Introduction: Tennis Ball Mortar

Picture of Tennis Ball Mortar


The tennis ball mortar is a great project for many reasons: all the materials are cheap and readily available, its construction is extremely simple, and it gives off a nice loud *pop* which the video doesn't do justice.

Quick and dirty explanation on how it works: The mortar is composed of three sections of Pringles cans duct taped together. The metal bottoms of the top two cans are cut to form baffles, which will focus the force of the expanding hot gas created by the burnt vaporized naptha, onto the center of the tennis ball. Thanks to the near exact match in diameter of the ball and can, the force of the compressed gases is trapped behind the tennis ball for the whole length of the top can.

As you can probably guess this design has room for improvements. For example, if the length of the top can were extended, the ball would have a longer time to accelerate and thus achieve a faster speed, but at what point does the downward air pressure on the ball overpower the structural integrity of cardboard and duct tape? How does increasing the volume of the cans affect overall performance? What effect would adding a few more baffled cans have? I'm sure the answer is only a simple math problem or two away, but you look bored and like your enjoying a few too many fingers. (More after the video)

Today (June 1st) I am beginning a contest (Shhh! Its not an official contest so don't tell my bosses Eric and Christy) to see who can come up with the best tennis ball mortar design. No one characteristic defines "best", it is a combination of performance, creativity, adn 1's aBiLiTy 2 not tlak LIEK Dis!!!1!1 I am judge and jury of this contest, and my decision is final.

How to enter: Join the group Tennis Ball Mortars (Its moderated) If you feel your design is truly innovative, and that you are making great advances in the field of tennis ball mortarology, write a new instructable and post it in the group. If you just have some pictures, or if the only difference between your mortar and someone else's is the color of the duct tape, post it in the forums, and then add it to the group.

Now for the good part *THE PRIZE*. I'm sure your dieing to know what sacrificing several fingers, gaining numerous pounds, and clogging all your arteries will win? ::Drum roll:: The ULTIMATE SUPER GRAND PRIZE is ...
a cookie, thats right you win a cookie (Specifically: (1) Entenmann's chocolate chip cookie mailed in plain white envelope to any address in the world ( Its internationally delicious!! )). I know what your thinking "Damn Tetranitrate you cheapskate, even Fred, the guy who sits in his van by the playground is more generous with sweets then you", to which all I reply is "After all those Pringles you don't need anymore junk food, and you should probably tell a trusted adult about Fred."

**DISCLAIMER: By entering this contest, thinking about entering this contest, or even just reading this, you retain all liability should you happen to blow up or injure yourself in an attempt to build this.

(edit: I ate the cookie)

Step 1: Materials

Picture of Materials

1. (3) Pringles Cans
2. Duct tape
3. Lighter fluid
4. Tennis balls (edit: or aerosol hairspray)

(Told you it was simple)

Step 2: Building the Mortar Tube

Picture of Building the Mortar Tube

Step 1: Eat the chips. Vomit when necessary. Repeat. (I was making a joke about the flavor of the chips, but it also works nicely as a beginners guide to bulimia)

Step 2: Wash out the cans with soap and warm water. Do not get the cans too wet or the cardboard will lose some of its integrity. Dry cans.

Step 3: Cut out a circle in the center of two of the cans metal bottoms. The diameter of the hole should be equal to the radius of the metal bottom.

Step 4: Stack the two cans with baffles (holes) on top of the solid bottomed one, and duct tape heavily ( 7 - 12 times around) at the seams.

Step 5: Completely cover the cans in duct tape at least three times (three layers of duct tape thick)

Step 6: Poke a 1/4" hole 1" from the bottom of the mortar

Step 3: Firing

Picture of Firing

Safety first: Lighting the mortar without a stand (like I did in the first shot of the video) is asking for trouble. A simple and fast stand can be made from PVC pipe and coat hanger as demonstrated in the photo. If no stand materials are available at least lean the mortar against something (bench, rock, etc.) so it isn't at risk of falling when you are trying to light it.

Tip: 3" PVC pipe will fit perfectly around Pringles cans with just the right amount of duct tape on them. A hole can be drilled through the PVC and cans for lighting. This provides extra structural reinforcement to the cans lessening the chances of a blowout.

Tip 2: Use a barbecue lighter, or like in the video a quick & easy torch (made by bending coat hanger around paper towel). This will put distance between your fingers and the bottom of the tube, in case of a blowout.

Generic safety stuff: Use adequate eye, ear, nut-sack, and various other body part protection.

To prepare for firing: Set up the mortar in a large open area where you have little risk of hitting someone. Squirt about 1-2 teaspoons of lighter fluid down the barrel of the mortar, making sure to aim for the bottom can. Spray a little extra through the hole in the bottom, to help aid in lighting, or, if using hairspray, you can spray hairspray down the mouth of the barrel for a few seconds. Drop the tennis ball down the barrel. The mortar is now loaded, and from now on no one should pass in front of it.

To fire: Wait about two minutes after pouring, to give the chamber enough time to fill up with the evaporating lighter fluid (Pouring the perfect amount of fluid, and waiting till exactly the right time to light are the two things to master when it comes to tennis ball mortars). Light the barbecue lighter or torch, and hold it close to the hole on the bottom. If all goes well you should hear a loud bang, and see the ball sail off into the distance.


