Wrong power value. Some advice needed..

[youlsa]

Hi,

My PowerPod displays wrong power value in comparison to my 4iiii PRECISION power meter.
Should I edit some coefficients to get accurate value?

I attached my ibr ride file and tcx file from Garmin. tcx file has data from 4iiii power meter.
Would you please provide me with some useful advice?

Regards,
Nate Park

power_comparison2.png (42.44 KiB) Viewed 4865 times

[Velocomp]

The answer is shown in your picture. Notice that there are some notches in the speed readings...

In fact, your speed sensor is not working properly. Here is same data, with no filtering:

Screen Shot 2016-03-05 at 5.59.01 AM.png (184.09 KiB) Viewed 4860 times

Make sure your speed sensor is properly located and that the magnet passes 1-2 coin widths from it.

You will need to have good speed readings to get good power readings.

[youlsa]

In speed graph...
Green line is data captured by Garmin 520.
White line is data captured by PowerPOD.

That's same garmin new magnet-less speed sensor.

I don't know why PowerPOD data is strange like that, although garmin data is normal and sane. Same sensor, different data... What's wrong?

Is there any possibilities of data reception problem on PowerPOD side?
or, should I move my speed sensor from rear wheel to front wheel to improve Powerpod's data reception?

[Velocomp]

Garmin will default to GPS speed when it is not working properly with the speed sensor.

Try moving your speed sensor to the front wheel; that should help!

[youlsa]

OK. I'll test that.
Well, it's raining here in Korea, so that'll be next week.

Thanks for your kind advice.

[youlsa]

I followed your advice and changed Speed sensor placement from rear wheel to front wheel to improve sensor reception. This time, speed values from PowerPOD and Garmin matches almost exactly as following comparison graph.

But, power values are completely different from each other. White lines are power value from PowerPod, green lines are from 4iiii precision power meter recorded with Garmin. What's wrong?


During first half of the ride, I rode with tail wind. and during the second half, I rode with head wind.

I think I should change some parameter related to wind speed or something like that to get appropriate power value from PowerPod. Would you please give me some advise? (I attached my ride files. tcx file is 4iiii power data from Garmin, ibr file is from PowerPod.)

powers2.png (49.7 KiB) Viewed 4813 times

[Velocomp]

Because this is an out-and-back ride where you rode solo (no drafting) it is a great ride file to illustrate some things:

1) For the first 8 minutes of a ride, if your PowerPod has been reattached to your bike (as is the case with yours) then PowerPod will recalibrate itself. This is why your PowerPod was a bit different from your 4iii during the early part of the ride. Notice that the readings become close after 8 minutes!

2) Since this is a solo, out-and-back ride, connect your PP to Isaac, then use the Isaac command "Analyze/Check Calibration..." to automatically improve your PP profile settings. Check Calibration will "fix" the slope difference for the early part of the ride, and it will also improve the wind calibration of your PowerPod.

3) When in the Check Calibration window, click the "Send to iBike" button to upload your corrected settings to your PowerPod.

The Check Calibration file is very close. No two power meters will ever be exactly the same, and since 4iii is one crank arm only it's tough to know whether the differences are due to measurement differences or leg strength differences. In fact, your PowerStroke shows large power accelerations from each leg (large deviations from green oval), so your riding style may compromise some the 4iii reading accuracy.

I've attached the corrected file. By the way, when you merge tcx files with your PowerPod file, if you save the file then the merged information is saved, too!

[youlsa]

Oh, that's very helpful. I think you should write something about this "analyze/check calibration" function somewhere in manual.

Anyway, now I can get rid of other power meters I have. I love my PowerPod. Thanks for this wonderful power meter.