Working with Velocomp Aero - some fundamental questions

[Bergauf]

Dear Velocomp team,

I have just reactivated my AeroPod to do aero tests for time trialing, but lack some understanding as to how the new Aero Windows app deals with the data. I will try to summarize how I understand the data processing at the moment - maybe there is already some misunderstanding on my part - and will add a couple of question.

Thank you very much for your support!

Setup:
I test in profile 4 with a roadbike and a TT bike. Of course I change the settings in AeroPod when I move to another bike, and before testing I do a fresh calibration ride. If I am not mistaken, the calibration ride basically does two things: it calibrates the tilt of the unit and it calibrates a scaling factor that is needed to convert the measured differential air pressure into air speed, and then (by comparison to the ground speed from the speed sensor) into wind speed.

Is it correct that the new Windows App gets the raw data from AeroPod so that profile values like system weight or Crr can be changed afterwards without impairing the data accuracy?
Does setting the FTP in the profile have any influence currently?


Test route and conditions
I do my tests on an L shaped out and back course (4 km per 'lap') that sees very low traffic and is as flat as it gets around here as I do not have a suitable loop for testing. Both legs of the 'L' are approximately 1 km long and when I turn from one leg to another I stop pedaling for a couple of seconds but do not have to break. I ride both legs of the L to get more data and, in case, of wind, I could potentially cut out and disregards the leg with more crosswind.

Would it be better in your experience to just test on one of the parts (2 km out and back in a straight line)?

Wind gusts and strong wind should be avoided. Especially cross wind can impair the data quality since it is not directly measured. Currently, I do not have a pitot tube (my AeroPod was a bought as a PowerPod) which increases the sensitivity to cross wind.

How much difference does the Pitot tube make? I shy away from the high shipping costs to get one to Europe.

Data processing on the ride

While testing in profile 4, aeropod internally integrates the measurement for each lap. Until the lap button is pushed, it calculates an average CdA for each test, so the displayed number changes gradually and for longer test laps with in constant conditions should not change much towards the end of a test.

Data visualization after the ride

When I download a file from the device to the windows app, there is three different parts that show data: the graphs, the lap data (bottom left), and the advanced stats (top left). Here is where I have some confusion.

After initially loading the file, the lap table (bottom left) shows the integrated CdA values from the ride.
How is the CdA number calculated that is shown in the advanced stats? If I mark one of the laps there is a big gap between both numbers. I would have expected both to be show the integrated or averaged value.
What exactly is shown in the CdA graph? I guess not the integrated CdA that was shown during the ride but rather a calculation of the CdA along each lap. So its average value per lap should represent the lap CdA.

Example data

I will attach a test file with three laps done with a TT bike with only changes in body and head position. Head up relaxed position, head down agressive position, head down agressive position with different hands position. The file was modified with the "Switch profile After-the-ride" feature to correct the Crr value to 0.003.

Data after switching the profile
Lap Table Advanced Stats (when lap is selected)
L1 0,215 0,233
L2 0,195 0,212
L3 0,205 0,212

Data after using the "Apply analyzed CdA" feature
Lap Table Advanced Stats (when lap is selected)
L1 0,215 0,222
L2 0,191 0,202
L3 0,194 0,202

TT_Test_Haltung_2024_07_08_1909_13_km_CHANGED_PROFILE.ibr

(115.38 KiB) Downloaded 164 times

[Velocomp]

Do you have a .FIT file from your Garmin from this ride? If so please post it; it will help me understand the test route you are riding.

[Bergauf]

Thanks for the quick reply. Fit file is attached.

16308718753.zip

(35.88 KiB) Downloaded 165 times

[Velocomp]

I merged your FIT file into your AP file.

Lots of comments:

1) Your test route has a sharp "elbow" in it. This is not good for testing:

Screenshot 2024-07.png (184.52 KiB) Viewed 7259 times

A test route should either a straight out-and back (such as the horizontal portion only of your test route):

Screenshot 2024-07-13 .png (318.03 KiB) Viewed 7259 times

The "horizontal" O&B route is about 1.33 miles long--this is long enough for CdA testing

2). You should ride for at least 5 minutes before beginning any testing--this recalibrates everything. Your lap 2 (your first CdA test) ends at 6:53; this lap cannot be used for CdA measurement.

3) So, you have two laps where CdA test results can be counted: laps 3 and 4.

4) For each test configuration (head up, head down, head down with changed hand position), you should do at least 3 laps per configuration. You did one lap for each; this is not enough to discern fine changes.

At the start of a test, click the lap button. Ride out, turn around, and when you return to exactly the start point, click the button again. If you want ride a bit farther down the road to turn around; then, when you reach the start point (for the next measurement of your test), click the lap button again. Repeat this for each test of your configuration.

I will make other comments in the next post.