PROJECTILE PRO (author)2017-11-17

wow, awesome

thedog458 (author)2008-04-19

hey really good Instructable. now this is gona be a really dumb question but do u have to use the lighter fluid?(coz where I live they don't sell it) :(

Tetranitrate (author)thedog4582008-04-19

Yeah, you kinda do need the lighter fluid. Where do you live that they don't sell it, North Korea?

pian0man (author)Tetranitrate2009-05-11

I got a garage shop ballistics book, and it says that hairspray can work too, which makes sense. Would the whole thing just blow up?

PikesPeak (author)pian0man2009-08-21

Yes, you'll be amazed what hairspray and a lighter can do. Instant blowtorch.

PastTheVoid (author)PikesPeak2009-10-25


codz30 (author)PastTheVoid2009-11-16

This is an old wives tale,
Fire needs oxygen to burn, their is no oxygen inside aerosol cans or else they could spontaneously combust at anytime.
Therefore, flame has no way of getting into the can, no back-feed

Phoghat (author)codz302017-10-16

because science

M4industries (author)codz302010-06-26

There is an issue however. The flame can melt the regulator or nozzle and all the propellant can come out at once. But it won't go back in the can.

Damp Cuttlefish (author)codz302010-06-22

hmm everyone seems to think that. if i put a match near a deodorant can all my freinds go OMG IT WILL BLOW UP AAAAAAHHHHH. it never has although i was once near an almost empty butane canister when the gas blew back twas F*****g scary

macmccune (author)codz302010-01-15

wow. thank you. i never thought of it that way. i have always been terrified  to hold a flame for more than a second on an aerosol can. it makes a lot of sense. thanx. :D

thedog458 (author)Tetranitrate2008-04-19

lol no I live no coober pedy. but thanks any way.

pyromanizak (author)thedog4582008-06-14

spray some butane in there

Phoghat (author)pyromanizak2017-10-16

if you ue butane, make sure you have good medical coverage

jdoucette83 (author)pyromanizak2009-04-16

Gotta be careful of that stuff, it'll go without even needing the "perfect" air mixture. For my potato canon I usually use Starter Fluid because its strong as hell and if you get too much the chances of it blowing up without enough air are pretty slim. I haven't made one of these yet, but I'm going to try to make it out of PVC instead...Pringles cans seem more like a cardboard pipe bomb.

M4industries (author)jdoucette832010-06-26

PVC potato cannon with starting fluid is a potential is pipe bomb held under your arm. Just to make a point that only hair spray is the safe propellant

TXTCLA55 (author)M4industries2011-02-04

why are you putting lighter fluid it that? I just use Axe, or Right Guard and that potato fly's damn far.

M4industries (author)TXTCLA552011-02-09

Same here, but we were discussing starting fluid, a VERY flammable liquid that can aerosolize by dripping down the inner surface of the spud gun.

TXTCLA55 (author)M4industries2011-02-09

oh I see. well based on my experience you better be using some really strong PVC; I built two spud guns in the past, both firing chambers cracked with in 15-20 uses.

joseph marcotte (author)TXTCLA552015-08-15

Try talking to a contractor at the hard ware store high density pvc looks like the regular stuff

xs0skill3dx (author)pyromanizak2011-04-14

na dont use butane... last time i tried with it the whole thing just caught alight... the result was a 30inch candle and a flaming tennis ball rolling down my street..not cool

jackh94 (author)thedog4582010-04-05

 you seem to have the internet, anything can be got on the internet, including lighter fluid

Thundertydus (author)thedog4582009-08-02

Yes they do No matter where you live, they sell light fluid

freakytail (author)thedog4582009-08-02

are u serious?? where on earth do you live???

Everett_McKinley (author)2011-05-06

I want to use it for airsoft and I wanted to know if anyone knows how to make the tennis balls explode and shoot BBS everywhere.
Any ideas?

Phoghat (author)Everett_McKinley2017-10-16

How about a #4 coffee filter (as for a Mr Coffee) add your BBs, fold over the filter to cover, stuff down the tube. (Might even use 2 filters together, experiment)

get a ton of scratch anywhere natches break off all the tips cut a small hole in the tennis ball to fill with the match heads and bb's then cover the hole with duct tape when the ball hits a solid object it should ignite the match heads because of the friction and burst the ball sending the bb's flying in all directions...this is just an idea. never did it with bb's mixed in only with match heads to make a little fire ball but i think its worth a sgot if you have time

No explosives you go to jail for that one. But if you cut the ball in to six pieces sort of like an orange and barely enough paper tape to keep it together with extra at the bottom so you dont get an awesome shot toy but then again thats pretty cool

Maybe put a small explosive in the center of the tennis ball, and fill it with BBs. Then leave the fuse to the explosive trailing out of a hole in the tennis ball, and launch it from the mortar with the fuse on the back of the tennis ball so the action of firing it lights the fuse.

just wrap the BBs in aluminium foil or place a paper ball underneath it

what i did was put a hole in the tennis ball with a drill and add a fire cracker...filled it with bbs....but you need to take a knife and cut make the tennis ball a little thinner by cutting some of the stuff off it....also try other things that the fire cracker will explode easier like a ping pong ball with weights or something

Joetim555 (author)2017-03-13

My cannon won't light. How did you get yours to.

dylancotton (author)2012-05-11

If you duct tape it horizontally to a skateboard, would it move the skateboard?

