Why are triangles so strong?

A triangle cannot be squished — a square can. Push the corner of a square made of beams and pins and it squashes flat. A triangle keeps its shape no matter what! That is why bridges, cranes and roller coasters are full of triangles.

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Try it yourself

Make a square from 4 beams with grey pins and squish it. Then add a diagonal beam. Now try!

Build it: 24 builds that teach triangle bracing

  • 🛒 Push Buggy: A sturdy buggy with a push bar held up by super-strong triangles. (level 2 of 5, about 15 minutes, 12 steps)
  • 🛻 Bouncy Monster Truck: Four big wheels on four springy shock absorbers. Boing, boing! (level 4 of 5, about 45 minutes, 29 steps)
  • ⏱️ Pendulum Metronome: Give it a nudge: tick… tock… tick. Move the wheel to another hole and count again! (level 1 of 5, about 10 minutes, 9 steps)
  • 🐦 Woodpecker Automaton: Turn the handle and the woodpecker pecks: tok-tok-tok-tok! (level 2 of 5, about 20 minutes, 16 steps)
  • 🌀 Pull-back Diff Racer: A spring racer with a real differential, so it zooms round curves without skidding. (level 3 of 5, about 40 minutes, 23 steps)
  • ⚙️ Clutch-Gear 2-Speed Car: Push the gear lever and a driving ring grabs a different gear: 1st climbs, 2nd races! (level 3 of 5, about 45 minutes, 18 steps)
  • 🎛️ One Motor, Knob Steering: The motor drives, YOU steer — turn the knob as you walk beside it. (level 3 of 5, about 40 minutes, 21 steps)
  • 🔥 Twin-Piston Engine: See inside a car engine: two pistons race up and down in turns! (level 3 of 5, about 40 minutes, 22 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)
  • 🥁 Cam Drummer: Crank the handle and two drumsticks play a beat all by themselves. (level 3 of 5, about 30 minutes, 18 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)
  • 🦾 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)
  • 🔄 Reverse-to-Turn Car: Only one motor — but it can still turn! Drive backwards and the wheels swing round. (level 4 of 5, about 50 minutes, 24 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)
  • 🦾 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)
  • 🏆 RC Racer: A real remote-control car: motor drive, differential, servo steering and headlights. (level 5 of 5, about 75 minutes, 38 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)
  • 🏆 Independent Rally Car: Every wheel on its own springy arm, a differential, universal joints and Ackermann steering. (level 5 of 5, about 90 minutes, 47 steps)
  • 🌐 AWD with Central Diff: All four wheels driven, with a differential in the MIDDLE of the car — like a rally car. (level 5 of 5, about 90 minutes, 28 steps)
  • 🧭 South-Pointing Chariot: Push it anywhere — the pointer keeps pointing the same way. No magnets, just gears! (level 5 of 5, about 75 minutes, 34 steps)

In the classroom

Common engineering questions

How can I try triangle bracing at home?

Make a square from 4 beams with grey pins and squish it. Then add a diagonal beam. Now try!

Which builds teach triangle bracing?

24 MightyCog builds teach it: Push Buggy, Bouncy Monster Truck, Pendulum Metronome, Woodpecker Automaton and Pull-back Diff Racer and more. Start with Push Buggy: 12 steps, about 15 minutes.

Ideas that go with it