🐢 Pull-back Tortoise: step-by-step build

Slow but super-strong: a spring car that can climb up a book!

The tortoise never hurries, but it always gets there. In this spring car a tiny 8-tooth gear on the spring engine turns a big 24-tooth gear on the wheels. The wheels turn three times slower — but with three times more pushing power, enough to climb a steep ramp. Top it off with an armoured shell, and your tortoise is ready for the hill climb!

Level 2 of 5 (easy)
About 30 minutes
12 steps, 38 parts
Powered by: Pull-back
Series: Gearbox & Drivetrain Cars

What you will learn

Stored Energy: Energy can be saved up in a spring and let out later.
Mounting a Motor: A motor must be pinned tight, or it spins itself instead of your wheels.
Torque vs Speed: Slower gears are stronger gears.
Gear Ratio: Fast or Slow: A big gear turning a small gear makes it spin faster.

Build these first

🏁 Pull-back Racer: Pull it back, let it go — ZOOM! A racer with a spring for an engine. (level 2 of 5, about 12 minutes, 10 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

1 × Pull-back motor
1 × Axle 10
14 × Black pin (grippy)
2 × Open frame 5×7
2 × Beam 11
1 × Tiny gear (8 teeth)
2 × Half bush
2 × Axle 12
1 × Medium gear (24 teeth)
3 × Bush
4 × Small white wheel
2 × Long pin-axle block
2 × Red axle-pin
1 × H frame 7×11

Steps

Take the pull-back motor, long body pointing forward, and push a 10-long axle through the cross hole at the bottom, one hole further out on the left.
Push a black pin half-way into the front one of the two top holes of the motor, and into the first and last hole of its bottom row, on this side. Press a green 5×7 frame onto the three pins.
Same on the other side: three black pins half-way in, then the second green frame.
Push black pins into the outside of both frames: the 2nd hole up at the back and the 2nd hole up at the front.
Press an 11-hole beam onto each pair of pins: the motor axle goes through the 3rd hole.
Put the tiny 8-tooth gear on the left end of the motor axle with a half bush outside it, and a half bush on the right end.
Push a 12-long back axle through the first holes of the beams, with the big 24-tooth gear next to the tiny one and a bush on the other side. Push the left back wheel on right away — it holds the big gear in place.
Push a 12-long front axle through the last holes, with a bush on each side.
Push on the other three wheels.
Shell supports: push black pins into the outside of both frames' top bars, in the 5th and 7th holes.
Press a long pin-axle block onto each pair of pins, and push a red axle-pin up into the middle hole of each block, pin end on top.
Press the big H frame onto the two red pins — the tortoise shell!

Play time

Make a ramp from a book and a board. Pull the tortoise back all the way and let it climb! Make the ramp steeper each time — then try the Pull-back Racer on the same ramp.

Real-world inspiration

Crawler "low range" gearing — https://en.wikipedia.org/wiki/Transfer_case

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)