With the end of the quarter approaching quickly, we initiated our final phase of design development and are working towards our final prototype. As shared in our previous blog post, the compost tumbler that we were testing with was not very effective for crushing glass because the tumbler was suspended in the air, is made of plastic, and has protrusions on the inside of its walls. As a result, all of the impact necessary to crush glass is absorbed. From our adventures with the dryer, we were able to isolate the drum, and we thought it would be the perfect vessel with which to create a final prototype from a material and accessibility standpoint. Before we began that process, we conducted an experiment to confirm whether the dryer drum provided enough height from which the ball bearings would be dropped so that they would produce enough force to crush the glass. The max height the ball bearings could fall from is 25", since our dryer drum is 25" in diameter, and based on the width of the fins we were using, we figured that a lower boundary would be 15". We tested the amount of times it took to break a glass bottle with both a 2" and 3" steel ball bearing from either 15" or 25" above the ground:
Even though the larger ball bearing accomplished the task more quickly, we wanted to use the smaller ball bearings since they would subject the dryer drum to less force and therefore better preserve its longevity. This experiment was validation that we could use the smaller ball bearings in our final design. We were then able to move forward with constructing a higher fidelity prototype. We split a PVC pipe in half length wise and drilled each half into the inner wall of the dryer drum to create the two-fin bridge design that we deemed most effective in testing weeks ago: Next, we placed a glass bottle in a bag, put it in the dryer drum along with two 2" ball bearings, and taped plastic bagging to seal both sides of the drum. We went outside to test whether this design would be effective in crushing glass when rolled on asphalt: The results: we crushed glass! The fins were picking up the ball bearings and the bottle and dropping them in the center of the drum as intended. We decided to bag the glass bottle to prevent shards from flying everywhere, but the bag inevitably broke. This was actually a good thing because we were able to see that the smaller pieces were passing under the bridge fins just as the design intended.
For our final deliverable, we plan to use this prototype but reinforce the sides with better, more protective material, and we also hope to create a rigid stand with rollers so that we can demonstrate our design in place. Thank you so much for joining us on our glass crushing adventure!
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Since our last blog post, we’ve been working towards creating a higher-fidelity prototype of our glass crusher. Our goals for this round are for our prototype to be at a larger scale, closer to that of the final product, and to actually crush glass rather than chips. The lovely Shoshanah was able to source a tumble dryer machine for us that was going to be disposed of. Additional shoutouts to our CAs Matt for picking up the dryer and Marshall for allowing us to store it in his lab. We were very eager to begin modifying the drum to incorporate the fin design we determined was optimal for crushing from our experiments (see our previous blog post for details). However, we could not power the dryer in the lab because there were no 240-volt outlets. We were unable to find any adaptors, so our next step was to see if we could remove the heating element and rewire the dryer so that we could power the motor directly. In hindsight, this was not the best idea, as it didn’t occur to us that the design of this old dryer would require us to fully disassemble it in order to access the motor. It got to the point where attempting to put the dryer back together was simply not a worthwhile endeavor, so we decided to cut our losses and move on with a different approach. (Above: CAs Marshall and Matt with our fully disassembled dryer). We then ordered a manual compost tumbler from The Home Depot. We had some doubts about whether glass bottles would break inside of it since it’s made of plastic and has not-flat sides, but we decided to test it anyway. To incorporate our fin design, we cut a PVC pipe in half and secured each half to the protrusions coming from two of the drum walls with really strong tape. We then fully assembled the compost tumbler, and threw in a glass bottle and some large steel ball bearings to see if anything would happen. Unfortunately, our speculations were correct, such that the plastic and the protrusions were absorbing the impact when the bottle would fall. And while our fin design was effective in picking up and dropping the steel ball bearings, they weren’t landing on the glass bottle at all. Ultimately, we’ve hit a bit of a roadblock, and we’ll have to come up with a new approach for the next couple of weeks.
Since our last blog post, we have been working on refining our crushing mechanism in order to proceed with a higher-fidelity prototype. After our initial brainstorming and rapid prototyping sessions, we have decided to move forward with a tumbler system (pictured below). Overall, the idea of our glass-crushing mechanism is to repeatedly pick up and drop steel ball bearings onto the glass via these “fins” attached to the inside of the tumbler drum in order to facilitate the crushing process. As the glass becomes finer, it will exit through measured holes drilled into the tumbler's walls. With this mechanism, we hope to be able to crush multiple bottles at the same time with relative ease and efficiency. Since our last post, we have been running several experiments, testing for the optimal fin shape and number of fins. Overall the two different shapes we tested were a rectangular fin and a “bridge” fin, which allows smaller pieces of glass to slide under while picking up the ball bearings and larger pieces of glass. Above: our prototype testing 3 rectangular fins Above: our prototype testing 3 bridge fins Additionally, we tested whether two or three “fins” would be more effective. We ran three test trials for each combination of fin type and number of fins, resulting in 12 total tests. Since this is a very early-stage prototyping phase, we used an empty pretzel container as our tumbler drum and rice crackers as our “glass. The results from our tests are compiled below. Based on consistency and relative amount of , we concluded that the most effective combination was 2 of the bridge fins. We plan to move forward with this design in a higher fidelity prototype next week!
We're Team Kick Some Glass! From left to right:
We’re working with the Maa Trust, a non-profit organization based in the Maasai Mara region of Kenya. The Maa Trust prioritizes preserving wildlife while encouraging sustainable business practices in the process. The Maa Trust is based in an economically male-dominated region and they aim to empower women and youth by increasing their financial independence through various sustainable initiatives, one being the glass crusher project. After talking with the Maa Trust about their desire for a glass crusher, the goal of our project is to design and prototype a mechanism to take in glass waste in the form of wine bottles and crush it into a sand-like material. As a result of local tourism, wine bottles are a significant form of waste in the Maasai Mara. Unfortunately, there is no convenient way to recycle these bottles, as the closest recycling centers are hours away by car. Thus, we hope to bridge this gap, both helping the Maasai Mara ecologically and helping the Maa Trust’s various programs that empower women and youth. Initially, we had planned on working off of last year’s team’s final design concept, which consisted of two crushing phases: a bicycle-powered crank and slider mechanism to crush bottles into smaller pieces and a motorized impact mill to crush the pieces into fine glass, as shown below. Due to changes in the project brief and discrepancies with our user requirements, we ultimately decided to pivot and to essentially restart the project from scratch. After much research and conceptualization, we decided to pursue a tumbler design, which consolidates the crushing process into one phase rather than two. At the end of last quarter, we very briefly began our prototyping process, and our plan moving forward is to continue to refine and eventually solidify our design. We plan to present a fully functional, highly refined prototype by the end of this quarter that is motorized, to scale (able to accommodate at least 3-5 glass bottles at a time), and easy to use. We are excited to keep you updated on our progress!
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