Robert Kimball

← All projects

Personal project

Robotic Treasure Chest

Problem
Design a fully 3D-printed storage chest with Arduino electronics to make an interactive desk toy.
Date
Dec 2025 – Jan 2026
My role
Personal project: mechanism design, CAD, printing, electronics and Arduino code
Size
70 × 75 × 67 mm closed
Tools
SolidWorks, 3D printing, Arduino C++, servo motor, piezo buzzer
Result
Working desk toy whose custom gear assembly opens the chest in sync with the classic Legend of Zelda tune
Robotic treasure chest: product demonstration
Three printed treasure chest prototypes side by side with their gear partsOpen larger image
All design iterations
SolidWorks isometric of the closed treasure chest with the bevel gear pair visible at the back cornerOpen larger image
Final assembly, isometric, lid closed
Rear isometric of the chest showing the servo, the two bevel gears and the lid hinge shaftOpen larger image
Rear view: servo, 1:1 bevel gear pair and lid hinge shaft
Section view through both gear axes showing two 45-degree bevel gears meeting at a right angleOpen larger image
Section through both gear axes: 45° miter gears at 90°, lid hinge shaft (left) and servo (bottom)
Close-up of two meshing 12-tooth bevel gearsOpen larger image
The two 12-tooth bevel gears (Ø16.1 mm)
SolidWorks render of the treasure chest with the servo and bevel gears mounted at the hingeOpen larger image
Full CAD assembly
First printed chest, opened, showing the spool mechanism insideOpen larger image
Original design with spool

Mechanism iterations

  • Brainstormed and prototyped several opening mechanisms based on the Arduino components available.
    • First iteration: a servo with a custom spool tensioned a string from inside the chest. The lid could not open at different speeds; it only opened rapidly once enough tension built up.
    • Second iteration: custom bevel gears driven by the servo, attached to the back of the chest near the hinge. This allowed more dynamic movement, but the assembly was too fragile and broke during adjustments.
    • Third iteration: improved tolerances and hinge design for easier installation and lower stress on the gears and hinges.

Specs (from the final CAD)

  • Overall: 70 × 75 × 67 mm with the lid closed; 5 parts (base, lid, servo and two gears).
  • Drive: the servo turns a pair of 12-tooth straight bevel gears with 45° cones (a 1:1 miter pair at 90°, Ø16.1 mm). The second gear sits on the lid's hinge axis, so the servo rotates the lid directly.
  • Hinge: Ø3.8 mm pins on the lid snap into Ø4.0 mm open hooks on the base (0.2 mm diametral clearance).
  • Walls: 2.0 mm lid shell and 2.0 mm base walls.

Bevel gear versions (CAD)

  • v1: Ø12 × 4 mm gear with 23.6° / 33.3° tooth cones and a Ø4.0 mm bore.
  • v2: grown to Ø16.1 × 6.5 mm with 45° cones, so the two identical gears form a true 1:1 pair at 90°; bore opened to Ø4.5 mm.
  • Final assembly: a no-bore version of the v2 gear.

Electronics & code

  • Added a piezo buzzer that plays a song in sync with the opening motion of the chest.
  • Wrote Arduino code that translates strings into musical notes for the piezo buzzer.
    • Converts strings like "C4" into the correct integer frequency based on A440 tuning.

Result

  • Fully functional desk toy (see the demo video) that uses a custom gear assembly to open the chest in sync with the classic tune from The Legend of Zelda.

What I learned

  • Designing custom bevel gears
  • Creating dynamic assemblies with multiple moving parts in SolidWorks
  • Programming servo motors and piezo buzzers in Arduino C++