Fab Lab Mini Siege Engines - SCOPES Digital Fabrication

Lesson Details

Age Ranges
Fab Tools
MS-ETS1-1, 3-5-ETS1-3

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Noah Rasor
K-12 teacher


In this project you will be working in small teams to create a device capable of throwing a ping pong ball.


The device must be made with (and only with) the materials provided.

A full assembly of the parts required must be created in Inventor and all parts must be laser cut. No

modifications to any part may be done by hand (drilling, cutting, filing, etc). Remember all wood pieces will be .200” thick.


The device must sit on the ground when firing (no hand held devices). Power for propulsion may not

come directly from a human source (no throwing, hitting, flicking, etc)


Materials provided:

1- Ping Pong Ball (may not be modified)

1- Rubber Band

1- 2” 10-32 bolt

1- 1” 10-32 bolt

2- 10-32 nuts

1- 12×9” piece of luan (.200” thick)

Hot glue (for assembly of parts only)


Scoring will be determined by three categories:

Maximum distance


Design quality

What You'll Need

  • .200 luan plywood (or similar material)
  • rubber bands (various sizes, or all the same, your choice)
  • 1/4-20 bolts (various lengths from 2″ to 4″)
  • 1/4-20 nuts
  • ping pong balls


The Instructions


Introduce the project to the students

This is totally up to your preference how much backstory you give, but I tend to explain a bit about siege warfare and how catapults (and many other types of siege engines) came to exist.


I’ll then explain that the students will all be creating their own catapults and will be challenged to throw a ping pong ball as far and as accurate as possible.


Distribute rules and specifications

Next, I’ll give the students a sheet detailing the exact materials they’ll be working with. I won’t distribute the materials yet.

The students then will discuss design plans and make sketches of possible designs.


Pass out materials and start fabricating

The students will then receive materials and start fabricating their designs.

Once parts are cut they may start assembling and testing their machines.


Testing the catapults!

Once all teams are completed with the project, we will line up the catapults to a tape line on the floor and test for distance. Each team will get 5 chances.


After the distance test, we will place a small box (about shoebox sized) at a distance of 10 feet. Teams will have 5 chances to make a shot into the box.


Assigning a grade for the project

Team grades will be assigned based upon:

-distance score

-accuracy score

-design complexity

-construction quality

-teamwork and participation


  • (MS-ETS1-1): Define the criteria and constraints of a design problem with sufficient precision to ensure a successful solution, taking into account relevant scientific principles and potential impacts on people and the natural environment that may limit possible solutions.
  • (3-5-ETS1-3): Plan and carry out fair tests in which variables are controlled and failure points are considered to identify aspects of a model or prototype that can be improved.

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