Using Arduino with propellers

What sketch would you use to get the results of the number of turns a Brush-less dc 5v motor will turn every minute.

Tachometer code might be of use, but you may need to figure out how to detect a rotation.

5V brushless motor? What an odd voltage for a motor, they are usually on the 3/6/12/24/36/48V series (if sensored) or a whole number of LiPo cells (for RC style).

Do you have a link for this mysterious beast?