Week 11 — Machine Week

For machine week I joined the candle team with Alex. The shared goal was to design a mechanism that could make five LED candles tilt and fall on command: each candle sits on a circular platform driven by a servo underneath. Alex focused on the servo mechanism and I focused on the candle geometry, internal electronics, and how the candle would behave mechanically when tipped.

Process

Mechanism & Roles

We began by defining the overall mechanism: five LED candles arranged on individual circular platforms with servos underneath that tilt the plates. When the plate rotates past a critical angle, gravity does the rest and the candle falls. Alex concentrated on the servo mounting and plate design; my role was to define the candle’s dimensions, mass, and internal layout so that the candle would be stable at rest but easy to tip.

Torque & Tipping Calculations

I started with simple hand calculations to understand the relationships between:

candle width and height,
estimated candle mass (including batteries and LED), and
servo torque and lever arm length.

The idea was to make sure the servo has enough torque to push the candle past the tipping point while not over-designing the mechanism.

Torque and tipping calculations page 1 — First page of torque and tipping calculations.

Torque and tipping calculations page 2 — Additional notes on lever arm length and required torque.

Next, I looked up the datasheet for the specific servo we used and plugged its rated torque into the equations. With that fixed left-hand side, I could choose reasonable values for candle diameter, mass, and the distance from the servo horn to the plate pivot, then back-calculate an “ideal” candle height that would fall reliably.

Servo specification sheet used for design — Servo specification sheet used to anchor torque calculations.

LED Power & Circuit Prototype

We decided to keep the electronics simple: a single LED powered by AAA batteries inside each candle. I used the LED’s forward voltage and current to decide how many batteries were needed in series and then prototyped the circuit on the bench.

Testing LED brightness and behavior under different battery configurations.

Measuring AAA battery voltage for the LED candle — Measuring AAA battery voltage while planning the internal power layout.

Prototype circuit: LED, switch, and AAA batteries before integrating into the candle body.

Measurements & 3D Candle Design

With the electronics roughly defined, I measured every component—battery pack, switch, LED, and the interface to the servo-driven plate—and translated those dimensions into a 3D-printed candle shell. Several iterations were needed to balance:

internal space for components,
external diameter for a stable base, and
overall height that still tips easily when the plate tilts.

Initial component measurements — Initial measurements of the internal components.

Additional component measurements — More detailed dimensions for batteries and switch.

Measuring cylindrical housing geometry — Measuring the cylindrical housing geometry and clearances.

Checking clearances for internal wiring and the LED mount.

Refinements to candle body dimensions after the first test print.

Side view measurements of candle prototype — Side view measurements used to adjust the height-to-diameter ratio.

Top view measurements of candle layout — Top view: layout of batteries, LED, and central axis.

Bottom interface measurements to servo plate — Bottom interface dimensions for connecting to the servo-driven plate.

3D model of the candle shell with internal volume for electronics.

Joint detail between candle and base — Joint detail showing how the candle attaches to the tilting platform.

Kit of Parts & Final Prototypes

After iterating on dimensions and assembly, I arrived at a kit of parts that could be repeatedly printed and assembled for all five candles.

Kit of parts for the candle design — Kit of parts: body, cap, base insert, and internal supports.

Interlocking details of candle parts — Interlocking details that keep the components aligned while still serviceable.

First printed prototype of the candle — First printed prototype to validate fit and tipping behavior.

Refined candle prototype — Refined prototype with adjusted height and cleaner assembly.

Set of finished candle designs — Set of finished candles ready to mount on the servo-driven plates.

Alternative view of all final candle prototypes — Alternative view of the complete candle family.