Occasionally I get that I-wish-I’d-thought-of-that feeling. And these cunning little tins produce exactly that. The lid is firmly attached until by pressing the centre of the lid, the lid suddenly snaps down. It moves a millimetre or so and, by distortions in the metal I never expect to understand, the clips around the edge spring apart allowing the lid to be lifted away.
I measured the force with the post room scales and it turns out to be an effortless-feeling 2.2kg (21.5N for pedants). Similarly 1.2kg applied sideways to the clips snaps the top back on. Neat, simple, functional. Admittedly, some work better than others, and a few are barely bistable, but that does not detract from the essential brilliance of the idea. How anyone ever invented this mechanism, let alone got it to work with so little movement and so little force, is beyond me. If there are mechanisms or circuits that similarly inspire you? Get in touch, via the Comments field below. Alice (special contributor) By the way, the title An Engineer in Wonderland was inspired by the 1967 book ‘The Engineer in Wonderland’ by Professor Eric Laithwaite: champion of the linear induction motor.