🕹️ Sliding-Gear 2-Speed Cart: step-by-step build

Sliding-Gear 2-Speed Cart, completed model

Your first real gearbox: slide the crank axle to switch between strong gear and fast gear!

Real cars have a gearbox so they can be strong when climbing and fast on the road. Now you will build one! The crank axle carries two gears. Pushed in, a 16-tooth gear meets a 16-tooth gear: strong and steady. Pull it out one hole and a big 24-tooth gear meets a tiny 8-tooth gear: three times faster! Both pairs of gears are exactly two holes apart — that is the secret of every gearbox.

Level 2 of 5 (easy)
About 22 minutes
8 steps, 25 parts
Powered by: Hand-crank
Series: Gearbox & Drivetrain Cars

What you will learn

Gearbox: A box of gear pairs where you choose which pair works.
Gear Ratio: Fast or Slow: A big gear turning a small gear makes it spin faster.
Torque vs Speed: Slower gears are stronger gears.

Build these first

🎡 Crank Cruiser: Turn the handle and the car rolls — every turn of your hand spins the wheels three times! (level 2 of 5, about 18 minutes, 9 steps)
⚙️ Gear Friends: Three gears holding hands — spin one and they all dance. (level 1 of 5, about 8 minutes, 6 steps)
🧪 Gear Speed Lab: Two cranks, two gear pairs: one makes things FAST, one makes things STRONG. (level 2 of 5, about 20 minutes, 13 steps)

Parts you need

2 × Beam 11
3 × Axle 10
4 × Half bush
4 × Black pin (grippy)
2 × L-beam 3×5
1 × Tiny gear (8 teeth)
1 × Bush
2 × Small gear (16 teeth)
1 × Medium gear (24 teeth)
4 × Small white wheel
1 × Hand crank

Steps

Stand an 11-hole beam on its edge — the left side.
Push 10-long axles through the 2nd hole (front) and 10th hole (back), and put a yellow half bush on each axle end outside the beam.
Push two black pins into the inside of the beam, holes 6 and 8, and snap an L-beam tower onto them. Then slide a tiny 8-tooth gear onto the back axle, right next to the tower.
On the back axle, slide a grey bush as a spacer, then a 16-tooth gear, then a second L-beam tower. Push a black pin into the tower's outside face, at hole 6.
Push a second pin into the tower (hole 8), slide on the second 11-hole beam over both axles and the two pins, and lock the axle ends with two more half bushes.
Now the sliding axle: thread a 10-long axle through the tops of both towers, with a 16-tooth and a 24-tooth gear between them. The 16 must sit on the 16!
Four small wheels.
Push the crank onto the long end of the sliding axle, outside the wheel.

Play time

Crank the cart along in gear 1, then pull the crank out for gear 2. Which gear is easier to turn? Which one goes further per turn? Try pulling a toy up a book-ramp in each gear.

Real-world inspiration

Sliding-mesh ("crash") gearboxes of early cars — https://en.wikipedia.org/wiki/Manual_transmission#Sliding-mesh ; Sariel gears tutorial — https://sariel.pl/2009/09/gears-tutorial/

Build next

🎚️ Two-Speed Pull-back: Choose your gear before the race: CLIMB or SPRINT! Slide the back axle to swap gears. (level 3 of 5, about 35 minutes, 13 steps)