Metabolizer - A recycling center powered by trash!

A deployable power plant that eats trash and turns it into energy, electricity, fuel, and eventually very nearly anything else.

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The Metabolizer is a proof-of-concept waste-to-energy power plant and recycling center that is powered entirely by trash. It is intended to have the same basic metabolism as a living organism, capable of breaking down wastes, including plastics, and turning them into useful things like heat, electricity, fuel, building materials, and 3D printed objects.

This project combines many existing components and projects into a whole system that is (hopefully) more useful than the sum of it's parts. I call it the Metabolizer, because ultimately what we are doing is developing a closed-loop machine metabolism that breaks down complex molecules into simpler ones, and powers itself in the process- like cyborg mushroom!

This project isn't ready for step-by-step instructions, so instead I layout each component of the system in detail, discuss what it is, what it does, and what it could ideally do, and what design challenges remain to be solved, so that we can all work on solving them

Problem Statement:

Unlike all healthy living ecosystems, which regenerate wastes back into living things in an infinite loop powered by sunshine (with fascinating but negligible exceptions), human tend to just make stuff out of stuff that we've either dug up or cut down, and then just throw that stuff away when were done with it. The problem is that we're rapidly running out of "away", and all that stuff we're making is piling up faster than natural systems can break it down again. Waste plastics are a particularly problematic example of this paradigm of consumption, because very few living organisms exist that can break plastics down, and none exist that can do it as fast as we're currently producing them. 

However dire our current situation may be, it is not unprecedented in Earth's history. 360 million years ago, plants suddenly evolved the ability to synthesize Lignin- which was up until that point the most complex organic compound that had ever been synthesized on Earth. For 60 million years (!!!) trees grew, died, fell over, and we're buried, but the solar energy trapped in their chemical bonds was never broken down and released- because no fungi or bacteria existed at that time that could break down woody biomass. That's where most of the worlds coal came from. It wasn't until white-rot fungi evolved specialized enzymes that wood became the 100% compostable component of living systems that we know it as today.

Plastics are mostly made of the same stuff that wood is, and they are extraordinarily energy-dense. A gallon of plastic has roughly the same energy content as a gallon of diesel fuel. So whether or not humans survive the Anthropocene, we'd be flattering ourselves to believe that we could end ALL life on Earth, and that means that eventually SOME living organism will almost certainly evolve a metabolic pathway that can convert the nutrients and solar energy locked up in the plastics in our oceans and landfills, and use those resources and energy to synthesize the physical structures that allow them to continue to live, grow, and self-replicate. It's only natural! It's what life does. 

But why should we wait for humans to go extinct? We built the systems that made the plastic, we can build systems that break them down. We can designs systems that can break down our wastes and use the energy and material in them to meet human needs, for things like food, water, shelter, energy, and information.  We can create human-made systems that integrate with the local ecology, that behave as living organisms do, that resolve the conflict between modern human society and the rest of the biosphere. Don't believe me? Great! That's what makes this project interesting! 

Check it out:

It's possible to use plastic and biomass to make a flammable gas that can power internal combustion engines.

It's possible to use internal combustion engines to do things like shred waste and make electricity. 

It's possible to thermally decompose many common plastics into liquid fuels that can run unmodified gas and diesel engines.

It's possible to use electricity and and shredded plastics to 3D print or mill plastic objects in very nearly any shape (that's why it's called plastic)


The Design Challenge:

This project is my best attempt to design a machine that mimics the metabolism of a living organism, that meets or strives to meet the following criteria:

1) Is capable of metabolizing as many common household waste materials (cardboard, paper, plastic, glass, aluminum, etc, etc, etc) as possible into the resources and energy required to power itself as long as there is trash or biomass available to eat.

2) That is capable of synthesizing and replicating ALL of it's own parts, enabling it to grow, adapt, evolve, and self-replicate. Similar to the Rep-Rap project, the goal would be to...

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helical turbine v1.skp

SketchUp version of turbine design

SSEYO Koan Play File - 9.91 MB - 10/04/2018 at 16:36


Turbine Grasshopper

Grasshopper definition of parameters. Requires Rhino in order to create cut files, but can be viewed here:

gh - 63.09 kB - 10/04/2018 at 16:36


coroplast turbine cut files.dxf

First draft of cut files generated. Experimental, subject to change.

