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This weekend, make the spud gun which was featured in the MAKE: 03 magazine.You’ll be able to make a potato go farther and faster than it has ever gone before!I made a few changes to the plans for my “tazer-totter.” I used ABS instead of clear PVCand so I also had to use ABS cement instead of PVC cement. I used zip-ties instead ofhose clamps to attach the stun gun to the barrel. I insulated the inner terminals on thestun gun with Shape Lock and I used Aqua Net hairspray instead of Right Guard forpropellant.A lot of people have made spud guns, so it’s worth it to spend some time on the internetchecking out what other people have made so that you can learn from what they havedone.

Spud Gun (a.k.a. Tazer-Totter)ExplodeImplodeReset3D PDF InstructionsSpud Gun ComponentsThis 3D model of the Spud Gun can be rotatedand examined from any angle. Just click theimage to activate the 3D model; then use theExplode, and Implode controls to see theanimation in action.Cannon BarrelTo view a specific part, click the link in thecomponent list to the right.Clamp #1Additional controls to zoom, pan, and more,are available in the 3D PDF toolbar above the3D model.Reducer CouplingEnd CapFemale AdapterClamp #2Hardware (nuts, connectors, etc.)Stun GunWiring3D Spud Gun model created in Alibre DesignTo learn more about creating 3D PDF documentswith Alibre Design visit www.alibre.com

www.makezine.com/03/spudgunPhotograph by Casimir A. SienkiewiczPROJECTS: spudgun108Make: Volume 03

The NightLighter 36By William GurstelleLaunch potato projectiles200 yards with thisstun-gun triggered, highpowered potato cannonwith see-thru action.(Good thing potatoes arebiodegradable.) Set up: p.112 Make it: p.114 Use it: p.118Make:109

PROJECTS: spudgunwww.makezine.com/03/spudgunPotatoes, bewareThe potato cannon, a.k.a. the spud gun, isa popular and very entertaining amateurscience project. It’s simple to make, andfew devices offer such bang for the buck.You can use the Night Lighter both day andnight, but when it’s dark, the clear PVCprovides an excellent view of the interiorballistics. Also, the stun gun gives betterperformance than weaker sparks frompiezoelectric or flint/steel igniters. It’s funboth to fire and simply to watch in action.A basic spud gun can be built with plain,white PVC for less than 25. The NightLighter 36 costs more, but I scroungedleftovers from plastics suppliers and builtmine for less than 50. After masteringbasic gun construction, the intrepid potatocannoneer may want to design and assemble more complex and artistic devices.William Gurstelle enjoys making interesting things that go whoosh then splat. He is the author of Backyard Ballistics(2001), Building Bots (2002), and The Art of the Catapult (2004). Visit backyard-ballistics.com for more information.110Make: Volume 03

BEVELED EDGE Loada spud, and the sharpened front edge cuts aplug that seals airtightagainst the barrel.PRINCIPLES OFSPUD GUNNERY:Serious spud gun designerstinker with the ardor of hot-rodbuilders. Our NL-36 improvesupon the basic potato cannonby substituting transparenttubing and a stun gun igniter.BARREL The three-footbarrel guides the potatoplug along its trajectoryas it picks up speedfrom the explosion.IGNITION CHAMBER Aspark from a stun gunignites hydrocarbonrich aerosols, causingthe internal combustionthat sends the spud.You can watch it allthrough the clear PVC.CHEMICAL REACTIONFire, everyone's favorite exothermal reaction, breaks aerosolpropellants into hot, expandingCO2 and water vapor.range COMPARISONS WITH OTHER FAMILIAR PROJECTILESOur spud gun propels a 9-ounce potato plug approximately 200yards. Here's how this compares with some other launch events.Shot put: 16 pounds, 25 yards (Olympic record)Cell phone toss: 4-5 ounces, 90 yards (Savonlinna record)Football punt: 14-15 ounces, 98 yards (NFL record)Baseball throw: 5.25 ounces, 149 yards (Guinness record, 1957)Civil War cannon: 6-pound ball, 1,500 yardsIllustration by Tim LillisSCUD-B missile carrying 10-ounce potato payload: 186 miles2590186 miles981491,500Not to scale.Make:111

