Spudguns: Potato Cannon Guide
spudguns.org
spudguns.org
We had a couple incidents and nobody got really hurt, but later I came to the same feeling of 'fun, but no thanks'
That's enough to possibly kill someone if it hits their chest.
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.
One example: https://www.cbsnews.com/news/texas-teen-gravely-injured-by-h...
1. We strengthen the pressure vessel enough so that it gives way at higher pressure, making a "stronger bomb"
2. We strengthen the pressure vessel enough so that it doesn't give way, making it not a bomb at all.
It's not at all clear if the duct tape will do 1 or 2 or something else, and this first-order logic / first-impressions design doesn't smell to me like a rigorous solution.
I thought, for safety reasons, it was worth replying to the comment suggesting to wrap "a ton of" tape around it. At the time I replied there were no other replies.
Not trying to win a debate with you. Just trying to share that it could be a bad idea. Rather than just assuming that making the shards less sharp or fragmented was the only possible outcome.
You're replying reasonably and I'm dragging that into my top-level comment about rigor. Impedance mismatch.
This is something I would suggest buyers do at every store they shop at.
Strange, since combustion based cannons tend to reach about 30 to 40 psi at most, while pneumatic easily can reach 100 psi.
Butane and propane can easily produce > 100 psi when used in engines, and are commonly used as replacement for gasoline and other hydrocarbons in generators and fork lifts to do just that.
In a confined enclosure (potato gets stuck or the like), it’s a pipe bomb.
Quite effectively too.
There is also some nice research on proper high explosive detonation of similar mixes when using proper detonators.
It requires rather extreme amount of willful ignorance to think lighting a mixture of oxygen and butane or propane inside a enclosed space is only going to be 30-40 psi maximum, instead of ‘thank god it only hit that maybe because the potato moved’.
[https://colab.ws/articles/10.1134/s0010508211010114]
There was a good research paper I found that had a quantified set of numbers, but it required paying for it. Meh.
Still waiting for that cite.
[https://parts.spearsmfg.com/sourcebook/SCH40TECH_40WHTPIPE-1...]
And as noted in the prior declassified paper, shock fronts from these mixtures can easily move in excess of 280 meters/second even unconfined in air, with the right mixes.
Goofy? Perhaps. Life altering? Perhaps [https://youtu.be/KqstP9ics2A?si=Omtp8N7xPW91A5TU] - and yes, while many of those failures in the video are clearly due to improper glued joints (which is a big hint at the pressures involved, and way better than other kinds of failures!), many also involve the PVC shattering. Several in the first few minutes, actually.
I made a ton of potato guns as a kid, btw. Typically using propane. But I always respected the forces involved, because I wanted to not lose an eye, kill anyone, etc.
Looks like some enterprising MIT alumni + the air force academy did some internal ballistics reseaerch [https://arxiv.org/pdf/1305.0966].
Note - I highly recommend against using acetylene, which they did for some of the tests, as it will perform a proper super-sonic detonation [https://www.icheme.org/media/10611/iv-paper-08.pdf] under the right conditions and turn your potato cannon into an IED even if the projectile moves, or potentially even with no projectile at all. Per that paper - “It appears that Acetylene is unique in that it will propagate a detonation at initial pressures below those of which it is capable of sustaining deflagration”. I would have checked this paper which even more directly addresses the topic [https://link.springer.com/article/10.1007/BF02671917] (because I love this kind of thing, obviously), but $40. :(
So looks like as long as everything goes well, they are in the approximate range of 20 psi while driving the projectile, except for acetylene which hit a hair under 90 psi. They used stoichiometrically ‘perfect’ mixes.
My guess is the failures in the videos (and anecdotally) were driven by too lean fuel mixtures, easy to do in some conditions. But this paper [https://www.scientificbulletin.upb.ro/rev_docs_arhiva/full14...] seems to indicate the opposite, and also pressures >= 120 PSI. So I don’t know.
