How to Build a Working LEGO Catapult Without Any Special Pieces

Inside: This working LEGO Catapult is the ultimate treat for any LEGO lover. Step-by-step instructions, a simple scientific explanation, a demonstration video, and a ton of catapult science printables are waiting below.

A pile of LEGO bricks is a blank canvas of possibilities. It can become anything a child wants it to be: a cat, a castle, a cute monster, or an Easter basket. Creativity, curiosity, and imagination come out to play in full force when you believe in the promise of endless possibilities.

All is possible!

Test your #engineering skills with the LEGO catapult. Make it with the pieces you already have in your house. Includes #STEM #printables #kidsactivities #kidminds #handsonlearning #LEGO #catapult #STEAM #laughingkidslearn

LEGO bricks are so satisfying to manipulate. They can be touched, connected, moved, taken apart, lined up, combined, redesigned, separated, divided, and put back together again in infinite ways.

LEGO bricks are even more fun when combined with other materials! I speak from experience. In the past, we’ve combined LEGO with baking vinegar and soda to make an erupting volcano.

We added a marble or two to create a fun LEGO marble maze:

And today, we are adding a rubber band to create a working catapult. If you are thinking right now, it sounds like fun, but I don’t have any special pieces to build a LEGO catapult.

Don’t you worry!

The main purpose of this post is to show you how to build a working catapult with no special pieces. We’ve discovered that there are, in fact, endless ways of making a working catapult with any type of LEGO blocks you have! All you need is to grasp the anatomy of a basic catapult.

How We Went About It

For this project, I gathered all my kids in our LEGO room one fine spring morning and dumped a pile of LEGO pieces in the middle of the floor.

We talked about the main parts of the catapult and the essence of what makes it work. Next, we sketched (very roughly) and brainstormed different ways of going about it. Finally, everyone unleashed his or her inner engineer and came up with his or her own way of building a catapult.

We had so much fun that I actually didn’t take any pics, but today I’m going to grab some pieces and explore once again how I can put them together to create a catapult quickly and easily.

I’m sure you can build an even better one. I’m just here to inspire you.

Disclaimer: I want to reassure you that no dogs were hurt during the testing of this catapult, despite how it might look on the video. Yep, my ancient dog was determined to star in this video (and lick my face while she was at it 🙂

How to Build a Working LEGO Catapult

What you need

LEGO bricks (lots of them 🙂

Rubber bands

a pad and a pencil to sketch ideas

What to do

Prep Work

1. Gather your pieces

First, gather your loose LEGO pieces. You will want to look at a variety of pieces for an expanded sense of possibilities. Breathing life into your kids’ LEGO ideas is pretty much a process of trial and error. You never know what it’s going to take.

2. Brainstorm

Now, study the parts of the catapult image I included above, and start sketching some ideas for your own catapult. What are the main parts that make it work? What pieces do you have that can bring it together? How can you combine the blocks you have to achieve the desired effect?

Don’t worry about having just the right parts. We’ve done it in different ways with different pieces, and we always made it work. The only secret is to stick to the basic form: base, arm, and structure. Some of our ideas were sturdier than others, but it’s always fun to experiment and shoot the projectiles.

LEGO Catapult: The Main Work

1. Build a frame

The size of my catapult is determined by the size of the baseplate that you found for this project.

I started with building a frame.

2. Build an arm

The arm of the catapult can be thick or thin. I decided to go with the bare minimum.

One can easily build a bucket by arranging LEGO bricks in a square fashion. But I picked a balcony from one of the Friends sets just because it looked just right for my purpose. Plus, it was cute.

3. Attach a rubber band

Attach a rubber band in a way that creates tension. I tested one, which wasn’t enough, so I added another rubber band.

And tested again.

The test showed me two things:

I needed to add even more rubber bands
The arm slid forward, so I needed to block it with bricks.

4. Put it all together

Insert the arm into the cradle and make sure everything fits together well. You can watch the video above for the details.

5. Test

Testing is the best part 🙂

I used small LEGO pieces as projectiles.

The Science of Catapults

In case you just need a quick recap, here is how catapults work:

Catapults are all about storing up energy in some form and then releasing it, i.e., converting potential energy into kinetic energy. The more energy you manage to store before the release, the farther the projectile will fly.

Catapults come in a few forms. The simplest might be a slingshot. You pull back on a taught, resistant cord, along with your projectile, building up potential energy, then suddenly releasing it when you let go, and the cord snaps back into place with a vengeance.

In ancient Greece, a device called a “ballista” stored energy in the form of twisted ropes that, when cut, would rapidly untwist and fling a spear. The Romans gave us more familiar-looking catapults that would use a counterweight to store potential energy that, when released, would move an attached arm that flung the projectile forward.

In all cases, including our rubber band and pencil setup, it’s the sudden conversion of potential into kinetic energy that does the trick.

We talk a lot about catapults in previous posts: Check out The Basic Catapult, Star Wars Catapult, and Acorn Catapult.