Build a Simple Gear System (Perfect for a School Project)

Here’s a clear, beginner-friendly plan with two build options (cardboard or LEGO/3D-print), the key math, and a tested recipe you can finish in an afternoon.

What You’ll Make

A gear train that changes speed and torque between an input (hand crank or small motor) and an output (wheel/fan/lifter).
Option A: Cardboard + skewers (cheap, fast, A+ demo).
Option B: LEGO/3D-printed gears (cleaner, more accurate).

Prefer a ready parts pack? Grab a classroom-friendly DIY Gear Transmission Experiment Kit or a Hand-Crank Generator STEM Kit to use as the input/output of your system.

Materials (choose a path)

Option A — Cardboard build

Corrugated cardboard (shoebox or shipping box)
Wooden skewers or BBQ sticks (axles)
Drinking straws (bushings) + small washers (reduce friction)
Compass, ruler, pencil, scissors/craft knife
Glue (hot glue or white glue)
Push-pin or nail (to start axle holes)
Rubber bands (optional belt drive)
Coins, tape, and a paperclip (for a simple crank handle)

Option B — LEGO / 3D-print / mixed kits

LEGO Technic gears + axles + beams, or
3D-printed spur gears (3–5 sizes) + M3 screws as axles + printed frame
For a plug-and-play motor stage, pull a motor + small pinion from a Solar Robot STEM Kit.
For structural parts (plates, connectors, shafts), use a STEM Building Set.

Want a quiet first stage? Borrow a belt/pulley from the DIY Animation Projector Kit as a pre-gear speed change.

Gear Basics (mini-crash course)

Gear ratio = (teeth on driven gear) ÷ (teeth on driver gear).
- Example: 40-tooth driven by 10-tooth → ratio 40/10 = 4:1 (output spins 4× slower, ~4× more torque).
Compound gear trains multiply ratios: total = stage1 × stage2 × …
- Example: (40:10) × (36:12) = (4:1) × (3:1) = 12:1.
Speed vs torque trade-off: higher ratio → slower but stronger; lower ratio → faster but weaker.
Meshing rule: shafts of meshing gears are parallel; tooth size must match (module/DP).
- Using the same templates from the DIY Gear Transmission Experiment Kit keeps teeth compatible.

Step-by-Step Build (Cardboard Version)

1) Plan your ratio

Pick a simple goal:

Power lifter (strong): aim 8:1–12:1.
Spinner/fan (fast): aim 1:2–1:4 (increase speed).

Example we’ll build: a 4:1 reduction using a two-stage train (2:1 × 2:1). It’s smoother than one big jump.

2) Make gear templates

Draw circles: two large and two small (e.g., diameters 80 mm and 40 mm).
Around each circle, draw evenly spaced triangles (teeth). 16 teeth on the big, 8 teeth on the small works well.
Laminate each gear with a second cardboard layer for stiffness.

Tip: If you have the DIY Gear Transmission Experiment Kit, use its spur gears as tracers to mark tooth spacing fast.

3) Add hubs and axles

Poke a centered hole with a push-pin, widen to skewer diameter.
Slide a short straw bushing on the skewer before the gear; add a small washer and a glue dot to limit drift.
Repeat for each shaft point.

4) Build the frame

Cut two parallel side walls and a base.
Use a spare gear to mark shaft spacing so meshing gears just touch (no gap, no squeeze).
Poke axle holes; glue walls square to the base.
No time to cut frames? Use plates and connectors from a STEM Building Set as a rigid chassis.

5) Assemble the 2-stage train

Stage 1: small gear (driver) on input shaft → large gear on middle shaft.
Stage 2: glue a small gear co-axially to the large gear on the middle shaft; that small gear now drives the final large gear on the output shaft.
→ (Large/Small) × (Large/Small) = 2:1 × 2:1 = 4:1.

6) Add a crank & a load

Make a paperclip crank on the input shaft; or mount the Hand-Crank Generator STEM Kit as your input.
On the output shaft, tape a spool to lift coins with string (torque demo) or spin a paper fan (speed demo).

steam-education-DIY-Hand-Crank-Generator

7) Tune it

Grinding? Increase shaft spacing by a paper shim.
Wobble? Add a second bushing on the far wall; keep shafts square.
Slipping under load? Add a tiny felt/paper washer; check that each gear sits fully on the shaft.

Step-by-Step Build (LEGO / 3D-Printed / Mixed Kits)

Mount two parallel beams (or a STEM Building Set frame).
Start with 8-tooth → 24-tooth (3:1), then 8 → 24 again (another 3:1) → total 9:1.
Use the motor from a Solar Robot STEM Kit as your input stage; attach a small driver pinion.
Keep center distances fixed by beam holes for perfect mesh.
Want a quiet first stage? Put the DIY Animation Projector Kit pulley/belt before your gears.

Pick a Ready-Made Ratio (cheat sheet)

2:1: 20T → 40T (simple, smooth)
4:1: (20→40) × (20→40)
6:1: (12→36) × (12→18)
9:1: (8→24) × (8→24) (great with kit parts)
12:1: (10→40) × (12→36)

Most of these tooth counts come standard in the DIY Gear Transmission Experiment Kit.

Extensions (if you have time)

Belt first, gears second: Use the belt unit from the DIY Animation Projector Kit for quiet speed change, then compound gears for torque.
One-way lift: Zip-tie pawl as a ratchet on your spool.
Speedometer: Mark one tooth and count RPM to verify your calculated ratio.

What to Explain on Your Poster/Write-Up

Goal & use case (lift a 100 g load, or spin a fan 3× faster).
Gear math with your exact tooth counts (show stage multiplication).
Trade-offs (why torque vs speed).
Design choices (bushings, spacing, frame).
Results (measured speed or lift) + improvements (friction, alignment, stronger frame).

Quick Troubleshooting

Teeth skip → shafts too far apart.
Gears bind → shafts too close or not parallel.
Won’t lift → increase ratio or reduce spool radius.
High friction → add straw bushings/washer; check warped gears; reinforce frame (or swap to a STEM Building Set frame).

Panda Crafty parts that plug right in (internal links recap)

DIY Gear Transmission Experiment Kit — spur gears, shafts, bushings for the core train.
Hand-Crank Generator STEM Kit — human-power input or LED output demo.
Solar Robot STEM Kit — DC motor + pinion for a powered input stage.
STEM Building Set — rigid frames, connectors, and axles for alignment.
DIY Animation Projector Kit — belt/pulley components for a quiet pre-gear stage.