AeroPod, PowerPod and Newton

I have been driving my powerpod for a few months now. A good calibration seems difficult. The watts that are displayed do not always seem to match the effort I make.

Recently done a new calibration according to the booklet. There was hardly any wind during the calibration and the sensors were found well. Before I did the calibration, I had driven a few miles, so that the powerpod could re-calibrate itself from last time. Also because I was in a place where I could perform a calibration without traffic and other crowds. In addition, the air pressure and temperature would then also become reality.

Things seemed to go well, but I doubt the wind scaling that appears. Depending on the various O&B rides of the past months, the wind scaling varies from 2.3 to 2.9. This seems very high to me when I read other comments on this forum.
In particular when there is strong wind, the watts deviate greatly. This is true with a high wind scaling, but in my opinion it does not match the effort I make.

Attached an O&B ride from yesterday about 9km. Would you like to check this? The wind was around 10km / h (6.25 m / ph) from WNW direction. The first 2 km I drove south, then 2 + km to the east. Made a turnaround and back to the starting point. Look for the map: https://drive.google.com/file/d/1BVUE7N ... sp=sharing
I have been in the same gear all the time and have kept the speed around 30 km / h.
The difference in wattage at the start of the ride compared to the end of the ride is great, without me thinking that I have supplied so much extra power

The position of my powerpod is in the middle of my front stem. Mounted on a go-pro mount for the Giant Conduct system: Like this: https://images.app.goo.gl/rhc2tPiP5uotmmzu6
My situation: https://drive.google.com/open?id=1KBMLc ... SKJjITMPAl
My body weight = 69 kg
Weight of bike & Gear = 14.5 kg
I think my CdA at 0,35 and Crr at 0,0037 are OK.

Attached my O&B ride of 9 km.
Also included my combined .ibr file from my 6km warm-up, 9km O&B and 26km workout.
I drove these three pieces one after the other without a change of wind and without traffic.

I would like to hear your opinion about the calibrated wind scaling.

Another thing: The measured height differs in many journeys. I usually live and drive at sea level (0 meters), but the powerpod think I am about - / - 50 below sea level. The actual height profile also corresponds reasonably well with reality. I can restore it every trip, but can I do it differently?
When I try out the 'Set atmospheric pressure' option, I get an error message: Error 18000 occurred at URL Get HTTP Document:
Invalid protocol
Possible reason: Internet Toolkit: Invalid URL Protocol.
Do I need this option, or can I set the standard altitude / air pressure elsewhere?

Did you buy this unit second hand? It was manufactured about 3 years ago.

You can correct the elevation in Isaac, "Analyze/Analyze Device Settings..."

The starting elevation is controlled by barometric pressure (i.e. weather). It has no effect on calculations.

I don't see any obvious problems with your calibration. Wind factor can vary significantly from bike to bike, depending on the actual location of PP on the bike

Watts variation follows HR variation closely. I think you're fine.

Dear John,

Thank you for your response. Indeed, my unit is second-hand. Is it a problem that it is now 3 years old? How reliable are the sensors in the unit after 3 years?

Thank you for your response regarding the wind scaling. I will drive this calibration in the coming period and experience it.

gjmeer wrote: ↑Tue Sep 03, 2019 5:22 am Dear John,

Thank you for your response. Indeed, my unit is second-hand. Is it a problem that it is now 3 years old? How reliable are the sensors in the unit after 3 years?

Thank you for your response regarding the wind scaling. I will drive this calibration in the coming period and experience it.

Just curious about its vintage...sensors should be OK

John,

I get this same problem whenever I try to adjust atmospheric pressure. I've tried several nearby Weather Underground Station IDs, but all give the same error message. My starting elevation is always about 200-400' too low, and it is frustrating to have to adjust it in the Analyse Device Settings screen after every ride. Do you have any suggestions for eliminating this Error Message?

Also, it appears that the barometric pressure reading does have some measurable affect on power measurement, since atmospheric pressure goes down as altitude goes up. I've noticed (generally small) changes in the average power reading after I've altered the Starting Elevation setting.

Any help would be appreciated.

- Sam Byassee

Byassee wrote: ↑Wed Nov 06, 2019 1:17 pm John,

I get this same problem whenever I try to adjust atmospheric pressure. I've tried several nearby Weather Underground Station IDs, but all give the same error message. My starting elevation is always about 200-400' too low, and it is frustrating to have to adjust it in the Analyse Device Settings screen after every ride. Do you have any suggestions for eliminating this Error Message?

Also, it appears that the barometric pressure reading does have some measurable affect on power measurement, since atmospheric pressure goes down as altitude goes up. I've noticed (generally small) changes in the average power reading after I've altered the Starting Elevation setting.

Any help would be appreciated.

- Sam Byassee

This is a bit of a complicated thing to explain, but here goes:

1) Our products do not measure wind speed; they measure differential air pressure [wind port pressure - static pressure].

2) Air pressure readings, not wind speed readings, are used in the firmware to determine the aerodynamic portion of opposing force/power. Among other things, this means that changes in atmospheric pressure, due either to elevation or weather changes, are 100% accounted for in our wind sensor.

3) In Isaac, wind speed readings in the ride file are used to backwards-calculate aerodynamic forces/power.

4) While it is true that barometric pressure affects wind speed measurements, barometric pressure does not affect differential pressure measurements. So, in the FW it is not relevant if absolute elevation readings are exact

5) Barometric pressures recorded by the baro sensor are correct, although their conversion to elevation readings may be somewhat incorrect. This is because barometric pressure at a given elevation can change due to weather changes

6) Isaac calculations might show a slight change in power levels if the elevation is changed. Generally this change is extremely minor.

7) In any event, the power computed on the device does not depend on accurate absolute elevation measurements.

8) There is no way to override in the FW the elevation setting. Again, baro setting at a given elevation will change from day to day, and correcting the elevation in the FW will have no effect on power accuracy.

Thank you, John. I very much appreciate your detailed explanation.

By the way, what is the purpose of the Set Atmospheric Pressure function, and what causes the consistent error message when attempting to use it?

Thanks,

- Sam

Byassee wrote: ↑Wed Nov 06, 2019 9:24 pm Thank you, John. I very much appreciate your detailed explanation.

By the way, what is the purpose of the Set Atmospheric Pressure function, and what causes the consistent error message when attempting to use it?

Thanks,

- Sam

This is a hold-over from very old days. It no longer functions... :=(

That explains it. Thanks.

- Sam