[Velocomp]

Dear Velocomp team,

RESPONSES BELOW IN CAPS

I have just reactivated my AeroPod to do aero tests for time trialing, but lack some understanding as to how the new Aero Windows app deals with the data. I will try to summarize how I understand the data processing at the moment - maybe there is already some misunderstanding on my part - and will add a couple of question.

Thank you very much for your support!

Setup:
I test in profile 4 with a roadbike and a TT bike. Of course I change the settings in AeroPod when I move to another bike, and before testing I do a fresh calibration ride. If I am not mistaken, the calibration ride basically does two things: it calibrates the tilt of the unit and it calibrates a scaling factor that is needed to convert the measured differential air pressure into air speed, and then (by comparison to the ground speed from the speed sensor) into wind speed.

CORRECT

Is it correct that the new Windows App gets the raw data from AeroPod so that profile values like system weight or Crr can be changed afterwards without impairing the data accuracy?

CORRECT
Does setting the FTP in the profile have any influence currently?

NO


Test route and conditions
I do my tests on an L shaped out and back course (4 km per 'lap') that sees very low traffic and is as flat as it gets around here as I do not have a suitable loop for testing. Both legs of the 'L' are approximately 1 km long and when I turn from one leg to another I stop pedaling for a couple of seconds but do not have to break. I ride both legs of the L to get more data and, in case, of wind, I could potentially cut out and disregards the leg with more crosswind.

Would it be better in your experience to just test on one of the parts (2 km out and back in a straight line)?

YES; SEE RESPONSE IN PREVIOUS POST

Wind gusts and strong wind should be avoided. Especially cross wind can impair the data quality since it is not directly measured. Currently, I do not have a pitot tube (my AeroPod was a bought as a PowerPod) which increases the sensitivity to cross wind.

How much difference does the Pitot tube make? I shy away from the high shipping costs to get one to Europe.

IF YOU CAN AVOID HIGH WINDS THEN I THINK YOU'RE OK. PLEASE POST MORE RIDE FILES FOR ANALYSIS (SEE PREVIOUS POST)

Data processing on the ride

While testing in profile 4, aeropod internally integrates the measurement for each lap. Until the lap button is pushed, it calculates an average CdA for each test, so the displayed number changes gradually and for longer test laps with in constant conditions should not change much towards the end of a test.

CORRECT

Data visualization after the ride

When I download a file from the device to the windows app, there is three different parts that show data: the graphs, the lap data (bottom left), and the advanced stats (top left). Here is where I have some confusion.

After initially loading the file, the lap table (bottom left) shows the integrated CdA values from the ride.

CORRECT
How is the CdA number calculated that is shown in the advanced stats?

THIS IS THE "DEFAULT" CDA THAT RESIDES IN YOUR PROFILE. THE VALUES IN. THE TABLE ARE THE MEASURED VALUES. If I mark one of the laps there is a big gap between both numbers. I would have expected both to be show the integrated or averaged value.
What exactly is shown in the CdA graph? I guess not the integrated CdA that was shown during the ride but rather a calculation of the CdA along each lap. So its average value per lap should represent the lap CdA.

IT IS THE CUMULATIVE CDA FOR THE LAP.

Example data

I will attach a test file with three laps done with a TT bike with only changes in body and head position. Head up relaxed position, head down agressive position, head down agressive position with different hands position. The file was modified with the "Switch profile After-the-ride" feature to correct the Crr value to 0.003.

Data after switching the profile
Lap Table Advanced Stats (when lap is selected)
L1 0,215 0,233
L2 0,195 0,212
L3 0,205 0,212

Data after using the "Apply analyzed CdA" feature
Lap Table Advanced Stats (when lap is selected)
L1 0,215 0,222
L2 0,191 0,202
L3 0,194 0,202

TT_Test_Haltung_2024_07_08_1909_13_km_CHANGED_PROFILE.ibr

THE APPLY ANALYZED CDA VALUES ARE EVEN MORE ACCURATE THAN THOSE MEASURED ON THE ROAD.

LET'S SUPPOSE YOU DO 3 LAPS PER TEST CONFIGURATION. L1 IS YOUR WARMUP; IGNORE IT. L2-L4 IS TEST CONFIG 1; L5-L7 IS TEST CONFIG 2; AND L8-L10 IS TEST CONFIG 3.

TO GET YOUR CDA FOR TEST CONFIG 1, HIGHLIGHT L2-L4 IN THE LAP TABLE, THEN CLICK "ANALYZED CDA". THE NUMBER WILL BE THE BEST FIT CDA FOR ALL 3 LAPS OF TEST CONFIG 1.

REPEAT FOR L5-L7, THEN L8-L10.

[Bergauf]

Thank you Jon, this is already very helpful as I have made some mistakes (eve after reading your manuals).

A test route should either a straight out-and back (such as the horizontal portion only of your test route):

I thought it could be advantageous to ride a horizontal and a vertical part with the option to later on cut out one if there were cross winds. I will stick to just one of the segments depending on wind direction.

