[HN Gopher] Spudguns: Potato Cannon Guide
___________________________________________________________________
Spudguns: Potato Cannon Guide
Author : cenazoic
Score : 102 points
Date : 2024-06-26 11:59 UTC (1 days ago)
(HTM) web link (www.spudguns.org)
(TXT) w3m dump (www.spudguns.org)
| laweijfmvo wrote:
| These are so fun and easy to get started, but quite challenging
| to tune and make optimal. The differences between "i just glued a
| tube together and hair sprayed it a bunch" and having optimal
| chamber/barrel ratios with a proper air/fuel mix are incredible
| to see!
| spacecadet wrote:
| Made many spud guns as a kid. Spud mortars. It all ended when we
| fired a rotten crab apple, missed our target, but struck the door
| of a passing car. The drive chased us through the woods of our
| property for a while before giving up. Now my buddy works in
| defense lol.
| dylan604 wrote:
| Now that brings back memories. As a kid, my friends and I knew
| the woods/creek like the back of our hands, and there were many
| instances of losing a tail that way. The thing that I found the
| most interesting was civilian tails seemed much more engaged
| than the boys in blue ever did. Not sure what the civilian
| rationale was, but I know the boys in blue didn't want to deal
| with that much paper work for stupid teenage pranks.
| rolph wrote:
| not to avocate violence,but when i was a kid minors were
| basically immune to prosecution, it was also well known that
| when a kid got caught doing a bart simpson they would get the
| hell thrashed out of them until they escaped.
|
| ideally that was supposed to quench the problem right there.
|
| then again those were the days of a burning bagfull of [X],
| on the front steps type of pranks.
| dgemm wrote:
| I feel like we would have been friends in high school
| rolph wrote:
| PSI rating on your spudgun, shouldnot be overlooked
|
| e.g. https://www.klkntv.com/one-man-injured-after-potato-gun-
| expl... [2017]
|
| [ALSO] dont exceed rated pressure, and know that constant
| pressure is different than repeated shocks
|
| https://www.engineersedge.com/fluid_flow/steel-pipe-pressure...
|
| https://www.engineeringtoolbox.com/pvc-cpvc-pipes-pressures-...
| indoordin0saur wrote:
| Has anyone tried supplementing the hairspray with the sort of
| canned oxygen you can find at ski resorts?
| temp0826 wrote:
| Not a traditional spud gun, but my father (who has been a
| welder for his whole life) built a couple differently sized
| cannons out of aluminum (one fired wine corks and the other
| was about tennis ball-sized). We used acetylene gas. Honestly
| kind of terrifying and incredibly dangerous, not recommended.
| They only come out on independence day.
| gorgoiler wrote:
| We built one using acetylene as the source gas generated
| from calcium carbide and water, ignited by a spark gap from
| an electric fence. The combustion chamber was a 40 gallon
| oil drum and the barrel was a 20' scaffold pole.
|
| Round 1 worked a treat, firing a champagne cork sized
| wooden baton far away into the distance.
|
| Round 2 was a disaster. Calcium carbide needs water to
| react into acetylene. Our method involved putting a few
| pints of water into the oil drum (on its side), then a few
| rocks of calcium carbide, then the igniter, and finally the
| scaffold pole resting under it's own weight in the small,
| off centre oil drum aperture.
|
| On this second round the end of the pole was accidentally
| submerged in the puddle and the wooden baton got jammed.
| This meant the explosion forced water up the gun barrel --
| a pole just resting there in the mouth of the oil drum --
| launching the entire pole down the garden. It must have
| gone a good 50 feet or so. This is a steel javelin weighing
| a good 30lbs.
|
| Round 3 ruptured the oil drum. It sounded like a bomb going
| off.
| fkyoureadthedoc wrote:
| Best my pals and I ever did was engine starter fluid and like
| 40PSI of air with a duct tape diaphragm to hold the air in.
| We shot old D batteries wrapped in duct tape out of it. Shot
| it at a stop sign once and it made a perfect hole with sign
| peeled back like shooting BB guns at a coke can. The whole
| thing was stupidly dangerous.
