2008-01-10: Mike Teal and I built an anemometer.

Can you guess what the cups are made of? The yellow arms are three swizzle sticks for Flor de Caña rum; I got several dozen of them for a few pennies the last time I was in Costa Rica, and the "angular velocity sensor" was cannibalized out of an old cassette tape recorder. When the wind spins it, the motor acts as a generator and produces a measurable voltage, proportional to its speed which is proportional to the wind speed.

In the final version, an upside-down plastic cup mounted on the axle under the yellow part, protects the "angular velocity sensor" from moisture.

We calibrated it by "mounting" it on the car roof and driving at 20, 40, and 70km/h and measuring the voltage to (a) check that it was linear with speed (it is) and (b) to get the slope and x-intercept of the voltage → windspeed equation.

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