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DIY catapult out of plastic building bricks with The Children's Museum of Indianapolis

DIY Catapults

Here's one of the cool things about engineering—when something doesn't work, you can keep changing and adjusting until it does work. Failure is part of the engineering process! Learn from each attempt and try again.

Plastic brick catapult

Use the images below to build your Lego brick catapult. You can use similar size bricks if you do not have the exact bricks and Legos in the images.

1. Collect your materials. Gather the pieces shown in this photo. Feel free to substitute similar pieces if necessary.

Plastic bricks for basic catapult

2. Build the catapult base. Assemble two wheels and an axle. Place two 2x1 bricks on top after attaching the wheels.

Basic catapult step 2

3. Build the launch basket. 

Basic catapult step 3 launch basket

4. Place a long flat brick on top of the catapult base. This will be the catapult arm. Leave room on either side for the launch basket and for your finger to press the arm.

Basic catapult arm

5. Place the launch basket on the catapult arm. The end of the arm should stay elevated until you provide the energy to launch an item from your catapult!

Assembled basic catapult

6. Test that the base, arm, and launch basket are secure by pressing a few times on the elevated side of the catapult.

Testing basic catapult

7. Launch that payload!

Launching payload on basic catapult

Consider making these tweaks:

  • Experiment with different brick sizes to make your basket
  • Adjust the basket's location on the arm
  • Adjust the arm's location on the base

Remember, engineering is about observing and making adjustments. What did you learn?

Rubber band catapult

Ready for a more advanced catapult? Try building one that uses a rubber band instead of your finger to launch your payload.

1. Collect a rubber band and these plastic building bricks.

Rubber band catapult materials

2. Gather four flat bricks for the catapult frame. Press them into a frame.

Rubber band catapult step 2

3. Place two 1x8 bricks parallel to each other on top of the frame. Be sure to leave some of the 1x8 bricks hanging over the ends of the frame.

Rubber band catapult step 3

4. Build the frame that will hold the catapult arm axle. 

Rubber band catapult step 4

5. Place the axle holder on top of the frame (as shown). Get ready to feed the axle (a long stick) through the holes.

Rubber band catapult step 5

6. Find two long bricks with holes in the sides for the catapult arm. You might have to connect the yellow bricks (as shown) so they work as one long brick.

Rubber band catapult step 6

7. Use two 1x2 bricks to connect the longer bricks together.

Rubber band catapult step 7

8. Feed the axle through the axle holder, then the arm, and through te second axle holder. The arm should move freely on the axle. Add 2x1 brick "stoppers" to the catapult arm. Push the small cylinders—one on each side of the axle.

Rubber band catapult step 8

9. Wrap the rubber band around both the end of the base you built earlier and the catapult arm. If you're using a larger rubber band, you might have to twist yours once more around the arm to make it tighter.

Rubber band catapult step 10

10. Test your catapult! Hold the base while pressing down on the back. Then quickly let go. How does the rubber band make the catapult arm and its payload move?

Rubber band catapult

Check out the engineering video below to see how these catapults work. You'll also see how to make a bonus marshmallow catapult!

Marshmallow catapult

Here's what you'll need to construct a marshmallow catapult. 

  • Marshmallows
  • Skewers
  • Masking tape
  • Plastic spoon

Use your engineering skills and creativity to make up your own design! Remember: as we saw in the Gumdrop Challenge, triangles are your friend and large bases can hold more weight!

Did you know? Modern catapults like this rubber band design can be found on aircraft carriers.

Have fun engineering your catapults at home! Share your catapult successes and failures with us by using #TCMatHome on social media!


LEGO® is a trademark of the LEGO Group of companies which does not sponsor, authorize or endorse this post.

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