Bull Bear Seesaw

A desk seesaw with a brass-coloured gear train on show. Tip it, and whichever animal rises turns its face: the bull breaks into a grin, the bear bursts into tears. Bring it back to level and both go back to a straight face.

The seesaw tipped bull end up: the green bull grins, the red bear below it keeps a neutral face, brass gears between them.

One session on the desk

Open

Beam level, both faces neutral. Nobody is up, nobody is down.

Rally

Press the bear end down. Once the bull has risen 4.5°, its face starts to turn, and by the 18° stop it has come round a full 180° to a grin.

Under the hood

With the front rail faded out: a pinion rolls around a fixed sector as the beam tips, and every degree of tilt becomes 6⅔° at the gears under each animal.

Pullback

Back to level, and the same gear teeth turn the grin back to neutral. It's driven all the way back, not left to drop back on its own.

Sell-off

Tip it the other way and the bear rises. Its face turns 180° to the crying side: a frown and two blue tears. The bull, now low, keeps a straight face.

Close

Level again, both neutral. Only the animal on the way up ever changes face.

From a tilt to a turned face

There's no motor and no spring. Your hand tips the beam, and six stages of gearing turn that tilt into a half-turn of the face on the rising end.

Close view of the gear train under the bull with the front rail faded: the large compound gear, an idler, the output gear and the flip gear that turns the grinning face.
The bull's side of the train at the stop, front rail faded out.

  1. Fixed sector

    A 40-tooth sector is keyed to the stand and never moves.

  2. Rolling pinion

    An 18-tooth pinion on the beam rolls round the sector as you tip it, and spins the 54-tooth compound gear it is fixed to.

  3. Idlers and outputs

    18-tooth idlers carry the turn out to each end. By the output gears, one degree of tilt has become 6⅔°.

  4. One-way coupling

    A 28-tooth coupling with most of its teeth left off. For the first 4.5° it slides past; then only the rising side's teeth catch its 14-tooth flip gear. The low side stays locked.

  5. Miter pair

    Two 16-tooth miter gears turn the motion through 90° onto an upright shaft inside the head.

  6. Two-sided face

    The shaft turns the face block 180°, finishing on the grin or the tears as the beam reaches its 18° stop.

Three positions, three faces

Bull end up: the bull grins with a white tooth band, the bear stays neutral.
Bull end up. The bull grins. The bear stays neutral.
Beam level: bull and bear both show neutral faces.
Level. Both neutral.
Bear end up: the bear frowns with two blue tears, the bull stays neutral.
Bear end up. The bear cries. The bull stays neutral.

Put one on your desk

Size
9.3 × 4.5 × 6.7 in
Beam
8.7 in, tips ±18°
Printed parts
45
Weight
14.9 oz
Material
PETG
Print time
39.3 hours

The motion on this page is computed from the CAD model's own gear train.