Introduction: Portable Pumpkin Catapult

Picture of Portable Pumpkin Catapult
I built this catapult (actually a trebuchet) based on an article in Make Magazine by William Gurstelle.  It worked extremely well!  Was able to launch basketballs 80 - 90 feet, and small pie pumpkins over 100 feet.  I think fine tuning of the sling release could further enhance the performance.

It is made of plywood, a few 2 x 6's, and a lot of plumbing parts.  The folding design is great for storage, and in my case, the catapult actually went up on the roof of a church for the main launching event.  It fit up a ladder through a roof hatch with no trouble.  (Well, other than the fact that it is bulky and heavy).

The counterweight is two 60 pound bags of concrete, which gave about a 100:1 ratio for the pie pumpkins and basketballs.  After the pictures were taken I also added several bungee cords (2 x 18" and 2 x 24") to assist with pulling the weight down, and it added another 20 feet or so to overall distance.

Just something fun about catapults!
 
 
 
 

Step 1: Building the Platform

Picture of Building the Platform
The base is made of 3/4" plywood.  It uses about a full 4 x 8 sheet, which I cut up into four 2 x 4 sections to make it easy to work with.  The uprights are two 28" long pieces of 2 x 6 lumber glued and screwed together.

When you cut the plywood sections to size there are three pieces of wood per section.  The platform piece itself, and then two narrow reinforcing pieces that go along the edges.

Cut the plywood and 2 x 6s to size, and glue and screw together.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Step 2: Assembling the Folding Base

Picture of Assembling the Folding Base
Lay the assembled plywood sections out as they will be in the final assembly.  The sections are attached together with door hinges so they can easily fold.  When I was attaching the door hinges, I set one hinge at each end of the gap between sections, with the hinge "bulge down" to make sure the spacing between boards was correct.
 
 
 
 
 
 

Step 3: Attaching the Uprights to the Base

Picture of Attaching the Uprights to the Base
Next step is to attach the uprights to the base.  They are only attached with a pair of hinges, so they can fold flush with the platform for transport or storage.  Wire cable (1/8") and turnbuckles are used to tension the arms and keep the solidly upright for launching.  

Also in this step, attach 1" flanges to the uprights, which will hold the throwing arm assembly.

Two screw eyes go in the top of each upright, and then matching screw eyes go on the base platform, in line with the uprights.  This is where the wire will attach to hold things in place.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Step 4: Wire Rigging for Uprights

Picture of Wire Rigging for Uprights
Tensioned wire rope is used to add rigidity and stability to the uprights.  Use S hooks and turnbuckles to connect wire between the screw eyes on the uprights and the screw eyes on the platform.
 
 

Step 5: The Counterpoise - Concrete Holder

Picture of The Counterpoise - Concrete Holder
The counterpoise platform is a 16" x 20" piece of plywood with 1" pipe flanges attached.  The rest of the platform is made up of pipe nipples, 90 degree elbows, and a tee fitting.  This will swivel at the tee fitting, so I lubricated with grease.  Make sure it is not so tight that the tee will not swivel freely.
 
 

Step 6: Assembling the Throwing Arm

Picture of Assembling the Throwing Arm
The throwing arm is made of 1" pipe.  Six foot long section connected to a 1" cross fitting.  (Had a lot of trouble sourcing this part.  Eventually had to order it from Amazon).  The throwing arm is also tensioned with wire rope and turnbuckle to help with rigidity.

Drill a hole through the cross to insert a long eye bolt.  Two other eye bolts are also inserted into the throwing arm, one at the end, and one at midpoint.

A cap is attached at the end of the throwing arm, with a hole drilled through to allow insertion of a bolt.  This will be what the free end of the sling attaches to.  

The counterpoise assembly connects to the opposite end of the cross fitting, and two 8" nipples are attached to the sides of the cross fitting.

The arm assembly is attached to the uprights with close nipples and 1" pipe unions.  Thread the close nipples into the flanges on the uprights, and then thread the non-removable side of the union onto the close nipple.
 
 
 
 
 
 
 

Step 7: Attach Throwing Arm to Uprights.

Picture of Attach Throwing Arm to Uprights.
Assemble the throwing arm to the uprights using the unions.  Also attach wire rope to eyebolts on arm, and tension with the turnbuckle.  Don't over tighten.  You don't want to bend the eye bolts or the arm.
 
 
 

Step 8: Quick Release Mechanism

Picture of Quick Release Mechanism
The catapult release is made with chain and an equestrian panic snap.  The panic snap releases with a downward tug, allowing the arm to quickly rise.  The panic snap is connected to a steel ring on the arm, which is attached with a hose clamp.  The other end of the panic snap is attached to a chain, which is attached to the platform with a conduit clamp.

In order to be able to remotely trigger the panic snap, I lashed some cord around the body, and liberally soaked with thin CA glue.  The cord then goes through an eye attached to the deck of the catapult.  
 
 
 
 

Step 9: Sling and Final Assembly

Picture of Sling and Final Assembly
The sling I used is a modified veterinary sling that I had from our dog's recent hospital visit.  It was the perfect size for cradling a pumpkin, football, or basketball.  One end of the sling is attached to a ring on the throwing arm, held in place with a hose clamp.  The other end of the sling has a ring attached, and it slides onto the bolt that is protruding from the pipe cap at the end of the throwing arm.