| gnicholas wrote:
| I was surprised to see hairspray as the recommended fuel,
| since that what we used growing up 30 years ago, with no
| particular engineering expertise. I assumed there would be
| more advanced options now (if for no other reason, because
| hairspray smells!)
| tlavoie wrote:
| I find the 99% isopropyl alcohol from the pharmacy works
| well, and it's cheap too. Also, I'd get funny looks buying
| hairspray, when I have very little hair.
| petee wrote:
| Aren't many hairsprays just propane? I think its just a
| convenient option, otherwise you need a tank and/or a hose
| of something else
| annoyingnoob wrote:
| I always used starting fluid
|
| https://www.petes-tools.com/what-is-starter-fluid/
| petee wrote:
| Friends and I used MAPP gas mixed with oxygen...had a pretty
| good kick but you were really just rolling the dice on the
| ratio
| no_way_1209567 wrote:
| The way to do this with oxy-fuel is to light the torch,
| adjust to a neutral flame, then extinguish the flame. The
| resulting gas coming out of the torch should be pretty
| close to stoichometric, and should be treated with extreme
| care.
| ben1040 wrote:
| 30 years ago I was a teenager a friend of mine had a giant plot
| of empty land in his family, and so we'd go out there and do
| stupid teenager things things like playing with fireworks and
| building and shooting potato cannons.
|
| We'd discovered dry ice bombs alongside internet plans for
| potato cannons, and in our infinite wisdom we tried to build a
| dry ice bomb powered potato cannon. In our mind the sudden
| increase of air pressure would've sent the payload going
| ridiculously far.
|
| Thankfully when we went to use it the first time, we were smart
| enough to run as far as we could before it went off. It was far
| far more pressure than the pipe could handle and it sent little
| bits of PVC shrapnel flying everywhere.
| blastro wrote:
| My best friend in grade school was a bit of a deviant and we
| definitely experimented with these things. Very powerful!
| skrbjc wrote:
| I remember the first time we fired one of these. It was dusk and
| my brothers and I had rigged a remote igniter, and I was elected
| to hold the cannon itself. We loaded it up, sprayed hairspray in
| and my brother pushed the igniter.
|
| None of us had any idea of how powerful one of these was! The
| flame that came out the front was over a foot long. We thought
| maybe the potato would reach the back fence of our yard, but it
| was launched into oblivion. Luckily our house backed up onto a
| nature preserve, so at least no-one had a surprise potato land on
| them.
|
| We had much fun that summer iterating on designs and trying every
| type of various projectile we could find.
| lagniappe wrote:
| You probably started a small field of potatoes if it stayed
| mostly intact!
| mavamaarten wrote:
| I remember shooting a potato into a wall, hoping to laugh at
| the potato becoming mush. There was no mush. Only potato dust.
| rolph wrote:
| you have to freeze the potato for more "lolz"
| RicoElectrico wrote:
| If you freeze it, it won't cut to the diameter of the
| barrel.
| rolph wrote:
| you make a number of spud pellets, you freeze them after
| BizarroLand wrote:
| I like how when someone offered an idea that turns a
| mildly dangerous toy into a decidedly lethal weapon,
| rather than dissuade others of the terrible notion we
| went into problem solving mode to increase reliability,
| quality, and to minimize the potential hassles inherent
| with the lethal solution.
| katbyte wrote:
| Use paper towel as wadding
| ahartmetz wrote:
| Same with an apple, only a wet patch on that steel door.
| Bouncing potatoes off the surface of a lake was fun, too.
| sandworm101 wrote:
| You get better range if you swap out the hairspray for black
| power, and the barrel for a metal pipe.
| lowdest wrote:
| The links on the 404 page bought me to some very nostalgic
| feeling pages. Very late-90s aesthetic. An MP3 directory index. A
| webcam with a frame that hasn't refreshed since 2009. I miss the
| old internet.
| jasonpeacock wrote:
| > Took a bit of doing to code the design by hand in Notepad with
| all the nested tables originally, however with Dreamweaver it's
| only taken a few hours, not weeks.
