Hi all,
I have had yet another idea for wind speed and direction sensing. This time more conventional but with a twist. I need help evaluating and designing it.
Starting point: one of those really cheap Maplin/Fine Offset 3 cup anemometers. Click here for inside pictures about 2/3 way down the page.
But this only measures wind speed, right? Well, I discovered someone invented a way to use them to measure direction also. I think his name is Derek Weston, and he called it a Rotorvane Anemometer. Unfortunately his original web pages describing it have disappeared, but here is one of several DIY versions based on it.
The technique would involve modifying just one of the 3 cups, adding a small fin to it. This would deliberately "unbalance" the anemometer, so that it does not spin with a constant speed, even in a constant wind. As the extra fin sweeps upwind, the anemometer slows down slightly. As it then sweeps downwind, it speeds up slightly. Overall the speed of rotation is about the same, but within a single rotation there is variation.
To use this variation to resolve the wind direction, it will be necessary to measure the rotation speed in several parts (at least 3 I guess) within a single rotation. I am thinking that could be achieved using the Maplin unit by replacing the reed relay pcb with one containing 3 or more hall effect sensors at 120 degrees to each other. The time taken for the cups to rotate each 120 degrees could the separately measured. The maths of resolving these 3 periods into a compass direction would be too much for a picaxe alone, so would need an i2c maths chip or pass the periods to a PC or Rasp Pi for calculation.
Thoughts? Suggested hall effect sensors?
Thanks!
Paul
I have had yet another idea for wind speed and direction sensing. This time more conventional but with a twist. I need help evaluating and designing it.
Starting point: one of those really cheap Maplin/Fine Offset 3 cup anemometers. Click here for inside pictures about 2/3 way down the page.
But this only measures wind speed, right? Well, I discovered someone invented a way to use them to measure direction also. I think his name is Derek Weston, and he called it a Rotorvane Anemometer. Unfortunately his original web pages describing it have disappeared, but here is one of several DIY versions based on it.
The technique would involve modifying just one of the 3 cups, adding a small fin to it. This would deliberately "unbalance" the anemometer, so that it does not spin with a constant speed, even in a constant wind. As the extra fin sweeps upwind, the anemometer slows down slightly. As it then sweeps downwind, it speeds up slightly. Overall the speed of rotation is about the same, but within a single rotation there is variation.
To use this variation to resolve the wind direction, it will be necessary to measure the rotation speed in several parts (at least 3 I guess) within a single rotation. I am thinking that could be achieved using the Maplin unit by replacing the reed relay pcb with one containing 3 or more hall effect sensors at 120 degrees to each other. The time taken for the cups to rotate each 120 degrees could the separately measured. The maths of resolving these 3 periods into a compass direction would be too much for a picaxe alone, so would need an i2c maths chip or pass the periods to a PC or Rasp Pi for calculation.
Thoughts? Suggested hall effect sensors?
Thanks!
Paul
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