The Techno-Teachers go up against The Manic Mechanics to see who can harness the forces of Mother Nature and build a windmill to power a machine crucial to life as we know it — a coffee grinder! One team constructs a conventional fan-bladed windmill, while their opponents go for a vertical-axis Savonious rotor. Quick on-screen sketches reveal which is best for which wind conditions. But a half-hour before the competition, the weather services release a gale warning, forcing one team to clip the blades off their windmill for fear of having them ripped off. But at competition time, the wind doesn't get over 2 miles per hour.

• Helen Czerski
• Robert Llewellyn
• Lisa Rogers