🌬️ Oscillating Fan: step-by-step build

A desk fan that turns its head left and right all by itself!

Have you ever watched a desk fan slowly turn its head from side to side, as if it is saying "no, no, no"? There is only one motor inside! The motor spins the blades fast. At the same time a worm gear on the motor axle turns a gear 24 times slower, and that gear has a little crank on it. A beam from the crank is pinned to the base, so as the crank goes round it pushes and pulls the whole head on its turntable. That trick — beams and pins turning spinning into swinging — is called a linkage.

Level 3 of 5 (medium)
About 40 minutes
18 steps, 53 parts
Powered by: Motor
Series: Mechanical Wonders

What you will learn

Worm Gear: The Lock: A worm gear turns a gear super slowly — and never slips back.
Linkages: Beams joined by pins change one motion into another.
Turntables: A turntable lets a whole model spin round.
Electric Circuits: Electricity flows from the battery, through the motor, and back.
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

📡 Spinning Radar: A motor-driven radar dish that sweeps round and round on a turntable — with a blinking light. (level 3 of 5, about 25 minutes, 15 steps)
🏗️ 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)
🦀 Lazy-Tongs Grabber: Squeeze the handles and the criss-cross arms shoot out to grab things far away! (level 2 of 5, about 20 minutes, 11 steps)

Parts you need

1 × Open frame 5×11
4 × Blue long pin
2 × Split pin block
3 × Red axle-pin
4 × Beam 5
1 × AA battery box
13 × Black pin (grippy)
1 × Open frame 5×7
2 × Long pin-axle block
2 × Axle 2
1 × Axle joiner
1 × M motor
1 × Axle 7
4 × Half bush
4 × Bush
1 × L-beam 2×4
1 × Axle 4
1 × Worm gear
4 × Medium gear (24 teeth)
1 × Axle 5
1 × Turntable

Steps

Lay the 5×11 frame flat, long side facing you. This is the base.
Push blue long pins up into the 1st and 3rd holes of the base's back side and press two split pin blocks onto them, one on top of the other.
Push a red axle pin into each block, pointing out the back, and press a 5-hole beam onto them, standing up.
Stand the AA battery box behind the base with its left flap against the post, and push two black pins through the post's 3rd and 4th holes into the flap.
Fan head: lay a 5×7 frame flat. Push black pins up into the 1st and 3rd holes of its right-hand side and press a long pin-axle block onto them.
Push black pins up into the 5th and 7th holes of the same right-hand side and press a second long pin-axle block onto them.
Push a 2-long axle into the block's cross hole, pointing left, add a yellow axle joiner, and push a red axle pin into the joiner, pin end out.
Lay the M motor on the frame, output pointing forward, and press it onto the red pin: it goes into the round hole just below the orange cross. Push a 7-long axle into the motor's cross and slide on a half bush and a bush.
Push a black pin into the motor's front hole beside the orange cross, on the side facing the middle of the frame. Press the black L-beam onto it: short arm standing up, long arm lying along the frame. Push a 4-long axle through the second block's cross hole and the L-beam's end hole, and add a bush.
Fan: slide the worm gear, a bush, a half bush and a 24-tooth hub onto the front of the axle. The bushes squeeze the worm so it stays right over the gear.
Push two black pins into the hub's holes above and below the axle and press a 5-hole blade onto them, standing up.
Push two blue long pins into the hub's side holes, right and left of the axle, and press on the second blade, crossways.
Hold a half bush and a tan 24-tooth crank gear under the middle hole of the frame's right-hand side and push a 5-long axle up through them and the frame. Put a bush on top.
Slide a 24-tooth gear onto the top of the axle, meshing with the worm, and lock it with a half bush.
Turn the head over and push two black pins into the 2nd hole of the frame's left side and the 2nd hole of its back side, sticking out underneath. They will plug into the hub.
Put the turntable in the middle of the base. Push a 2-long axle into it and slide a 24-tooth gear onto it as the hub.
Put the fan head on the turntable: press its two black pins into the holes of the hub gear. Slide the orange switch on the battery box!
Push a black pin down into the tan crank gear, one hole from its middle, and another into the 10th hole of the base's back side. Join them with a 5-hole link.

Play time

Switch on and feel the breeze sweep across you. Flip the switch: the blades spin the other way — does the head still swing? Move the base pin one hole along: does the head swing more or less?

Real-world inspiration

Oscillating fan gearbox (worm + crank linkage) — https://en.wikipedia.org/wiki/Mechanical_fan#Oscillation