AutoCAD DXF - 476.92 kB - 10/04/2018 at 16:35


Flake Extruding Print Head SketchUp Model- V1 9-29-18.skp

Most current 3D model of flake extruding head I'm using on the MPCNC. So far, I know it works, in that it extrudes a consistent bead of plastic (currently PP, #5) in response to computer control of the stepper motor. Many improvements can (and will) be made to this design, but it's low cost, easily sourced parts, and good-enough performance warrant documentation. This model is MOSTLY to scale, but not in any technical way, so go by the stated measurements, rather than the model measurements, and make sure to check everything against what you can actually find at your local hardware store.

SSEYO Koan Play File - 4.74 MB - 09/29/2018 at 22:29



All 3D print files for building the MPCNC with exactly 1" (25.4mm) OD stainless steel or aluminum tubing (NOT for conduit)

Zip Archive - 3.98 MB - 09/28/2018 at 18:56


View all 7 files

  • 1 × "Precious Plastic" Open-Source Plastic Shredder Full plans available at
  • 1 × 5HP-8HP internal combustion engine Easy to come by on craigslist for free- $50 - search for used for lawnmowers, edgers, chippers, and rototillers, or search "Briggs and Stratton"
  • 2 × 2" tri-clamp compatible distillation cups These are optional if you want to be able to capture liquid hydrocarbons for making fuels. If you don't use these, you can design the system to just re-flow the liquids back into the reactor. Fuels are dangerous and potentially carcinogenic. Handle with care.
  • 2 × Band Heater Elements
  • 1 × 3" ABS Y-fitting

View all 18 components

  • What is plastic? (It maybe won't hurt me, won't hurt me- I know more...)

    Sam Smith5 days ago 0 comments

    In the process of learning how to recycle plastic, I've learned a TON about what plastic actually is, how it's made, what it's made of, and why the different types have the particular (sometimes peculiar) properties that they do. 

    It's not only fascinating, it's really empowering! For my whole life, plastic has been a material that I have had zero control over. I couldn't make it, I couldn't work with it, and I didn't get to decide what gets made out of it. When I started this journey, basically all I knew about plastic was what most people "know" about plastic:

    1) It's made out of oil, and oil is both running out AND killing the world, and you should feel bad about that.

    2) It can't be burned, and if it is, it produces a poisonous smoke, and you should feel bad about that.

    3) It doesn't decompose, EVER, and it's piling up in the oceans and killing the world, and you should feel bad about that.

    4) It's everywhere, it's in everything, and is extremely difficult not to use, and you should feel bad about that. Especially straws. 

    5) It's made out of toxic chemicals and is probably leaching poison into our water bottle right now, and you should feel bad about that, and probably buy a new water bottle.

    Our society's relationship with plastic sums up the feeling I get from our entire industrial economy- Nebulously terrifying, clearly unsustainable, manufactured by a corporate system that is entirely outside of my control, but also still definitely MY FAULT for the fact that it's killing the world.

    It's a lot easier to be afraid of things we don't understand, and most people don't really understand plastic. That's why I think the term "Precious Plastic" is so brilliant. In two words it reframes our assumptions about plastic, and refers to it as the precious, abundant, disruptively useful meta-material that it really is.

    And of course, all that being said, plastic CAN INDEED be toxic and dangerous. But that's exactly why understanding how, why, and when plastic is toxic is so important- because plastic is far more benign that people often think that it is. When you understand a material, it empowers you to be reasonably cautious about it and to take appropriate safety measures, instead of just being generally afraid of it. Fire is dangerously hot, but it's really, really easy to take the proper precautions to have a fire and not burn yourself. Plastic is the same way. It can be dangerous, but it's fairly easy to avoid danger if you know what to look out for. 

    SO! This post is going go over all the very-specific ways plastics can be dangerous, so you can take reasonable precautions. It's is accurate to the best of my knowledge, but the best of my knowledge is constantly changing- so revisions, additions, and factual corrections are always welcome. Now, let's revisit over those 5 things people "know" about plastic that I mentioned earlier..

    1) Plastic is made out of oil, and oil is both running out AND killing the world, and you should feel bad about that.

