Anemometer - Wind Speed
This device measuring the wind speed by spinning magnets that are attached to the bottom of the shaft.
Please check out this instructable for assembly information:
http://www.instructables.com/id/Air-Pressure-Rocket-Launcher-System/step3/Anemometer-3D-print/
Wind tunnel test:
https://www.youtube.com/watch?v=L9_lE5_IwN8