Ping-Pong Anemometer

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Maker/DIY

GPLv3

A free software license that requires that all work based on this must also be free software as in freely remixable and sharable by anyone under the same license but may be used commercially.

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Description

Sphere anemometers are simple devices that use the wind drag force on a sphere
to determine the wind speed by equating the weight of the sphere with the drag
force in a pendulum like configuration. Modern versions of this device use
ping-pong balls. By measuring the angle of deflection of the ball one can
measure the wind velocity.

There are 4 STL's files available with different scales:

m/s (two scales: engraved and 3d)
knots (engraved)
mph (engraved)

There's no need for a conversion table to measure the wind velocity.

The dots on the scale are 5 degrees apart. Note the two vertical dots at
zero angle.

More details here: http://www.diale.org/Ping-Pong-Anemometer.html

Materials and methods

Lets do some physics!

For large Reynolds number (https://en.wikipedia.org/wiki/Reynolds_number) the
drag coefficient for a sphere is about Cd=0.5. The typical mass and diameter of
a ping-pong ball is about 2.7g and 40mm, respectively, and thus with a
density of 0.081g/cm^3

The drag force is

Fd = 0.5 rhoair C_d A v^2

and the weight is

Fg=4 pi/3 R^3 g rhoball

For a given angle of deflection alpha one gets Fd=Fg tan(alpha) and thus

v=8.5524 sqrt(tan(alpha))

So by measuring the angle of deflection of the ball we can measure the wind
velocity.

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Comments

Mini img 20171029 103434tca published this design ago