🛠️ Ratchet Car Jack: step-by-step build

Crank the handle — click, click, click — and lift a toy car. Let go and it stays up!

When a real car gets a flat tyre, the driver uses a jack to lift it off the ground. Your jack has a toothed post, called a rack, and a little gear that climbs it when you turn the crank. The clever part is the pawl: a small catch resting on a gear. It lets the gear turn one way — click, click, click — but blocks it from turning back. So the car stays up, even if you let go of the handle!

• Level 3 of 5 (medium)
• About 35 minutes
• 15 steps, 41 parts
• Powered by: Hand-crank
• Series: Mechanical Wonders

What you will learn

• Ratchet & Pawl: Lets something turn one way but not the other.
• Rack & Pinion Steering: A gear rolling on a straight rack slides it sideways.
• Torque vs Speed: Slower gears are stronger gears.
• Gear Ratio: Fast or Slow: A big gear turning a small gear makes it spin faster.
• Frames: A frame is a ready-made strong rectangle.
• Pins: Grippy or Smooth: Pins join beams together — some hold tight, some let things swing.

Build these first

• 🏎️ Steering Go-Kart: Turn the steering wheel and the front wheels really turn — just like a real car. (level 3 of 5, about 30 minutes, 25 steps)
• 🎯 Spring Catapult: Cock the arm, click the trigger, FIRE! A spring flings the ammo across the room. (level 2 of 5, about 25 minutes, 14 steps)

Parts you need

• 1 × H frame 7×11
• 6 × Blue long pin
• 2 × Cross block
• 2 × Long pin-axle block
• 1 × Axle 7
• 10 × Black pin (grippy)
• 2 × Beam 13
• 1 × Beam 15
• 1 × Steering rack
• 2 × L-beam 2×4
• 2 × Beam 3
• 2 × Axle 5
• 1 × Medium gear (24 teeth)
• 2 × Tiny gear (8 teeth)
• 3 × Bush
• 1 × Hand crank
• 1 × Thin beam 4
• 1 × Red axle-pin

Steps

1. Lay the H-frame flat. This is the jack's foot.
2. Push a blue long pin up into each side rail, in line with the first cross bar, and put a cross block on top of each, its cross hole pointing back.
3. Hold two long pin-axle blocks upright behind the cross bar, 2 holes apart, and slide a 7-long axle through both cross blocks and both of them.
4. Push two black pins into each upright block, pointing to the front.
5. Press a 13-hole guide onto each pair of pins by its 1st and 3rd holes.
6. Lifting post: take a 15-hole beam and pin the black toothed rack to its front.
7. Pin an L-beam to each side of the top: this is the lifting saddle.
8. …and the second L-beam on the back.
9. Slide the lifting post down between the guides.
10. Hold it in: push two blue long pins through the guides and add a 3-hole beam across the front.
11. Push a 5-long axle through the right guide near the top: tiny pinion in front on the rack, 24-tooth gear behind and a bush on the back end to hold it on.
12. Push a blue long pin into the left guide and add a second 3-hole beam in front.
13. Crank shaft: push a 5-long axle through the right guide below the big gear, with a bush in front of the guide and an 8-tooth gear and a bush behind it.
14. Put the crank on the front end of the crank shaft.
15. Pawl: push a blue long pin into the top of the left guide, hang the black 4-hole pawl on it by its 2nd hole (a round one) and push a red axle pin into the cross hole at its far end.

Play time

Put a toy car on the saddle and crank — click, click, click — it rises! Let go of the crank: does it drop? Now lift the pawl with your finger. Watch out below!

Real-world inspiration

Ratchet and pawl — https://en.wikipedia.org/wiki/Ratchet_(device) ; rack-and-pinion jacks