There's some interesting projects over at Matthias Wandel's. Potato cannons, marble machines, and many wood projects including his homebrew pipe organ.

I also built a pressure regulator for the organ. This regulator consists of a simple bellow, about 20cm x 20cm, but with only 3 cm of travel. This bellow was not so much intended for a reservoir, but more as a pressure sensor. When the bellow falls, the valve at the bottom of the bellow opens further to let more air from the blower in, thus maintaining the pressure. The pressure is controlled by piling various amounts of rocks on top of the bellow, as well as by a special foot pedal which can be used to apply extra pressure to the bellow for 'expression'.

Anyone who can expense legos (see pager rotating machine) must have a finely tuned sense of fun and discovery.

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