⚖️ Balance See-Saw: step-by-step build

A see-saw that is also a scale. Can one gear beat two?

Archimedes, a clever Greek thinker, once said: "Give me a lever long enough and I can move the world!" A lever is just a bar that rocks on a pivot, like a see-saw. On your see-saw a gear far from the middle pushes down much harder than a gear close in. Hang gears on the pegs and try to make the pointer stand perfectly straight.

  • Level 1 of 5 (super easy)
  • About 12 minutes
  • 10 steps, 30 parts
  • Powered by: Gravity
  • Series: Mechanical Wonders

What you will learn

  • Levers: A bar on a pivot multiplies your push.
  • Centre of Gravity: Keep the heavy stuff low and in the middle and your model won't tip.
  • Torque vs Speed: Slower gears are stronger gears.
  • Axles: An axle is a cross-shaped rod — anything on it turns together.
  • Frames: A frame is a ready-made strong rectangle.

Parts you need

  • 1 × Open frame 5×7
  • 5 × Blue long pin
  • 4 × Split pin block
  • 7 × Red axle-pin
  • 2 × Beam 7
  • 1 × Axle 9
  • 3 × Bush
  • 1 × Beam 15
  • 2 × Black pin (grippy)
  • 1 × L-beam 2×4
  • 3 × Medium gear (24 teeth)

Steps

  1. Lay the 5×7 frame flat.
  2. Push a blue long pin up into the 2nd and 4th holes of the front short end. Press two split pin blocks onto them, one on top of the other.
  3. Do the same on the back short end: two blue long pins and two split pin blocks.
  4. Push a red axle pin into the middle cross hole of each block: the front ones pointing out to the front, the back ones out the back.
  5. Stand a 7-hole beam at the back and press its 2nd and 3rd holes onto the red axle pins. Push the 9-long axle through its 4th hole and slide on two bushes.
  6. Slide the 15-hole beam on by its middle hole. That is the plank!
  7. Push black pins into the 4th and 6th holes of the plank. Press the black L-beam onto them (its corner hole goes on the axle) as a pointer, then add a bush on the fixed axle. Leave the plank free to rock beside it.
  8. Press the front post onto the two red axle pins, sliding the axle into its 4th hole. Push a blue long pin into its 6th hole, pointing back: the "level" mark.
  9. Push three red axle pins into the plank as pegs: two at the back, one at the front.
  10. Hang a 24-tooth gear on each peg.

Play time

Move the gears to different pegs. Can you balance one gear with two? What about three gears on one side? Hint: multiply each gear by how many holes it is from the middle.

Real-world inspiration

Archimedes' law of the lever — https://en.wikipedia.org/wiki/Lever

Build next

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  • 🎯 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)
  • 🐦 Woodpecker Automaton: Turn the handle and the woodpecker pecks: tok-tok-tok-tok! (level 2 of 5, about 20 minutes, 16 steps)
  • 🚧 Parking Barrier Gate: A long striped barrier that lifts with a tiny turn — thanks to a heavy counterweight. (level 2 of 5, about 20 minutes, 9 steps)