Introduction: Cardstock Catapult
Ready to Start an Office Siege war? Paper can be used for your physics project, or cubical conundrum.
- Paper (I used 120 pound card stock)
- Glue (I used gorilla wood glue, see build step)
- Source of energy (I used an exercise band)
- Counterweight (paper doesn't weigh much, my assembled catapult weighed approx. 18 oz)
- Projectile (my catapult was designed to launch tennis balls)
Total cost for mine: 10$
For a school project over the past 9 weeks we had to build a catapult capable of launching tennis balls with accuracy. Being the overachiever I am I decided to make my catapult unique, by creating mine out of paper.
Paper is one of the most versatile materials I know of, forming anything from writing paper to cardboard, my own goal was to make a Sudo-wood that could outperform traditional wood. I went a little too far with my design and it ultimately failed, but the guide is here for future catapults.
My catapult consisted of principles from the 3 classes of catapult recognized by "Punkin' Chunkin'," Torsion (rubber band), trebuchet (sling, this was the fail point), and Centrifugal (the arm rotates beyond 360*). In the end I overlooked the design of a sling, they use what is called a finger to release the sling at about 45*, doesn't work when your arm is spinning around 7 times before it is ready to launch. If I had had time I could have installed an electric trigger but I didn't.
Step 1: Design
First thing you will want to do is sit down with a sketchpad or graph paper and create your catapult. I have included my Sketchup file and blueprint made from it of my design. My design changed as I constructed it (simplified) but the principle is still the same. The catapult is constructed from overlapping "planks", 14 sheets of paper thick, some cut paper long ways, some short.
I tested the strength of glues as follows:
- I glued 2 strips of paper together with one of 4 adhesive, I left 2 strips unglued for a control
- Allowed glue to set for 36 hours between 2 clipboards.
- After removing the planks from the boards (wood glue took some clipboard with them :P, using wax paper makes sure glue wont stick to things it shouldn't) I creased the planks in the middle and allowed them to sit against gravity.
- 12 hours later the results were clear, see picture, gorilla glue didn't budge.
Later planks take didn't break/snap under conditions a similar piece of wood did so my sudo-wood outperformed, perfect.
Step 2: Build
This step is by far the most time consuming, gluing planks together; luckily they make 1" sponge brushes that make gluing 1" by 11" or 8.5" planks a breeze. 50 planks and 1 gear, totaling at 700 strips of paper, 30 gear cutouts, around 95 sheets of paper later, the planks were ready to take shape. Using a wooden dowel for the fulcrum. (didn't trust paper there) Assembly was unique (ever drilled and/or sawed paper?) As stated in the intro paragraph this is as far as construction went, my sling concept could not have worked (tried for 6 hours to fix it).
Step 3: Enjoy
My catapult in its current form will never launch a tennis ball due to a principle I overlooked about a trebuchets sling, but don't let that discourage you. Paper can be used to make a very capable white catapult.
Attached I have a video of my first test fire, skip to 0:35 for the action.
Good luck in your cardstock catapult endeavors.