|
| So many memories...
| Certified wrote:
| I wish Supah Valves [1] were still available so I could recommend
| them. They use a smaller sprinkler valve as a pilot to move a
| much larger piston based valve _very_ quickly. That lets a lot
| more of your reservoir pressure get to the barrel before your
| projectile has shot out the end. The result? More range. More
| grins.
|
| [1]
| https://www.spudtech.com/store/index.php?main_page=product_i...
| lenerdenator wrote:
| This is going to be the last week someone in this thread has all
| ten of their fingers, working ears, or both.
| kedarkhand wrote:
| You can bet it is going to be me!
| jetrink wrote:
| I was doing ecological work in a lake when we came under spudgun
| fire. Someone (kids?) began slowly firing from a distant treeline
| on the side of one of the hills that surrounded the lake. I knew
| the distinctive thump, so I was looking out for the first splash,
| which ended up being much closer than I expected it to be! I had
| assumed they would be aiming somewhere else. I informed my
| shipmates that we were under attack and we rowed to shore as fast
| as possible. They got in about three or four shots, but we
| escaped injury and no one was ever caught.
| umvi wrote:
| I wonder if most of the dangerous levels of kinetic energy in
| the potato would have bled off from air resistance though by
| the time it reached your ship. Sort of like how you can shoot a
| shotgun at animals that are way off in the distance without the
| BBs being able to penetrate skin because they've bled off too
| much energy to air resistance.
| lazide wrote:
| A potato likely has a pretty good ballistic co-efficient due
| to its mass to surface area ratio. It would be even better if
| it was denser of course, but if a nice green one, it's still
| pretty dense.
|
| That's why artillery can hit 20-30 miles away even though
| muzzle velocities are roughly the same as a rifle, which
| would be lucky to go a couple miles even if fired at the same
| angle.
| cantSpellSober wrote:
| >> _sees link to slashdot in the header_
|
| Can we add (2008) to the title please?
| gnicholas wrote:
| The site is old-school, but don't "(year)" markings only go on
| articles that were published on a particular date, as opposed
| to websites that are modified over time?
| cantSpellSober wrote:
| I don't see any updates in the archive since then
| epiccoleman wrote:
| William Gurstelle's Backyard Ballistics and The Art of the
| Catapult were two extremely influential books in my development
| as a young engineering minded person. Countless hours of fun were
| had experimenting with spud guns of varying designs.
| Ductapemaster wrote:
| Ahh good memories. Over the summer in college, I made a pretty
| advanced propane-powered one with an integral mixing fan for the
| chamber and an cheap taser for electronic ignition. Fired every
| time. Had great fun with my roommates shooting them out into the
| ocean off our balcony (UCSB -- how lucky we were!).
|
| Sadly it was confiscated by the police shortly after. They drove
| by me loading it into my car at night. The 8ft barrel was fairly
| obvious...
| Qworg wrote:
| If this is of interest, be sure to check out
| https://www.spudfiles.com/ - multiple types and versions of
| cannons, including very clever single inlet piston style ones
| that shoot incredibly far. Here's an example:
| https://nighthawkinlight.wonderhowto.com/how-to/make-powerfu...
| ubj wrote:
| Potato cannons first inspired my love of physics. In high school
| I was amazed when I discovered that I could fire one vertically,
| time how long it took for the potato to hit the ground, and then
| mathematically reconstruct both the potato's exit velocity and
| the maximum height it reached. It felt like magic.
|
| I ended up performing a science fair project on the effect of the
| potato cannon barrel length on the potato's max speed and height.
| (My experiments also led to a short encounter with the police,
| but that's a different story.)
| dtx1 wrote:
| Fun Fact: There are Countries where Spudguns are illegal and
| treated like a weapons charge. Germany being one of them.
| mschuster91 wrote:
| Fellow German here, I think this actually makes sense.
