Spud Guns
 

I thought i would post this as a guide for someone who might want to make one.

This materials list is to build a very simple starter model potato launcher, with the intent to get the most bang from your buck (so to speak). By no means is this the only way to build a launcher, or nearly the coolest, but still able to provide hours of fun.

MATERIALS:
Obtain the following items: (qty 1 unless so indicated in [])
10" of 4" SCH40 PVC water pipe (chamber body)
36" of 1 1/2" SCH40 PVC water pipe 4" PVC coupler
4" x 1.5" PVC bushing (if not available combine two, like 4x3 and 3x1.5)
4" PVC FSxFNPT adapter
4" PVC MNPT threaded plug
PVC primer, one with dye in it if possible (purple, blue)
PVC pipe cement, medium body is best
[2] #8x2 1/2" flat or round head allthread machine screws, drive not important
Two feet of 16g or lower stranded insulated wire
Electrical and Duct tape (of course!)
Red button BBQ ignitor/striker, a replacement found near new BBQ's

EQUIPMENT/TOOLS:
Suggested tools for building the potato launcher:
Hand wood saw (or hacksaw, for cutting pipe, maybe you already got it cut at the store)
Pocket knife
Needle Nose Pliers
Soldering Iron w/PbSn or Pb free solder (or just use tape and hope it works)
Drill motor with bit 0.010" larger than machine screw shank
Appropriate driving tool for machine screw (probably Phillips)
Medium half round file for shaping pipe (or a lathe if you got one)
Rag for PVC cement clean up (disposable)

Step 2: Preparing the materials for assembly

To make sure everything goes together properly and smoothly, proper conditioning and sizing of the materials is necessary. Pay particular attention to the shaping of the pipe ends, as this is a major factor in proper solvent welding with the fittings.

PVC PIPE SIZING
Cut the two pipes to size, 10" and 36" with the saw unless you already did so in the store. Using the file, take off the sharp corners on the inside AND outside of the pipe. Radiusing the inside helps reduce the amount of potato scud that can build up in the launcher, and breaking the outside corner ensures proper solvent welding, if this is not done leak paths may result. Cut ends should be as square as possible. To one end of the 1 1/2" pipe it is suggested that the inside be chamfered about 0.020" and the outside filed or turned down to almost meet the inner chamfer, creating a blunt knife to help size the potato. It will work without out this step, but a lot messier!

PVC FITTINGS
Inspect the fitting for really bad weld lines or possible large dislocations that may result in premature failure. Remove all paper tags or labels by peeling, scraping, even using a bit of primer to clean off the last adhesive. File off any sharp sprues that may hamper your ability to grip the fittings firmly when assembling.

IGNITION SYSTEM
Cut the wire into two equal lengths. Strip and twist each end about 3/4" back. Taking the BBQ igniter, upon inspection you should find a plug on the tail end (one electrode site) and close inspection should reveal a very fine wire embedded in the side body of the igniter, close to the button lip. This fine wire is attached to the igniter nearest the button, as the wire is just pressed into this slot which might be about 3/4" long. Carefully extract the other end of the wire with the knife, removing all but the last 1/4" or so from the slot. Carefully twist this wire to one end of one electrode wire stripped previously. Immediately solder this connection together taking care to not break or extricate the fine wire from the plunger body. Cool with spit (really!), dry, and tape this joint back against the body with electrical tape, using enough to immobilize the wire with gentle tension.

Take the wire supplied with the igniter, the one with the plug that fits on the base, and cut leaving about 2" from the plug end that will fit into the base of the igniter. Strip and twist this stub to the other electrode wire, soldering, and taping over the solder joint. You now have an igniter to make a 'remote' spark. Try it holding the two free electrode wire ends about 1/4" apart--don't touch them! (your BBQ igniter may be a bit different, the idea is to get both electrodes away from the igniter, so you don't make a big hole in the launcher combustion chamber.)

Now you get to stick all the stuff together, using pipe glue and tape and more solder if you like! Just don't breathe too much pipe glue solvent...it'll make you nuts!

