What should I build next?

[gwoloshyn]

I have $80 from Christmas (along with a brand new Dremel accessory kit!) and I'm looking to build either a basic combustion (but a really cool design) or a massive huge air cannon. I am leaning towards the air cannon because I already have a 2.5" piston valve laying around waiting to be used.
But then again, a combustion would be nice for the winter months to come.

Any thoughts?

[jon_89]

Here is my idea for a massive pneumatic. Two inch chamber that is about six feet long and a one and a half inch eight foot barrel with a one and half inch union (burst disk). According to ggdt at 50 psi you should get more than 350 foot pounds of energy.

[pizlo]

I'm just guessing but I really doubt that a huge chamber at low pressures will yield any great results. when the potato is half way out of the barrel the pressure through out will be very low.

[jackssmirkingrevenge]

I'm just guessing but I really doubt that a huge chamber at low pressures will yield any great results. when the potato is half way out of the barrel the pressure through out will be very low.

When you go for larger calibres, you'll be surprised what power will be exerted even at low pressures. For example, for a 3" barrel, a pressure of just 10 psi will exert just over 70 lbs of pressure on the projectile. For a 4" barrel at the same pressure, this climbs to over 125 lbs of force - you get the idea.

gwoloshyn, I would go with the huge pneumatic if you have the space to fire it

[pizlo]

Ok. But I do recall someone (you?) saying that when they ran the numbers that a small chamber at high pressure had a larger yield than a larger chamber at a low pressure.

[jackssmirkingrevenge]

Ok. But I do recall someone (you?) saying that when they ran the numbers that a small chamber at high pressure had a larger yield than a larger chamber at a low pressure.

Yes, definitely, especially for small launchers - but as you scale things up, it becomes harder and more expensive to get high pressure fittings, the advantage of massive pneumatics is that if your valve is good enough, you'll still get loads of power even if pressures are relatively low.

[gwoloshyn]

Here is my idea for a massive pneumatic. Two inch chamber that is about six feet long and a one and a half inch eight foot barrel with a one and half inch union (burst disk). According to ggdt at 50 psi you should get more than 350 foot pounds of energy.

You initiated a thread hijacking massacre! LOL, JK, thanks for the idea.

[tansit234]

I have what I dubbed BFG in my garage, (3) 5 foot air chambers of 2 inch pvc (its hard for me to find larger in PW unless I go to a supplier an hour from here). I have a little extra volume from a front and rear manifold holding everything together, it all fires with (3) 1 inch orbit valves all modded and manifolded together to one pilot valve. Problem is the 30 pound sucker is difficult to aim at best and at 100PSI I only shoot a few potatos before I worry about cops because of the loud crack that echos around my neighborhood for a mile or better. All but my propane tank gun are 2 inch barrel and I've been neglecting the tanker.

The bigger they are the less you fire them. I have 4 pneumatics since its easier for me than combustion. Now I find that I'm going smaller, (8.) AA batt. cannons, some I kept some I sold or gave away, and a BBMG vortex rifle.

[DYI]

The damage you can do with burst disk guns is impressive, but they're not the kind of thing you use very often. For ease of use and continued enjoyment, a good piston gun which can use readily available ammo is probably the best choice. Having to make custom ammo always decreases the use a launcher gets.

350 ft/lbs is very, very little. I have a handheld burst disk gun with a .75" barrel that can do 450. For something that big, you're looking at 1000 at the very least for it to be enjoyable enough to be worth setting up. The original SCTBDC was built only with parts available at the local hardware store, and could do ~1200 ft/lbs before the massive upgrades that turned it into the v1.5.

[jackssmirkingrevenge]

350 ft/lbs is very, very little.

Tell that to anyone who's been shot with a '45 :p