I also saw MAPP gas apparently being used in one of them too (the yellow cylinder attached to a plumbing torch), which would also be unwise.
Maybe not yours, but we tapped ours. This held the potato near the chamber after compressing the gasoline-air mix. I have no idea how well it held, but if you didn't seat the potato into the threads it would push the broom back out. You'd hear a poor seal leaking.
It was terrifyingly loud. We'd wrap stones in duct tape, spray them with oil, then shoot them through sheet metal. Put a few through some old steel chairs. Tore the cover off some golf balls.
I suspect it may have reached higher pressures than my bike tires, but I never really considered trying to measure it.
But today of course it would be a problem cause its guns and a problem because its a waste of food.
When I was a kid, my uncle absolutely shredded his kids’ plastic playplace (his kids, my cousins, were accomplices rather than victims). But those holes were 6 inches circular and even broke some chunks of brick wall (less impressive).
I evolved it to pneumatic with my friends, and frankly that scared the crap out of us more. In retrospect, must have felt sort of like the uneasiness of being on the Titan. At any moment pressure could have instantly exploded us. Eyes, guts, something bad.
However, it was totally kosher! ;p We had denim jeans and duct tape around the combustion/compression chamber, like the internet said.
I think my friend claimed he smoked banana peel from the Anarchist’s Cookbook around the same time. True science, really.
(Haha… it was scary as hell, and we stopped after a few weeks of terrifying afterschool experiments. The banana kid also claimed he was making a nuclear weapon after stealing plutonium from “this science guy’s house”)
PS: none of us ever wore safety glasses. Dumb luck, emphasis on dumb.
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.
Maybe you had more important things to do, but this is what I would have done. Playing artillery on humans is not a prank I think.
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-...
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.
Search on youtube for some hydrogeh/oxygen baloon explosions to see what I mean.
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.
If you nick it, drop it on something, etc - the rating no longer applies.
Over the years numerous shops have used PVC pipe "because the compressor only goes up to 100psi and the pipe says 250", that sort of thing...and had the pipework explode and injure/kill people.
~100 psi in a PVC pipe is enough to tear through a sheet of drywall and then fatally injure someone.
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.
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.
On the flip side, like so many others here, I had a friend who went overboard with his. Automatic reloading systems, piezo trigger so you did not need lighters and such, scopes, automatic cutting devices for the spuds. He tore it apart after a spud went through both sides of a car (it was a junk car he was intending to shoot) and ended up "who knows where" on the other side.
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.
Pretty sure I would have dropped something else and RUN away
Was that a MRAP (mine resistant anti potato)?
Naturally, I went home and decided to construct a much bigger version of the one he showed us. After convincing my parents to drive me to the hardware store, I picked out what I needed -- including 7 feet of PVC. The clerk immediately figured out what I was building and that was the first time I heard the term potato cannon. They seemed concerned that my mom was on board with the whole thing, but I stuck to my guns and said it was a science project and was for shooting socks. I had figured I could wrap the sock around a smaller projectile, but that clerk made me realize I didn't even need the sock.
My friend and I put it all together pretty quickly the next day and set it up in my backyard for testing. I think we probably started with socks, but I honestly can't recall. What I do remember is taking a hacky-sack I had lying around that fit perfectly into the barrel to try and fire it at our back fence. We were using a piezo igniter from a lighter I had disassembled, and it took some trial and error to get the fuel to air mixture just right. It took both of us to operate: one person aimed the barrel, the other operated the trigger. This time, I was aiming and he was lighting. But it just wasn't lighting... so I turned around to try and help and BOOM the cannon went off like, well, a cannon. Except I wasn't pointing at the fence anymore, but well above it. The hacky-sack tore through the branches of several trees before exploding on the metal siding of the house on the opposite side of our block. The sound could probably be heard for blocks.
