🦾 XL Power Crane: step-by-step build

The strongest motor plus a worm gear: 24 times slower and super strong.

Remember the Worm-Gear Crane? Cranking was hard work! Let's give it a robot arm: the XL motor, the strongest motor in the box. The XL motor turns the worm, and the worm turns the 24-tooth gear just one tooth per turn. That makes the boom move 24 times slower than the motor — and 24 times stronger. Because a worm gear locks, the boom stays up even when you switch the motor off.

Level 4 of 5 (tricky)
About 35 minutes
27 steps, 74 parts
Powered by: Motor
Series: Starter Builds

What you will learn

Bushes & Spacers: Bushes stop things sliding off an axle.
Worm Gear: The Lock: A worm gear turns a gear super slowly — and never slips back.
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.
Drive Train: The chain of parts that carries power from the motor to the wheels.
Electric Circuits: Electricity flows from the battery, through the motor, and back.
Switching Direction: Flip which way electricity flows and the motor spins backwards.
Triangles Are Strong: A triangle cannot be squished — a square can.

Build these first

🏗️ Worm-Gear Crane: Crank the worm gear to lift the boom — then let go. It stays up by itself! (level 3 of 5, about 30 minutes, 15 steps)
🔋 Motor Buggy: Your first car that drives by itself — with a forwards/backwards switch and headlights! (level 3 of 5, about 30 minutes, 20 steps)

Parts you need

1 × Open frame 5×11
10 × Blue long pin
2 × Axle 5
16 × Bush
6 × Split pin block
6 × Red axle-pin
2 × L-beam 3×5
2 × Axle 8
6 × Half bush
1 × Worm gear
1 × XL motor
4 × Beam 11
6 × Black pin (grippy)
2 × Beam 3
1 × L-beam 2×4
2 × Axle 4
1 × Medium gear (24 teeth)
2 × Axle 7
1 × AA battery box
1 × Long pin-axle block
1 × Direction switch

Steps

Lay the 5×11 frame flat.
On each long side, push a blue long pin up into the 8th hole and a 5-long axle down through the 10th hole, so one hole of axle pokes out underneath.
Slide a bush onto the bottom end of each axle. These bushes are the winch's back feet.
Slide two split pin blocks down each pin-and-axle pair, cross holes pointing out.
Lock the top of each axle with a bush.
Left tower: push a red axle-pin into the cross hole of both left blocks, pointing out, and press an L-beam onto them — the long leg straight up, the short leg along the bottom.
Right tower: the same on the right blocks.
Stand an 8-long axle in the middle hole of the back short end. Slide a bush on underneath, and a bush and a half bush on top, so the axle can't fall out.
Slide the worm gear onto the axle so it rests on the half bush, and lock it with another half bush on top.
Take the XL motor. Find the four little tubes on its sides — those are its mounting holes.
Push a blue long pin into each of the four side tubes.
Press an 11-hole beam onto the two blue pins on each side, hanging down below the motor.
Lower the XL motor onto the tall axle, output facing down, until the axle is in its orange output. From the outside, push a black pin through the bottom hole of each 11-hole beam into the end of the L-beam's short leg.
Brace the left side: a 3-hole beam lying along the outside, a black pin into the 4th hole of the 11-hole beam and a blue long pin through to the tower, 4th hole from the bottom.
The same brace on the right side.
Boom: take an 11-hole beam…
…hold the L-beam hook and the second 11-hole beam beside it, and push the tip axle through beam, hook, beam.
Push a blue long pin through the 6th hole of both boom beams, and lock the tip axle with half bushes.
Slide the boom in from the front between the towers, hold the 24-tooth gear between the boom beams and push the drum axle through tower, bush, boom, gear, boom, bush, tower.
Lock the gear to the boom with a long pin; half bushes on the drum axle ends.
At the front of the right long side, push a 7-long axle down through the 2nd and 4th holes and slide a bush on underneath each one — two more feet.
Slide a split pin block down both axles, cross hole pointing out, then a bush on each axle to hold it down.
Slide two more bushes down each axle. This stack is a spacer for the top block.
Put a second split pin block on the tops of the axles, resting on the bushes, and push a red axle-pin into the cross hole of each block.
Press the AA battery box onto the two pins: they go into a low and a high hole in the end of its ear.
Switch holder: push black pins into the bottom and top holes of the box's far ear, on the outside, and press a long pin-axle block onto both. Its cross hole points away from the box.
Slide the direction switch onto a 4-long axle through the cross hole under its lever, then push the axle into the holder's cross hole. Plug in the XL motor.

Play time

Hang a small toy on the hook and lift it. Switch off halfway — does the boom fall? (No! The worm gear locks it.)

Build next

🕷️ Klann Walking Spider: A robot that WALKS instead of rolling — beams and pins turn a spinning crank into steps. (level 4 of 5, about 60 minutes, 17 steps)
🤖 Robot Arm with Servo Claw: Swing, lift and grab! Three motors and a remote turn you into a factory robot operator. (level 4 of 5, about 60 minutes, 30 steps)