some tips when making a potato cannon?

>>1167280
Dont buy cheap ass parts that dont hold pressure.
Do a good valve trigger.p

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>>1167287
thanks man, also.

does 90 degrees angle have trouble under pressure? what im going for is something like this

>>1167294
Use a piston valve
https://www.youtube.com/watch?v=G1VCZEXi384

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>>1167303
il be checking the vid out now, in the mean while.
someone tell me what would break first with this design. and maybe how to improve the design.

>>1167303
that seems like quite the job for a first time project

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>>1167313
this is what i might go for, as an (hopefully) easy first try

the tank goes over the shoulder so if it blows up hopefully it goes behind the shooter and not in his face.

whats the science behind the combustion chamber?

where is it best to put the igniter, and how much does it matter?

>>1167294
Use piston valve, selenoid ones need more work to get right

>>1167355
>whats the science behind the combustion chamber?
air and fuel mixture combusts, heats up and increases the pressure inside the combustion chamber

>where is it best to put the igniter, and how much does it matter?
I don't think it's that much of a deal. The whole mixture should have been combusted way before the potato has moved in any significant way
Getting the stoichiometric ratio right is probably the hardest part

>>1167280
Made a ton. Opted for $15 electric propane ignitor this time. Tried lantern strikers and red push button.

I highly suggest cheap taser. I will try this next.

Aquanet hair spray

When i was a kid we did 2-4" chamber and 2" barrel. I find most potatoes in Kansas here do netter with a 1 1/2" barrel.

Make chamber about half or a little less the entire length.

Make the gun not taller than about eye level. You will be lifting a broom stick over the top to ram the potatoe or risk bumping the striker and taking a spud to the dome. I imagine this woukd kill u...

Drill a hole about an inch or so above the change over where the barrel connects to the chamber and shove a welding rod through there or put a bokt through it for a stopper for your spuds.

There is a local turnip field here a guy plants and lets people pick free. Sadly there is a lot of waste when someone gets a spot on one or the wrong size. They just uproot them and drop them. I check it daily and cart off half a pickup load of rejects for free ammo. Sticky as fuck but the old salad shooter loves them.

For the back where u spray hair spray in i always use a threaded plug with the square on the end in case u need a wrench. Doesnt need to be but finger tight. After u shoot it the sticky fuck will be tight as hell.

Take a gringer to the tip and sharpen the pve barrel end to cut the tater excess as u shove it in the barrel. Be fucking careful not to slice your hand loading it.

Maybe rig up a 2 button safety switch or a key so u dont bump it. I blew my back glass out and almost burned my fucking car down. Buddy loaded it and we ran out of hair spray. 4 hous latter he reached back to get a beer and bumped the trigger. Bad jewjew

Highly suggest 4" chamber to 1/2" barrel. Barrel fits spuds and 4" is easier to get in and work on it. My bear claws almost fit so tiny hands should be fine.

Consider a threaded barrel so you can break it down and throw ina car or change barrels

>>1167303
The most in depth overly complicated shit i have ever seen. Fucking legit tho.

>>1167330
I always john wayne style hip shoot with my boys turned away. Rather take pvc shrapnel to the hip than the neck. But if using oressure rated u should be fine. Especially if air and not hair spray

>>1167355
My experience the ignitor placement doesnt matter. Highy suggest a roll of electricians rubber tape if using a tazer and bolts tho. If using longer bolts at an angle or opposite each other i would imaging it works well for fine tuning best spark.

>>1167355
My experience the ignitor placement doesnt matter. Highy suggest a roll of electricians rubber tape if using a tazer and bolts tho. If using longer bolts at an angle or opposite each other i would imaging it works well for fine tuning best spark.

Keep your face the fuck back tho. Lol

When I was looking into it, I was recommend to use black pvc at least for the chamber, because it's rated for higher pressure. I'm not certain if that's the case, but I would definitely say use the best pvc you can find for the chamber.

>>1167844
*1 1/2" barrel. And sorry i forgot to proofread. Entire post is autistic spelling...

>>1167330
That looks scary as fuck. Just think the part that is the most likely to explode is right next to your head. Enjoy shrapnel lodged in your skull.

>>1167860
It is higher pressure. Also, consider schedule 80. Its thicker. (Normal pvs like u see in the plumbing section is non pressure rated white schedual 40pvc. Most all schedual 80 pvc is grey) used to work at a pvc fitting plant. Kek

>>1167863
Protip:

You wont. And shit explodes into razors.

>>1167355
>>1167821
>>1167859
https://www.youtube.com/watch?v=_TNSUIsjdpY

>>1167893
fuck me, guess i'm wrong
I thought the combustion would be fast enough to complete before the potato had any significant displacement
Notice at 1:03 how to front of the flame stagnates as the potato starts to accelerate, reminds me of the motion of a piston in an airsoft gun

Anyway, does this have a significant effect on the final velocity of the potato? I think getting the amount of fuel right is more important

Schedule 40 or 80 PVC...use nothing less

>>1167900
2 or 3 second shop of hair spray. Dont be using starting fluid or acetelene and shit. Dad figured it was a fod idea ro stuff one full of rags ina shop and blast right next to his cousin for lols. Blue the plug out of the back, the striker out, shot it 10 feet behind him, and blasted 15 fucking red rags into the street on fire right in front of the cops.

drill 2 screws in the combustion chamber and wire your igniter to them. don't just stick it on the end. you'll get way more consistent ignition

>>1167294
>>1167287

Why does everyone insist on doing complicated valve trigger? A simple ball valve works just fine and theres nothing that will break like your shitty sprinkler valve or modified air gun triggers.