We both just looked at each other with a mixture of delight and panic before immediately running back into my house. We saw someone come out of the house we hit looking utterly confused, trying to figure out what just happened. We started laughing uncontrollably, realizing how close we were to causing a lot of damage, or possibly injuring someone.
Luckily, nothing every came of that incident, and we made sure later tests were done in a nearby park. We never did attempt to put an actual potato in the thing. Perhaps 7 feet was a little overkill...
PS - Dr. Vince, if you're out there, thank you for being one of the best teachers I've ever had. I'll never forget that class, or that "sock cannon"!
Really interested run some tests based on things in this thread, like different propellants.
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.
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!
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.
Do I tell the thermite charge story? No no, not here.
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
If we're talking home made back garden arsenal, the go-to for my generation was the peg gun: https://www.instructables.com/A-Great-Peg-Gun/, which is, in retrospect, absolutely irresponsibly lethal with the right tension elastic bands.
My most sunkworks idea was based of atechnology connections video, to use a stocheometric ratio of liquid hydrogen and liquid oxygen, dump it into a steel pressure chamber....then let the liquids convert into a gas, then detonate the mixed gas using a high voltage arc. The detonation force blows a burst disk open and blasts the projectile slug forward at what I hoped to be hypersonic speeds.
Never really got to into it though cuz I'd need some machining equipment and a budget for the materials
[1] https://www.spudtech.com/store/index.php?main_page=product_i...
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.)
Don't just leave us hanging out here, what was the optimal barrel length for your chamber volume?
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
It also says if you use compressed air that completely disqualifies it from "destructive device" potential classification in the eyes of the law.
"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.
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.
The cannon was in a J shape, where the end of the J had a cap for spraying in fuel - like propane or hairspray. Near the end of the J shape we cut a hole to put in an elongated lighter.
This went against the design of the video we watched - the video suggested taking the ignition stuff out of the lighter and making it part of the canon. Cutting a hole and just gluing a lighter was the easiest option... but also caused a lot of problems - namely with ignition.
During the building of this, right as my mom came home, I looked down the PVC pipe (there was nothing in it thankfully) and asked my brother to click the lighter so that I could check to see if it was lighting or not. My father was not in the room.
This ignited the residual fuel in the pipe and burned ALL of the eyelashes off of my left eye. My father came running in and started to scold us, and then my mom came in the room asking what happened. We all hid everything, because my dad didn't want to get into trouble either.
We shot many potatoes that summer, and the whole experience made me realize how useful eyelashes are.
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, ...
The reason why it's never gets fixed for the US must be that the US also has total global socioeconomic dominance and none of you guys want to rock the boat and accidentally fix that too in the process.
The Nordic countries are not far behind on gun ownership, and I recently learned (I have my gun background from mandatory military training + farming/hunting, so mostly bolt action except in military) that even semi automatic are still very accessible than I assumed, you just need to know how.
The Czech Republic is even more liberal than that.
Several European countries also practice the storage of military weapons at home, actual full auto assault rifles meant to defend against an invader.
So again: the difference I think is more in culture than in the amount of weapons. Obviously control makes a difference as to who gets hold of the weapons, but again, the rules are pretty lax: a good reason (hunting and/or sports shooting), and, in the case of sports shooting (at least for single hand guns) a recommendation from a local club.
The American culture were guns are stored loaded around the house however and the glorification of gun violence, that however scares me.
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 :)
So many memories...
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...
I should really write up a thread on some of the stories from those days.
You have at least one guaranteed reader.
https://www.amazon.com/Backyard-Ballistics-Cannons-Cincinnat...
I had been inspired by a “science demonstration” at a science fair where “Doctor Bunhead” (of “Brainiac” TV fame) shot one through a tennis racquet to make “instant chips”.
Punkin' Chunkin' Championship https://www.punkinchunkin.com/
Mind your PSI and test your ballistics prior to using it for more, artful, purposes.
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
Can we add (2008) to the title please?