|
| Primarily, unlike the US we just lack the void space. Even if
| you're in a "rural" area you'll still annoy dozens of people
| firing a spud gun with compressed air, and one fired with
| explosives will be thought of as someone firing guns - which is
| damn rare to hear, only during hunting season in the forests.
| The same argument also holds valid for a number of other things
| common in the US but not in Germany like keeping entire
| residential properties filled with cars in various states of
| (dis)repair, firing guns in general, producing nuclear waste,
| flying experimental planes, starting planes and choppers from
| anywhere else than a licensed airstrip, ...
| jpt4 wrote:
| It makes no objective sense at all, and merely reflects
| hypersensitive German policy regarding civilian ownership of
| anything resembling the means of force application.
| GaryNumanVevo wrote:
| Here are some good tips for a spud gun: - Schedule 80 PVC where
| possible - Use anti-static spray instead of hair spray, it's
| cheaper and doesn't leave a tacky combustion chamber - Put a
| small PC fan into the combustion chamber to mix the fuel and air,
| this will ensure you get a fuller combustion.
|
| If you're an adult, you can make one out of metal pipe and use an
| oxy acetylene torch to fuel it. Perfect stoichometric ratio, very
| very energetic!
| rolph wrote:
| IANAL :
|
| Potato cannon legality
| https://en.wikipedia.org/wiki/Potato_cannon_legality
|
| in US: bare minimum it is a dangerous device as in pelletgun or
| archery equipment.
|
| how/why its used, as well as ballistic features may cross a
| threshold.
|
| if you construct a firearm, you must not have legal restrictions
| on ownership.
|
| if the projectile of a firearm,is an actual .50calibre or
| greater,that is a destructive device and you must be rigorously
| vetted to construct or own that
| msandford wrote:
| I just read the US section and it seems to contradict what you
| just stated above. If you use incendiary tennis balls it
| qualifies as a "destructive device" but then it's not really a
| potato cannon anymore.
|
| It also says if you use compressed air that completely
| disqualifies it from "destructive device" potential
| classification in the eyes of the law.
| rolph wrote:
| take note that dangerous device, and destructive device are
| different classifications.
|
| "it must be muzzle loaded, not rifled, and not use any
| projectile which is intended to be used as a weapon."
|
| compressed gas propulsion is not a firearm, unless it [gas]
| is produced by combustion or explosion of a chemical [incl.
| propane. ]
|
| magazine or breech loading, rifled barrel, a cartridge
| holding projectile, and charge as part of design will seal
| the deal for definition as firearm.
| 01100011 wrote:
| A friend of mine who is a former JPL mech engineer was working
| on an amazing, high pressure golf ball cannon until his city
| issued him a citation for his smaller gun. That pretty much
| ended his foray into pneumatic weapons. Shame, because his gun
| looked amazing. He even custom built a road case to store it
| all. Guy is on the spectrum and has ADHD which has resulted in
| some amazing, but completely over-engineered, work over the
| years.
|
| He engineered his own gluelam support beams in his garage which
| could lift a car. He rewired his house using all stranded wire,
| bus bars and crimp connectors and it was all mil-spec.
| eschneider wrote:
| In the immortal words of Bob Dylan, "Everything's legal if you
| don't get caught."
| ugh123 wrote:
| Can parts of these be 3d printed?
| mulmen wrote:
| Maybe external mounting brackets? Say for the ignition system
| or maybe a sight of some kind? I wouldn't trust a 3D print for
| any of the high pressure stuff but I don't actually know if
| that's feasible. I'd love to find out I'm wrong.
| wepple wrote:
| Not strong enough
| annoyingnoob wrote:
| If you like shrapnel.
| xivzgrev wrote:
| wow this is a fancy one. the one friends & I built in high school
| was more simple
|
| 1) a narrow tube to put potato in 2) a larger tube for firing
| chamber with a screw cap 3) a sealed hole cut into firing chamber
| for a lighter
|
| put potato in one end, unscrew the cap, spray hairspray liberally
| inside, screw cap back on, aim, and fire
| wepple wrote:
| I built the fauxtato a while back; a small capsule to simulate a
| potato but with a 32g accelerometer (8g is wildly insufficient)
| and WiFi to be able to log data and make basic analyses about
| different cannon & fuel usage.