    So to address this, let's start with something a little more basic- what even is plastic? There are many different types of plastics, and they all have different chemical and physical properties. However, all plastics are polymers, which just means that they are long, repeating molecular chains of a base-molecule, called a monomer. Poly-ethylene, for example, is just a long repeating chain (polymer) of the ethylene monomer.

    But where did that ethylene come from in the first place? Most people know that most plastics are made from oil, but are a little sketchy on exactly how. So here's a quick recap- crude oil is ancient organic material, mostly plants (basically fossilized sunshine), that were not fully decomposed by animals, fungi, and bacteria before being buried deep underground by sedimentation and/or plate tectonics, which cooked the material under heat and pressure in such a way that the organic molecules...

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  • [maniacal laughter] (cont'd)

    Sam Smith10/09/2018 at 15:59 0 comments

    Nathaniel and I met up at CTRL+H last night and hacked on the printer for nearly 5 hours. We successfully "printed" our first "objects" directly from shredded trash flakes, and we learned a lot in the process. One of the most promising things we learned is that coroplast sheet can indeed be used as a build plate. For a printer of this size, making a heated bed like a typical printer has is a daunting and expensive design challenge. But without a heated bed, how do you get your first layer to stick? 

    I knew that Polypropylene is very self-adhesive, and my hunch/hope was that maybe I could just lay down a sheet of cheap Polypropylene coroplast and that the molten PP would adhere to that, because they're the same material. That way you could just slide in a piece every time you print, and then cut off your object (and then shred up the scrap and print with it, of course). That part worked out quite well- the PP adhered much more strongly to the coroplast than it did to the wood underneath. That means that a heated bed upgrade isn't necessary- putting the cost to replicate this setup at under $500, using almost entirely 3D printable, laser cuttable, or widely available parts.

    We decided to try and print out the Hackaday logo [based on this model from Thingiverse], and this the result of our first attempt. It's more of an "ckaday" logo, but it was an encouraging first shot. Nathaniel adjusted the ratio of extrusion to speed, and we tried again. One of the challenges of this kind of printing is that the extrusion is non-linear. It's not moving a spool of solid filament, it's building forward pressure in the extrusion barrel, and so there's a 3-5 second delay between when the auger starts pushing and when the plastic actually starts coming out of the nozzle. Luckily Nathaniel speaks robot quite fluently, and after a bit of arguing, we got this:

    Not bad! Not, you know, great either, but pretty damn good for our second try. Next steps are to rebuild the extruder to be little sturdier (it was wobbling back and forth a little when extruding), mount the thermistors more securely (one of them got pinched and wouldn't read) and build an actual wiring harness and material feed. But all in all, I'm really happy with this test, and I am confident that this approach can produce useful (if not-very-detailed) objects.


  • Start your engines!

    Sam Smith10/08/2018 at 18:32 0 comments

    I had intended to just fire up the new setup to test to make sure my seals and connections weren't leaking (or if they are, where), and it ended up working so well I was able to fire up the engine! Still a very basic test, with no intermediate gas storage, but very promising!

    The last major step to demonstrating a working prototype is connecting the engine to the gear box, and the gear box to the shredder! From there, there are a million upgrades and re-builds I still want to do, but I'm trying to focus on getting a tangible proof-of-concept running in time for the Hackaday Prize deadline! Onward!

  • Throwback Thursday

    Sam Smith10/04/2018 at 17:09 0 comments

    I've been doing these logs sequentially, but today I wanted to do a throwback to highlight some work we did back in February, right before I pitched the Metabolizer to Hackaday in the Open Hardware Challenge. This project has been a huge learning process for me- lot of parts of it are right outside my skillset. 

    I'm a designer/inventor by nature, the kind of person who needs to understand how things work. So I'm really good at understanding what's possible with currently-available tech, but I rarely have the actual technical skills required to make it happen. 

    Luckily, I have very talented friends, who have helped me immensely on this project, and since I can't pay them anything for their help I want to make sure I at least give them proper credit!

    These are my friends Darcy (Hackaday user DRC3P0) and Matty (Hackaday user softjitter) assembling the MPCNC. Darcy works at the FabLab at Portland Community College, and so she help me print all the parts required to build the MPCNC, and Matty helped us get it moving. They are both rad and very accomplished makers, and you should check out their work!

