SpudFiles

A friend and I are making a mortar that fires foam projectiles powered by 12g CO2 cartridges. It isn't anything fancy, just a 3" PVC pipe with a nail at the bottom to puncture the cartridge and a bipod to hold it up. It's 4 feet long with a 3 inch bore, and can adjust it's trajectory​ between 45 Degrees to 75 degrees, just as the original Stokes mortar did.

I'll be uploading pictures of the finished painted product, various experimental shells, and possibly a firing video, along with the customary data on ranges and ballistics. If anyone's particularly interested I'll draw up some blueprints for you.

Consider eliminating the CO2 12g from the projectile by having it refillable like the Hades Arrow from Hakkotsu:

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I considered that, but couldn't come up with a cheap or easily manufactured design.

The closest I came to was a pressurized pipe with a very strong burst disk.

What about a toolies piston like this one; Some pics start about half way down the first thread, some pics of the mortars valve are in the second thread. Function is essentially the same.

http://www.spudfiles.com/pneumatic-cann ... 22848.html

http://www.spudfiles.com/pneumatic-cann ... 15933.html

I considered that, but couldn't come up with a cheap or easily manufactured design.

There's your cheap pre-made pressure chamber... drill a hole in the cap, sandwich a burst disk in there...

That's actually a really good idea, wouldn't I have to drill another hole and fit in a fitting for the pump though?

Well, I threw on a couple layers of olive drab paint, it's a bit spotty and I left the Axel it hinges on unpainted (it would rub off there anyways), but for all things considered it looks pretty good.

Cthulhu wrote:That's actually a really good idea, wouldn't I have to drill another hole and fit in a fitting for the pump though?

I would put the valve in the cap as it's the thickest piece of plastic. The burst disk could be in that small circular bead in the bottom of the bottle.

WizardNoodle wrote:
The burst disk could be in that small circular bead in the bottom of the bottle.

I'm not very familiar with burst disks, how would you attach it at the bottom?

I would put the valve in the cap as it's the thickest piece of plastic. The burst disk could be in that small circular bead in the bottom of the bottle.

I'd do it the other way round - the threaded cap is a convenient way to attach a burst disk in a reusable manner, while the bottom of the bottle is thick enough to tap for an [airsoft type fill valve](http://www.ebay.com/itm/MadBull-Steel-R ... SwopRYiFq7) epoxied in:

Those are pretty expensive valves for something that will probably fly away never to be returned to me hahaha.
Do you know of any cheaper alternatives? I might go old school and mix some vinegar and baking soda in the bottle and then quickly cap it with the end cap.

I would use a Simple Truth water bottle as the bottom doesn't have those annoying flimsy thin-walled prongs. Vinegar and baking soda are pretty weak & impractical relative to all the other ways you could achieve pressure. If you aren't hell bent on using CO2, I would install a Shrader valve into the rocket/mortar and pressurize the bottle with air. Make sure you first test how far the bottle handles pressure until it explodes so you don't accidentally overpressurize it while it is in your hands.

WizardNoodle wrote: If you aren't hell bent on using CO2, I would install a Shrader valve into the rocket/mortar and pressurize the bottle with air.

I'm willing to use whatever it takes to get it flying, where would you suggest installing the Schrader valve? On the cap or on the bottom of the bottle.


I experimented with vinegar and baking soda this morning, it was messy, annoying, and didn't fly. But the main issue I had was that gas was actually leaking from around the burst disk.

I would do what jackssmirkingrevenge suggested and install the Schrader valve on the bottom of the bottle. Use a Simple Truth or other flat bottomed water bottle. Cut a 1/2" hole into the bottle cap and that will be where you rupture the burst disk with a nail or other puncturing mechanism. If you need help with burst disk materials, go here.

Those are pretty expensive valves for something that will probably fly away never to be returned to me hahaha.

You can find them for about 3 dollars each, not exactly going to break the bank.

the main issue I had was that gas was actually leaking from around the burst disk.

How did you go about it?