Strange differences between CdA values

[aeropod.user]

Dear Velocomp team,

I'm a new user to Aeropod, just bought it and followed all configuration discussed in your documentation and instructional videos from Youtube.

I have following questions:
1) Last week I did calibration ride, and after that several rides within a time frame of ~1,5h. Environmental conditions were rather the same in this time frame, all rides were done on a racing circuit, rather flat and of the length of 4km. I was surprised that every ride showed very different CdA on my device, although I tried to be in similar position. No other setting (bike equipment, helmet or so) were changed between the rides. The values of CdA, which I could observed from Aeropod, varied significantly, I mean like 0.22, 0.24, 0.28, 0.18. Do you have any idea what I might do wrong and what could lead to this effect?
2) Also that the way CdA values changed was quite strange to me. E.g. the values were sensitive to wind direction. Although I did my best to keep the same position, CdA grew up when I rode against the wind direction with greater power values, and decreased when I rode with the wind with lower power values. How can it be explained?

I attach all files from my rides from that day, maybe they help in answering my questions. Question 2) is e.g. clearly seen on charts from the last ride. I also attach exported FIT file with GPS data, which corresponds to the 12km of the last ride from that day. Maybe it will be also helpful.

I'm using the newest Power2Max power meter, which is very reliable (I tested it with other power meters in the past), and Garmin speed sensor. Everything was correctly setup and calibrated before those rides.

Thank you in advance for your answers.

Regards,
Bartosz Zbierajewski

[Velocomp]

I'm embarrassed to report this, but your ride files reveal that there is a FW bug that disables Isaac's CdA features for the AeroPod model ("07" serial number). This bug does not affect AeroPod+ models ("06" serial number). We were not aware of this bug until your posting; we will get right to work to fix it!

Using special commands I was able to restore your files so that Isaac could read CdA data. Restored ride files are attached.

Your 10KM file, which appears to have been performed just after calibration, looks fine.

Your 17KM file has a serious problem. When using latest-generation FW, the first 5 minutes of any new ride are critical. You need to ride at reasonable speed (20KM/H +) at an even pace. At the beginning of your ride your speed was only 9km/h, and your speed fluctuated. The result of this is that your AeroPod was "locked in" with an incorrect tilt calibration.

Screen Shot 2019-07-23 at 3.47.34 PM.png (53.72 KiB) Viewed 4521 times

You can see the effect of the incorrect tilt calibration for the remainder of your ride file. Notice that, though your course is fairly level, you have a consistently positive slope (in red):

Screen Shot 2019-07-23 at 3.49.09 PM.png (133.59 KiB) Viewed 4521 times

When tilt is incorrect, CdA will be incorrect. In your case your AeroPod thinks you were going uphill during your ride (positive slope). So, opposing watts were higher, which forces CdA down.

Fortunately there is a way to fix this in Isaac: use the "Analyze/Analyze Route" command. Notice that, after applying the fix, that slope hovers around zero:

Screen Shot 2019-07-23 at 4.14.19 PM.png (134.05 KiB) Viewed 4520 times

Once the tilt is fixed, you can use the "Tools/Power Meter Comparison" feature to view CdA of the repaired file (the Tools/CdA Analysis item does not work with repaired files)

Screen Shot 2019-07-23 at 3.55.06 PM.png (122.05 KiB) Viewed 4521 times

Your CdA is around 0.235. I see 3 laps:

km 3.5-7.5 CdA = .237
km 7.5-11.5 CdA = .233
km11.5-13.5 CdA = .241

Lap 3 is shorter, so that may account for the slightly different CdA.

For your 10Km ride, I get:

km 0-4.3 CdA = .236
km 6.6-8.2 CdA = .240

So, I think your results are much better than you think!

YouR headwind/tailwind sections are very short; about 1 minute. This is too short a time to get a stable CdA reading. However, once the files are corrected I don't see a significant CdA change that is a result of wind changes

Screen Shot 2019-07-23 at 4.10.18 PM.png (140.04 KiB) Viewed 4521 times

[aeropod.user]

Hello John,

I'm really impressed by your comprehensive answer. Thank you for the effort you put in this detailed analysis. I will use this knowledge and wait on bugfix mentioned by you.

Regards,
Bartosz Zbierajewski

[Velocomp]

Hello John,

I'm really impressed by your comprehensive answer. Thank you for the effort you put in this detailed analysis. I will use this knowledge and wait on bugfix mentioned by you.

Regards,
Bartosz Zbierajewski

We've already checked the FW and we can't replicate this bug. Please do the following:

1) Press-hold AP button for 12 seconds, until light goes out and turns back on. Release the button. This does a hard reset of the device

2) Do a short ride (1 KM is fine) and post the ride. We want to see if the features are restored.

[aeropod.user]

Do I need to repeat configuration in Isaac, pairing of other sensors and do another calibration ride (out and back) before it, or it's not required?

Regards,
Bartosz

[Velocomp]

Do I need to repeat configuration in Isaac, pairing of other sensors and do another calibration ride (out and back) before it, or it's not required?

Regards,
Bartosz

No, you don't have to do a new sensor pairing or cal ride after a hard reset.

Just make sure that the first 5 minutes of your ride follow the instructions!

[aeropod.user]

Hello John,

Before your first answer to my question I rode a time trial on the same racing circuit as my previous rides. Not knowing your request I hadn't done any hard reset before that ride, just turned aeropod on, paired it with my other sensors (exactly the same bike and equipment as with previous rides), rode first 5 minutes with even pace to let the device calibrate, did some >10km warm up and then time trial. I've just downloaded the file to my computer and could run CdA analysis without any problems. I attach that file to this post. Could you please take a look at it and check if it also has the problem noted by you with previous files?

Regards,
Bartosz Zbierajewski

[Velocomp]

Good news; your DFPM data is there!

Your data looks great...good job with the calibration.

Your CdA is very stable at 0.254