This page chronicles the construction of a potato launcher (potato cannon, spud cannon, spud gun, tator tot bazooka -- whatever you want to call it) by a group of friends from Orange County, California. You can read about our other capers on the splorg page. These activities took place mainly in the summer/autumn of 1997. If you have any questions or comments, feel free to email Tobin, the creater of this page. Note: Splorg is the organisation which created this potato cannon; Splorg is not actually the name of the potato cannon itself.
``Just then there was an explosion from the deck behind the tavern, and we ran to the door. We should have known. I mean, this was Montana: outside, nothing more than two men shooting potatoes. Not shooting at potatoes but shooting them out of a homemade contraption called a spud gun. From the porch above a deep field reaching down to the Jefferson, a man named Parker and his assistant launched the potatoes to see who could get the farthest trajectory. The spud gun was about four feet long and made from four piecs of PVC plumbing pipe. the assistant rammed a raw Idaho potato down the barrel to the firing chamber into which he then injected a spritz of hairspray; Parker aimed the fun as his friend put a match to the igniter hole, and with a loud !whump! a spud went sailing some hundred yards toward the river.
``Parker handed the gun to me. "Try it." I said, I don't have time right now to get a new face. "There's no danger. Not much." Don't you have something smaller -- say, a parsnip pistol or a radish revolver? "I've thought about that," he said.
``The temptation was too much, so I loaded in a nice, firm Idaho and fired the thing into kingdom come. "Hey, you're a natural." I said, Not quite, although I nearly finished seventh at the Missouri Turnip Toss back in 'sixty-three. "These things were invented in California," Parker said, "but I hear they're illegal there now."
After we turned in, I heard across the dark room, "If Meriwether Lewis amazed the Indians with his air rifle, think what he could have accomplished with a spud gun." A long quiet, then through the blackness, "If only he could've gotten the boys to haul from St. Louis those two hundred cases of Aqua Net."''
-- William Least Heat Moon, River-Horse, p.407
Construction is simple. The cannon consists of a combustion chamber fitted to a barrel of smaller diameter. Our basic theory is that the combustion chamber should be large so as to produce a large volume of gas during the combustion, which will be forced at high velocity through the barrel, propelling our projectile.
Materials are all common and can be purchased for a small sum at your local hardware and grocery stores.
|10 foot length of 3" diameter schedule 40 ABS pipe||Home Depot||$8.55|
|10 foot length of 2" diameter schedule 40 ABS pipe||Home Depot||$4.25|
|3" to 2" reducing coupler, ABS schedule 40||Home Depot||$2.57|
|3" threaded (one side) coupling, ABS schedule 40||Home Depot||$2.67|
|3" threaded end cap||Home Depot||$1.38|
|small can of ABS welding cement||Home Depot||$1.71|
|Trigger-style butane/piezoelectric barbeque ignitor (see photograph)||Ralph's|
|10.5 oz Aqua Net hair spray||Ralph's||$1.63|
No special purpose tools are need for construction.
|Hacksaw||to cut the ABS piping|
|File||to taper the muzzle so that it can cut potatoes to size when we jam them in|
|Drill||to drill hole for ignition mechanism|
Just a few comments on instructions: Every few days, someone emails me asking for ``detailed instructions'' on potato cannon construction. I have no more detailed instructions than the diagrams given above, which should supply all the information needed to get started. Part of the fun of building such a thing is experimenting with the design. Furthermore, I have a feeling that if someone is not able to build a cannon given the above diagrams, then perhaps they shouldn't be building a cannon at all (I don't want anyone to hurt themselves by following step-by-step instructions without a clear idea of what they are doing).
I do have a comment on the ignition mechanism. Originally we used a flint-and-steel Coleman lantern lighter. This is a little assembly that produces a shower of sparks with a quick twist of a knob. We mounted the lighter through a hole drilled in the side of the combustion chamber. Unfortunately the flint/steel assembly doesn't hold up well to repeated firings, and failed pretty quickly. As a replacement, John and Eric discovered that a trigger-style barbeque lighter works amazingly well. This is sort of like a cigarette lighter, except with a trigger that produces a piezoelectric spark. The barbeque ignitor can be inserted through a hole in the combustion chamber as seen in the photograph above. It helps tremendously if the ignitor forms a tight seal with the hole; use ABS cement and maybe some duct-tape to form such a seal.
