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femoral

Weather station

by femoral Sep 2, 2013
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I'm putting one of these together and and thought I'd throw this out there for anyone else wondering how to calculate the wind speed.

From what I can tell the diameter of the anemometer is 130 mm and from that you can calculate the speed (not taking into account for drag that of course). Since we know the diameter is 130 mm then we can calculate the circumference to determine the distance traveled in one revolution.

Circumference = Pi x diameter = 3.14159 x 130 = 408.41
Convert that to inches = 408.41 / 25.4 = 16.079 inches

Now we can calculate Wind Speed in mph = RPM x 16.079 x 60 / 5,280
Calculate Knots = mph x 5,280 / 6,080

Example: If you count 100 revolutions per minute (rpm) then our formula is:
100 x 16.079 x 60 / 5,280 = 18.27 mph
or
100 x 16.079 x 60 / 6,080 = 15.87 knots

You cannot not take drag into account since drag is what makes this thing rotating. For determining the wind speed you need to solve equations of motion which come from analysis of drag forces on the cups: bigger when wind blows on the inside of the cup, smaller when on the outside. More detailed info is here: https://www.eas.ualberta.ca/jdwilson/EAS327/eas327wind.html (ctlr+f cup anemometer) yet it is only for simplified case with two-arm anemometer, however still shows the correct way of reasoning.

which hall sensor are you using? something digital like a ss41f paired with a neo magnet? any idea of the tipping bucket volume?

What bearings and threaded rod did you guys use?

sorry for the very late answer...added the info to the description

I'm in the process of building a weather station, and I like your compact anemometer. I was curious about the circuit you designed to measure the speed of the rotation. I understand you're using a Hall latch, but is there anything you do to the rod so that it triggers the latch? From the picture, it seems that you have just a threaded rod over the hall sensor, and I was wondeirng if that's all you used to get a reading.

Also, do you use the same circuit for both the anemometer and rain gauge?

Thanks!

You need to stick a magnet to the rod and measure how often it passes the sensor in one minute to get the rpm of the rod.
There is probably a way to use the area of the scoops, the length of the arms and the rpm reading to calculate the wind speed...

I`m developing something on this way too. get in touch

i printed and the 608z bearings i had were too big for the box to close....

I would really like to use this with an arduino.

I'd like to try this anemometer.

Is there a file for the part holding the table tennis ball pieces?

Do you think it'd work with http://www.thingiverse.com/thing:19439http://www.thingiverse.com/thi... ?

Anemometer Cups
by rlittin

Oh yeah there is one. I forgot to upload it. I'll search for the 3D object.
The other one you postet should also work. You only need to drill out the hole in the middle big enouth.
The one we made needs the ping pong balls like seen in the picture.