|
| Really interested run some tests based on things in this thread,
| like different propellants.
| wepple wrote:
| Correction: it was a ADXL375 200g sensor
| nehal3m wrote:
| That is amazing. Can you tell us if the potato referred to in
| this comment [0] could have done serious damage?
|
| [0] https://news.ycombinator.com/item?id=40798939#40812811
| wepple wrote:
| That's really interesting, I haven't spent much time
| looking at the data from the landing impact.
|
| I'm also not confident in my skills to translate G-forces
| into velocities or such. I guess it depends largely on what
| type of surface it lands on?
|
| You've definitely got me thinking now. There's a bunch of
| ways I could roughly come up with a model for this.
| flyinghamster wrote:
| A buddy of mine had a compressed-air spud gun that he made from
| an air compressor tank, a ball valve, and a length of 3" copper
| pipe. That thing could put dents in a 1/4" thick scrap steel
| plate.
| jprd wrote:
| I have NEVER EVER used one of these to fire across a US
| Interstate at night (successfully).
|
| Mind your PSI and test your ballistics prior to using it for
| more, artful, purposes.
| rehevkor5 wrote:
| Relevant: this video with some info about dangers/safety
| especially related to non-pressure-rated PVC:
| https://www.youtube.com/watch?v=KqstP9ics2A
| reducesuffering wrote:
| Silicon Valley, the show, is a documentary.
| https://youtu.be/Q1QPXyebhiY?si=5YWYlCuI2aJ2fu-l&t=474
| gnarcoregrizz wrote:
| I made few of these when I was a kid. My piece de resistance was
| a 10' 'coaxial piston launcher'. It scared the bejeezus out of
| most people... I usually shot ice slugs, which would throw a hole
| in a piece of plywood at 50 psi.
|
| A golf ball with a chipped off shell fits perfectly in a 2" PVC
| barrel. The problem with chipping off the shell (along with an
| unrifled barrel) is that it makes it like a knuckleball - you
| have no idea where it's going to go. They would curve violently
| in any direction. One of the few times I shot one of these, it
| curved directly upwards, and I'm guessing landed a half a mile or
| so away. Hopefully it didn't hit anyone or anything. That was the
| last time I shot it.
| eigenvalue wrote:
| I used to think these were really cool and harmless fun as a
| teenager. Then at college, some guys I knew made one (and they
| weren't dumb at all, pretty competent people). They were firing
| it near where people were sitting on the lawn and it suddenly
| shattered, sending sharp jagged pieces of PVC flying. One of the
| pieces hit a girl sitting nearby and gave her a nasty cut near
| her eye. Her face was covered in blood and it was totally
| horrific for her and everyone else. It made me realize that the
| fun of the activity was just significantly outweighed by the
| possible safety downside. It could have been so much worse, too--
| she could have been blinded instead of just gotten a nasty scar
| on her face.
| spike021 wrote:
| I think the key is using them in an open space away from people
| and where you can have some measure of safety. My friends would
| use theirs in an uninhabited valley off a ridge.
| eigenvalue wrote:
| Yes but even then the person firing it is at risk. At a
| minimum you should use serious eye and face protection.
| petee wrote:
| With a good sharp chunk you can potentially nick someones
| artery.
|
| We had a couple incidents and nobody got really hurt, but later
| I came to the same feeling of 'fun, but no thanks'
| ggreer wrote:
| These sorts of failures are usually caused by people
| constructing the potato cannon out of thinner schedule 40 PVC
| (usually colored white). If you use schedule 80 PVC (which
| tends to be dark gray) or ABS (which deforms instead of
| shattering), the risk is negligible.
|
| This is also why I prefer pneumatic cannons to combustion.
| Since there's not a quick spike in pressure from a combustion
| reaction, the maximum pressure that needs to be contained is
| lower (and you can measure it with a gauge as you're pumping
| the air tank up). Also if you make the air tank big enough, the
| pressure behind the projectile stays high for longer, so you
| tend to get higher velocities.
