Optimising an Air Engine

Right, that makes sense on the pressure side. I'll be curious if bottles from a multi pack (wrapped in plastic when you get 6 at a time) have less scratches, out of certain brands' bottles differ enough to offer additional thickness. (Thinking coca cola bottles, they usually have a pattern in the plastic with extra thickness). Regarding the flexible resin, I assume for warranty/wavelength reasons you're not keen on trying non formlabs resins? £200 /L sounds absurd! I'm looking at some that are instead in the 45-60 € range... Let me know if you want me to print a few and mail them over?

Jonathan Charnas

I looked at some of the formlabs flexible resins, but because the seals are so small, it seemed very expensive for what I needed. I think it's about £200 per litre, which if the material was too soft/hard, would be a big waste. Whereas, I can buy these 2 part rubbers/silicone for about £10-20 per litre. It's not limited by 60psi, but it is a safe pressure for the PET bottles. With my earlier engines, I would do a lot of testing in my bedroom, so I didn't want to risk anything exploding. So I've stuck with 60psi as a reference to compare performance. The bottles should be capable of taking double that pressure, but it's always hard to tell if they have been weaked by scratches etc whilst transporting to the shops haha.

Tom Stanton

Haha thanks for the support! I had the same issue, I couldn't justify the cost of a vacuum pump and a large vacuum chamber for such small molds. Also, I assume the syringe should pull a vacuum faster than a vaccum pump and chamber, for using faster curing materials. Hope the castings turn out bubble free!

Tom Stanton

Terrific video. I understand that the old CO2 motors could be adjusted by screwing the cylinder in/out of the crankcase. See article here: http://www.gasparin.cz/?show=frames&site=co2&page=co2/whatsnew/whatsnew&lng=en 2nd page, first column, about 2/5 of the way down. Evidently it's a power/run-time trade-off. This adjustment would alter the stroke length and would also affect the valve timing. I don't know which would have a greater impact. Have you experimented with the valve timing? Maybe by using a long threaded 'set screw' instead of a fixed metal pin? FYI: I illustrated this type of engine on my web site years ago. I should really update it: http://animatedengines.com/co2.html Thanks for all you do! -Matt Keveney

Matt Keveney

Awesome progress on the air engine! I just started using a resin printer as well, and I'm impressed with how well it's handling the pressure. I also saw that there are flexible resins for sla printers. Have you thought of looking at those for making your seals? Remind me why 60psi is your limit? Is that as much as you can reliably use in a pet bottle without it exploding?

Jonathan Charnas

Dude! I love these air engine videos. I had a few air hogs and was always amazed at them. Even went to school for aeronautical engineering so its doubly fascinating to me. But it's always the little things like the syringe vacuum that are the total icing on the cake for me. I am doing some small molding (but bigger than your seals) and I don't have a vacuum chamber or pressure chamber and was trying to think of how to do these castings. Now thanks to you I'll be doing that but with a giant syringe 300ml I use for cleaning out my vat in my resin printers. THANK YOU THANK THANK YOU THANK YOU THANK YOU... Going to take the money I save from buying a vacuum chamber and put it towards your patreon. Did I say thank you yet? ▼ Reply