Many people ask me whether something is necessary to "prevent the potato chunk from falling into the combustion chamber." Once you build a cannon you will quickly find the answer to this question yourself. The fact that the design given here does not reference such a component should be a strong clue.
We calculated the muzzle velocity by timing the flight of projectiles launched skyward and then computing some basic physics assuming constant acceleration and no drag. I think it would be far more interesting to place some optical detectors (LED, phototransistor pairs) along the length of the barrel, and to use these, in conjunction with some timing circuitry, to measure the actual muzzle velocity and velocity profile for travel through the barrel. Perhaps this would also be useful in optimizing the barrel length and other design parameters.
The prospect of automating the system is alluring as well. With an automated fuel injection and ignition system many variables of the launch procedure could be set reliably, and performance could be optimized. Specifically, the amount of fuel injected, and the time between injection and ignition could be controlled explicitly. With a fuel injection system, the fuel distribution should be less variable as well.
update! I just found a web page where someone has taken high-speed photographs of projectiles leaving a similar canon using a strobe lamp. Furthermore, the muzzle velocity has been measured. See here.
Looking for something else to do with all those potatoes? I suggest you try this.
In April 2002 Bryce [sorry, no web page] built a miniature spudgun using the same concepts as our full scale version described above. Here's a photo of his creation:
So I finally built a mini spud gun. Several of them could fit inside the combustion chamber of the Splorg spud gun.
The ported barrel is 1/8"x6" and the combustion chamber is 1/2"x2". I've tried denatured alcohol and propane as fuels and the latter is significantly better. Dunno what the range is but I'd guess that it's around 100-150' so far. I haven't really done much tweaking yet. It makes a nice satisfying bang and the velocity of the potato plug ammo is enough to make it splatter into chunks upon impact. Since the whole thing is made out of relatively thick metal pipe, I think I could use hydrogen without killing myself. Of course, hydrogen isn't easy/cheap to get/use so I'll have to figure something out. I'm also thinking of making the ultra-spud-gun. I'd like for it to be a semi-auto cartridge loader with a rifled barrel and fuel injection. That will probably have to wait until summer though.
This is the tale of how this came to be.
It was a boring summer day. We had nothing to do.. until someone suggested "let's build a spud gun!". John and I (Tobin) immediately ran upstairs to find some good ideas/plans and then headed out to Home Depot. We quickly found everything we needed except for an ignitor, hairspray, and of course, spuds within a thirty foot length of isle in the local Home Depot. John's car was just about as long as the ABS piping that we bought, so out came the twine and John's car was transformed into a tank with two 10 foot cylinders on top. We then ran off to Sport Chalet for the ignitor, and on this leg of our little trip we learned the resonant frequency of the tied-down piping - and tried to avoid it. On the way home we saw lots of people nearly get killed, for the lights were out for some reason (probably due to our recent spree of power outages). Anyway, we got back to Location Alpha and out came the hacksaws, screw drivers, crescent wrenches, pliers, and files. Soon we had a cool looking spud cannon and just had to wait for the cement to cure. While we were waiting for the cement to cure, we ate lunch and went out to get hair spray and spuds. Spraying the aerosol hairspray over a lit candle demonstrated that yes, it was quite flamable.
Eventually we gathered the courage to test the device. We placed it in two large bricks, each of which had a convenient circular hole in the middle.. and we set it off. With a satisfying thwump, our first spud was shot across my patio and into the garden. Jubilation ensued. Over the next few hours we developed the thwump into more impressive sonic effects and managed to destroy the chlorine dispenser duck in my pool (target practice.. it was broken anyway) and get spuds to the top of the hill in my backyard with a satisfying kaBang. We also learned that the Basset Hound that we're taking care of has a taste for spuds. He was stealing our potatoes and eating them!
We mounted the ignitor near the rear end of the combustion chamber, on the side. This allows for easy access, but it would probably be better to mount it in the endcap itself, for two reasons that we have found. First, when you spray the hairspray in, it is likely to get the flint+steel mechanism wet and decrease its functionality temporarily, and, secondly, it is more difficult to shove a ramrod thing through the whole contraption when the ignitor is obstructing the shaft. If you get your gun loaded and fueled up and it doesn't go off when you twist the sparker gizmo, it's not a good idea to open it up and look inside to see if it's sparking. This has a tendency to result in singed eyebrows or worse.. The problem is a lack of oxygen in the combustion chamber. Ventilate between shots. Anyways, more to come...
1 We're just doing our civic duty to uphold the public's luny idea that the internet's sole use is to distribute bomb making instructions to terrorists.
