🏁 Three-Speed Car: step-by-step build

Two little gearboxes in a row make a big one: crawl, cruise or fly!

You already built a 2-speed gearbox. What happens if you put a second one right behind it? Each box has a lever with two positions: slow (3 times slower) or fast (same speed). Slow + slow = 3 × 3 = 9 times slower: a crawler gear for steep ramps. Fast + fast = full speed. And slow + fast or fast + slow are both 3 times slower — the SAME speed twice. Four lever positions, three different speeds!

Level 4 of 5 (tricky)
About 60 minutes
20 steps, 60 parts
Powered by: Motor
Series: Gearbox & Drivetrain Cars

What you will learn

Gearbox: A box of gear pairs where you choose which pair works.
Compound Gears: Two gear stages in a row multiply their ratios.
Clutch & Driving Ring: A part that connects or disconnects a gear from its axle.
Gear Ratio: Fast or Slow: A big gear turning a small gear makes it spin faster.
Bevel Gears: Around the Corner: Slanted gears send spinning power around a corner.
Mounting a Motor: A motor must be pinned tight, or it spins itself instead of your wheels.
Plugging In: Power Functions: Battery box → (switch or receiver) → motor. Plugs stack like bricks.

Build these first

⚙️ Clutch-Gear 2-Speed Car: Push the gear lever and a driving ring grabs a different gear: 1st climbs, 2nd races! (level 3 of 5, about 45 minutes, 18 steps)

Parts you need

2 × Beam 15
3 × Axle 11
1 × Axle 9
9 × Bush
2 × Small gear (16 teeth)
2 × Clutch gear (16 teeth)
2 × Driving ring
2 × Clutch gear (24 teeth)
1 × AA battery box
4 × Blue long pin
2 × Beam 7
1 × L motor
1 × Axle 2
2 × Half bush
11 × Black pin (grippy)
2 × Beam 3
2 × Corner gear (12 teeth)
2 × Tiny gear (8 teeth)
4 × Yellow-hub wheel
2 × Gear shifter
1 × LED lights
2 × L-beam 3×5

Steps

Stand a 15-hole beam on its edge — the right rail.
Push an 11-long axle through the 2nd hole (front) and another through the last hole (rear).
Middle shaft: a 9-long axle through the 13th hole. Slide on a bush (right against the rail), a 16 gear and another bush — the 16 will turn the range box.
Range box: slide onto the rear axle a bush, the 16 clutch gear, a driving ring and the 24 clutch gear.
Fill the rest of the rear axle with three bushes, so the range box can't slide.
Battery pack: take the AA battery box.
Push blue long pins into the two lowest holes of both ears, all on the same side.
Press a 7-hole post onto each pair of long pins, hanging down.
Motor: take the L motor, push a 2-long axle into its output and slide a half bush onto it, right against the motor.
Push black pins into the 4 side holes on one side of the motor (2 at the front, 2 at the back).
Motor posts: black pins in holes 3 and 9 of the right rail (inside) and a 3-hole post on each, sticking up and down.
Press the motor onto the two posts from the left, output facing backwards, and slide a tan corner gear onto its axle.
Lower the battery pack inside the right rail: the front post sits at the 1st hole, the back post at the 11th. Push a black pin through the rail into the front post. Hold two bushes behind the back post and push an 11-long input shaft through the rail, the back post and both bushes.
On the input shaft, from the left end: a tan corner gear next to the bushes (it meshes with the motor's), a half bush, a 16 gear and a bush.
A tiny 8 gear on the end of the input shaft. On the left half of the middle shaft: a tiny 8 gear, the 16 clutch gear and a driving ring.
The 24 clutch gear goes on last. Slide the left rail onto all four axles and push on the two back wheels — now nothing can slide off. Plug the L motor straight into the battery box.
Push on the front wheels. Clip a gear shifter onto each driving ring: lever 1 on the middle shaft, lever 2 on the rear axle.
Headlights: push the two LED lights into the round holes on the front of the battery box.
Right door: black pins in holes 6 and 8 of the right rail (outside) and an L-beam on them.
Left door the same way.

Play time

Test all four lever combinations on a 2-metre track and write down the times. Which two positions give the same speed? Then build a steep book ramp: only 1st gear (both levers on slow, 9:1) makes it to the top.

Real-world inspiration

Range and splitter gearboxes in trucks put a 2-speed box after the main box; Sariel's compact sequential transmissions. https://en.wikipedia.org/wiki/Transmission_(mechanical)#Multiplier_(range)_and_splitter_gearboxes · https://sariel.pl/2015/04/4-speed-compact-sequential-transmission-v11/