PROJECTS: spudgunSET UP.MATERIALS36-inch length of 2-inchdiameter transparentSchedule 40 PVC pipe (1)14-inch length of 3-inchtransparent schedule 40PVC pipe (1)Used mainly in the foodprocessing industry,transparent PVC isavailable from industrialplastic suppliers such asHarrington Plastics orRyan Herco. Check yourlocal business listings.You can also order itfrom McMaster-Carr(www.mcmaster.com).Transparent PVC is generally expensive, but youmight find reduced-priceremnants at plasticssuppliers or foodprocessing companies.Large potatoes3- to 2-inch diameter PVCreducing fitting socketa.k.a. reducer coupling orbell reducer (1)3-inch PVC femaleadapter (1)3-inch PVC end plug (1)Use Schedule 40 gradefor all PVC fittings.Source from large homeor hardware stores orplastics suppliers.PVC primer and cementAvailable wherever PVCis sold.112Make: Volume 03www.makezine.com/03/spudgunVisit makezine.com/03/spudgun for source list.

Lexel sealant, or otherclear latex or siliconesealantI-inch drill bit15-inch long hoseclamps (2)¼-inch bolts, 2 incheslong, full threaded (2)Stun gun, 100,000 voltoutput or better (1)Available from supplierson the internet. I boughtmine from Cabelas(cabelas.com) for lessthan 20.Large crimp-on spadeconnectors (2)Sanding drum for drill¼-inch hex nuts (4)Crimp-on buttconnectors (2)2-foot length ofinsulated 12-gauge orthicker wire (1)Small wire nuts (2)Aerosol spray containinghydrocarbons (I usedRight Guard Unscented.)Electrical tape4-foot long/1-inchdiameter wooden dowel,or broom handle (1)Photograph by Kirk von RohrOTHER TOOLS:HacksawDrillScrewdriverPliersWire strippers or knifeWrench for ¼-inch boltMake:113

PROJECTS: spudgunMAKE IT.www.makezine.com/03/spudgunCONSTRUCTINGTHE MIGHTYPOTATO CANNON startTime: An Afternoon Complexity: Lowthe PVC1. Prepare1a. Cut pipes. Measure and mark acutting line 14 inches from one endof the 3-inch diameter PVC pipe. Usethe hacksaw to cleanly and squarelycut the pipe. This will be the cannon’scombustion chamber. Then measure,mark, and cut a 36-inch length of the2-inch diameter PVC pipe. This will bethe cannon’s barrel.1b. Taper end of gun. Use a file or adrill and sanding attachment to taperone end of the long 2-inch diameterpipe, so that it forms a sharp edge. Aclean, sharp edge is important, sinceit should cut the perfect-sized potatoplug projectile as you ram the potatointo the muzzle of the gun.14"3"2"36"When PVC gets hot, it releases poisonous chlorinegas. Perform this step in awell-ventilated area.2a. Drill electrode holes. Four inchesfrom one end of the 3-inch diameterpipe, drill a slightly undersized holefor the ¼-inch bolt. Drill a second holedirectly opposite the first hole, fourinches from the end.114Make: Volume 03The 3-inch pipe will contain the fuel and the spark,and act as the combustionchamber.Photography by David Albertsontheelectrodes2. Attach