I Chamber Assembly:
Prime both ends of the 4" pipe, also priming the 4" bushing, both 4" coupler sockets, and 4" slip on the adapter. DO NOT get any primer on the adapter threads! Immediately apply pipe cement to the three primed 4" fittings, then LIBERALLY to both ends of the 4" pipe. Start both the coupler and adapter fittings on the pipe, start the bushing in the coupler, then right the assembly with the threads up, pressing it together with body weight while twisting about 1/2 turn. Hold this position for at least 30 seconds. The pipe ends should bottom each about 1 1/2" inside the fitting socket. If they both do not bottom, either apply more force IMMEDIATELY somehow to get it to, or you are screwed and have to throw it out--start over with that. If the fittings and pipe are properly conditioned this should not be a problem. Wipe up any spilled glue with the rag, but leave a good bead at the external pipe/fittings line. If any glue got on the threads get it out of there as fast as possible! Any glue on your hands should just be left to dry and then peel it off. Using solvent to remove it will just increase your exposure to it.

II Electrode Installation:
Wait about 10 minutes for the glue to set. Using the proper size drill bit, put two radial holes 90deg apart about 1/2" back from the front edge of the adapter fitting--the plastic here is about 1/2" thick as well. Drive in the two machine screws nearly all the way, leaving about 1/8" between the screw head base and the plastic. The ends may touch or be far apart--the electrode gap will be calibrated after the electrode wires are connected.

III Barrel Introduction:
Prime one end of the barrel and the 1.5" socket on the bushing. If one end of the barrel was chamfered to a knide, prime the square 'regular' end of the pipe. Apply glue, liberally to the pipe, and press together, again using a 1/4 turn motion to bottom. Hold for 30+ seconds. After releasing place the unit upright for several minutes, to let the glue set a little more. Solvent welding is more of a curing than a drying process. Solvent is lost, hence the term drying, but the action of the solvent effectively cures all those individual plastic parts into one continuous physically joined piece of plastic. Properly done, solvent welds are always stronger than bulk pipe.

IV Wire it Up:
Tin the two free ends of the electrode wires if possible. With each end bend it around the screw shank, just below the head, in a clockwise manner (you may need needle-nose pliers if the wire is heavy). After the wire is at least 3/4 turn around the shank, tighten the screw, pretty good, biting the wire into the plastic a little. Liberally apply electrical tape, rubber tape, or silicone RTV to the exposed metal areas, as they will shock you all day long if not insulated properly. Before taping tug on the wires a little to make sure they are firmly gripped by the screw head.

V Electrode Calibration:
Setting the gap is next. The two screws may be in a variety of relative positions, depending on how straight and aligned the holes were drilled. Wearing leather gloves, you now want to somehow create about a 1/4" gap between the screws. This gap does not have to be measured from the very tip of the screw, and the spark will find the shortest route possible. Bend only one screw if possible, and dont bend it around a whole bunch back and forth, or it will get work hardened and break sometime. DO NOT test the spark device yet, as there are still PVC solvent fumes all over the place. Just wind sufficient tape around the ignitor body to fully insulate all metal parts from your hand when you grip it. Lash it to the side of the chamber if you like with electrical or duct tape, just don't press the button yet!
IT IS HIGHLY RECCOMMENDED THAT YOU WAIT AT LEAST 24 HOURS FOR THE GLUE TO FULLY CURE AND SOLVENT TO DISSIPATE. Many of the unfortunate potato launching accidents occur due to overanxious constructors/operators getting a little trigger happy a little too early. A few notable events include people chemically/thermally removing a majority of the hair on their head, or rapidly separating the supposedly single piece of PVC plastic back into its purchased components (or even smaller pieces!) Just wait...it'll be worth it.

In the mean time this is a great opportunity to gather what you may need when you do start running this device. On the top of this list is certainly a bag (or two...or three...) of good fresh potatoes. Never use old sprouting, skunky potatoes, this is just bad form! Buy a bag for $2 and relish in their crispness! Also a fuel, probably starting with hairspray, the old mainstay. Traditionally the 'Aqua-Net' brand has yielded to best results, but it will be mighty hard to find those folks who grew up on that. Once you get more experience you might graduate to propane...but wait a bit. A good location is also required...don't use this device in the middle of your subdivision out of your garage or you are guaranteeing that old grandpa down the way will call the cops!

Again, find a suitable location to deploy your potatoes, as the device can get quite loud with a good fuel load. Out in the sticks is best, but just not downtown!

