How to Make a Lego Catapult with Bricks You Already Have

This LEGO catapult design uses common LEGO pieces that you have already or you could substitute similar LEGO blocks. Kids of all ages can use the simple LEGO catapult idea and make working catapults at home or in the classroom. This simple STEM project is playful learning at its best!

Catapult made out of LEGO bricks finished and sitting on green background
Let’s make a LEGO catapult!

Homemade Catapult DEsign

Last week my family visited a Genghis Khan Exhibit and saw a real life size trebuchet that they could put their hands on (and shoot some ping pong balls across the museum).  Once we returned home, my kids have been creating catapults out of everything.

Related: 15 more ideas how to make a catapult

This LEGO catapult design was created by my 10 year old using just the bricks we already have. As with all things Lego, modify these instructions to use pieces that you might have at home!

Supplies Needed to Make a LEGO Catapult

How to Make a Lego Catapult

Step 1  

Construct the base.   The base platform and the catapult foundation consist of these pieces:

Lego catapult building step 1
These are the pieces we used for the catapult base

Step 2  

Add Lego blocks that allow for arm movement.  

The base built from pieces pictured above are on the left. The pieces used for the arm movement base are pictured on the right:

Lego catapult building step 2
Pictured on right are the pieces used to make the catapult arm move

Step 3

The base is now complete.   

You can see that the two small 2 x 1 stud bricks in between the gold caps are on a rod and can be rotated 360 degrees at this point.   This is where the moving arm will attach:

Lego catapult building step 3
This is the completed LEGO catapult base

Step 4

Build the catapult’s moving arm with the pieces shown here or similar:

Lego catapult building step 4
Now it is time to create the catapult’s swinging arm

Step 5

Finish the arm and attach it to the 2 x 1 bricks mentioned above:

Lego catapult building step 5
This is what the LEGO catapult arm looks like from the side

Step 6

Attach a rubber band.

Finished Lego catapult
The rubber band wraps around the side wheeled posts and the bottom 4 post circle

Step 7

lego catapult final image
This is what it looked like when we were done.

Launch projectiles across the living room.

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LEGO Catapult Set

The boys own one of the Lego Castle sets that includes a catapult. Many of the pieces used were from that set. He has modified that a little to increase projectile distance.  Here are some LEGO sets that include a catapult you can build and modity:

Catapult vs. Trebuchet

The exhibit was calling this type of catapult a trebuchet. We were wondering what the difference between the two weapons were and after a little internet search which included Wikipedia, this is what I understand to be true:

  • Catapult:   A catapult is a mechanical device used to hurl objects.   It is a general term and there are many types of catapults.
  • Trebuchet:   A trebuchet is a type of catapult.   The early models were called traction trebuchets and used manpower and ropes to launch a projectile.   Later models used pulleys and counterweights and improved the accuracy of aim significantly.

The type of catapult we just built out of Legos could be described as a traction trebuchet if you imagined the rubber band to be men pulling on ropes.

Prep Time
15 minutes

Active Time
15 minutes

Total Time
30 minutes


Estimated Cost


  • LEGO bricks – use ours as a sample of what you might use from your LEGO bin (feel free to substitute)
  • Rubber band


  1. Using the pictures in this How to Build a LEGO Catapult article, choose similar LEGO bricks from your LEGO collection — if you aren’t finding the exact bricks, then find some that might work and place them separated in a work area.
  2. Construct your catapult base: Choose a flat LEGO or baseplate that is large enough to balance your catapult once it is finished.
  3. Create a stabile centerpiece that attaches to the foundation piece. Use larger, sturdier bricks as this will be what the catapult arm will swing from. Add in a piece on each side that will allow for arm movement that you can attach the next step to.
  4. Add the movement arm.
  5. Attach a basket or brick at top to place what the catapult will throw to the movement arm.
  6. Add a strong brick near the bottom of the movement arm that will support the rubber band.
  7. Twist the rubber band around the lower part of the movement arm and the centerpiece so that when the upper part of the movement arm is pushed back, the rubber band will propel what is being thrown by the catapult into the air.

Looking for more trebuchet and catapult building ideas? 


More LEGO Fun from Kids Activities Blog

How did your lego catapult turn out?  How far can you launch projectiles across the room?

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