the 3rd (8") side of the triangle will fit along the circumference of the chair to see how many facets to cut. Since people are going to be sitting on the chair, take care to round any sharp edges to a curve, and to sand any burrs.[Image:PCSC - shear resized.jpg|thumb| Students using a beverly shear to cut aluminum facets.]
*Once the pieces are cut, gently flex them to fir the curved shape of the chair frame. Aluminum will maintain this shape once bent. First practice bending one to see how breakable it is before bending the rest.
*Now is time to use the drill. Measure in about 1/2" in and down from the corner of both sides of the 8" length of each facet, and drill a 1/8" hole. This is where the string goes to mount the facet.
*Stack all of the facets on top of one another and make a mark on the end piece you made for the bolt. Have someone with a steady hand press down on the facets so they don't slide and drill through the facets with your 1/4" drill bit. This will be easier than you'd expect, due to the softness of aluminum. Slide the bolt through and nut it so that the facets are like a fan.[Image:PCSC - bolt picture.jpg|thumb|The bolt is used to hold all of the facets together.]
*With the 1/4" bit, drill a small depression into the round circle of wood beneath where the cushion sits in the middle of your chair, so that the facets can sit in the center of the chair.
*Now it is time to spread out the facets and tie them down to the outer rim of the chair with the hemp twine. Be sure that they are flexed to shape of the chair before tying them down so that you can get an accurate parabolic focus later on. [tyingImage:PCSC - aim no shadow.jpg|thumb|Note how the facets are tied down to the rim.]
NOTE: It may be advisable to drill an additional hole 2/3 down the length of each mirror corresponding to where the frame lies under it, so that the mirrors can be tied close to the fame. This may facilitate a tighter focus. However, the chair we used was not a perfect parabola and it turned out that '''not''' having the additional ties allowed for a better focus.
===Suspension===
This part of the project is amazingly easy.
*Lay your 3 poles on the ground so that they are lying parallel next to each other. Spread your length of chain so that it too is parallel with the poles and has a few extra inches on one end of the poles. On this end, bundle the poles together so that the chain lies in the middle of all 3 of them. [Image:PCSC - inner tube tie.jpg|thumb| The top part of the tripod. With inner tube and chain.]
*Cut your bike inner tube so that the circle is opened. Now you can use it for lashing.
*You may want a 3rd hand here to hold the poles with the chain in the middle while you wrap the tube around them once, about 6 inches from the ends of the poles. Tie the wrapping so it is tight, and then tightly wrap the rest of the length of tube around the poles, taking case to tie it so that it will not come undone.
*Stand the poles up with the tie assembly facing up. Take a big breath and unfold it into the tripod that you just created!Make sure the chain can support the weight of a good tug without slipping. If it does not seem strong, take extra measures to make sure it is. Remember this will be holding boiling water! 
===Testing the focus with aiming device===
Now, look at the the facets; do they lie close to the frame? Does it look parabolic? Are the mirrors clean? If the facets float above the frame and look uneven, you may want to try the extra tie technique mentioned in the above "Reflector" section. This will allow for a better focus. If the mirrors are dirty, try using a small amount of citra-solv natural solvent and water on a rag to clean them.
*Fabricate the aiming device by inserting the chopstick into the ratchet head on the end where the ratcheter usually goes. Plug this onto the nut in the center of your facets. This creates a sundial. Now you will be able to tell when the cooker is facing the sun because the chopstick will cast no shadow. [pictureImage:PCSC - aim shadow.jpg|thumb|Note the shadow cast by the chopstick. This means the cooker is not aimed properly.] [pictureImage:PCSC - aim no shadow.jpg|Now it is centered on the sun, and the stick casts no shadow.] (Note- If your chopstick catches on fire, it is probably well aimed.)
[cd - practising aiming]
When it is aimed, and your mirrors are well shaped, a ball of concentrated light about 6inches in diameter should appear a few inches below the rim plane. Wearing your UV protected sunglasses, test this by placing your hand in the center till you find the hot spot. When you think your dish is well focused, try rolling the piece of black paper into a cylinder and float it in the hotspot. It should start to smoke and burst into flames within 30 seconds. If not, make sure your mirrors are clean and are forming a tight focus. Paper burns at 451 degrees farenheight, so if your cooker can ignite paper it can boil water, fry, and cook. In other words, it passes the test.
[Image:PCSC - smoke.jpg|thumb|Testing the focus by trying to burn black paper. Theres smoke...] [Image:PCSC - fire!.jpg|thumb|Theres fire!]
Now you are ready to cook! Your project should resemble this photo: [tacoImage:PCSC Standing hot.JPG|frame]

Navigation menu