1. After waiting the necessary time for the solvent vapors to dissipate, now you can test the ignition device. Depressing the plunger briskly should produce a good spark to jump across the screw threads. If all connections were made correctly and the gap is about 1/4" it should spark every time (or at least 9 times out of 10). If it doesn't check your connections, maybe set the gap a little closer (never less than 1/8") but get it to work, or potatoes are going nowhere (unless you throw them--boring!)

2. When a reliable spark is verified, test fit the threaded plug into the adapter. It shold engage the threads at LEAST TWO TURNS. If not, check for crud in the threads, and if clear, obtain a 60deg triangle diamond file, and size down the plug threads a little. The threads are at a 60deg angle, so careful filing about the first few threads is ok.

3. With the cap off, load a potato! With the chamber on the ground, place a potato over the muzzle of the launcher, and press it down with your palm, shaving off the excess, creating a cylindrical potato plug. Make sure the potato contacts the wall firmly all around, or it will not fire or not that well. Loading the potato sideways is acceptable, as it creates a more stable projectile anyway. Ram the potato down to within 2" of the breech of the barrel, using a smaller diameter PVC pipe or broomstick. Don't push it too far or it will fall out into the chamber...and just be subject to a short baking cycle.

4. With the spud firmly seated in the breech, pick up the launcher and holding with one hand, dispense a few seconds of hairspray directly into the chamber. Don't use too much; it will just make a mess. Quickly close by screwing on the end cap hand tight, do not use a tool to tighten to two turns or you will likely never get it off again.

5. Call out "Fire in the hole!", point the launcher in a safe direction, and depress the BBQ plunger. That potato you rammed down there should exit at a quite rapid rate with a sizable report, and depending on where you aimed and at what angle you pointed, it went anywhere from 6 inches to ~200 yards from the muzzle. Pretty cool. If you clicked the ignitor a few times and it didn't work, you are not alone, check out my next section.

6. If it worked, great! Remove the end cap (this may require a tool), vent the spent gasses getting a fresh load of air, and repeat as necessary!

Step 6: Debugging the Launcher

There are a lot of reasons why your launcher may not be working. First and foremost NEVER take off the cap and start clicking away at the igniter. This again has led to human fires and that chemical thermal hair removal thing again....

Hairspray in cold weather just does not go well. Too much of the burnable stuff in the spray condenses on the chamber walls, making it very difficult to burn. You might try warming the chamber by the fire if you are camping or graduate to a lighter, hotter fuel (propane....)

To 'defuse' a misfire you need to take off the cap, while pointing it in a safe direction. Allow the chamber to air out for several minutes, perhaps longer, to get the fuel load out. After you are certain the fuel has been vented, again verify the spark, just by turning the chamber enough so you can see where the spark should be. Never point the chamber bore directly at your face, or body, or anybody else. If it sparks then it is a fuel mixture problem.

One of the most common fuel problems leading to misfire is too much fuel! Not usually a problem with hairspray, other richer fuels can be overloaded above their UEL value, and they wont work. Always try less fuel rather than more fuel.

If you still can't get it to work I invite you to peruse the many other web sites that talk about how to troubleshoot your combustion launcher. Again I have made a partial list, and sadly just don't have the time to address very specific person to person launcher complications. I hope you do in fact figure it out and experience many hours of safe spudding.

Good Luck!

I prefer the air pressure version, instead of the explosive variety. Its safer, you can get better distance, and you can fine tune your ballistics by varying the air pressure.

Supplies

3 feet of sch40 1.5" pvc (you can go bigger if you want)
2.5 feet of sch40 2" pvc
1.5" brass ball valve
1.5" male and female screw adapters
1.5" to 2" adapter
2" end cap
car/bike tire valve
lots of 2-part epoxy

hacksaw
something to mix in and spread the epoxy with

Epoxy one of the 1.5" screw adapters to the barrel (the 3' segment). Set that aside to dry for the time being. Epoxy the other one to the front of the ball valve.

Take the 2" end cap and drill a hole in it. Put the air valve through the hole, and fill the surrounding area with epoxy. Make sure you don't cover the air valve, as this could cause some problems ;). Set that part aside until it dries.

Epoxy the 1.5" to 2" adapter to the ball valve, then when that dries epoxy it to the 2" pvc. Hopefully, by now the end cap will be dry. Epoxy the end cap with the air valve onto the rear end of the compression chamber.