|
| When I was in high school I made a potato cannon, played around
| with it in the woods with some friends, and _then_ told my
| parents about it. My mom wasn 't too happy, but my dad took it
| as a challenge. He built an even more powerful pneumatic
| version with a tripod, sights, and a solenoid trigger
| mechanism. The whole family loved it. I used some extra PVC
| pipe to make molds for cement slugs. With a little paper
| wadding to get a good seal, they'd go fast enough to embed
| themselves a couple feet into the side of a hill. It was
| spectacular.
| andrewstuart wrote:
| As I kid we had die cast spud guns that had a barrel width of
| maybe half a centimeter - pretty harmless.
|
| But today of course it would be a problem cause its guns and a
| problem because its a waste of food.
| m-i-l wrote:
| Surprised to see people talking about spudguns firing whole
| potatoes! I didn't even know that was a thing. The spudgun I had
| when I was young just fired small parts of a potato, with a whole
| potato enough to last for ages. I think it was the Lone Star
| Spudmatic. Not only safer but less wasteful.
|
| FWIW, it looks like Wikipedia differentiates the smaller spudgun
| from the larger potato cannon:
| https://en.wikipedia.org/wiki/Spud_gun vs
| https://en.wikipedia.org/wiki/Potato_cannon
| ElCapitanMarkla wrote:
| This takes me back. Dad was a plumber so I had ready access to
| all the gear for this growing up. I was introduced to it when he
| turned up at home one day with one, we launched a few spuds into
| the neighbouring paddock using Mum's hairspray.
|
| I was about 13 at the time so I spent hours on this site planning
| different launchers. Managed to blow my friend's Dad's air
| compressor up while firing a smaller one. I don't know how the
| hell I still have all my fingers / eyes but I had some fun :)
| vlachen wrote:
| In the summer of 2004 I was enjoying the mountainous view and
| ample sun of Kandahar, Afghanistan. It was there, eating one of
| my allotted MREs, that I noticed the MRE heater was printed in
| large letters "Do not expose to flame." Being a bored jarhead, I
| couldn't help but try and figure out why. Being able to rub a few
| brain cells together, I thought about how the heaters are
| activated by the addition of water. Since water is hydrogen and
| oxygen, I was willing to bet that those were some of the reaction
| products. I never bothered to look it up, but I did find that
| whatever was coming out with the steam was also quite flammable.
|
| Once that was proven, I recalled that recently a contractor had
| dug a well near our work site. I ambled over and found a 3 foot
| long, ~3 inch diameter steel pipe that had a 90 degree elbow with
| a quick release cap. All that was required after that was a touch
| hole, added with a drill, some MRE heaters, and projectiles.
|
| Potatoes were not available there, but fruit like oranges and
| pears were. I started with an orange and just jammed it into the
| very end of the barrel, it was too big to go all the way in, and
| went for it. The distance was laughable, 1 or 2 feet, but the
| sound? Everyone came running out of the work center tents because
| they thought I had just loosed a round from my weapon.
|
| After being called an idiot by the local Lieutenant, I switch to
| only pears, which were easy to jam in hard enough to cut the
| excess off. At this point, I was lobbing pears across the
| perimeter road, into the scrub / minefield outside the wire.
| Never found a mine with it though.
|
| All my fun ended one faithful day when I accidentally dropped a
| pear in front of a Romanian MP truck on patrol around the
| perimeter. The 50 cal on top turned to point at me, I dropped the
| pear cannon and walked away, never to return.
| bityard wrote:
| > The 50 cal on top turned to point at me, I dropped the pear
| cannon and walked away
|
| Pretty sure I would have dropped something else and RUN away
| vlachen wrote:
| Kind of like a cat, I didn't want to tickle their predator
| instinct. If I was on the other side of the wire, it'd
| probably be a different story. Or no story.
| vlachen wrote:
| Well, I wasn't wrong about the hydrogen part:
| https://en.wikipedia.org/wiki/Flameless_ration_heater#Chemic...
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