    I had never worked with any kind of CNC machine before, although I've been aware of them and had friends with access to them for years. Without Darcy and Matty's help, I wouldn't have known where to start!

    Here's a funny picture of Darcy. Sorry Darcy. You're great.

  • It's parametric! (cont'd)

    Sam Smith10/03/2018 at 18:11 0 comments

    Dallas and I hacked on this parametric wind turbine design again last night, and made some real progress! The model now auto-generates flattened array of individual layers, and adds number tags, so they can be turned into individual cut-files required for CNC fabrication. I really want to make a turbine that is as tall as the patio heater is (I'm a sucker for symmetry, I'll admit). That's about 7 feet, or 84 inches. At 5 layers per inch, that's 420 layers of 4mm (3/16") coroplast. By my estimates, that would require around 20 sheets of coroplast, which go for about $11/sheet. So a couple hundred dollars, if using virgin material. But coroplast is also easy to find in the waste stream in the form of lawn signs (and there will be lots available come November 6th...) So if I can "recover" a few of those, that should bring down the cost significantly.

    This is my most-current design on Shape diver. You can play around with it too! Check out the live parametric model here! Unfortunately, shapediver doesn't let you download the file, or the cut-files, which would be really epic, but it does at least give you a taste of the power of parametric design, without all the expensive hardware and difficult to learn software. And I'm uploading the Grasshopper definition file to the Files section, so even if you don't have Rhino/Grasshopper yourself, you can find the parameters you like on shape diver, and then send the values and the open .gh file to someone who does, and they can compile the cut-files for you. And of course I will also post the cut files for the version I end up building either way.

    But I really like the idea of letting people play around with the parameters of this design. This will not be an efficient wind turbine, and efficiency is not my top priority at this point. But I think it's cool that people could tweak the design to suit their preferences and then test their results against mine, and together we could find more-and-more efficient versions moving forward. It's sort of a microcosm of how I hope this whole project could be improved systematically over time by a community of folks, like the Precious Plastic machines have been. 

    But if that's gonna happen, I've got a lot to do in the next 3 weeks!


  • You must create the documentation you wish to see in the world

    Sam Smith09/29/2018 at 18:56 0 comments

    "Open Source Hardware" is a much more nebulous concept than open-source software is. "Open-source" originally meant to "open source-code", which is as easy as copying and pasting text to the internet (which to be fair, isn't that easy, all things considered). The development of git and distributed version control has allowed for very rapid, decentralized, mass distributed development of OS software, and it has drastically changed our world.

    While many people understand the disruptively useful potential of applying this same kind of massively distributed approach to designing and building the physical objects and infrastructure (Sieze the memes of production!) the physical nature of hardware presents a completely different set of technical challenges to widespread sharing than open source software does.

    It's not enough to just say that your design is open source, but then fail to actually provide detailed technical information and well-thought-out step-by-step instructions in an accessible format, and doing so is much, much harder than posting code to the internet. It's work. Specialized work. And honestly, people who are good at building stuff are often not very good explaining their work in an accessible way.

    One shining example of successful open hardware documentation is the Precious PlasticProject. Dave Hakkens not only designed a set of useful machines, he ALSO posted a wonderful set of detailed plans, including DXF cut files and schematics, along with HOURS of detailed, engaging, and accessible instruction videos on an easy-to-find website. He then went traveling in India for several months with limited internet access, and when he came back, he found that hundreds of people around the world had independently replicated, and begun to improve upon, his designs.

    I was one of those people- I built a shredder following his plans in November of 2016. His documentation made it seem much easier than it actually was to build, but the detail and support he provided allowed me to stand on his shoulders, so to speak, and create a machine that I could not have designed on my own.

    Open hardware, at best, lowers barriers the to entry for a given technology. As the deadline for the Hackaday Prize nears, I find myself being torn between working on my project, and working on my documentation. I'm something of a perfectionist, and I always feel that what I have actually built always falls far short of what I am trying to build, and that often keeps me from sharing my designs. Not because I don't want to, but because the NEXT version will always be better, so why waste time documenting THIS version, you know?

    In order to combat that very counter-productive mindset, I'm working hard to meticulously document what I'm building, bugs and all, so that at least people can see what I'm doing and how I'm doing it. It's surprisingly vulnerable. So, here, I present my current design for my open-source flake extruding 3D print head. The 3D assembly model can be found on the SketchUp warehouse.