Let everything dry for at least a day. Now you're ready for some fun. To operate, close the ball valve, attach a bike pump to the air valve, and pump it up till it hits 80-90 psi. I wouldn't suggest getting much over 100 psi, because if I remember correctly, the breaking point for sch40 pvc is 150 psi. Pvc shrapnel isn't fun.

To core various fruits and vegetables, I'd suggest using either another piece of 1.5" pvc sharpened at one end to cut things, or sharpening the end of the barrel. It really depends on how you want your cannon to look.

If you built it well, it should last quite a long time. If something breaks, it's usually not difficult to make some sort of repair. Just remember-epoxy is your friend.

Hey ashton, where did you pick up the electric sprinkler valve and the pressure regulator? I was looking for those when I made mine, and couldn't find them...

With the pneumatic version, the potato gets fired with the release of pressure. It seems like using a ball valve isn't the best way to let it all go at once. Are there any other design options (mechanical or elelctrical)?

i have one of the explosive variety... just get some butane in an aerosol can... put a lil tiny squirt in the chamber

and turn the sparker... we used a coleman lantern sparker... its a ton of fun...

yeah I perfer the explosive variety my-self.... packs a bit of a kick....

I've heard an electric sprinkler valve will open immediately and let all the air out at once. Since I couldn't find one, I just went for a big-ass ball valve, and open it quickly. Trust me, it works pretty well ;).

Make sure you never look down the barrel- unless you want to end up on the local news, lol.

Spud guns can be fun, but I think they are more dangerous then guns. If anyone keeps up w/ fark there have been at least 2 articles about kids really hurting themselves with those things.
Personally if you want to go and do something fun where you shoot stuff go paintballing and rent the gun. It is safer and a hell of a lot more fun I think, it can be expensive if you get your own gun, camo and such[which i do]

The spud gun itself is not inherently more dangerous... it just depends on the person using it. If you do a shitty job making it, then screw around with it, you're probably going to get hurt. But if you realize that whatever's coming out of the end has something like 95 pounds per square inch of air pressure behind it, and treat it accordingly, it can be very safe. As long as you don't shoot someone with it, or look down the barrel?? you'll be fine. Besides, what kind of an idiot looks down the barrel of a loaded spud gun? Maybe a darwin award candidate...

You wouldn't know anything about shooting people with it, would you? :D All will bow to me (http://www.boomspeed.com/mrcactus/bowdown.gif)and my propane powered gun this summer.

I use oranges and a spark plug seems to work good as the igniter..and normall hair spray as the flammable

That frog thing happened near where I live. Jacked that kid up BAD. THose things are fun, even better when you make one that's a good size for a tennis ball!! (coke cans are EXACTLY the right size) Tennis balls fly real well because of the nice perfect shape! but for the love of GOD, be careful!!! the spark plug is good, but I'm rather partial to my compressed air one.. Got a tire valve on it to charge it up from my compressor, and I can shoot a tennis ball about 3 good blocks if the wind is right! (air time, not just roll time)

We used to make giant spud guns, but instead of a solvent, we would inject butane into the chamber until all of the 'air' was driven out, and then some oxygen (experiment until you get the right ratio). The result was a spud gun that would shoot a potato core clear through those barrels that are used as trash cans at parks these days. It would bend the can in two and split through the front and back. The potato would probably travel for at least 600 yards.

Also, we got better results when we put a little sealant about 4 inches past the chamber end of the barrel, it forced the pressure to build up a little more before releasing the potato. Oh, if you put a nail through the barrel about 1/2 inch from the chamber, it prevents the potato from falling into the chamber and makes the loading process a little more uniform.

yeah, we had issues with the gun splitting into two different pieces, but it always occured along a join, and we could just glue it back together a little stonger than before. We also played around with reinforcing the chamber with wire and packing tape. That seemed to strengthen it enough to handle any pressure we could generate (although we did worry about the shrapnel potential).

I have a couple of pneumatic spud cannons. My buddy and I built nearly identical models, except that he used a large ball valve and I used a solinoid (sprinkler) valve. Same size tank, switchback piping, and barrel. Mine cost about $20 more, but it outshoots it by 25-100% with identical pressure and projectiles.

