The Robinson Cooker is a faceted parabolic cooker with a square shaped reflector, 84.6 cm X 84.6 cm. It has been designed by James Robinson. By carefully orienting each facet, places the focus about 2 cm below the corners so that the rotation point falls within the spreaders. The solar collection area is .75 square meter. The cooking vessel of this early version is a 15.75 cm dia, 15.5 cm tall coffee can with a 6.5 mm x 100 mm bolt, with sleeves that fit snuggly in the tube that supports the cooking vessel. This method of support eliminates the usual structure that intercepts some of the concentrated radiation blocking it from the target. The photo shows a glass cover for the cooking vessel, however the designer suggests a metal cover would work as well.
This cooker may represent a breakthrough in parabolic solar cooker design due to its portability and ease of construction. The reflector is made from a single 4ft x 3ft (122 cm x 92 cm) sheet of corrugated cardboard that will fold up accordion style for storage or transport. Like the CooKit, it is made from a single 4ft x 3ft (122 cm x 92 cm) sheet of corrugated cardboard. Also the support structure for the cookpot is simple and novel.
Robinson Cooker Construction Instructions
ROBINSON COOKER CONSTRUCTION INSTRUCTIONS
There are two options for building the Robinson cooker. The cooker can be made collapsible or not. If collapsible, it is recommended that the reflector be made from a single piece of corrugated cardboard, though it can be made from separate pieces connected with heavy tape or other means of connection. If built not to fold up, the cooker is still relatively compact and easy to store.
The first step is to assemble the materials for the frame (Beam, Keel, Uprights, Upright Keepers, Blocks, and Spreaders).
The thickness and width of the material specified for the frame members on the drawings is suggested. If material of this size is not readily available other sizes may be substituted, but should not be less than the thickness and width specified. The following member lengths must be adjusted for material of thickness different from the drawings:
1. Beam: Length equal to 82.4 cm plus the (thickness of the Spreaders) X 2
2. Uprights: Length equal to 46 cm plus the thickness of the Beam and 2 Blocks. The width of the Uprights must be the same as the Beam.
3. Blocks: Blocks need to be the same thickness as the Keel and same width as the Beam.
Begin by cutting the Beam(1), Keel(1), Blocks(4), Uprights(2), Spreaders (2) and Upright Keepers(2).
Use the template provided to mark the compound cuts on both ends of the Spreaders (2). Make certain that the faces of the compound cuts are on the same side of each Spreader. The length of the Spreaders is overall (i.e., the long point to long point of the cuts). Use a block sander to finish the cut edges. Drill the 6mm holes in the Uprights and Spreaders as shown on the drawings. Drill the holes in the Beam and Keel. The diameter of these holes should be the same as the outside diameter of the tube used for the Pot Support. The Pot Support should fit snuggly in these holes. Glue the four Blocks on the top and bottom of the Beam ends with wood glue. It is important that the Beam ends and the Block ends form a flat surface perpendicular to the Beam. Next glue the Upright Keepers on the sides of the Beam end and attached Blocks. The Keepers should extend beyond the end of the Beam 3 cm. After the glue has dried place the non drilled end of each Upright in the pocket formed by the Keepers. Drill a 6 mm hole through the Upright and 1 cm deep into the center of the end of Beam. Remove the Upright and drill the hole started in the end of the Beam 2cm deeper with a 3 mm drill bit. Screw one 6 mm Hanger Bolt into the Beam end. Replace the Upright and fix in place with a 6mm Wingnut and 6 mm Washer. Repeat for the opposite Upright. Place the Beam atop and perpendicular to the Keel, align the holes and insert the Pot Support tube. Put the 6 mm Carriage Bolts through the hole in the Spreaders from the inside. The head of the bolt will be on the side opposite the face of the compound cuts. The bolt then goes through the 6 mm hole in the top side of the Upright. Install 6mm Wingnuts and Washers to secure. The stand is now complete. It is a good idea to paint or seal the wood at this point.
Cut the Reflector Tabs (3 mm cardboard). It is easier to cut the Reflector from a single sheet of corrugated cardboard, 92 cm X 122 cm, 3mm thick. If the Reflector is built up from pieces, tape the pieces together with packaging tape applied to the reflective (front) face of the Reflector. The measurements for the Reflector are taken from the centerlines of the whole Reflector. The drawing (Figure 6) shows only the lower right quadrant or quarter of the Reflector. It makes the layout much simpler if a quarter template is made. The slot shown is shared by the lower two quarters and is omitted from the top two. Waterproof tape is applied to those edges of the Reflector arms and slot highlighted on the drawing to prevent water penetration caused by boil over. The lower center portion of the Reflector is the area susceptible to this sort of damage. Crease the folds by carefully dragging a dull knife along the fold lines using a straight edge. Do not cut through the surface of the cardboard. Bend the folds. The reflective material is now applied to the Reflector. If aluminum foil is used, lay a thin bead of white glue on the perimeter of each square and triangular facet. The collapsible cooker will use adhesive backed Velcro tabs to hold the Reflector arms together. Cut eight, 5 cm long, 1.5 cm wide pieces of both the hook and the loop Velcro. Remove the adhesive backing tape from the 5 cm piece of hook type. Pull two of the Reflector arms tightly together making certain that the ends of the arms are flush, not offset. The Reflector will begin to assume a curved shape. Apply the adhesive side of the hook Velcro across the junction of the two arms 1 cm in from the ends of the arms. Repeat this for all the Reflector arms. The Reflector should now have the correct dish shape. Use a sharp razor to cut the 5 cm hook Velcro strips just applied along the junction of the Reflector arms. Leave the protective tape on the 5 cm long loop pieces of Velcro. This loop Velcro will hold the two cut pieces of the hook Velcro on the Reflector arms together. It will be removed to fold the Reflector accordion fashion for storage or transportation.
See James Robinson.