Ping-Pong Anemometer




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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:

Materials and methods

Lets do some physics!

For large 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



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Mini tca bwtca published this design ago