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How to build a Catapult

Updated on May 21, 2010

Water Balloon Catapult Instructions

Free plans on how to build a catapult for launching water balloons,or as we discovered Zip Lock Baggies work awesome.Your kids will love it!

In the process of building the balloon launching catapult,letting the kids go crazy with it a few things came to light.When a large balloon is launched from the backyard siege weapon,the throwing arm bends and releases sort of like how a golf club loads up and releases which is very cool because it gives it extra distance. With the load forces generated it is a good idea to glue AND use self tapping screws on each joint.Check out the video at the bottom of the page its hilarious!

I put together this water balloon catapult for the kids in about an hour on the morning of my sons birthday party and it was a SPLASH hit! We ran out of water balloons way too soon and the kids had so much fun it made me glad we put this great idea for kids fun together.

The kids had a ton of fun with the water balloon catapult,squirt guns and archery setup we had in place for the day.Next time the kids have a birthday we will need to a least double the the amount of water balloons on hand.I am offering the use of this fine seige weapon to our local community for parties and neighbourhood fun days-and just about any other excuse we can think of to cool off in summertime.

There are some relatively simple mechanics involved which are incorporated into this design so all you need to do is build it from the plans and it will work fine.I had originally planned on making a trebuchet but it flings way too far for my small yard.If you would like to know what minor changes are needed to convert these free catapult plans to a trebuchet just contact me.

****We had another day with the catapult and it was more family fun and tons of laughs! We ran out of balloons early so we had to improvise with-Zip Top Baggies! They Rock! Quick and easy to fill and closing them is way better than tying balloons.***** My son took one square in the chest and it DRENCHED HIM! He loved it!


There is no leftover PVC pipe from this build so measure twice,cut once.

4 X 8' PVC pipe, 6 x short 90 degree elbows(elbows have 2 female ends), 5 x 3 way T junctions, 2 x 45 degree spigots(spigots have 1 male, 1 female end), 3 end caps, 3" bolt with nut, 2 washers, PVC cement.


1) Cut 6 42" pieces for the base and arm supports.I used my chop saw and it worked great but a hacksaw will work fine too.Set aside the 3 12" leftovers you will need them later

2) Cut 1 68" piece for the throwing arm.

3) From the 28" piece left over cut a 12" piece.

4) From the 16" piece left over cut 2 3" pieces.

5) Cut the remaining 10" piece in half.


1) I recommend fitting it together without cement first and then do final cement after you have checked out the fit.One thing to remember if you want to keep the pivot hardware out of sight you will need to use a self tapping screws on that connection.The reason is so you can get access to the pivot hardware to tighten it if necessary.

2) Lay out the base first with the 3" piece between the T connectors,with the connectors pointing up 45 degrees. Set the 12" pieces on other side of the T connector then fit the 90 degree elbows.

3) Place 42" PVC pipe into corner 90 degree elbow on both sides.

4) Repeat step 2

5) Set the 4 42" PVC pipes into the T connectors.

6) Drill the 68" throwing arm PVC pipe 24" from the end.

7) Drill on the inward side of each 90 degree pivot elbow.

8) Set 45 degree spigots on 42" support arms.

9) Secure the throwing arm onto the 2 90 degree elbows with the nut,3" bolt and set the washers between the throwing arm and supports.

10) Attach the elbow/throwing arm assembly to the supports.

11) Attach the ammo basket with nylon ties. Set the basket at a fairly severe angle so the ammo will not fall out when the arm is in motion. Use one of the end caps here.

12) Attach last T connector to throwing arm end then put the 2 5" PVC pipe pieces in.It is important to cap the ends here because this is where the kids pull the throwing arm.

*Note:Use screws only to attach the 90 degree elbow where the pivot pin is.You want to have access to this spot in case you need to make any ad

13) Grab a beer - Nice Job!

Nick and his catapult

Our Next Project ?

Blue Balloon is 1 microsecond from bursting
Blue Balloon is 1 microsecond from bursting
Siege weaponry aftermath! Check out all the balloon shards in the yard!
Siege weaponry aftermath! Check out all the balloon shards in the yard!
I commandeered the spaghetti strainer for the ammo basket.
I commandeered the spaghetti strainer for the ammo basket.
If you connect the pivot pin into the pre-drilled 90 degree elbow you have no hardware visible.
If you connect the pivot pin into the pre-drilled 90 degree elbow you have no hardware visible.


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    • IM Wannabe profile imageAUTHOR

      IM Wannabe 

      9 years ago from Guelph,Ontario

      We are just loading up some baggies to launch at my son.Last time we played with it he took a baggie of water square in the chest and totally soaked him.He Loved it!

    • profile image


      9 years ago

      Love it. Simple basic design, but looks like hours of good family (and neighborhood) fun.

    • ThePartyAnimal profile image


      9 years ago

      Now that is very cool - Must share with my Husband and Son - they loves stuff like this.

    • profile image


      9 years ago

      Isn't using PVC cement a little bit too dangerous to be around kids? Just wanted to know.

    • profile image


      9 years ago

      For water fights maybe you could put the catapult on a wagon for mobility.

    • profile image

      iFAIL uFAIL 

      9 years ago


    • IM Wannabe profile imageAUTHOR

      IM Wannabe 

      10 years ago from Guelph,Ontario

      Hey Kelly - Your best bet is to check out a trebuchet -they have good distance capabilities.I haven't made one because we don't have the room for it-Scott

    • profile image


      10 years ago

      do you know how to make one that goes 100 feet?

    • IM Wannabe profile imageAUTHOR

      IM Wannabe 

      10 years ago from Guelph,Ontario

      Kelly-they go about 15-20 feet

    • profile image


      10 years ago

      how far do the balloons go?

    • profile image


      10 years ago

      That was really easy to build and worked out great when we used it. Mine didn't fall apart though... Thanks!

    • sunstreeks profile image


      10 years ago from Western Washington

      That looks like a blast to play with. I want my own catapult now!

    • Gypsy Willow profile image

      Gypsy Willow 

      10 years ago from Lake Tahoe Nevada USA , Wales UK and Taupo New Zealand

      This looks like great fun but the design may need some tweeking I feel before it comes to the market! My 4 yr old grandson would love one! Well done , Dad!


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