Break it, spin it & connect it

We hang weights on the bridges you designed and 3D-printed — and pull until they snap. Strongest-for-its-weight wins.

Each bridge gets mounted on the rig and pulled while a sensor called a load cell — basically a digital scale — reads the exact force at the instant it breaks. Your score is the breaking force ÷ the weight, so a light bridge that holds a lot can beat a heavy one. We guess the breaking force out loud before every pull (your guesses get sharper all session — that's literally what engineers do). One newton is about the weight of a small apple, so "snapped at 250 N" means it took about 250 apples pulling at once.

We printed fidget spinners in one piece — bearing and all — then dissolved away a special plastic to set them free to spin.

A 3D printer can't print on thin air, so it lays down temporary scaffolding called support. Ours was printed in PVA — a plastic that dissolves in warm water. Drop the print in, the support turns to slime and vanishes, and you're left with a clean spinner whose center bearing — a ring of tiny balls — spins freely. Those little balls turn rubbing-and-sliding into rolling, which is hundreds of times easier, so a good spinner just keeps going and going.

We keep driving the robot cars you built — and find out how the remote talks to the car: invisible radio.

Every robot car is run by a micro:bit, and every micro:bit has the exact same little antenna — a zig-zag of copper printed right onto the board — and the exact same radio. That means out of the box, they can all hear each other. So how does your remote drive your car and not your neighbor's? You pick a channel (a "radio group") — just like two walkie-talkies have to be set to the same channel to talk. Same antenna, same radio, different channel. And because radio travels at the speed of light, your steering message beats across the room the instant you press the button.

You put together a real working Bluetooth speaker — no soldering — then paired a phone and played your own song through it.

Inside is a coil of wire (an electromagnet) sitting next to a magnet and glued to a paper cone. Your music is electricity that wiggles back and forth; it flips the coil's magnetism, the coil gets shoved like a piston against the magnet, and the cone punches the air — and air you can feel is sound. Faster wiggle = higher pitch; bigger push = louder. The Bluetooth part is a tiny radio: your phone turns the song into 1s and 0s and beams them over as a short-range radio wave the speaker decodes and plays.

Using nothing but sugar cubes, you built an arch bridge that holds itself up with no glue at all.

You stack the cubes over a curved form and drop the keystone into the middle — then slide the form away and… it stands! An arch carries weight by squeezing: each cube pushes on its neighbors, so pressing down on the top makes the whole arch press together tighter, not fall apart. That's the secret of a stone arch — gravity is what holds it together, so it needs no glue and no nails.