  • It's parametric! (do do do do Do do)

    Sam Smith09/21/2018 at 18:05 0 comments

    This is my friend Dallas Swindle (yes, that's his real name). Dallas does parametric design using Rhino/Grasshopper, a skillset I am deeply envious of. Luckily for me, Dallas is a cool guy who was kind enough to donate his time and extremely specialized skillset to my cause.

    "Parametric Design" is still a rather new concept, but it's disruptively useful, and if you don't know about it, you should! It's basically a way of doing 3D modeling where instead of modeling something like you would in say, Sketchup, creating a static model, you instead define a series of relationships and parameters, and let the computer generate a model based on those relationships and parameters.

    I wanted to build a helical wind turbine made of stacked, offset sheets of plastic, but in sketchup, at least with my skillz, there was no easy way to do that except by rotating each layer individually, one at a time, which is not only intensely tedious, it also makes it functionally impossible to see what small changes to the parameters have on the overall shape. If I want to see what a 2 degree offset looks like, rather than a 3 degree offset, for example, I have to do it all over again. 

    With Grasshopper (a third-party plugin for Rhino that has now been incorporated into Rhino's codebase) all you need to do is slide a slider back and forth, and you can watch your model change in real time. That is, of course, IF you have Rhino, a hella-fast computer, and a knack for abstract problem-solving.

    Luckily for me, Dallas has all of those things! He also showed me a really cool website called ShapeDiver, which is kinda like thingiverse- it's a place where you can upload your grasshopper sketches for other people to use. 

    The neat thing about it tho is that it let's you play with all the parameters defined in the sketch within your browser, without needing to own the expensive software that is required to actually build the sketch. That lowers the barrier to parametric design considerably!

    We're working towards building a sketch that not only lets people define the parameters, but also flatten them, pack them into user-defined sheets, and generate cut-files that can be used to fabricate the parts using a CNC router or laser cutter. We're not there yet, but we're getting close!

  • HDPE floats

    Sam Smith09/20/2018 at 19:04 0 comments

    In order to collect and store the gas produced by the metabolizer's reactor, I designed this floating-drum style gas collector using two plastic barrels. I had originally seen this concept used for storing biogas from anaerobic digestion, and I was reminded of it back in June when Hackaday posted about YouTuber [NightHawkInLight]'s gasometer build.

    The principle is pretty simple- people have been using this tech since the early days of coal gas to store low-pressure gas. It works sort of like a battery or capacitor stores and smooths out electrical demand- it accumulates a gas that is produced slowly or intermittently, so that it can be used all at once, on-demand. It's low-pressure, pretty safe, and cheap and easy to build.

    [project link for photo]

    One problem with the floating drum approach is that if the inner barrel gets too full of gas, and isn't supported in some way, it can get kind of tippy, which both looks bad (IMO), and can potentially lead to the gas escaping from the barrel. I wanted to do something to make sure that didn't happen. One night I had the idea that maybe I could use bulkhead fittings, and two different sized pipes, so that the drum could float up and down along a central pipe, keeping it neatly upright, and making the whole thing look cleaner and more stable. Here is the original concept drawing I did that night (sorry for the bad contrast):

    A few weeks ago, I built a first prototype, and was pleased with the results. I was able to use 2 different sized threaded bulkheads (1.5" and 2"), which then thread to correspondingly-sized pipes (ABS, PVC, HDPE are all fine and very common in the waste stream. I got mine used at Rebuilding Center), and the two sizes sleeve together nicely. The smaller pipe goes into the bottom of the bottom barrel, the bigger one goes onto the top of the smaller floating barrel, turning it effectively into a big floating donut, and when the floating barrel fills with gas it slides up and down on the inner pipe, keeping it from tipping over, even when really full. This also increases the effective storage capacity slightly. Then I cut a big hole in the original barrel top, which stabilizes the inner barrel from the sides, and I think it looks cool.

    Just the other day, I build a second iteration, making some minor improvements on the first. On the first attempt, I had tried to use the 2 bung fittings that the barrel already had as the two gas input/output holes, which seems intuitively obvious at first- why cut new holes when there are already 2? But I found them hard to seal, and they required special fittings from the hardware store. I ended up having to cover them in silicone caulk in order to get them air tight- and air-tightness is very important in this case. 

