2022 Fila-Buster

Abstract

Along every step in our daily lives, we encounter plastic. However, few of us think about what happens to plastic products or packaging after they have served their purpose. With 3D printing machines becoming more common in institutions and people’s homes, the plastic waste they produce is also on the rise. Fortunately, one of the most common 3D printing plastics is biodegradable under the right circumstances. PLA, also known as Polylactic acid, is not petroleum-based and can be broken down in industrial conditions within 1-3 months. This is achieved by heating it up to greater than 140F and providing enough water, along with certain microbes. In the wild, it would take PLA 80 years to decompose. Our team created the Fila-buster, a PLA filament shredder and composting bin. Fila-buster is designed to help speed up the process of PLA degradation, mimicking some of the conditions found in industrial settings, and can also be used to shred plastic for recycling purposes. In addition to the motorized shredder, our product also features heating pads, insulation, a temperature sensor, a safety lid, and a trap door for easy disposal. We used a variety of manufacturing techniques to create our prototype, including 3D printing, laser cutting and water jetting. If further developed, it would allow hobbyists and labs to cheaply dispose of their failed or unused 3D prints in an environmentally friendly way.

Problem Statement

To help minimize the negative impact of humans on the environment, the aim of this project is to create a PLA filament shredding and composting bin that enables people and institutions to compost their 3D printing waste in-house and in a timely manner, therefore reducing the amount of plastic that ends up in landfills.

Brainstorming

Our group formed through a shared desire to address some of the pressing environmental issues of our time. We used research and the post-it notes to help us pick more specific problems, as well as a mind map.

One of the brainstorming techniques we used was a mind map. A mind map works by word association and helped us formulate different specific environmental issues we could focus on. In the middle circle, we had our big theme, the environment. Around our big theme, there were many branches of the environment including water, air safety, and habitat conservation. We came up with many different product ideas to address different environmental issues, including renewable power, waste management, plant care, and CO2 emissions. Some of our early ideas:

an app that tracks co2 emissions from car exhaust

solar powered portable phone charger

PLA shredder and composter

filament extruder

smart pot that helps take care of houseplants

Deciding Alternatives and Ranking

To rank all of our ideas, we set up a weighted decision matrix which had different criteria we agreed upon for our project. We gave each idea a number from one to five and multiplied it by the weight, then added up the scores for each idea. The idea with the highest score ended up being the PLA shredder and composter.

Final Design And Testing Results

Electrical Systems

To turn our shredders, we ran a 24 volt rated DC motor originally designed for scooters. However, this required us to use a clunky power supply which did not integrate well with the rest of our box. We also used a relay and a speed control system to control when the motor turned on and off.

Since our design included a shredder meant to crush plastic, we knew that we had to include some kind of safety mechanism to prevent accidents, such as hair getting pulled in or fingers getting crushed.In order to achieve this, we connected the power supply and motor to a relay that only transferred power to the motor if two limit switches were pressed. We installed the switches near the rim of the shredder, and they are activated if the lid is closed. This system does not require an Arduino or other microcontrollers.

We included two heating pads in our design on opposing sides of the box. We connected it up directly to a 9-volt battery. Although it’s rated for 5 volts, experiments have shown that the heating pads can handle even 12 volts. However, we couldn’t hook it up directly to the 24-volt power supply because we didn’t want the heating pads to melt, which did happen to other users.

Another electrical component of our box is the thermistor; a simple device which need a microcontroller and can read the room temperature at an acceptable level of accuracy. Currently, the only way to read the thermistor is by connecting the Arduino to a computer with the appropriate software. We were successful in measuring temperature with the thermistor, though we noticed that it would give inaccurate readings when we held the tip of it in our palms. This is why we mounted it so that it would measure the temperature of the air just above the compost and not the compost itself. More testing would need to be done to determine whether it would be possible to submerge the probe in the compost without affecting the quality of the reading.