I woke up around ten or eleven or twelve in the morning. It's difficult to be sure here since the power has gone out so many times in the last two days and all the clocks in my room are blinking 12:00. We've been having a tremendous heat wave, and it might be related. (everyone using their airconditioners and such) And an airplane crashed into some 500 kilovolt lines up in Tejon pass.. But that's not the point of this story. I woke up, and soon I checked my email. There's a message from Eric wanting to know if it's okay if he came over to see our new creation. John picked up Eric, and Eric brought me some size 12 rollerblades that no longer fit him, too. To The Point. Gradually we developed an optimum launching protocol. We keep the device horizontal and spray in about 2 seconds worth of Aqua Net hair spray. Then we casually close up the back of the combustion chamber and let it sit for another 5-10 seconds. Finally, we rapidly move the gun into firing position and twist the ignitor knob. This extended both the projectile range and the noise significantly. We fired all kinds of things. Wet socks work well.
We tried Butane as a fuel. It didn't ignite.
The next hinderance we encountered was that we used up all the flint in the little Coleman lantern lighter gizmo that we had purchased. We went to Home Depot to look around for ideas and ignitors, but the only thing we found was a piezoelectric barbeque sparker, for $12. Too expensive and it wasn't very impressive. We then went over to Sport Chalet and found a nice click-on flame gizmo for lighting things for a mere $3.00. We enlarged the hole where the former ignitor was and we stuck this in instead.
The result: A dramatically louder gun! Now it ignites and fires with a tremendous bang and a flash of fire out the muzzle. Very impressive. Having done this and run out of potatoes, we decided to call it a day..
Our nifty new lighter seems to have died. The general consensus is that John killed it. In search of a new ignition mechanism, we decided to go to R-Vac to scout around for parts. Although we learned that they now carry picture frames and home grown vegetables in addition to their complement of weird electronic goodies in a monumental testament to the first law of thermodynamics2, we did not find anything suitable for our purpose. There was, however, an automotive supply place in the plaza across El Toro, so we went there and purchased a Spark Plug for a little less than $3.00 and went back to Location Gamma. Once back there, Bryce supplied an array of ten nine volt batteries and an ignition coil and we were in business! We headed up to the nearby park and boy was our contraption loud! In addition to a satisfying bang, and a high velocity potato, we now had the element of surprize since it took awhile to get a good spark... Eric caught most of this on film. I'll of course be scanning these asap.
For some reason this system decayed as well until it no longer worked at all. Hairspray residue on the spark plug? We relocated to location alpha for known supplies of lead-acid batteries and other such goodies. However, the spark plug refused to ignite the system.. John had to go, so the splorg[oldes]mobile was no longer available. After messing around with the sparkplug setup and trying lots of different things (by now we had it hooked up to a four amp, 12 volt power supply going into the ignition coil), we decided to go back to the clicky-ignitor-gizmo setup. We hopped onto bicycles and ran downto Ralph's (didn't have them) and then Savons, where we got two for a very good price.
These items - kept out of John's hands (he wasn't present) - brought our SpudCannon back to its full glory and we enjoyed several hours of successful spud shooting - well into darkness - and provided entertainment for a handful of spectators as well!
The Cops check us out - Today we were demonstrating the Device to members of Splorg who had not yet had the opportunity to witness the pride and joy of Splorg in operation. We did several altitude tests (over 200 ft) a few distance tests (over 130 yards) and a few close-range projectile-obliteration impact tests. Somewhere in there a citizen decided to alert the police that "four juveniles were firing BB guns at public property." How one mistakes a large black tube for a BB gun and a potato for a BB is beyond the comprehension of Splorg's Engineering department; however, Splorg's Behavior Psychology unit points us in the direction of Bruce Schneier's insight that "anything can happen when people get scared" plus the ancient maxim that "people are stupid." Well, the "peace officer" who came to check out the scene was pretty nice and seemed like he regretted that he had to tell us to go elsewhere. He said that he had to deal with people who "had forgotten that they were kids once" and that he'd rather see us doing this than other stuff. At first he thought we were going to blow ourselves up, but we showed him how it all functioned and assured him that we had researched its safety. It's amazing how bad the internet's public image is: Officer: "Where'd you find out how to build this? -- and don't tell me the Internet." / John: "Well, actually, yes." / Officer: "Oh no, more Timmothy McVeighs." / John: "Oh, no, we don't want to be associated with people like that.." But the officer left with something of a grin asking "What's the range on this thing anyway?"
