Bridges: Why Triangles Are Strong

Golden Gate Bridge. Eiffel Tower. Construction Cranes. They are all made of Triangles. Why not squares? Squares stack nicely. The answer lies in Geometry and Force.

The Wobbly Square

Imagine a square frame made of 4 sticks and 4 hinges. If you push on the side (Shear Force), the square collapses into a rhombus (parallelogram). A square has no inherent structural stability. It relies entirely on the strength of its joints (the corners).

The Rigid Triangle

Now imagine a triangle made of 3 sticks and 3 hinges. Push on a corner. It doesn’t move. To change the shape of a triangle, you physically have to break one of the sides (Compression or Tension). You have to snap the wood.

• The Triangle is the only polygon that is geometrically rigid.

Trusses in Robotics

In FTC, we have a weight limit (42 lbs). We can’t build our robot out of solid steel blocks. So we use Trusses (or “Skeletonizing”).

• C-Channel: The aluminum beams we use (like GoBilda or REV) are punched with holes.
• Isogrid: Advanced teams use CNC mills to cut triangular patterns (“Isogrid”) into solid aluminum plates.
  • Result: It removes 80% of the weight but keeps 90% of the strength.

The Chassis Frame

When we build a robot chassis, we cross-brace it. If we just build a rectangle drivetrain, and the robot hits a wall, the frame might “parallelogram” (twist). By adding a single diagonal cross-brace, we turn the rectangle into two triangles. The frame becomes invincible. Civil Tech meets Robo Tech.