Introduction: School DT Projects: Model Roman Catapult

About: I'm an engineer and a dad who has a love for designing and making toys, STEM projects and anything electronicy.

A while ago, I started making projects for teaching in school which were manageable, fun and educational. The first project we made was this model Roman catapult. Since making it, a number of teachers and students have asked for instructions for how to make it, so here we go!

Please note: If you're a teacher wondering how do-able this is, I've made this with a whole class of Year 3s (7-8 year olds) working in pairs and other teachers have made this with Year 5 and 6 classes so it's definitely do-able!

Below is my video tutorial to run alongside the Instructable. Apologies for the length at times - I forgot to speed up the longer gluing parts!

Step 1: Materials and Tools You Will Need

For this project, you will need these materials:

  • 2 rubber bands
  • 1 plastic bottle cap (milk bottles work well)
  • 1cm square dowel (TTS/Consortium do value 100 piece packs)
  • 5mm wooden dowel
  • A drinking straw (wide enough so the dowel rotates freely inside it)
  • 1 sheet of card
  • 1 sheet kitchen towel/piece of thin craft foam
  • 3 flat-headed thumb tacks (push pins)

You will also need these tools:

  • Junior hacksaw
  • Hot glue gun
  • Ruler
  • Pencil
  • Scissors
  • Sticky tape (optional)

Step 2: Prepare Your Wood

Use your hacksaw to mark and cut the following lengths of wood for your frame:

Square cross-section wood

  • 2 x 30cm (base)
  • 1 x 20cm (firing arm)
  • 4 x 8cm (base + support arch)
  • 2 x 9cm (support arch
  • 2 x 9.9cm (supporting arm)

Round dowel

  • 1 x 10cm (supporting firing arm)

N.B. When you cut the 9.9cm pieces, cut the ends at 45 degees (see pic).

Step 3: Glue Your Base

For the base, you will need:

  • 2 x 30cm pieces (square x-section wood)
  • 3 x 8cm pieces (square x-section wood)
  • 12 x 2-3cm short-sided card triangles

Lay your base pieces out like in the picture below. Then, use a dab of hot glue to join a joint together (making sure each piece is at 90 degrees to the other), securing by gluing a card triangle on top of it. Repeat for all the remaining joints, then flip the base over and repeat with card triangles on each joint to give it strength.

Step 4: Gluing the Support Arch

To make the support arch, you will need:

  • 1 x 8cm (square x-section wood)
  • 2 x 9cm (square x-section wood)
  • 4 x 2-3cm card triangles

Just like the previous step, add a dab of hot glue between the pieces of each point, making sure the joint sits at 90 degrees. Then, hot glue card triangles on top of each joint, flipping it over and repeating for a second set of car triangles for each joint to add strength.

N.B. Make sure the 8cm piece sits between the 9cm pieces, rather than on top of their ends (see pic and video at 5:09. This is important for the next step!

Step 5: Attach the Arch to the Base and Front Supports

For this step, you'll need:

  • 2 x 9.9cm pieces (cut with 45 degree ends)
  • 6 x card triangles

Next, turn your base sideways and rest your arch up against that 8cm piece you glued in the middle of your base. This way, the base and support arch rest against each other and you can glue knowing they'll stay at 90 degrees to each other!

Add a dab of glue underneath each arm of the arch to join the arch to the base, then reinforce with card triangles. See pics and video at 6:17.

Next, use dabs of hot glue to secure your front supports (9.9cm pieces) to join each side of the arch to the base. Use card triangles to strengthen each joint at the top and bottom of the front supports.

See pics and video at 7:14.

Finally, add card triangles to the inside of the supporting arm joints to add strength.

See pics and video at 9:15.

Step 6: Create Supports for the Firing Arm

For this step, you will need:

  • 10cm piece of wooden dowel
  • Drinking straw

Cut a 1cm piece of drinking straw and feed it onto the dowel so it is roughly in the middle.

Next, add a dab of hot glue behind each of the support arches where they join the base.

Then, gently press the ends of the dowel onto the hot glue to secure it to the base. The straw should be able to freely turn around the dowel!

Now, add extra hot glue to secure the dowel firmly to the base.

Step 7: Add Padding to the Support Arch

One thing you can do to help dissipate the force of the firing arm following through is to wrap a length of kitchen towel/craft foam around the top of the support arch. I found the firing arm lasted longer when I did this.

Step 8: Create and Attach Your Firing Arm

For this step, you will need:

  • 1 x 20cm (square cross-section wood) firing arm
  • 1 x plastic bottle cap (milk bottle is ideal)
  • 1 x metal thumb tack/push pin

Line up your bottle cap with the end of the 20cm piece of wood. Push a thumb tack firmly through the bottle cap into the piece of wood to hold it in place.

Next, line up your firing arm and the free piece of 1cm straw so they are half-way between the base pieces (see pic) and use a dab of hot glue to attach the firing arm to the piece of straw. After cooling, the firing arm should freely rotate on the piece of dowel!

See pics and video at 18:04.

Step 9: Add Thumb Tacks and Rubber Bands

You're almost done! For this final step, you'll need:

  • 3 thumb tacks
  • 2 rubber bands

Push a thumb tack half wayinto the top of the front of each side of the support arch. Now, hook a rubber band around each thumb tack and push them in firmly to hold the rubber bands in place.

Next, lift up the firing arm and push a thumb tack half way in into the firing arm half way along the underside. Pull each rubber band up over the support arch and hook it onto the thumb tack under the firing arm.

Finally, push the thumb tack underneath the firing arm all the way in to hold the rubber bands in place.

Step 10: Congratulations, You're Finished!

Well done, you are done! Give your catapult a dry runs, bracing the base with one hand and pulling back the firing arm with the other. Don't be afraid to really let it fly!

Fun projectiles to play with include:

  • Blocks of blue tack (flies very well)
  • LED throwies (great fun!)
  • Balls of foil
  • Sweets (wine gums fly rather nicely)
  • Ping pong balls (shorter distance, but safe!)

Other improvements you can make include:

  • Use thicker/more rubber bands for a stronger force (bearing in mind the strength of your catapult!)
  • Scaling the project to make it larger
  • Moving the dowel to the front of the base to make the firing angle 45 degrees (I have heard good feedback about doing this!)

Thanks for reading my instructable and I hope you found it interesting.

I'd love to see any pictures of you making one yourself. Feel free to PM me with any questions about the project and happy making!!