In Progress
Machines
Bottle Cap Sorter
This research will focus on an automatic bottle cap sorter that we have named the "Bottle Cap Sorter." Sorting bottle caps is very complex and one of the main problems in plastic recycling because it takes a lot of time and resources. When sorting plastic, you have to sort one cap at a time, which is probably one of the reasons why only bottles, i.e., PET plastic, are mostly the main plastic recycled in the big industry. The idea of our solution is to create an affordable device for sorting plastic caps (beta) and later for all other types of plastic (not just caps). Inspired by various industrial machines, we realized that we need to have a conveyor belt with sensors and "pushers" that push the caps into boxes arranged by color. As a cap "feeder," we used a large drum that centrifugally ejects the caps onto the belt. We will improve our current version with better motors, sensors, a larger belt, and detailed documentation so you can also create your own plastic sorter.researchother machinesorting
More Information
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1
Upcoming steps for the following months
Created 12 months agoUpdated 10 months ago
1. Outlining idea - defining the final specification and features of the Bottle Cap Sorter
2. Preparing drawings and design - finalizing 3D drawings for 3D printed parts, as well as the final blueprint for the electronics
3. Ordering & Receiving materials - defining and producing the final hardware (motors, sensors, and PCB development)
4. Production - Bottle Cap Sorter v1.0 development and implementation
5. Documentation - making it ready for the Precious Plastic community! :)
6. "Impossible" goal - making the device sort by plastic type (HDPE / PP)
2
Outlining idea
Created 10 months agoUpdated 8 months ago
After receiving funds (June 25) we have got the necessary equipment to build beta version of Bottle Cap Sorter.
We have outlined the ideas that will be researched and developed in the following months.
Features
- Plug&Play ready system (printed circuit board)
- Cap feeder - faster feeding with barrel system
- Unjamming mechanism - in previous version there was a big jamming problem, which will completely be redesigned and fixed
- Custom belt - custom made for better durability
- Position sensing (to detect cap position)
- Color sensing (to detect cap color)
- Pusher (to push the cap to container)
- Touch screen controls
- User color calibration
Specification
- Arduino Mega
- Arduino Mega screw terminal board
- Alucobond barrel
- Aluminium extrusion profiles 30x30
- TT-775 DC gear motor
- BTS7960 motor driver
- NX4832T035 display
- Custom made belt
- TZT TCS34725 color sensor
- TCA9548A multiplexer
- TCRT5000 obstacle sensor
- JF-0530B Push&Pull
Video shows current version (v0.9)
0:15 - first preview
0:27 - barrel
0:30 - electronics
0:35 - preview
0:48 - pushers
0:53 - calibration
1:24 - run
1:35 - sorting
3
Developing circuit board (PCB)
Created 9 months ago
All the parts for Bottle Cap Sorter (motors, sensors, belts) have arrived, tested and integrated.
Everything works as expected, even better after some tweaks (70-90% precision sorting - depending on the batch cap colors).
In the upcoming months we will be sketching and simplifying electronics for the development of PCB (Printed Circuit Board).
We have found partners in Croatia who will manufacture PCB for us.
Second round of payment will be used for the manufacturing of PCB.
Our focus will be on quality and low cost electronics which will be available to anyone who wants to build Bottle Cap Sorter themselves.
The research and development of PCB will take up to 3 months.
In the meantime we will also upload all .stl's for the 3D printed parts needed.
After that period we will publish final documentation and order link for the PCB board.
We will as well provide kit version for anyone that wants to order Bottle Cap Sorter machine.
Next to the kit version there will be fully free open-sourced documentation provided.
4
Challenge #1 - PCB development
Created 8 months ago
Developing PCB is too expensive for this phase of the project and takes too long to complete.
**Solution**
We discussed with PCB manufacturers and concluded that it will be an overkill for the first version of the machine and that it is best to leave it for the future (v2 or v3). We have simplified the electronics scheme and will publish it in the separate documentation (current progress visible in the attachment (non final), note: 12V step down to 5V). Electronics are now simple to assemble even without advanced knowledge and in terms of expenses quite affordable.
