Introduction: Ballista Catapult

Hi, My name is Ryan and I am a 6th grader from Central Massachusetts. Today I will be showing you how to make a Ballista Catapult from different items I found from around my house.

Step 1: My Goal

My goal for this project is to learn about Ballista Catapults and how they work. I want to build a Ballista Catapult that will launch a projectile at least 4 feet in distance. I would like to build a small version of this catapult, so I can use it inside my house. I'm hoping to keep it small enough so it can be portable and sit on a desktop.

Step 2: What Is a Ballista Catapult?

A Ballista Catapult is a catapult that was used in ancient warfare to hurl large stones over a large distance.

Around 400 BCE the Greeks invented the Ballista and in later times the Romans used this invention but made modifications to fit their own needs.

A Ballista uses tension to launch projectiles.

The Ballista is a catapult mixed with a crossbow.

Step 3: Materials

The Materials I used were:

  • 2 inch wood Block
  • 1 Straw
  • 2 Popsicle sticks
  • 1 rubber band
  • 2 beads
  • 2 Clothespins
  • 1 mini Clothespin

The Tools I used were:

  • Saw
  • Scissors
  • Hot Glue gun
  • Pen
  • Ruler
  • Drill
  • Bench Grinder

Step 4: Design Process/Methods

Here is the design process and methods I used to create my Ballista Catapult:

  • Researched about different Ballista Catapult designs
  • Sketched out a Ballista Catapult
  • Gathered my materials from around the house
  • Built my catapult
  • Made the necessary adjustments and modifications needed
  • Tested my catapult and measured the distances of each launch

Step 5: Building Process

Here are the pictures of the steps in my building process:

    • The first thing I did was to cut the ends of the popsicle sticks
    • Next I drew holes using a pen so I knew where to drill and would make sure everything lined up
    • Then we drilled the holes into the popsicle sticks and into the block base
    • After I drilled holes, we cut out a center notch into the red base. This will provide a spot for the straw to sit
    • Next we put the nails through the popsicle sticks and block base
    • Here I am adding some glue to the nails so they would not fall through the holes and would be more secure
    • Then I took apart two clothespins, and removed the wire "fulcrum" inside
    • I glued the wooden clothespin halves together
    • After, I glued the red block base onto the clothespin base
    • Here I am cutting a straw in half to use as the shoot for the projectile
    • Then I glued the mini clothespin to the back of the catapult
    • Here I am cutting an elastic
    • Then I threaded a bead onto the elastic
    • Finally I tied the elastic to each nail on both sides of the catapult. When stretched, this will create tension and stored energy.

    Step 6: Testing My Ballista

    I decided to test my Ballista a few times to see if the distance the bead flew was about the same or if the distance varied.

    I launched the bead 5 times and here are the results:

    • Launch #1 - Traveled 54.5 inches
    • Launch #2 - Traveled 44.0 inches
    • Launch #3 - Traveled 48.0 inches
    • Launch #4 - Traveled 49.5 inches
    • Launch #5 - Traveled 49.0 inches

    I noticed the bead flew approximately the same distance each time.

    The average distance the projectile flew was: 49.0 inches

    Step 7: Final Product

    Here is a picture of my final product

    As you can see, I achieved my goal of keeping it small and it easily sits on a table.

    I found this project to be fun and easy for anyone to build.

    I learned a lot about the Ballista Catapult as I was building mine. I can see how a much larger version could be used to propel large objects a great distance.

    I also learned how the Ballista Catapult works. The catapult works by building up tension and releasing it. Then tension is built up from the elastic and is released once the clothespin lets go. This causes the projectile to be launched.

    Step 8: Resources

    This is one of the videos I found to help me with this Project.

    This is an Intractable I found to also help me with this Project.

    Step 9: Modifications

    I had to make a few modification while building my Ballista Catapult

    The first modification I did was to build up my base by taking apart another clothespin. When I first built the ballista, I found the nails were hitting the surface when I pulled back on the elastic. Therefore, I decided to build up my base and used another clothespin to give it more height.

    The second modification I did, was I cut back the sides of the straw at the front of the launch. I found the elastic kept getting caught on the edges, so I cut them down and found the elastic could launch better after I did this, causing the bead to fly further.