Okay, well, Paul was over and we decided for some reason or another to build another potato cannon.. So we did. It has a longer but thinner barrel than SpudGun I and a slightly longer combustion chamber, but it works about the same.
Have something to add? Email me.
Mike form Kansas City sent me this entertaining note. I particularly enjoyed the noun-phrase ``weapon of mass stupidity.''
Date: Thu, 18 Oct 2001 12:14:43 EDT From: Mike from Kansas City Subject: spud cannon Hey Tobin, my name is Mike and I'm from Kansas City, Missouri. The other day I got this crazy idea to build a potato cannon.Where did I go to look for some specs on one? The Internet of course, which is what lead me to your site. I printed out the list of materials and was able to find everything I needed at Lowe's, and next door at Wal-Mart. I put one together exactly like the one on your page, except I made mine out of PVC. (Believe me it works just fine!) After annihilating a few potatoes against my privacy fence, I took this weapon of mass stupidity over to my local diving range. The owner said it was okay so I fired off a few shots. Most of them went over 200 YARDS! Potatoes work well, but I found that Jonathan apples work just as good, if not better. Well, take care and thanks for posting those plans! -MIKE
Gratuitous use of attention-getting tyvek suits, a marketing attempt for ``thinking putty,'' you decide!
Date: Wed, 24 Oct 2001 09:53:15 EDT Subject: Potato cannon experiments Tobin, Hi! My name is Elizabeth, and I am too a fan of potato cannons! I thought you may be interested in taking a look at some potato cannon experiments we conducted this past summer. We shot pounds of Thinking Putty (a silly putty like substance) out of our cannons directly at our video camera (the camera was protected behind some bullet proof glass). There are some videos as well as pictures on the site. I hope you and perhaps your web site audience enjoy seeing our experiments. Please let me know what you think! Thanks again :) Here is the link: http://www.puttyworld.com/putandpotcan.html Let me know if you have any questions! Best, Elizabeth
Chris Davenport sent me the following suggestion. Oxy-Acetelyene? Golf Balls? It sounds like a disaster waiting to happen, but I suppose that's the nature of these things:
Date: Tue, 30 Oct 2001 20:04:36 -0600 From: Chris Davenport Subject: potato gun if your feeling like attempting something more powerful or higher muzzle velocity, try golf balls. My friends and I also used oxygen acetelyene mix a few times, but if you go to higher compression ratios make sure to put a bluejean pant leg around the firing chamber in case it shatters. The bluejean leg will prevent shrapnel. Just admiring your web page, Chris Davenport
If you're in the market for a giant see-through kite of doom, then Dr. Mike Kornostar is your man.
Date: Wed, 14 Nov 2001 11:53:49 -0700 From: Mike Korenowski hey man, i love your site, and i thought you would like to know that we too have been experimenting in weapons of mass destruction. My latest project produced a giant, see thorough kite of doom with a remote targeting bomb sight camera and a hefty payload bay. Drop me a line for the plans... Best, Mike P.S. We are currently making a 'big bertha' pumpkin cannon, as well as a trebuchet. You'll hear from me when i am complete. -Dr. Kornostar, Phd THERE IS ONLY ONE...
Bill from Tennessee writes with some BBQ ignitor tips:
Great site! My name's Bill, and I'm from Jackson, TN. I am new to the wonderful world of spud-launching, but I tried this ignition device and it worked. Get a B.B.Q. ignitor and two long wood screws... Screw the screws into opposite sides of the combustion chamber so the ends are aproximately an 1/8 of an inch apart. Next, attach the leads of the B.B.Q. igniter to the screwheads. When you trip the igniter, a spark will jump the gap between the screws, much like the spark plug, but this device should resist hairspray build up a little better.
Date: Sun, 30 Dec 2001 23:25:35 EST Subject: potato cannon Thanks for everything. I fired my cannon Friday and I had a potato to go 93 yards. That's the farthest. Thanks, ninetedo99
Hmmm. Sometimes I worry about these people:
Date: Sun, 23 Dec 2001 22:09:16 EST Subject: (no subject) if u think that is cool look around more and make a pneumatic...more reliable. More fun. Try special ammo. I like smoke bombs and flares. Put in potato, get all ready to fire. Then add smoke bomb or flare ontop. So cool. Don't start fires! Don't Reply....dads email account and he'll be pissed