    Not only do you not want to lose your gas, but wood gas also has a component of Carbon Monoxide, which can be toxic in large quantities. Best to not have any leaks. And additionally, if O2 can get into the barrel, the mixture inside can become combustible. The barrel-in-barrel design is such that if the gas does happen to combust/explode (which is rare), the barrel will simply pop off, dissipating the energy and preventing a true explosion. That's an inherent is a fail-safe of the design, which is cool I guess, but ideally we'll do everything we can to prevent that from happening. So, the point is, you want your thing to be truly gas tight.

    So on my second iteration, I just flipped the inner barrel upside down, and used 1/2" bulkhead fittings I got at my local hardware store, which worked waaaaaaay better, and was way easier to do. This version was perfectly air-tight (the barrel doesn't fall at all after being filled with gas). I left the original bungs open on the submerged side, and now they just allow water to pass in and out from the bottom. Much better! 

    One neat side effect of all this is that it makes a water-tight through-hole that goes through both barrels,...

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  • [maniacal laughter]

    Sam Smith09/19/2018 at 00:48 0 comments

    We got the MPCNC moving AND pushing plastic last night, a milestone I've been working towards for nearly a year! It would be generous to say that we successfully 3D printed anything last night, but this is a major step forwards towards that goal.

    In Portland, every other Monday, there is a meetup called "Dorkbot" at CTRL+H, one of the local makerspaces. Dorkbot is a great place to get help on projects, as it's mostly very smart people who like solving problems. If you can bring smart people interesting and worthwhile problems to solve, they will often do very valuable work for free. (See also: "Sometimes the best way to get people to help you do something is to just start doing it wrong in front of them."

    Nathaniel Garst, local 3D printing wizard, stayed troubleshooting with me (read: doing all the work) and at about 12:30am we got it pushing plastic and moving at the same time! The next step is to start dialing the temperature settings and speed, and see if we can build some large-format, low-resolution objects directly from recycled plastic flake.

    This was the first time I have extruded polypropylene (#5), and it's exciting because this was plastic I had shredded up just a few hours earlier, with my precious plastic shredder. The flakes it's printing from were previously scraps of coroplast I had lying around from other projects, which makes it the first real piece of my house trash I've turned into something else! Not something useful yet, but you know, one step at a time.

    There's still several lifetimes of troubleshooting ahead, but I feel pretty confident that the concept is sound, and of course, people are already doing this! It's not like it's my idea, it's just a good idea, and in my opinion kind of inevitable. My goal with this build is just to see if I can help make the tools required to do it a little bit more accessible. This whole setup, MPCNC and Extruder, should only cost $500 or less! If we can get it actually printing useful stuff, any kind of useful stuff at all (Wind turbines? Bike frames? Building trusses?) directly from plastic flakes, directly from the open-source shredder, that would be disruptively useful!

    Stay tuned!

  • The answers are blowin' the in the wind

    Sam Smith09/14/2018 at 22:40 0 comments

    I've been using SketchUp badly for many many years, and over the years I've slowly gotten pretty good at it. It's now my go-to sandbox for designing stuff. I wish I could use a more full-featured program Rhino/Grasshopper or Fusion 360, but alas, sometimes you gotta stick with what you know. 

    My approach for this project was to create 2 different Sketchup models- a concept model that I can use to explore the shapes and dimensions and aesthetics I want, unconstrained by annoying things like "reality" or "physics" or "how thing actually fit together", and then a working model, that reflects as best as possible what I have actually built. Then I work to systematically bridge the gap between theory and practice. 

    I really love the toroidal shape of the electromagnetic field, and that's been guiding my design for this. It helps that most of the tubing I've been working with comes in coils, which makes it easy to pull and sculpt them into cool-looking spirals and helices. 

    The tapered shape of the patio heater I'm using as my support structure for the distillation tower lends itself well to that shape, but only half of it. To get the balanced look I want, I'm trying design a lightweight turbine that goes on top, to balance out the look of the thing for that nice vortex feel.