We've never been able to build a pvc or abs combustion model that can compete with the pneumatic ones.

I found that you could add spin and accuracy to the potato buy rifleling the barrel. Just drill small holes in a spiral pattern through the last quarter of the barrel. You'll loose a little distance but accuracy is greatly improved.

Beware the world if they ever try to take on the TFP with some of the things in this forum

:D

Ashton, my friend built a pneumatic cannon but the sprinkler valve seemed to open too slowly. Instead of firing a quick shot, it kinda made this hissing farting cound. the air chamber wasnt very large, maybe that was it, or not enough pressure?
any suggestions?

IMO, pvc pipe is kind of dangerous to use, because it is brittle and if anything goes wrong, it tends to shatter and send shrapnel evrywhere, which might hit u in the eye or somewhere.

the alternative to pvc is abs pipe, which wont shatter, it only splits and stays in one peice

just letting u guys know if u hadnt already knew

have fun with those potato guns

Aren't these things frowned upon by local law enforcement? Has anyone here had any problems with the law using a spud gun?

About the same time that kid shot himself in the face with a frog from a spud gun, I thought there was some chatter about these being classified as zip guns or destructive devices or something like that.

http://www.spudtech.com

The science dept. at my school had a spud gun for chemistry and physics demonstrations. Then they blew it up.

With ONE gram of hydrogen gas. Creepy. Potato went ~300yds tho...:)

my friend was gonna make one, but after he realized it was too much work and a lot more than he wanted to work with he just made a little one. i've seen pix of like rile like air guns, i'd go with one of them if you want a spud gun but not a huge thing.

On the safety note, we do our best but there is of course always the problem of man's desire to know...

...which can lead inexorably to trying to put too much into the device, or to hair-brained ideas like trying to achieve a better seal on the charge by ramming a little wet newspaper down there with the potato.

Top tip: If you're gonna try this, let your buddy have a go in case there's a breach explosion. Worked for me. His hair grew back eventually.

Yeah I built a combustion spud gun recently with ABS plastic...shit I still can't believe how far it shoots, anyway I'm probaly going to build a pneumatic version some day, they seem like more fun.

I made a small one used half inch pipe for the barrel and 1.5 inch for the fire chamber. I made it so the barrel and firechamber seperated so it would fit into my lunch box. I made it specially for shooting a smart a## I worked with. I bought a bag of tater tots let them thaw out then loaded it up. The handling required to load it made the tater tots break down enough so that when I shot it the tater tot scattered like a shotgun.

The best part of it was that I blasted the dude while he was eating lunch in the break trailer and everyone but him knew it and all ducked just in time. The results were incredible next time I am going to try cold mashed potatoes in it (you know the real stiff ones).

The amazing thing is it shot the tiny peices of tater tots over 60 feet.

Here's a couple more things you can try with your spud guns...

1) - File the end of the barrel down so that the edges are sharp as knives... kinda like this: /| |\ - The filed edges will cut into the potato smoother making a more uniformly shaped projectile.

2) - Remove the small plastic button from the hairspray can. Drill a hole in your chamber about the same size as the button and epoxy it into the chamber so that the spray hole is inside the chamber and the hole that once connected with the can is open to the outside. Then by inverting the hairspray can you can inject the hairspray directly into the chamber without removing the lid! This prevents any loss of fuel durring recapping. Just becareful of how many and how large your holes are... I once nearly blew off my leg when a weakened chamber exploded on me.

potato gun
 

http://members.cox.net/leprakrotch/000_0141.JPG
Whats left of 2 speakers after 1 shot each
http://members.cox.net/leprakrotch/000_0143.JPG
A soda I shot of a barrel into a tree, and yes it was stuck like that when I found it
http://members.cox.net/leprakrotch/000_0144.JPG
I was shooting from the picknick table to the barrel. The tree is a little bit to the left of the barrel

Any pictures of the gun itself?

Seems like a pretty badass gun. Either that or some pretty badass potatoes.

the gun air powerd? or combustion?

mines combustion... i use the butane in an aerosol can... works great

Combustion, also use butane just a normal 1.5/1 gun. But the potatoes are herd as hell. And cheap.

the potato gun I had was never that destructive

more fire: maybe you didnt point it at the right objects... did you use hairspray? i find the butane gives it a lil more umph....