>>1167893
thats neat

>>1168723
Sounds like the gun was constructed poorly

Forget the flint and hairspray - got with a compressor and tire valve.

My dad made one - the trigger is a lawn sprinkler valve. I'm sure you can Google the tutorial. So much better than failed lights and sticky reside.

>>1169059
Nah, i know another guy that used acetylene and blew the fucking barrel off.

Do not dick with acetylene

A lot of people use way too much fuel in their combustion chamber. Measure the volume, either through it's dimensions if it's simple or by brimming it with water and measuring how much is in there and work out from this what a stoichometric ratio is.

I used to fill mine using a syringe with a luer lock cap that had a fine hole pierced in it so it mixed with the air in the chamber as it was injected.


If you are comfortable risking the whole thing exploding in your hands then you can almost double the range by using nitrous oxide. Increase the fuel load by 150% (i.e. add 2.5x more fuel than you otherwise would) and, prior to fuelling, purge the combustion chamber with nitrous oxide. Do this after loading a projectile or plugging the proximal end of the barrel because a pure nitrous load in the barrel will detonate. In addition to effectively raising the oxygen content to 50% (1 oxygen atom per molecule means half the oxygen for a given volume compared to diatomic oxygen gas), nitrous oxide itself decomposes exothermically and produces one mole of nitrogen gas (and half a mole of oxygen gas) for every mole of nitrous oxide consumed. When it goes right, you'll get a shot that makes propane/butane & air look laughable. When it goes wrong, the entire device will be blown to bits and, if you're not wearing motorcycle leathers, you'll end up with PVC shards embedded in your body. I was fortunate, my PPE was effective but I did find pieces of the ex-combustion chamber twice their own length deep in the hard clay soil.

>>1169952
>add 2.5x more fuel
*2.5x the fuel

>>1169952
Or you could be an absolute madman and try to obtain a pure oxygen tank

Now then. How difficult and or viable would it be to make the barrel from metal tube with some sort of a backstop, and have it launch firebombs/molotovs? I guess one would have limited velocity due to being stuck with only the length of the bottle for acceleration, as I wouldn't want a burning rag inside a barrel. Would some sort of internal piston pushing the bottle out and venting the gas off at the end of travel? Would that overpressure and go boom in my hands or be unreasonably heavy?

I don't really want any post-apoc feeling shtf firebomb launcher, it just sounds like a lot of fun for dicking around. Eh, who am I kidding. I do want one.

>>1170201
I'm not convinced the evolved pressure would be significantly greater. When one factors in the enthalpy of formation of nitrous oxide, the ability to burn twice as much fuel (I'm using butane for my calculations) only results in an energy release 30% greater. Then there's the amount of gas evolved to consider:

>Pure oxygen:
2 moles butane + 13 moles oxygen (diatomic) --> 8 moles carbon dioxide + 10 moles water vapor

-5.755 MJ

>Nitrous
1 mole butane + 13 moles nitrous oxide --> 4 moles carbon dioxide + 5 moles water vapor + 13 moles nitrogen

-3.944 MJ (combustion of butane + disassociation of nitrous oxide)

>>1170345
I always wanted to launch sticks of dynamite bit it is ignighted by preasure and fire and both are being used to launch it. Plus when it doest go off u are holding a fucking bomb. U go ahead and do it tho. Lol. Livestream

>>1170402
Seriously? What's wrong with you? I'd say stick to M80's but you sound like the sort of idiot who got them banned too.

>>1170374
If you're able to calculate that it shouldn't be too hard to calculate the final pressures assuming a constant volume and adiabatic conditions, no?

For a basic ass potato gun, just use 4" PVC for the blast chamber and 2" for the barrel with adapters. Threaded cap on the end of the 4" for fueling. Drill two small holes near each other in the blast chamber, run two thin screws into them so the tips are < 1/8" apart. Get a dollar store BBQ lighter (the kind with the trigger) and strip all the gas stuff out, leaving just the trigger part with the wires. Wire it to screws and tape it into place on the gun so it has an actual trigger.

Use gasoline in a small body spray bottle. It's like fuel injection, one or two sprays works wonders and won't gum up like hair spray. It also mixes better than something heavy like butane.

You can use potatoes or just cram a piece of cloth down the barrel as wadding and fire everything out of it. Including pie.

Don't use too much gas. A lot of people think more is better but it isn't true. A perfect air to fuel ratio is what gives you a good bang, adding to much decreases your bang or even doesn't let it bang at all

Paintball regulator before and after the expansion chamber.
CO2
Ball valve
No combustion required

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Go for broke and make full on Potato Pack Artillery

http://www.instructables.com/id/Howitzer-Potato-Cannon/

>>1167280
Cover the whole thing in cloth tape. That way if it explodes you're less likely to be showered with fragments.