Introduction: DIY Catapult
This is a guide to show how to build a simple catapult. Dependingc on the means of equipment and knowledge of the builder, this can be achieved with lumber and wood screws or a 3D printer even. In this instructable you will learn how to use relationships among parts to produce an outcome, that being to launch an object without having to throw it.
DISCLAIMER: During the process of creating this catapult, weather conditions unfortunately caused planks of 2x4 to slightly warp, affecting how some pieces fit to one another. Because of this, no specific dimensions will be given as this could happen to your wood. When creating this project approximate as humanly possible the dimensions for its pieces. The more accurate the pieces, the tighter they will fit together.
Depending on the builders’ equipment and knowledge, a very small model could be built in a 3D printer. If the builder does not have a 3D printer a larger model can be built using common materials obtainable from most hardware stores, which is the model we will be following. Here’s what is necessary to build this catapult
· Power saw
· Table saw
· Power drill
· Ruler and/or measuring tape
· Appropriate drill bits for screw heads and drilling pilot holes for the fastening srews
· Carpenter square
· 2x4 planks of wood
· Pvc pipe
· 4x4 planks of wood
· 10x3” wood screws (box of 62)
· 1&3/8-inch diameter, 4-foot-long dowel
· Waffle ball, tennis ball, small fruits, eggs or other small and light objects as projectiles
· Hooks (to anchor the bungie chords and aid in creating tension)
· Bungie cords
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Step 1: Creating the "outer" Base
To begin the catapult needs a base to stabilize it. Using atable and/or power saw, cut two pieces of 2x4 into 3-foot long sections and two pieces into 2-foot sections (the base will be 3’x2’).
After you have your pieces, make 45-degree angles on the short side (2”) of your pieces from the upper corners inward using your carpenters square. Next, if you have a table saw set the saw blade at a 45-degree cut and set its guide to line up with your markings. The edge of the saw blade should line up the outside of your markings, depending on which direction you’re cutting from. Your three-foot and two-foot sections should fit snug in the corners, creating a box.
Next is fastening them together. In the corners, have four markings evenly spaced apart: two on one side, two on the other.
Each set of two should run down the perpendicularly-connecting sections midline. Then drill pilot holes to guide your screws in, and finally fasten them together.
Step 2: Housing for the Swinging Arm
The next piece for our catapult is the housing for the swinging arm that will launch our projectiles.
To begin, measure from the inner edges of the 2’ sections longwise (in the direction of the 3’ sections). Cut two sections of 2x4 to fit snugly inside the base.
Then cut a six-inch and three-foot long piece of 4x4, fasten the six-inch piece longwise to one end inside the 2x4’s and the 3-foot piece vertically to the other.
The hole for our dowel is next (this is where he swinging arm rotated about). With a 1&3/8th inch drill bit, bore a whole through both 2x4’s in-line with each other.
Step 3: The Swinging Arm
Cut a piece of 2x4 about 6 feet long. Using a compass, makean arc on one end on its long side (4”) setting its length to 2”. This will give the arm clearance to freely rotate without it hitting the ground. Then drill a 1&3/8th inch hole in the Compass’ base position (the point which it rotated about).This will allow the piece to freely rotate our dowel will be anchored via its housing.
Next, measure from the outside of the swinging arm to the inside of its housing. Cut two pieces of pvc pipe to that length, these will go on the sides of the swinging arm and prevent it from moving and becoming off-center.
Finally, cut a piece of dowel. This will allow the arm to freely swing and hold it in place. Put the dowel through the arms housing, pipe, arm, pipe, and other housing side. Set the housing with its attached arm inside the outer base, aligning its ends up at their center points at both ends
Step 4: The Swinging Arms' Stopper
The next part will be needed to stop the swinging arm. Cut a piece of 4x4. From one of its corners, make a 30-degree angle with its opposite side. After you’ve cut the angle fasten it to the vertical 4x4 up from the inner housings’ top of its 2x4s’, with the 4x4s’s center line matched to its position on the 3’ vertical 4x4.
Next, cut two pieces of 2x4. From one of their corners, cut a angle at 30-degrees using a table saw. This will give our launch arm a 60-degree launch angle.
Next, from the outside edges of these pieces, measure the distance between them. Cut a length of 2x4 so that it may sit on top of these pieces.
Next cut a piece of 4x4 the length from the inside of the 30-degree cut pieces.
Cut two pieces of 2x4 the length of a 4x4 and 2x4 short-side (we’ll call it “top-wood” for reference).
Cut two pieces of 2x4 at least six inches long.
Fasten your top-wood to the top of the 4x4, making sure the edge and outer corners are aligned. Then fasten you 6-inch 2x4’s to the top-wood, aligning the corners and edges. All these pieces together will act as a stopping mechanism for the swinging arm.
Step 5: Hooks and Bungie Chords
On the swing arm, drill two pilot holes. One the end and another one inch from it along the boards midline. One of these hooks will be to loop a bungie-chord, the other for a person to pull the swing arm back and create tension.
On the outermost side of the vertical 4x4, drill a pilot hole three-inches from its top along its center line. This hook will also be used to loop two bungie chords and create tension.
Loop your bungie chords through one another and hook them to your rubber bungie. The rubber bungie will attach to the swing arm while the nylon bungies will loop around the vertical 4x4. We have created tension!
Step 6: Projectile Basket
Lastly, we will need a basket to hold our projectile before it launches. You can use a variety of items, form lacrosse sticks to rubber caps (in this case).
Here I used an old rubber cap, cut half of its outer lip off, and bolted it with a washer and bolt to the top of the swing arm. Don’t forget your pilot hole, as it will help prevent splitting our wood!
You now have a basic catapult. Mine does not launch items far, but I do not mind avoiding the risk of breaking one of my neighbors’ windows…