https://youtu.be/SAIH7HYbdSI. Here is a variation on the big shot I made a couple of years ago. Wanted something short that I could shoot like a gun. Skateboard wheels for pullies, archery trigger. Worked okay up to about 75 feet. Regular big shot is better. I still just hand throw. Fun project though.
I liked this fellow's modifications to the APTA -- he calls it the "APTA Old Fart Edition" (reticle sight, longer pressure chamber, mortar position):
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and with a Butterfly valve instead of a ball valve:
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Having the butterfly valve is a huge improved over the ball valve. Not because it is stronger but because it dumps the air chamber faster and with less physical movement. I also agree with OF that launching from a shoulder position is the least consistent. Not a fan of CO2 (as it will change with temperature) for the load force or the use of a red dot sight that limits you to positioning yourself to sight down it. With a 12oz bag and 1.75" zing-it the APTA should reach close to one vertical foot per pound of chamber pressure.
You are correct in very low handle angles, but it soon takes over the butterfly valve. I didn't realise that a plug valve (usually used for natural gas and is easier to come by than a butterfly) is better than both both and is still a quarter turn valve. Anyways you can also reduce up to a larger valve to help with flow. Anyways, they are all really similar, and maybe a spring loaded valve actuator (ie a bungee cord with a trigger mechanism) would be an actual improvement? I dunno, i need to build one, but i already have a big shot....
If you look closely at that chart, (assuming I'm reading it right) it shows that the butterfly valve dumps a lot more than the others when it is just beginning to open.
Being that it is holding high pressure air, that makes a big difference and gets things going with authority.
I really, really want to play around with a coil spring under the valve arm. A trigger would make it way better and its damn good as it is.
Frans, that sounds like an invite, and i would love to see the redwoods, let alone climb them! Although at this moment in my life, that graph would be especially boring, because i can't possibly swing that for quite awhile
You are right about the chart, but they are all very similar in performance was my attempted point. I have made this explicitly clear before, i do trees part time as best, but I'm a union steamfitter and pipeliner as a day job, so piping is something i can actually contribute on. And if i built one, just on that challenge alone i would have to do a welded one, that i could pressurise to a couple thousand psi, so