I haven't talked about this on here, but I've been working on a design for a low-cost air purifier (<$100) suitable for a kid's bedroom. Looks like this (iphone X for scale)
filter is $35 from bunnings, used in multiple cheap shop vacuums. HEPA H13 rated. The design uses a 120mm computer fan (~$35) and runs on a portable power bank, like you charge your phone with.
so you can run it off mains power using a USB phone charger, or battery pack. A 5,000maH pack will run it for ~8hrs.
here's a clip of it clearing smoke from a plastic box. This was a 2min test to see if the fan had enough static pressure to draw through the filter. I sped up the clip so it takes 10sec.
so my goal here is to somehow get this out to communities that can't afford a $500+ 'single room' air purifier. If you have any contacts or ideas about how to do that, let me know.
last post on it for now: the print takes ~8hrs and uses about $5 worth of PLA. Its a very easy print, I played with the design so there's no supports required. You do need a decent size build area, I'm using an Ultimaker 2+.
@Kels_316 This is awesome.
@Kels_316 the future is both amazing (3D print a machine) and horrible (air purifier for child’s bedroom)
@liamvhogan yeah it's dystopian scifi areas.
@Kels_316 @liamvhogan There's probably a word in German for dystopiawesome.
@Kels_316 neato! What's the widest point of the print? Fairly sizeable printer needed?
@Kels_316 bugger, just a bit big for mine!
@twiddlekins you could do it in four parts and glue it together, let me play with the file and see if I can make it work. What sort of printer do you have?
@Kels_316 I figured it could probably be split. Flashforge Dreamer
@twiddlekins split into 4, put a .25mm gap on the slots so it should go together without much sanding. Had to lose the '12v' under the socket. Biggest dimension is 136mm now, should fit?
@twiddlekins you'll have to use supports under the notches
@Kels_316 should do yup!
@twiddlekins I should have the info to upload a bit later today, I'll put the STL files for this version up as well. Will post a link. If you print it let me know how you go.
@Kels_316 I shall do!
@twiddlekins github page is here: https://github.com/Kels316/DIY-Air-Purifier/blob/master/README.md
it has a folder for the quartered STLs. Have fun!
@Kels_316 cool thanks I'll have a look!
@Kels_316 two halves printed up and joined. Pretty good fit with just the slightest bit of post processing! Will finish the other two tomorrow.
@twiddlekins ah nice one!
@Kels_316
Thank you, this is the kind of problem solving we need. Overconsumption and greed has gotten us into this mess, the least we can do is mitigate with community, pragmatism, and open source. 
@boyd strong agreement!
Server run by the main developers of the project 
It is not focused on any particular niche interest - everyone is welcome as long as you follow our code of conduct!
so over the next couple of days I'll tidy up the design files and upload them to github with the BOM and some instructions. You do need to be able to solder to make the connector plug, and have access to a 3D printer for the top piece.