Thanks. The transistor for the solenoid actually burned out last weekend, so I put another MOSFET there, same kind that I used for the blower. Now it works again. I also took the opportunity to fix a bug, simplify the display, and add a 5 minute idle timer to lower power consumption when (not if) I ...

Now I wonder why I didn't use a spreadsheet to do the calculations. That'd've (is that a word?) been a lot easier. Having used this device now on several occasions, I'm very happy with its accuracy and speed. The only misfire was when the propane tank tipped over, and liquid got into the regulator. ...

Let's do the math for puff metering a hybrid with a closed chamber. We'll use numbers a bit different from mine, to make the example clearer. I've sanity checked the result and double checked some of the math, but if someone wants to check and verify (both thinking and actual math) it's appreciated....

That's a good writeup covering many fueling scenarios. If you wanted to expand on it, you could add liquid metering and my method (let's call it puff metering ). I'm halfway through writing the formulas, but I've been coding all day (the software is done, two hardware bugs were found and fixed, smok...

Thanks for your thoughts, Mark. There are no pulse width issues with my design (apart from too short pulses leading to inaccuracies). When the solenoid is on, gas is being led to a small metering chamber (equivalent to having the first ball valve open on a traditional meter), and when it's off, the ...

Hi all, I've been away from the forum since forever, but I'm still firing my old cannons now and then. They all reside at the airfield where I skydive, since it's there I have the most space and the best audience. My carrot combustion cannon (showcased here ) has been my go-to since it's not tied to...

Too bad about the car. My old 1" copper tube piston hybrid (actually the first ever piston hybrid, afaik) can fire pneumatically, and has in fact almost only been used as a pneumatic, because of fuel mix issues I never got the time to resolve. It's an over/under rather than coax though. Coax gets ex...

The gas explosion handbook may have some interesting info in the chapter about explosions in vessels, pipes, channels and tunnels: http://www.gexcon.com/article/handbook-chapter-9

You could also use a spring to produce the recoil force, and use pneumatics to compress the spring. Advantages: The spring is most powerful when fully compressed (or stretched), so the acceleration will be quick The penumatics need less flow, as the resetting of the spring can take much more time Th...

How about launching water out the back? That can be made as heavy as you like and is relatively harmless.

Interesting ideas. As already mentioned, you need the front pistons to be larger than the back piston in order to get a net force pointing forwards. You'd also need the fuel/air mixture in the measuring tank to be at atmospheric pressure or very close, if it's not it will push the mechanism forwards...

The list of old members popping back for a visit keeps growing :) other hobbies Like? Skydiving, fireworks-making, and girlfriend+teenage stepdaughter are the things that have eaten my cannon time. I may dust them off and bring them to the skydiving club next year, as some of my friends there are i...

This is wonderful, I'm glad to see that this style of hybrid valve is catching on at last. I'm sorry to say that my own proof of concept cannon using this type of valve has been sitting idle for >5 years now, with unresolved metering issues, in favor of other hobbies.

In my airsoft semi, the reload mechanism is connected to the piston in the main valve itself. I know another member has copied the design for firing marbles. If I were to build it again, I'd try to use a spring between the piston and the reload mechanism, instead of a solid rod - the piston generate...

Maybe I'm late to the party but here goes: For recoil- or gas-operated systems, you get a lot of force for a very limited time, which can be difficult to handle. My idea is to use this force to tighten (stretch or compress) a spring, and nothing else. I think a long stretch-type spring from a table ...