Just had a major "EUREKA!" moment! CLEAN PORTABLE 120V/60HZ POWER ON DEMAND FROM TRASH GAS! One thing that's been bugging me as the deadline for the Hackaday Prize approaches is that the reactor part of the system is very simple to build and requires almost no specialized skills- not even welding or cutting. It can be built entirely out of readily available parts that you can get on Amazon or at any hardware store (detailed BOM coming soon). I did that on purpose, because I wanted this project to be as easy to replicate as possible. But the engine/shredder/generator I built, while a neat proof-of-concept and technically what I had hoped to build, is super-janky, highly technical, and would be very difficult for others to replicate since it's all custom parts and custom attachments.
Powering the shredder with electricity is much easier to do than direct engine power, and it lets you easily reverse the motor if it gets jammed. It may not be quite as powerful or efficient as direct engine power, but the gains don't really make up for the added difficulty to build. It's also WAY quieter, which is important if you want to be able to actually talk to people.
So as a last experiment before the deadline, I took a chance and bought a Harbor Freight "Predator" generator for $550 (including the 1-year unconditional replacement policy, of course) to see if I could get it to run on trash gas. I took off the side access panel, and the cover to the air filter, and removed the foam filter that came with it and replaced it with another piece of foam I had- so I could put it all back together and return it if it didn't work.
I copied the shape of the air filter cover, and used my girlfriend's Glowforge to cut out the parts in clear and black acrylic. The Glowforge has a "trace" function that makes making simple parts like this super easy- no CAD! I had to play around with the air-fuel mixture, and promptly ran out of gas (you can see the barrel emptying in the vid), but I was able to get it to run with enough speed to produce clean, 120V/60Hz house power, which is huge!
While there is still a lot of testing to do (total wattage output, long term wear...) this a major step forward! This means that even if you bought all of the parts of the system new on Amazon Prime, which is the most expensive way you could do it, it would all still come in at under $2000 for everything (not including the Shredder ($600-$1200) or 3D printer (>$500)), and it would let you produce around a kilowatt of clean AC power from any reasonably dry biomass- woodchips, pellets, grass clippings, dog poo, cardboard, paper, even the Amazon packaging all the parts came in... AND it produces hot water in the process!