🏗️ Worm-Gear Crane: step-by-step build

Crank the worm gear to lift the boom — then let go. It stays up by itself!

Cranes lift enormous weights, and they must never drop them. Their secret weapon is the worm gear: a gear shaped like a screw. It turns the big gear super slowly and super strongly, and the big gear can never push it backwards. You will build the crane base, then the boom as a separate part, and join them on the big gear. Then crank, crank, crank — and watch the hook rise!

Level 3 of 5 (medium)
About 30 minutes
15 steps, 39 parts
Powered by: Hand-crank
Series: Starter Builds

What you will learn

Worm Gear: The Lock: A worm gear turns a gear super slowly — and never slips back.
Torque vs Speed: Slower gears are stronger gears.
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

🧪 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 × Open frame 5×11
6 × Blue long pin
4 × Split pin block
4 × Red axle-pin
2 × Beam 5
1 × Axle 6
6 × Bush
5 × Half bush
2 × Axle 3
1 × Worm gear
1 × Hand crank
2 × Beam 11
1 × L-beam 2×4
1 × Axle 4
1 × Axle 8
1 × Medium gear (24 teeth)

Steps

Lay the 5×11 frame flat. This is the crane's base.
Push two blue long pins up into the 8th and 10th holes of the left long side. Press two split pin blocks onto them, one on top of the other.
The same on the right long side: two blue long pins and two split pin blocks.
Push a red axle-pin sideways into the middle cross hole of both left blocks, pointing out, and stand a 5-hole beam on the two pins, just outside the frame.
The same on the right: two red axle-pins and the second tower. These two towers will carry the drum axle.
Stand a 6-axle in the middle hole of the short end so it pokes out 1 hole underneath. Slide a bush on underneath, and a bush and a half bush on top.
Give the crane two more feet at the other end: push a 3-axle into each corner hole so it pokes out underneath, and slide a bush on below.
Lock the two feet with a bush on top of each.
Slide the worm gear onto the axle.
Push the red hand crank onto the top of the axle, handle up.
Boom: take an 11-hole beam…
…hold the black L-beam hook next to it and the second 11-hole beam beside that, then push a short axle through the end holes: beam, hook, beam.
Push a blue long pin through the 6th hole of both boom beams, and lock the tip axle with half bushes.
Lower the boom between the two towers, hold the 24-tooth gear between the boom beams and push the drum axle through tower, boom, gear, boom, tower.
Lock the gear to the boom with a blue long pin, and put half bushes on the ends of the drum axle.

Play time

Turn the crank to lift the hook. Let go — does the boom fall? Now try pushing the boom down with your finger.

Build next

🦾 XL Power Crane: The strongest motor plus a worm gear: 24 times slower and super strong. (level 4 of 5, about 35 minutes, 27 steps)
🚜 Skid-Steer Loader: No steering at all: left motor, right motor — spin it round on the spot! (level 4 of 5, about 65 minutes, 25 steps)
🧗 Worm-Drive Crawler: Super slow, super strong: worm gears drive both axles and it never rolls back. (level 4 of 5, about 50 minutes, 20 steps)
🏰 Castle Drawbridge: Wind the handle and the heavy bridge slowly rises — and stays up when you let go. (level 2 of 5, about 30 minutes, 15 steps)
🌬️ Oscillating Fan: A desk fan that turns its head left and right all by itself! (level 3 of 5, about 40 minutes, 18 steps)
🛢️ Nodding-Donkey Pump Jack: A slow crank rocks a long beam up and down — nod, nod, nod, all day long. (level 3 of 5, about 45 minutes, 30 steps)
🛗 Scissor Lift: Turn the crank and the platform climbs straight up on criss-cross legs. (level 3 of 5, about 45 minutes, 29 steps)
🎡 Ferris Wheel: A big wheel turns slowly while its gondolas always hang the right way up. (level 3 of 5, about 45 minutes, 28 steps)
📦 Conveyor Belt: A factory belt that carries your parts from one end to the other — and drops them in a box. (level 3 of 5, about 50 minutes, 22 steps)
🏹 Counterweight Trebuchet: The heavy battery box drops, the long arm whips up — and your bush flies across the room! (level 3 of 5, about 40 minutes, 17 steps)
🚞 Cog Railway Climber: A mountain train that grips a toothed rail — it climbs super steep ramps and never slides back. (level 4 of 5, about 55 minutes, 20 steps)
🦾 Crank Excavator Arm: Crank the worm gears to swing the digger round and lift the boom — then dig! (level 4 of 5, about 50 minutes, 22 steps)
🚂 Sun-and-Planet Beam Engine: James Watt's steam-engine trick: a gear that never spins makes the flywheel turn four times per pump! (level 4 of 5, about 50 minutes, 17 steps)