I wrapped some duct tape around the bolt to allow the ring to slide off more easily.

 
 
 
 

Step 10: Final Notes

Picture of Final Notes
Catapult ready for launch.  The weight is provided by two 60 pound bags of concrete.  In the final version, I also added some bungee cords that run from under the counterpoise platform to the turnbuckles at the rear of the platform, adding more force and speed to the falling concrete weight.  

Also during testing, the sling would drag slightly on the plywood platform, so I added a piece of horse butt leather for testing.  This was later replaced by a piece of slick MDO plywood.

Basketballs were launching from 60 - 80 feet, and footballs about the same.  It actually throws a football in a spiral, which is cool to see.  The furthest pie pumpkin (1 - 1.5 pounds) went over 100 feet.
 
 
 

Comments

ezd360 (author)2015-10-23

what is that on the back of it

TheMayneLine (author)2014-10-28

Really great design!! Built it with 4 adults and 4 high school kids in about 5 hours. Cost somewhere in the neighborhood of $300. You could save money by finding a plumbing supply house vs a "big box" home center. Also we are going to replace the concrete with free weights. If you use the concrete, you can soak the bags in water and make them "solid" blocks. First shots were last night. 1 lb spaghetti squash, 125 feet :-) Oh, and after building this. You can not help but smile.

greglinda (author)2014-10-27

Build went good but not getting any distance at all. Mot stalling but seems to rotate slowly. Played with sling length and relase pin angle to no avail. Lithium grease seems really thick. Not sure how far to tighten pipes and still allow for quick rotation but still remain safe. Also 2 bags of cement will not fit on counter weight union so I used 11 inch pipe uprights instead would this slow it down and reduce power? Thanks.

meikj (author)greglinda2014-10-27

Mine took a lot of fine tuning. It threw best with small pie pumpkins or footballs and basketballs. I didn't have a problem with bags of concrete, so not sure how changing the pipe length would affect things. The unions need to be able to spin freely.

I also added some bungee cords to hooks on the bottom of the counterweight to make it pull down faster. That helped with distance.

Dani78 (author)2014-10-16

that's really nice instructable!

I have difficulties with watching the video, could you please upload it in youtube?

sophiacat15 (author)2014-10-12

Hello this is a great pumpkin launcher. We're looking to build it for a physics project. We have a question: what makes the pumpkin actually launch? Do you cut a string? Please let us know, thank you!!!

meikj (author)sophiacat152014-10-12

Look at step 8. It uses an equestrian panic snap that hooks on to a ring on the catapult arm. Cord is lashed around the panic snap body and pulling that cord causes the snap to open and release the ring. Hopefully that makes sense!

rgnordstrom (author)2013-10-22

I built this, it works well. couple of tips/suggestions.
- make the middle plywood section wide enough to allow for sling slide without hitting hinges
- offset the the two posts on the side plywood base so that folding is easier/tighter. It wont look centered but travels easier.
- cut handle holes in outside of plywood
- use a stainless anchor shackel for the trigger, add a safety chain you pull just before firing
- If you make the posts taller say 36 instead of 28, you can extend the weight a bit farther and add some yardage

Great design though. Kids love the thing.

sviens (author)2013-09-14

I noticed in your photos you didn't include wheels. Think the MAKE instructions recommended castors. I found a reference to a PBS/Nova article about adding wheels to a trebuchet will increases distance. Here's the reference.

http://www.pbs.org/wgbh/nova/lostempires/trebuchet/wheels.html

meikj (author)2013-09-12

I think I have about $200 or so in lumber, fittings, pipe, etc. It was a fun build!

agelix (author)2013-09-07

How much did it cost to build this?

willywoozle (author)2012-12-07

2 questions:
How well would this work with a bunch of snowballs?
Could you make a video showing it in action?

meikj (author)willywoozle2012-12-10

Should work fine for snowballs. You may need to adjust sling length and release. Sweet spot for this is about 1.5 - 2.5 pounds.

No more video! It's folded up in the garage for now. I'll shoot some vid the next time I set it up.

willywoozle (author)willywoozle2012-12-07

I meant in the ible.

d3r3k1997 (author)2012-11-11

Actually that is a Trebuchet

Kiteman (author)2012-11-06

That looks very nice (I didn't know you could buy branded pumpkins?).

It would be nice to see a video of it in action?

meikj (author)Kiteman2012-11-06

Pie pumpkins are a type of small, sweet pumpkin, usually used for making pies. They generally weigh between 1 - 2 lbs. which makes them the perfect size for this catapult.

I have a short video of a test launch that I'll post soon.

Kiteman (author)meikj2012-11-06

Cool.

meikj (author)Kiteman2012-11-09

Short video of a test launch during tuning phase. Throwing a football, which hits a tree!

http://flic.kr/p/doYTba

Kiteman (author)meikj2012-11-09

Nice shot!

Jobar007 (author)2012-11-07

If you build a proper chute for the projectile to run down you can fine tune your accuracy for left and right... just like they did during historical sieges.

Lorddrake (author)2012-11-07

Awesome design. I love that it is collapsible for easy transport/storage.
All your steps are well documented and easy to follow.
5 stars!

im3733 (author)2012-11-07

Very cool. Though this is technically a trebuchet, which, IMO, are more awesome than catapults. http://en.wikipedia.org/wiki/Trebuchet

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