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EB-30D Prototype
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First EB-30D Prototype 

Our second EB cooker prototype was an EB‑30D.  For double cone EB cookers, the target diameter is the cooker diameter divided by 5.  For triple cone EB cookers, the target diameter is the cooker diameter divided by 7.  Thus, the EB‑42T and the EB‑30D both have the same 6‑inch diameter target sphere.  Because of the larger target size, we recommend the double cone design only for cookers with diameter less than or equal to thirty inches.  For thirty-inch diameter cookers, either a double cone design or triple cone design can be used.  It takes more time to cut out and assemble the triple cone.  However, with its smaller 4.3-inch target diameter, it can focus all of the reflected power onto smaller pots.  Also, for larger pots the sun can move a few more degrees off axis before it starts to miss the pot.  The EB‑30D prototype has been completed and we plan to build an EB‑30T Prototype next.

 

Figure 1 shows baked apple slices being removed from the EB‑30D prototype at an Earth Day Fair in Springfield MA.  The potholder structure that can be seen in Figure 1 used some of the principles used by Zhu. 

The design was modified to use a grill on the circular supports rather than place the pot directly on the circular supports.  This modification makes the pot more stable and allows the use of a variety of pots rather than designing the cooker for a specific pot.  The cooker is mounted on a base and is tilted with a wedge under the base.

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Figure 1

EB‑3D Prototype at Earth Day Fair

 

Figure 2 shows the EB-30D prototype as it was mounted on the plywood base.  Note: The potholder structure shown on Figure 2 was later modified to that shown on figure 1.

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Figure 2 

EB-30D Prototype Mounted on a Plywood Base

 

Figure 3 shows a profile view of the EB-30D.  If the sun is on axis, the dashed lines show the path of rays from the edges of each cone section.

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Figure 3

Profile View of EB-30D

 

Figure 4 shows the layout of the cone sections ready to be cut from a single pieces of material.  The first EB‑30D prototype was built from sheet aluminum.  The center disk is not shown on Figure 5 and has a six-inch diameter.  As an experiment, we tried polishing standard aluminum sheet material and used it for the outer cone section.  We are not satisfied with the reflectivity of the polished sheet and probably will cover the outer cone section with higher reflectivity material.  The inner cone section was cut from brite aluminum.

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Figure 4

Layout of EB-30D

 

The following table shows a summary of the dimensions for an EB30D in both inches and centimeters.  It also shows the dimensions for an EB24D.

 

Dimensions of Cone Sections for EB
Double Cone Cookers
5/21/2007 21:55
   EB-24T     EB-30T  Cutout
Cooker Diameter (inch) 24 30   Angle
    (cm) 61.0 76.2     (deg)
Outer Cone Section Outside Rad (inch) 16.97 21.21 105.4
(cm) 43.10 53.9
Inside Rad (inch) 10.17 12.71
(cm) 25.83 32.3
Inner Cone Section Outside Rad (inch) 8.05 10.06 38
(cm) 20.44 25.6
Inside Rad (inch) 2.68 3.35
(cm) 6.81 8.5
Center Disk Radius (inch) 2.40 3.00
(Target Radius) (cm) 6.10 7.6
0.00
Target Sphere Diameter (inch) 2.40 3.00
(cm) 6.10 7.6

If the cone sections are cut as shown in Figure 4, straps are used to join the ends of the cone sections and to join the cone sections together.  For thin material, tabs can be used to attach the cone sections together.  Figure 5 shows the inner cone sections with tabs.  This section can be constructed by cutting the outer circle with the one-inch larger radius and then cutting out the notches.  Also, a single tab similar to the one shown on the inner cone in Figure 5 should be added to the outer cone section to join the two ends together.

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Figure 5

Layout of Inner Cone Section With Tabs

 

Figure 6 shows the Center disk with tabs.

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