Not the way you want it will move you at best two meters because the energy is used in an instant and focused on the ball and not the base of the mortar

nboe1 (author)dylancotton2012-06-19

Yes, because newtons law number 3 says with every action theres a reaction, so if the tennis ball shoot out, the skateboard will be pushed back!
(7th grade science)

ErinM6 (author)2015-05-20

If you can find 2.70" pipe. that is the size of a tennis ball.

yashwanthg (author)2015-01-21

what is the material used for giving the force to push the ball ?

where can we get it?

ReneA2 (author)2014-09-05

try using automotive starting fluid! It has ether in it and is super explosive. Make the canon out of electrical conduit and cast iron pipe fittings. Use model rocketry electrical igniter plugs, which usually are 9 volt to set the fuel mixture in the base of the canon off. Make sure the tennis ball fits snugly into the barrel,but not too tight. It has to be able to escape without a lot of resistance. Oiling the barrel slightly with a WD 40 will help, plus it is also flammable, so when it goes off with one hell of a bang, a nice blue flame ejects with tennis ball. Originally, I made a ether canon out old coal stove piping about 8 feet in length, with an empty quart paint can as the projectile. The damned thing would send the can so high into the air, it disappeared from sight, only to come down somewhere in the neighborhood 30 or so seconds later. The BOOM that thing made rattled windows and made half a dozen dogs in the area begin to bark and go nuts. I finally stopped using it when the cops began "looking for some idiot setting off dynamite" as they told a neighbor they questioned. You can make a pretty good canon out of automotive exhaust pipe too. A straight length of it is cheap and it'll weld up nicely too. The whole trick to these canons is is getting air to fuel ratio just right, so that when ignited,it detonates all of the mixture with a good compressed explosion. It took me many tries and failures before I hit on the combinations. What I want to perfect is an all metal, lightweight, ether fired, golf ball canon, that will go through a car door, or house door every time. This thing would be lethal or extremely harmful to human beings. A head shot certainly would be the end of any one! Aren't you glad you're a nut job American and we've got the readily available resources at our fingertips to come up with stupid shit like this for the fun and hell of it? I am! ;)

The1andonlyDaniel (author)ReneA22014-12-31

But wouldn't that make the mortar explode? Like break?

jxmorris12 (author)2012-09-02

When I light my mortar, a small flame appears by the hole (nothing explodes). This is without lighter fluid. What is the reason for the lack of combustion?

toohardbasket (author)2012-06-24

When i was younger, we made ours out of a spray paint can and PVC pipe. Head to the hardware store with a tennis ball and find the right size PVC pipe. Get about a metre or so. Also buy a can of spray paint and some duct tape. You just carefully cut off the top section of the can(small ring at the top with the nozzle) and remove the nozzle - and paint if there is any - *might be safer to empty out the gas first. The larger ring of the can 'should' fit inside the end of the pipe. *might pay to try this before you buy it - they come in slightly different sizes. Then you duct tape the join. Drill a small hole(2 - 3mm) about 30-40mm or so up from the bottom of the can on the side. Cannon complete. All you need to do now is push a tennis ball down the tube until it sits on the top of the can(use a cut down broom handle or what ever you can find). Spray any aerosol - we used fly spray - into the small hole then light a cigarette lighter right next to the hole. Flame will 'suck in' through the hole and - BOOM! - tennis ball launched. If you point it straight up, you should almost lose sight of the ball. We later updated our model with an electric stove lighter so it became like a tennis ball bazooka!!! Unfortunately, here in Australia it is now illegal to make home made fire arms with a fine of around $40,000 if you are caught. Enjoy, and be safe as I claim no responsibility if any injuries are caused while using this design. We never had any issues but you never know.

LittleBigMikey (author)2012-05-09

Is it possible to use a PVC Pipe ?

xs0skill3dx (author)2011-04-14

how many shots will the mortar last for? and if i were to make one out of the metal tube that the tennis balls come in ( i think its made of a similar, but thicker material as the bottom of a pringles can, aluminum or whatever) how many shots would that last for?

the original one lasts about 5-6 shots depending on what you use as fuel

dtc-joey (author)2010-01-10

can it whit 2 cans???

skipster2 (author)dtc-joey2011-08-02

yes you can put a hole in the top can

Achan20 (author)2011-04-10

hmm. slight modification and it could shoot golf balls......

ElQuirko (author)2010-02-07

Can you ditch the pringles and just use PVC piping?

Doctor Someone (author)ElQuirko2010-02-07

 i tried making one with pvc, 2.5" is too small, and 3" is too big for tennis balls 

There is a spudgun site that sells 2.75" pvc. It's somewhat expensive, but the piping can be used for pneumatic tennis ball cannons as well as combustion.

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