The Creation of the Final ISEC
After spending the duration of the lab time during the quarter experimenting, discussing and designing our prototype, it became time to build. We built the prototype using the knowledge we had gained throuout the quarter.
The video above is from our final class presentation and it gives a quick summary about our ptototype and its construction. For more details, please read this blog.
6/5/23 - Formwork Creation
Although we had spent quite a bit of time creating a concrete formwork for our ISEC prototype that we originally envisioned to be square... we decided to pursue different approaches becuase formwork that took us beyond 8 hours of lab time was not efficent and realsitc for Malawi.
Instead, we decided to build the prototype in buckets - something we imagine is more effiecent. Our orignial prototype was designed to have 1" thick walls and a bottom of the same thickness. However, due to eniornmental and weight concerns (we calculated that the prototype would be around 60 pounds...) we opted to go with thinner walls.
The formwork for the final prototype was made with 2 buckets. A 5 gallon and 3 gallon bucket. We were not able to find one that was 4 gallons. Because there was a gap between the 2 buckets that was larger than 1" we added carboard and foam to the smaller bucket to lessen the gap. We used a dremel to cut the larger outside bucket in half to make it easier to take it off once the concrete is cured. We duct taped the bucket back together. However we forgot to cut the inside bucket in half.
Figure 2: Creation of Formwork for Final Prototype
Left: Cardboard around inner bucket; Middle: Our completed formwork; Right: The exterior bucket cut in half
6/7/23 - Concrete Pouring
Now that the formwork was completed, we started to mix and pour the concrete. To start off the process we measured and cut out wire mesh. We found some scrap wire mesh on campus, which we used the walls. The mesh that we found had a larger surface area for the concrete to grab onto, so we thought it would be good in stregnth. We used a different wire mesh that was in the lab for the bottom layer.
We started by cutting the wire mesh into the sizes we needed. We ran into some difficulties here - unfortunatly it did not stop here. The wire mesh we found was very stiff and hard to bend. It took all of us and alot of manuvering to get it to curve inside the formwork in the way we wanted. We got it in the shape we wanted and trimmed off the excess. We started off using a pair of pliers that was in our tool room but that was taking a while. We went to the shop and they reccomended us to use a dremel. However, the dremel sparked alot and was not very effective. We decided to continue to take turns and use the pliers. In hindsight, we should have used metal scissors - a tool we would use later on.
Figure 3: Reinforcing for the Concrete
Left: Concrete Experiement we performed in earlier weeks where we use the same scrap mesh ;
Middle: putting together the scrap mesh for the exterior ; Right: The wire mesh used for the bottom
The scrap mesh was a bit damaged so we stepped on it to straighten it out. We used zip ties to keep the wire mesh in the curved shape we needed. Contrastingly, the wire mesh we used for the bottom was very maleable and easy to cut. The only problems we faced were innacurate cuts despire making markings on the mesh.
Once we finally finished setting up for the pouring of the concrete it was finally time to mix and pour the concrete. We mixed the concrete in batches in a metal bowl we would later use as our lid for the ISEC. We first started by creating a bottom layer. We added about 1/2" of concrete, addded our wire mesh on the bottom (Figure 3: Right), and added another layer that was about 1/2". Now it was time for the walls. We mixed another batch and realised that the walls were too thin for us to easily add the concrete in our formwork. We decided that the best way to get the concrete in the thin space was to coat both the exterior and interior bucket with a thin layer of concrete and from there combine them.
Figure 4: Adding the Concrete
Left: Concrete mixing ; Middle: Adding a thin layer to the interior ; Right: Adding a thin layer to the exterior
However, this plan did not work. The interior bucket only made it less than 1/4 into the bucket. It would not budge no matter how hard we pushed. We decided that the only solution here was to flip the formwork upside down, remove the exterior bucket, add the concrete, and put the exterior bucket back on. We went through with this plan. While flipping the formwork upside down, because it was heavy, we messed up some of the mesh at the bottom. Because we added the concrete without restrictions of walls, the concrete did not have the same dimensions as we planned. We were not able to easily reattach the exterior bucket perfectly, and it definitely was not serving its purpose of reinforcing the walls.
Figure 5: Concrete curing
Left: The concrete with the exterior bucket removed and flipped upside down ;
Right: How we left the concrete to cure
We were extremly worried about how the concrete would cure and hoped it would be fine when we came back.
6/11/23 - Progress
We came back to see how the concrete cured. The surfaces were not smooth, and the wire mesh in some places were exposed. We added more concrete than planned. Despite this, the concrete was strong and not brittle. Getting the interior bucket out was challenging but we were able to do so after cutting the bucket and using pliers.
From here we started to work on the wiring and insulation in the ISEC.
We filled the interior of the ISEC with fiberglass and rockwool insulation. We made a lid out of the bowl we used to mix the concrete and we filled that with insulation as well. We added a handle for the bowl using a wire that we found.
We attached metal sheets to the lid and to the bowl to close the ISEC. We used metal scissors to cut a hole to attach it to the ISEC.
So users are able to pick up the pot, we added a detachable handle. We went through multiple design ideas including string, magnets, and using a stick with the addition of strings, but we went with adding a malleable but stiff wire. We poked holes in the pot with a hole puncher at the shop. We used a copper wire that we found. In real applications we would recommend something more stiff.
We started to work on the wiring of the ISEC. We decided to use Diodes, like in Pete's paper, Hot Diodes!: Dirt Cheap Cooking for the Global Poor?. We decided to use diodes because it is inexpensive, and can heat up the ISEC with lower power. Pete taught us how to solder the diodes together. Huge thanks to Pete for helping us with this on such a short notice. None of us had ever soldered before. We strung them all together but had some difficulties with the solder so we decided we would come back to this the next day.
6/13/23 - Wiring and Testing
Now, all we had left to do was wire the diodes, finish the ISEC and test it. We were having issues with the solder the day before. It wasent heating up properly and before that we couldnt get it to stick to the wires. We figured out our main issues.
We had plugged the solder gun into an extnesion cord. We hypothesize that this led to voltage drops to the solder leading to the gun not getting to its maximum heat potential
We arent sure why but we changed the end of the gun and it started to work. We changed it back to the original bit and it wokred again later...
Bonus: there was an event going outside of Bonderson and the nice catering ladies fed us thorugh the gate.
We all took turns soldering and we got pretty skilled at it! We started to run into the same isues again and we changed outlets and bits but we couldnt get it to work so some connections arent soldered, but the majority are.
We tested the diode chain with the solar panel we read that there was a little over 20V accross the diode chain with the use of a multimeter. We measured this as a success and we finished up our prototype. We attached the diodes to the bowls, and added more insulation.
Conclusions
Over the course of the quarter, we made significant progress. We experimented, designed and came thorugh obstacles as a group. We all learned somehting new and gained a few new skills. Something we would do differently next time is using lab time and the resources we were provided more efficently. We would also be more open to guideance from Pete.
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