FAIL - 12 gram launcher

[PVC Arsenal 17]

Some time ago I had the idea of making a 12 gram C02 cartridge launcher. The idea was simple, it just involved a spring loaded bolt with a nail on the end. The bolt was cocked back and held in place by a simple sear. The sear consisted of a pin to hold back the bolt. When the pin was pulled, the bolt moved forward and the nail pierced a 12 gram cartridge which was held in place at the other end.

When I first had the idea, I built most of the thing except the sear and for whatever reason I set the whole thing aside. I suppose it was because the launcher was going to be a "torpedo tube" for an ROV project I was interested in at the time, and when I didn't have the money to complete that, I put this aside too. Recently I restarted the ROV project so naturally I dug this thing up too and finished it.

It was both a success and a failure, but mostly a failure. The bolt pierced the cartridge flawlessly and it shot pretty far in air. Unfortunately, the heavy bolt broke through the PVC fitting it was supposed to stop at. The fitting was a 1" slip x 3/4" female NPT adapter. I attempted to reglue it with epoxy but it just broke apart again. I'm going to need to rebuild this thing out of a stronger material or at least lenthen the fittings so that the bolt completes its stroke before hitting that fitting.

I'll have to build a more solid version so I can test it in water and figure out how to stabilize the cartridges.

Here's a pic:



Parts used:

For the body (all PVC)
1" threaded plug
1" threaded female adapter
1" coupling
1" slip x 3/4" threaded female adapter
1" length of pipe straight through the previous 3 fittings.

For the barrel
-3/4" threaded male adapter (holds 12 gram cartridge in place)
-3/4" length of pipe (technically unnecessary)

For the bolt
-2x 1/2" NPT brass plugs.
-1/2" metal conduit coupling
-Nail
-Spring

For the sear
-1/8" NPT nipple cut in half and slotted so it can be installed with a flathead screwdriver
-Unthreaded section of a 1/4"-20 bolt

[c11man]

i would definetly fix this thing if it works well

and no the barrel is not unnessesary. when the co2 is released the gas builds up some pressure behind it giving the gas that is still exiting more thurst and it tries to expand pushing the cartrage faster.

and when you say pretty far, how far did it realy shoot?

[PVC Arsenal 17]

30 feet maybe? I held it at a pretty steep angle. I was paying more attention to the barrel that went flying than the cartridge though.

[inonickname]

C11, the principle of "every reaction has an equal and opposite action" applies more here than pressure building up behind the projectile. The biggest boost in performance is from the stability gained.

Though it does give a small pneumatic ram effect.

And also, could a bumper just be added?

[POLAND_SPUD]

normally I would say that 12g cartridges are a total waste of money but I can't think of anything cheaper that could be used for this particular application

For more stability you could attach a piece of foam that would be slightly packed while inside the barrel but would expand once leaving it.. basically, a drag stabilised torpedo... it might work but since I am not into rockets you should wait till others confirm that the cartridge would be stable

so you haven't tested it underwater ? that's a shame... I suggest using a stronger spring and/or sealing the gun because water could, in theory, slow down the bolt enough to not let it puncture the cartridge

EDIT
spelling...

[far_cry]

what for this design is ?

[psycix]

I can't think of anything cheaper that could be used for this particular application

Bottle rockets are cheaper, and more efficient due to the capability of ejecting a liquid instead of a gas.

Fun project though, it has been discussed lots of times on spudfiles. Any chance on a vid?

[PVC Arsenal 17]

I can't think of anything cheaper that could be used for this particular application

Bottle rockets are cheaper, and more efficient due to the capability of ejecting a liquid instead of a gas.

Fun project though, it has been discussed lots of times on spudfiles. Any chance on a vid?

Bottle rockets aren't available where I live, and I don't think they'd work underwater.

As soon as I build another one I'll post a video. Hopefully we don't close our pool by the time I get around to that.

[skyjive]

Of course I can't say for sure without trying it first hand, but it seems to me as though the normal gun effect of the released CO2 building up pressure in the barrel and pushing the cartridge will have a far greater capacity to accelerate it than the rocket effect of the CO2 leaving the cartridge under pressure, since the rocket effect depends on the mass of the propellant and rocket, and the metal case clearly is far more massive than a little bit of gas. Meaning the barrel is actually important.

[pizlo]

I love it when people take plans I had in my mind and think them up too, but they actual build! thanks you!

[jonnyboy]

I can't think of anything cheaper that could be used for this particular application

Bottle rockets are cheaper, and more efficient due to the capability of ejecting a liquid instead of a gas.

Fun project though, it has been discussed lots of times on spudfiles. Any chance on a vid?

Bottle rockets aren't available where I live, and I don't think they'd work underwater.

As soon as I build another one I'll post a video. Hopefully we don't close our pool by the time I get around to that.

I think he's referring to water rockets made out of plastic bottles based on his comment of expelling a liquid instead of a gas.

[psycix]

Yes, I am referring to the rockets made out of soda bottles filled with water and compressed gas.