Note: Our allocated funds from PPOSF for development of PCB will be used to complete the electronics board + documentation on how to assemble the electronics part (if allowed by PP).
5
Challenge #2 - Color Sensors Precision
Created 8 months ago
Current sorter was able to sort bottle caps per color up to 70% precision. Still it sometimes make some random errors which was mostly happening because of the external light source and the position of the sensors.
Test #1
Positioning the presence sensor and rgb sensors on multiple positions
Result #1
Changing different positions have triggered different scanning results, which was implication that it can be adjusted better than in first version
Solution #1
The box through the bottle cap is going is now completely dark, and sensors are positioned in the proper position in the box to get the cleanest data of the bottle cap color as possible (positions visible in the attachment). Results are much more consistent at this point.
Test #2
We did testing with +30 different bottle caps colors and brands (for example - 30 different shades of blue).
Result #2
We have collected and created a detailed color matrix for Arduino sensors.
Solution #2
New detailed color matrix has been embedded into machine code and works much better.
6
Challenge #3 - Ideal belt size
Created 8 months agoUpdated 8 months ago
Test #1 - belt width same as the bottle cap
Result #1 - most of the bottle caps get stuck in the feeding zone
Test #2 - belt 1.5x size of the bottle cap
Result #2 - caps don't stuck and it is more comfortable to pass through
Test #3 - belt 2x size of the bottle cap
Result #3 - caps go together and it usually ends up in clogging
Conclusion
The belt size does not matter that much it is only important that it is between 1.5x and 2x than bottle cap width. Also, it is important that caps, traveling through the feeding tunnel end up on the left side of the belt (so they are as close as possible to the color sensor).
7
Challenge #4 - Ideal feeding tunnel height
Created 8 months ago
This was the most challenging task for new version of the bottle cap sorter.
The biggest problem is that the new “non-separable” caps have tip - small weird piece sticking out of them and it usually gets stuck in the feeding tunnel entrance (the part where barrel and tunnel connects). The EU obligated in July 2024 (Croatia) to be mandatory to use non-separable caps, but we found our way to sort them out - at least partially enough.
Test #1 - increasing the entrance to the tunnel
Result #1 - caps are feeding better but it gets stuck (when multiple caps enter on top of eachother) more often and requires human intervention
Test #2 - reducing the entrance to the tunnel (to the actual size of the bottle cap)
Result #2 - caps are feeding less frequently but the error is almost none (does not get stuck). Machine works slower.
Test #3 - make the returning mechanism if the caps get stuck
Result #3 - it works quite well and 5x less times does require human intervention. The machine does one circle turn in reverse, sucesfully gets the stuck cap out and keeps on feeding.
Test #4 - making the adjustable height entry doors to the feeding tunnel, which enables users to define certain height for their needs
Result #4 - this helps quite a lot to adjust feeding depending of the bottle caps current batch height. It will be good so the users can customize height for their needs.
8
Challenge #5 - Ideal feeding mechanism
Created 8 months ago
Test #1
We did a several different shapes in the barrel to keep the bottle caps going to the feeder (visible in the attachment).
Result #1
Some of the shapes worked well and some did not. Changing the motor speed also made results different.
Conclusion #1
The users can play around with different obstacles and get different results. We decided to go with "half-cone" shape in the middle of the barrel which quite decently mixes and pushes caps to the feeder.
Test #2
Some bottle caps gets stuck after entering feeder so there was some tweaking needed there as well.
Also, caps must be separated before entering belt because if they are together sensor will scan multiple caps as one cap.
We did different "separator" (as we call it) sizes and shapes. We tested soft and hard brushes to slow down and separate bottle caps. We tested the motor powered separator as well.
Result #2
Most of the tests with soft and hard brushed end up in these getting damaged or used-out.