2b. Attach electrodes. Screw in the2-inch long bolts, with nuts attached(two per bolt), into the holes in the3-inch pipe. The nuts go outside thebarrel. The bolts should tap themselvesinto the softer plastic, but don't overtighten or you'll strip the PVC. Positionand adjust the nuts as needed so thereis a ¼-inch gap between the bolt endsinside the barrel.This is the spark gap thatwill ignite the fuel, firingthe cannon.the PVC3. Solvent-weldThe spud gun is composed of PVC pipes and fittings that are solvent-welded in place using PVC cementand primer. To prevent leaks and weak spots where the parts are joined, the solvent welding must bedone properly. Meanwhile, the primer and cement are toxic and flammable, so you need to work in a wellventilated area, keep the chemicals away from open flames, and follow all safety precautions on the labels.First, we’ll solvent-weld the reducing connector to the front of the combustion chamber. Then we’ll followthe same procedure to attach the threaded adapter to the back of the chamber and to connect the barrel.3a. Inspect parts. Check the 3-inchpipe ends and 3- to 2-inch reducingconnector for cracks, dirt, and abrasion, and remove any plastic burrswith a knife. Don’t use damaged PVCpipe or fittings.3b. Weld parts. Following the procedure at right, solvent-weld the 3- to2-inch reducing connector to the endof the 3-inch pipe closest to the electrode bolts. Then join the unthreadedside of the female adapter to the otherend of the 3-inch pipe, and attach the2-inch barrel to the narrow end of the3- to 2-inch reducing connector.How to Solvent Weld1. Clean the weld surfaceswith PVC primer. Apply theprimer with a dauber orbrush (usually inside thecap). The primer cleansand softens the PVC andallows the cement to penetrate the surface.1.2.3c. Let the cannon dry for severalhours in a well-ventilated area beforeusing. You don’t want to fire it whilethe solvents are wet and flammable.3d. Screw the 3-inch PVC end pluginto the back of the chamber afterdrying.3.2. Brush on a thick coat ofPVC solvent, first to theend of the pipe, and thento the fitting socket. Leaveno bare spots.3. Immediately join thepipe and the fitting socket,pushing the pipe to its fulldepth and making sureit’s seated squarely with aslight twist. If you’ve usedenough solvent cement,you should see a small,continuous ooze of cementaround the fitting. Oncejoined, you can’t repositionthe pipes or otherwise fixerrors. If you accidentallyput the wrong fitting on apipe, you need to trim it offand start over. Make:115

PROJECTS: spudgunwww.makezine.com/03/spudgunwire the4. ignition4a. Test-fit butt connectors. Usinga sharp utility knife, remove excessinsulation from each crimp-on buttconnector. With the stun gun turnedoff, test-fit the trimmed ends of theconnectors over the gun’s main electrodes. These are the twin electrodesthat point forward, rather than towardeach other, and we’re hooking theseup to our ignition wires, in order tobring the spark into the combustionchamber.(Depending on the makeand model of the stun gun,you may need to modifythese directions and connect the wires in otherways, such as with wirenuts or soldering.)4b. Prepare ignition wires. Cut thewire into two, 1-foot wires. These arethe ignition wires. For each, attach acrimp-on spade to one end and theuntrimmed end of a butt connector tothe other end.4c. Attach ignition wires to stungun electrodes by crimping on themodified butt connectors.4d. Cover the stun gun test leads(inboard electrodes) with wire nutscut down to size, or other high-voltageinsulators. Insulate all exposed metalareas of the ignition path on the stungun and bolt electrodes, with electrical tape or silicone glue. It's easy forelectricity to find its way underneathany insulation gap at the base of theelectrodes.116Make: Volume 03Wire nuts need to betrimmed to fit onto thetest electrodes.

attachigniter5. the5a. Attach the stun gun body to therear of the chamber using two hoseclamps. Do not over-tighten. Positionthe stun gun body at a 90-degreeangle to the axis of the electrodebolts.5b. Attach ignition wires to electrode bolts, securing the spadeconnectors underneath the bolt heador between the nuts. You may haveto bend the spades to widen themenough to fit around the bolt.final6. insulation6a. Cover bolt connections with globsof silicone sealant. To further insulate,wrap the whole ignition area with bubble wrap, and tape down. The stun gunoperates at such high voltage that thewrap still may not completely preventshocks. Avoid contacting electrodeswhen operating the cannon. Don’t bethe path of least resistance!Congratulations! Your Night Lighter36 potato cannon is complete.FINISH XNOW GO USE IT »Make:117