One improvement we would want to make in the next iteration would be to improve our wire management. This would decrease the likelihood of wires getting disconnected, and it would also be more visually appealing. We would also want to automate when the heating pads are turned on, based on the information from the thermistor, which now would need to happen manually. We would like to add an OLED Display to show the temperature of the box, instead of having to read it from a computer screen. Another component we were originally planning to add to our box but didn’t have the time to add is a moisture sensor, which would tell you if you needed to add water to the compost by turning on an LED, for example. In order to be more environmentally conscious, we would love to make the box solar powered, by adding solar panels to the side of the box or to the top of the lid, where we have a lot of unused flat surfaces. Our team members had the opportunity to learn how to soldier, strip and crimp wires and choose the right connectors while they worked on this subproject.

Shredder

We started off our shredder design by researching existing plastic shredders, such as the Filabot. We designed a simple blade which we laser cut out of 1/4 inch cardboard. We wanted to modify existing designs to better utilize resources we had available.

Early on, we settled on a hexagonal shaft on which to mount our blades so we can stagger them. Hexagonal profiles are also very useful in high torque situations such as ours, so we had to find specific hardware which is compatible with hexagonal bores.

We determined that in order to be able to crush plastic, our blades had to be made out of metal, preferably steel. However, we determined that higher-grade aluminum would be easier to machine. We made our first prototype of a metal blade in on the colab waterjet machine, which was a bit difficult to work with. As we cut the rest of our blades, we noticed that there was a bit of inconsistency in the tolerances, so we were not able to use some of the blades. However, we were able to cut 20 blades that were usable, which was half as much as we were originally planning to use. however, we don’t think that this significantly affected out final design.

We used a chain to connect the motor to the shafts. A smaller sprocket drove a very big sprocket, which increased torque but decreased speed, which is what we wanted. In order to spin the shafts in different directions, we used gears. to make the housing of the shredder, we constructed a frame out of 8020 aluminum extrusion and we laser cut walls out of 1/8 inch acrylic. However, we noticed that sometimes 1/8 inch acrylic was too brittle to hold all of our components together and it cracked a lot. In future iterations, we would want to use a plastic such as polycarbonate, which is not as brittle as acrylic.

The spacers we designed for the 3d printer were a bit difficult to tolerance since every 3d printed part ended up being smaller than what we designed. We solved this through trial and error of different iterations. The spacing on our final product ended up being excellent. Unfortunately, after we tested our prototype, we discovered that the motor we installed did not have enough torque to crush thick plastic. We were able to shred thin pieces which only consisted of one layer, but in the future we would want to design some kind of gearbox which would enable us to get more torque out of the motor.

The Composter

Our composter was designed to be a climate controlled, sturdy, and easy to empty. Similarly to the shredder, we constructed a cardboard prototype first and then moved on to a frame made of aluminum extrusion, which we found in the lab. During our early prototyping, we discovered that slanted walls would enable more compost to leave the box than with straight walls. This design element was carried to our final prototype as well.

We added laser-cut polycarbonate walls which were more sturdy than the flexible, taped-on plastic that was there before. We also added legs to our box and a trap door which would enable the compost to fall through once it was done composting. The inside of the box was inlayed with a silver insulation material which would help keep the box warm and enable us to use less power while heating. The heating pads were sandwiched between the polycarbonate, insulation, and another thin layer of plastic which would be in direct contact with the plastic. The box also contained the thermistor and we mounted some electronic components on the sides.

Video

Conclusion

Although we struggled along the way and weren’t able to implement some aspects of our design which we wanted to have, our current prototype largely followed our design constraints and we are very proud of our accomplishments and what we have made. Learning different manufacturing techniques, electrical engineering concepts, CAD design and time management concepts was invaluable.

Meet The Team

Team members from left to right (and a mentor):

Katherine Patillo- Jordan High School, Senior
Andrea Basuroski- East Chapel Hill High School, Senior
Shree Manian- East Chapel Hill High School, Senior
Anika Rayburn- NCSSM, Junior

Some Sources

ScienceDirect.com
Filamentive.com
Bioplasticsnews.com
3Dinsider.com
Vegvare.com
Biosphereplastic.com
Earth.org
Packagingdigest.com
Mtpack.coffee
3Dnatives.com