Best result was definitely using motor which allows 1-by-1 bottle cap to go through (visible in the attachment).
Video in the next update.
9
Challenge #5 - Ideal feeding mechanism #2
Created 8 months ago
Here is the video of the different shapes inside rotating barrel.
10
To-do or Not-to-do?
Created 8 months agoUpdated 8 months ago
After a lot of testing and overcoming challenges, we started to think whether this sorting mechanism can be used at the level we want. We also started exploring new ways of sorting including AI and cameras. There are many interesting new technologies with which sorting can be done. But we didn't want to shut down this current project for several reasons:
- it is excellent as a basic version of the machine, it can be further developed in several directions
- speeds up the work of a person who manually sorts caps, up to 5 times
- it is very cheap and can be made relatively quickly
- we want to see what kind of use-cases people will find with this sorter
- we want people to test and hear feedback from the community
All of this led us to conclude that we should end this research with the current sorter idea, fulfill all the requirements of the PPOSF project, and then start a new period of discovery and experimentation with cameras and AI. It will take much longer, but we will not give up until we develop the perfect sorter machine 🙂
Next steps in Bottle Cap Sorter v1.0:
- finalization of STLs for printing
- publication of complete documentation for compilation
- after many updates at this month we will complete the research until Dec 1, 2024
And yes, PLEASE feel free to comment and join our research! <3
11
Quick update
Created 6 months ago
We have made a lot of progress since the last update.
- Feeding mechanism will not be barrel anymore since it is really hard to feed the bottle caps, especially the new, non-separable caps (the ones with small tip) to the belt with this mechanism.
- We will make vertical feeding system which will provide sorting bottle caps non dependent cap size and shape.
- Losing the barrel will provide much easier assembly system and machine will be much smaller
- We have made better mechanism for redirecting bottle caps to boxes (visible in the video)
- We removed position sensor (not rgb sensor detects bottle cap) - less electronics, cables and expenses :)
- We have written most of the assembly manual and documentation
- Assembly manual will be interactive and provide animated view of the assembly (visible in the video)
- Release of the Bottle Cap Sorter is expected in January 2025
12
Indexing the parts
Created 6 months ago
Here's the index of terms for the better understanding of the parts.
13
Last update before the final release! <3
Created 6 months ago
This is our biggest update yet! ♻️ Bottle Cap Sorter will be open-sourced and free for everyone to build, very soon! Our main goal is to enable recycling for anyone! 💪🐙 We had great fun during this whole research and cant wait to provide you with final results + guidance to build your own sorter. Here's the video of the previous month progress.
14
Machine completed (Preview)
Created 2 months ago
Preview of the machine
15
Machine completed (Parts)
Created 2 months ago
Parts of the machine
16
Machine completed
Created 2 months ago
We've finally finished the machine! 🎉
It was a much bigger challenge than we expected, but we pushed beyond our budget to bring the Precious Plastic community an open-source automatic plastic cap sorting machine. And we couldn’t be happier with how it turned out—both in terms of functionality and design!
🔧 New Features & Fixes:
✅ Switched from a barrel rotation system to a lifting system ('Lifter') – No more caps getting stuck at the entrance, less dirt buildup, and improved speed & accuracy.
✅ Added a 'Separator' – Automatically removes any caps that can’t enter the sorter.
✅ Upgraded the sorting mechanism ('Sorter') – Now easier to open in case of jams, simpler to clean, and requires less maintenance.
✅ Removed the presence sensor – Instead, the RGB sensor detects caps directly, reducing cost, components, and wiring.
✅ Optimized the code – Improved detection accuracy and overall speed.
📌 Coming soon: In the next few days, we’ll release a full How-To Guide with:
🖨️ 3D print files
🛠️ Interactive assembly instructions, with a detailed breakdown of all components
💾 The complete software code (GitHub)
We can't wait to share it with you all! 🚀♻️
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