My anemometer...so far

[motoman465]

Hey all,

I decided to try and build an anemometer mostly from things I had lying around the house.  I used a tailpipe adapter, JB Welded the motor from a hard drive to it.  I then used plastic knives and one half of plastic easter eggs for the cups.  I bought a cheap bicycle speedometer from Wally World.  I just wanted to get some input from the board because everyday I am awed by the work that everyone does.  Without further delay, here is what I have come up with.

Todd

P.S.  I hope the pics were resized correctly

[Warrior]

Looks good so far. I choose to make mine with a 10" diameter to measure really low winds. The problem I had was that the bike speedo didn't have a large enough wheel diameter to match the speed of the cups. Remember that the larger diameter the slower it turns (your's looks pretty large).

To solve the problem I glued a small magnet on each of the spokes, and then calibrated using my car's speedo.

Good Luck,

Warrior

[ghurd]

Put 2 magnets on it, 180 deg apart, set the circumference at half.

Most speedometers don't need much magnet to function properly.

G-

[ruddycrazy]

Hiya Guy's an Gal's,

                     On reading the microchip forum I came across a thread where they talk about making an anemometer and one thing poped up thats surprised me is that the cup style run at aprrox 1/3 of the wind speed. below is a wiki extract i copied from that post.

According to Wikipedia:

quote:

Unfortunately, when Hooke first designed his anemometer, he stated that no matter what the size of the cups or the length of the arms, the cups always moved with one-third of the speed of the wind. This result was apparently confirmed by some early independent experiments, but it is very far from the truth. It was later discovered that the actual relationship between the speed of the wind and that of the cups depends very largely on the dimensions of the cups and arms, and may have almost any value between two and a little over three. This had the result that wind speeds published in many official 19th century publications were often in error by nearly 60%.

Now I've made my own 3 cup anemometer and surprisingly by fluke I ended up with a raduis of 58mm from the centre to the centre of the cup, in that foum they mention the raduis should be 56mm or 188mm diameter to follow the 1/3rd rule.

Now just for my curiosity how many people here knew that 1/3rd rule using a cup anemometer?

Cheers Bryan :{)

[coldspot]

motoman465-

Nice !

Same bike speedo I have and am using but,

I used our hosts cups.

Can't remember what number I used for wheel dia.

I think that the cups can only handle so much wind speed and fail to turn any faster that about 14-16 mph.

I'd really like to know if the one third thing is true or not.

[wdyasq]

I did a bit of research and it seems the 'rule' set by Hooke could have as much as 60% error. And yes, he did state that and it has been taken as the truth. This causes many of the old wind reports to be less reliable than thought. Probably the root of all global warming..... Or, the great new Ice Age they talked about 30 years ago. I'm just glad I was here to contribute to the problem or the solution and that I am that powerful.

Ron

[asheets]

I did...  but they drilled it into my head in meteorology school

BTW...  fairly decent design there, though to keep consistant with NWS standards I'd shorten the arms a bit...

[alancorey]

Do you know where to find NWS standards for this online?

I thought I read somewhere that the NWS had decided that conical cups were better than hemispheres, but I don't know where I saw that.  A few searches on the NOAA web site and using Google didn't get me any confirmation or more details.  My impression was that the change to conical was fairly recent.

  Alan

[asheets]

Cups have been NWS standard since about 1975, according to my instrumentation textbook.  SOmewhere in a previous post I wrote out the current anemometer design standards (quoting from a newer version of the same book).

[asheets]

Here's the pertinent quote from my previous post.

"OK, here's the poop from "Instruments for Physical Environmental Measurements, Volume 1, 2nd Edition" by Wang and Felton, 1983, pp160-170 (this was my instrumentation textbook in 1991, so things don't change all that much).

The specs are:

*3 cup, for uniform torque balanced with a minimum of resistance

*semi-conical cup instead of hemispherical cup for rigidity

*beaded, rather than plain, cup edges to reduce turbulence effects

*a minimum of size and mass

*a linear relationship between tangental rotation and windspeed throughout the measurement domain, even if the domain is limited as a result.

Depending on the measurement domain, 2 different configurations are noted:

*7.5cm arm length with 5cm cups, for cutin speed of .5kts -- largely for research

*45cm arm length with 10cm cup with cutin speed of 5kts (domain limited to 4.5 to 47kts) -- NWS standard model manufactured by either Climet Instruments or Belfort Instruments."

[alancorey]

Thank you.  I guess I won't be buying any plastic Easter eggs this year.  :-)

  Alan (another one)

[asheets]

Actually, I've built plenty of anemometers with easter eggs, Leggs containers, whatever, over the years...  I haven't had too much problems with the wind regimes that are typical for the Front Range in Colorado...

[motoman465]

Thanks for all the comments!    With the light that you shed on the 1/3 rule, should I shorten the arms?  How many magnets should I use?  The speedometer that I have has calculations to use for different size bike wheels.  I guess putting it together was the easy part.  Now, I need input from you again as to magnet placement, number of magnets, etc.  Thanks!

Todd