Rocket Railway
This week's challenge was inspired by the incredible high-speed rocket sleds used by the US Air Force to test aircraft and spacecraft at supersonic speeds without taking to the air.
The teams compete to build superfast trains, but they're not allowed to send power direct to the wheels. So all the usual forms of drive such as chain and sprockets, belt drives and prop shafts are effectively banned.
It's a massive challenge, but the Brum Brums, motor mechanics from Birmingham, and The Aquarium Crew, giant fish tank builders from Weymouth, already have one win under their belts this series.
Find out if the teams are up to the rocket railway challenge >>
