What You'll Need

3-D printer + PLA filament
Catapult STL file (download or design your own)
Micro:bit v2
9 g mini servo motor
Micro:bit servo breakout board
10 × 10 cm wood or acrylic base plate
Super-glue or hot glue
Lightweight ammo (pompom, LEGO brick, bean etc.)
Optional: acrylic paint, stickers, melody file (.hex)

Safety First!

!Keep hands clear of the printer’s hot end and bed.
!Sand sharp edges on printed parts.
!Never place fingers near the arm while the servo moves.
!Avoid very small projectiles with children under 3.
!Use hot glue in a ventilated area and wear gloves.

Let's Make It! Step-by-Step Guide

Design & Print

Step 1 of 3

• Download the STL pack —or model your own catapult in Tinkercad or Fusion 360.
• Slice at 0.2 mm layer height, 15 % infill; orient parts so no supports are needed.
• Print the pieces, remove any stringing, and lightly sand the hinge pin so it rotates smoothly.

The Science Behind It

The catapult is a first-class lever: by comparing the effort arm (servo side) and load arm (scoop side) kids see mechanical advantage in action. PWM control of the servo introduces angular speed and inertia, letting learners experiment with the classic projectile-motion trio—angle, force and mass. Collecting range data, graphing results and refining the design turns playful launches into a mini engineering cycle.

Helpful Tips

Hollow out the arm in CAD to lighten the servo load.
If torque is low, shorten the arm or add a rubber-band assist.
Add set volume 255 + a “cheer” sound block for crowd-pleasing hits.
Stick a metric ruler on the baseboard for instant range measurement.
Paint each part a different colour so younger builders can match shapes easily.

Try These Variations!

1Elastic-Only Mode – Remove the servo, power the arm with a rubber band.
2Dual-Shot – Two servos, twin scoops, alternating fire!
3Target Tournament – Print scoring rings and host a family contest.
4Glow-in-the-Dark – Use phosphorescent filament for night launches.

3D Printed Mini Catapult