    So I started playing around with using stacked rectangles that are off-set from each other, in order to get an nice dynamic vortex shape, while still using rectangular layers that are easy to cut. My idea is to use coroplast, which is one of my very favorite materials.

    It's the stuff that political lawn signs are made of, it's widely available both new and in the waste stream (particularly during and after election cycles...) its extremely durable, lightweight, easy to cut, score, fold, bend... it's just a really great material to work with. And it's made out of Polypropylene (#5) plastic, which is reasonably UV resistant, strong, non-toxic and heat weldable. Neat!

    So my current plan is to see if I can take a bunch of Political lawn signs, impale them all on a stake, and see if I can use it to generate energy from wind and/or the updraft created by the hot exhaust gases. This is admittedly more of an aesthetic design choice than an efficiency/engineering choice, but it makes use of a common and widely available waste product, and I think there's something poetic about repurposing political propaganda to generate clean energy. 

View all 29 project logs

  • 1
    The Engine

    What it does: The engine turns chemical energy into rotational shaft power (and heat). 

    What it is: I'm currently using a 5HP Briggs and Stratton go-kart engine. These engines are cheap and they're everywhere- usually attached to go-karts, lawnmowers, chippers, etc. You can find them on craigslist for $0-80, and new from places like Harbor Freight for $100-200 Get one that doesn't require oil mixed in, and if you can find one with easy-to-modify exhaust and air-intake ports, that's a big plus, because we're going to be modifying them so that we can run the engine on a gaseous fuel.

  • 2
    The Gearbox

    What it does: The gear box takes the 2000-3000RPM shaft power from the engine and uses a series of gears to reduce the speed and multiply the torque. A gear ratio in the range of 30:1-50:1 is ideal, with an output RPM in the ballpark of 100RPM. This gets us the torque we need for the shredder to shred right through anything.

    What it is: There are many strategies for gear reduction- car transmissions, gear and pulley systems, hydraulics, worm drives.... It's a whole thing. I'm using a worm-drive style 40:1 industrial gearbox I found at salvage yard for $5. That was a lucky score- finding a good gearbox is one of the more difficult/expensive parts to source. Check craigslist.

  • 3
    The Shredder

    What it does: The shredder shreds up waste into small bits so that it is easier to process, and reduces waste volume significantly. Think of it as the metabolizer's teeth. It mechanically decomposes incoming feedstock to prepare it for further chemical decomposition.

    What it is: The shredder I'm using is a "Precious Plastic" open-source shredder. The shredder box cost me about $400 to get the parts cut, and a few days to assemble. You don't have to use a PP shredder, but they're the best open source option I know of. An industrial shredder might work a bit better if you can find one, but the scale of the PP design is ideal for backyard processing. Wood chippers don't really work well enough for our purposes, as they are designed for wood and tend to try to "whack" things apart, which doesn't work well for plastics. Industrial paper shredders are and option, but their motors are often under powered and must be modified. Don't even try using a cheap paper shredder.

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Tony wrote 06/25/2018 at 16:07 point

I'm afraid Manta103g has a few good points, but I don't think they're show stoppers. For instance, it'd be great to have this machine fuel itself off the plastics, but, if that's gonna spew toxic gasses then maybe we can find a way to just compress waste plastic into bricks. In fact I think they're already starting to make houses that way, so, theoretically we could start pressing plastic into slabs that a table top CNC machine could cut pieces that snap together to make tiny houses, or even little bike trailers people can sleep in and lock their stuff in for security... 

Then we'd have something we could get known for, enabling us to garner the attention and social capital to build something even more sophisticated, such as a robotic decomposer.  What do you think?

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Sam Smith wrote 06/25/2018 at 17:00 point

Manta103g does have a few good points, but they're not show stoppers, and it annoys me when people tell me so authoritatively that something isn't possible. 

To be fair, I'm learning too and by no means and expert, but I disagree with Manta103g's hot take, and with the caveat that I very well could be and am willing to be wrong, here is why: 

It's true that some plastics off-gas toxic vapors even when melted (not even burned). This is NOT true for all plastics, but it is for ABS, and it's true that ABS fumes from 3D printers are dangerous. It turns out that's actually caused by nano-particles or UFPs.

