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!
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.
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.
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.
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.
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.
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.
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!)
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.
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.
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.
The rated pressure is for water, and the rating assumes the pipe is in perfect condition. And no, constant vs shock pressure doesn't make it safer.
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.
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.
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.
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.
So many dead links... so many links going to AOL or CNN or domain-squatters.
Heck a lot of links on the first page are empty.
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.
> 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.
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.
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.
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.
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.
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?
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.
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...
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.)
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, ...
It makes no objective sense at all, and merely reflects hypersensitive German policy regarding civilian ownership of anything resembling the means of force application.
It's not just Germany that is very sensitive towards guns - that's an attitude prevalent on the entire continent, maybe except the Balkans and Switzerland. The UK has even stricter regulations on guns, and not just guns but also other kinds of weapons like knives.
No, it's the US gun control that is abnormally relaxed compared to the rest of the world, especially among developed nations. Not the other way around.
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.
Id argue that it is not so much American gun control that is different but American gun culture.
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.
Indeed, the United States is abnormal in the statistical sense, and superlative in the moral sense. Free men fear not to bear arms, and so this status befits us.
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!
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
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.
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.
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.
Theoretically yes with the right materials, but realistically 3d printing is too sensitive to safely and reliably print pressure vessels of any significant size without putting yourself in danger. Some plastics are going to have weak points between layers that could splint apart instantly and without warning, and other plastics that don't have that problem are often brittle and could throw large chunks. But pressure rated plastic pipe extrusions are fairly cheap (just be aware some are only rated for water pressure, not air pressure). And if you need something small and lightweight, pop bottles can hold up to 100 PSI. Tom Stanton's channel on youtube does a bunch of air powered RC planes and stuff using pop bottles to hold air.
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.
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.
155 comments
[ 3.6 ms ] story [ 198 ms ] threadideally 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.
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.
https://www.petes-tools.com/what-is-starter-fluid/
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.
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.
So many memories...
[1] https://www.spudtech.com/store/index.php?main_page=product_i...
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.
Can we add (2008) to the title please?
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 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?
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.
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!
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.
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
Really interested run some tests based on things in this thread, like different propellants.
[0] https://news.ycombinator.com/item?id=40798939#40812811
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.