You should ride for at least 5 minutes before beginning any testing--this recalibrates everything. Your lap 2 (your first CdA test) ends at 6:53; this lap cannot be used for CdA measurement.

This I misunderstood! I thought the initial 5 minutes re-calibrating were not needed if I had just made a calibration

For each test configuration (head up, head down, head down with changed hand position), you should do at least 3 laps per configuration. You did one lap for each; this is not enough to discern fine changes.

Understood. Especially with the length of a 'lap' now down to

At the start of a test, click the lap button. Ride out, turn around, and when you return to exactly the start point, click the button again. If you want ride a bit farther down the road to turn around; then, when you reach the start point (for the next measurement of your test), click the lap

Another mistake. I did hit the lap and the stop button in Garmin to safely stop and turn around, but totally forgot that AeroPod will continue recording data and the stop button. Thanks.

How is the CdA number calculated that is shown in the advanced stats?

THIS IS THE "DEFAULT" CDA THAT RESIDES IN YOUR PROFILE. THE VALUES IN. THE TABLE ARE THE MEASURED VALUES.

I understood that the default CdA in a profile does not change measurement and is used to calculate the "time advantage" that can be shown be riding in profile three.

If I highlight different laps in the App or mark different parts of the ride in the graph, this number changes. It also changes when I just the "anlayze CdA" function. As a CdA for the profile I would expect it to stay the same regardles of what is highlighted within a file. Could I ask you to explain this in some more detail?

LET'S SUPPOSE YOU DO 3 LAPS PER TEST CONFIGURATION. L1 IS YOUR WARMUP; IGNORE IT. L2-L4 IS TEST CONFIG 1; L5-L7 IS TEST CONFIG 2; AND L8-L10 IS TEST CONFIG 3.

TO GET YOUR CDA FOR TEST CONFIG 1, HIGHLIGHT L2-L4 IN THE LAP TABLE, THEN CLICK "ANALYZED CDA". THE NUMBER WILL BE THE BEST FIT CDA FOR ALL 3 LAPS OF TEST CONFIG 1.

REPEAT FOR L5-L7, THEN L8-L10.

Thanks, this is very clear. From the manual I would have understood to highlight all test laps of a file, not just the ones that represent the same test configuration.

Do you have plans to allow for csv export of the measurement data? I have some tools to analyse CdA as well and would like to have the possibility to dig deeper into the data.

[Bergauf]

I am looking into more testing this week and would like to have more control of the data. Alllow me to repeat my question whether you have plans to add a raw data export option (csv) to the Velocomp Aero App?

[Velocomp]

I am looking into more testing this week and would like to have more control of the data. Alllow me to repeat my question whether you have plans to add a raw data export option (csv) to the Velocomp Aero App?

I will see if this is possible.

UPDATE: Yes, it is possible and we will include it in the next release.

[Bergauf]

Thank you! I will post some results once I have them.

[Velocomp]

I am looking into more testing this week and would like to have more control of the data. Alllow me to repeat my question whether you have plans to add a raw data export option (csv) to the Velocomp Aero App?

I will see if this is possible.

UPDATE: Yes, it is possible and we will include it in the next release.

Release 0.40 should be available any minute now. It adds csv and .FIT export capability

[Bergauf]

CSV export works perfectly. Thank you for the quick implementation. I worked a bit on my own code to analyse the data and although I am sure yours is well thought-out, I feel more comfortable knowing how the data is processed. As expected, the absolute CdA you get is highly depending on the wind scaling factor of the sensor, and, as you point out very clear in your documentation, the measurements are delicate and very noisy. But for comparing different positions or gear on the same day, I believe I have found a working data routine.

Here is an example of what I get testing on an out-and-back course. I hope I will get some testing days before wintre is here.

20240708_TT_Test.png (75.66 KiB) Viewed 429 times

[Velocomp]

CSV export works perfectly. Thank you for the quick implementation. I worked a bit on my own code to analyse the data and although I am sure yours is well thought-out, I feel more comfortable knowing how the data is processed. As expected, the absolute CdA you get is highly depending on the wind scaling factor of the sensor, and, as you point out very clear in your documentation, the measurements are delicate and very noisy. But for comparing different positions or gear on the same day, I believe I have found a working data routine.

Here is an example of what I get testing on an out-and-back course. I hope I will get some testing days before wintre is here.
20240708_TT_Test.png

Yes, CdA is both a sensitive and very noisy measurement. In profile 4, we take the cumulative average CdA over the entire lap, then once the lap is done, post-process the CdA data both in AP firmware and in VA software. Remember: what we are seeking are differences in CdA of as little as 0.001, which translates to wattage differences as low as 1 watt. Second-to-second variations in watt measurement can be the result of wind variation, pedal style, vibration, body position, road surface variation, and more...the way to overcome all of this is by taking and averaging measurements over an extended period of time,