From wikipedia "ABS is stable to decomposition under normal use and polymer processing conditions with exposure to carcinogens well below workplace exposure limits.[20] However, at higher temperatures (400 °C) ABS can decompose into its constituents: butadiene (carcinogenic to humans), acrylonitrile (possibly carcinogenic to humans), and styrene.[20]

Lower temperatures have also shown that ultrafine particles (UFPs) may be produced at much lower temperatures during the 3D printing process.[21]Concerns have been raised regarding airborne UFP concentrations generated while printing with ABS, as UFPs have been linked with adverse health effects.[22]"

And all plastics, not just ABS, will decompose into a toxic smoke when heated.

But that doesn't mean that ABS cannot be safely decomposed into into a fuel, and in my mind, it actually is a decent argument for why ABS should be decomposed into fuel instead of being recycled, since melting/recycling it releases dangerous compounds whereas when used for fuel those compounds can be more easily contained. 

Check it out- ABS is Acrylonitrile Butadiene Styrene, chemical formula: (C8H8)x·(C4H6)y·(C3H3N)z). It's chemical structure is composed entirely of Carbon, Hydrogen, and Nitrogen. If you throw it onto an open pit fire, it will decompose into short-er but still fairly complex hydrocarbons, which can be all sorts of toxic compounds- styrene, benzen, toulene...

So don't do that! People have this idea that burning plastics is toxic, because it is when you do it in an open fire, at low temperatures.

If instead you shred ABS and heat it inside an air-tight reactor vessel, such that it gets hot and decomposes in the absence of oxygen, it will still break apart into smaller hydrocarbons, and some of them are toxic, but none of them are gaseous at atmospheric temperature and pressure.

If you cool the gas stream boiling out of the reactor in a condenser that cools the gas ALLLL the way back down to around 70F, which is what my condenser coil does, the only 2 compounds that remain gaseous at that temperature are Hydrogen (H2) and Carbon Monoxide (CO). 

H2 and CO are both combustible, and when mixed with O2, they combust into CO2 and H20- both non-toxic and 100% bio-compatible compounds. Now, I'm in favor of burning wood chips until I can guarantee the system is 100% safe and air-tight before working with more dangerous feedstocks, and I'm not there yet.

But ABS can in fact be thermally decomposed ALL the way back down to CO2, H20, and N2, and that makes those elements available to build built back into living things again. It essentially frees those organic elements so they can participate in the cycle of life again. 

And doing so releases heat, and also accumulates liquid hydrocarbons that condense out of the gas. I'm working on a centrifuge design that will sort them by their molecular weights, and then pump them into separate storage containers, so even the potentially dangerous ones can be stored without ever coming into contact with humans. 

The undesirable compounds- the ones that are either too heavy or too light to be useful by themselves, can simply be reflowed back into the reaction vessel, where they will break apart further into even smaller compounds, over and over, until they make it to CO and H2. And the desirable compounds- including analogues for gasoline and diesel fuels- can be filtered, stored, and used later as bio-fuel.

And the process necessarily produces waste heat and energy, which I intend to use to recycle as many of the other common recyclable and non-toxic plastics (HDPE, LDPE, PP, PET) into new objects- using molds, 3D printers, and extruders- which we could turn into building materials, and I think turning them into snap-together tiny homes is an awesome place to start!

Hope all that helps! Again, I'm not saying that doing any of this is trivial or easy, but I am saying that it is definitely possible, and I intend to figure out how to do it as best I can. 

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manta103g wrote 06/18/2018 at 23:35 point

No way to accomplish your target since some plastics, decompose to highly toxic gases, if heated. This is the reason, you should never print anything 3D in closed space to avoid inhaling highly toxic vapour gases. Many ppl are not aware, 3D printer should be operated in large,  ventilated space only.  Interest in ABS is below zero, since you cannot process ABS into fuel and workshops prefer clean ABS granules on input. Seperation of plastics is highly complicated issue, what comes next is cleaning and washing, just another highly expensive process. This is the reason China factories showed interest in PET bottles only, since PET can be processed alike nylon into usable PET yarn. I can tell you more and more and more about why the world doesn't love plastics processing. We have too much raw oil and gas to manufacture clean raw plastics, so interest in used plastics is low. What is hot today are metals and metals processing.

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Michael Barton-Sweeney wrote 05/02/2018 at 16:56 point

Nice project!

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