PowerPod wind speed calculation
Posted: Tue May 26, 2020 3:41 pm
Just bought a PowerPod and it seems pretty accurate once setup, and it got me thinking, this is amazing that we're even able to do this to such an accurate degree as a species.
I was wondering about how it does this and i found out more or less, but one piece of the puzzle was really curious to me! Because im the sort of person that cant sleep if there's an unsolved problem like this, i became more and more interested in how the device works.
Namely, how the device manages to get wind speed from a barometric air pressure sensor. I know its possible with pitot tubes, but there seems to be no tube here! Later revisions have it, and all is clear with them, but not this v1 unit. Is it a static calculation by some formula to convert air pressure (of the wind ramming against the sensor) to wind speed, for example a formula apparently used under hurricane conditions. P = 1014.9 – 0.361451w – 0.00259w2 where w is the wind speed in m/s and P is in mb.
Or is there some Bayesian factor to calibrate it? Basically treating it like a black box, taking an anemometer and placing the device next to it, and measuring the air pressure the sensor reads and correlating it with the measured air speed, finally producing a curve and thus a function by which it can "correlate" air pressure to wind speed? There are some formulas I assume it would have to have 2 air pressure sensors then, one to keep a track of the "reference" air pressure for the current altitude, that is not affected by wind. I guess that would be pretty nifty.
Before i bought it i was a bit skeptical, given that i've known that it just assumes the Cda, and we all know that just by varying the rider posture a little, the rider drag could be +-100w, and even scaling to even worse at higher speeds, but i gotta say it works surprisingly well! Really fine machine, John.
P.S, i had an idea perhaps for a method to modify Cda dynamically during the ride, by having some sort of a tilt sensing HR monitor it could alter the Cda based on if the person is more horizontal or upright. Or maybe make some static values rider can determine, for example if going over 40km/h assume the person is in the drops, or something to that affect. Just throwing it out there...
Best regards
I was wondering about how it does this and i found out more or less, but one piece of the puzzle was really curious to me! Because im the sort of person that cant sleep if there's an unsolved problem like this, i became more and more interested in how the device works.
Namely, how the device manages to get wind speed from a barometric air pressure sensor. I know its possible with pitot tubes, but there seems to be no tube here! Later revisions have it, and all is clear with them, but not this v1 unit. Is it a static calculation by some formula to convert air pressure (of the wind ramming against the sensor) to wind speed, for example a formula apparently used under hurricane conditions. P = 1014.9 – 0.361451w – 0.00259w2 where w is the wind speed in m/s and P is in mb.
Or is there some Bayesian factor to calibrate it? Basically treating it like a black box, taking an anemometer and placing the device next to it, and measuring the air pressure the sensor reads and correlating it with the measured air speed, finally producing a curve and thus a function by which it can "correlate" air pressure to wind speed? There are some formulas I assume it would have to have 2 air pressure sensors then, one to keep a track of the "reference" air pressure for the current altitude, that is not affected by wind. I guess that would be pretty nifty.
Before i bought it i was a bit skeptical, given that i've known that it just assumes the Cda, and we all know that just by varying the rider posture a little, the rider drag could be +-100w, and even scaling to even worse at higher speeds, but i gotta say it works surprisingly well! Really fine machine, John.
P.S, i had an idea perhaps for a method to modify Cda dynamically during the ride, by having some sort of a tilt sensing HR monitor it could alter the Cda based on if the person is more horizontal or upright. Or maybe make some static values rider can determine, for example if going over 40km/h assume the person is in the drops, or something to that affect. Just throwing it out there...
Best regards
