Build a chain reaction machine with at least 5 steps that travels at least 2 metres. The final action must pour water into a target cup without spilling. Once you trigger the first step, no one can touch it — the machine runs itself.
This is the most planning-intensive challenge of the series. Each step must trigger the next, which means teams think about sequencing, energy transfer, timing, and reliability. The Presentation is dramatic: trigger the first step and the whole room holds its breath.