Powertap comparison (way off for first few minutes)

[joep]

I compared the power readings from a powerpod with a powertap hub. Does anyone know why the powerpod reading is too high for the first 7 minutes? I did a calibration ride the first time I synced with my Garmin, but this problem continues. Notice that the powerpod agrees pretty well with the powertap after 7 minutes. Also when I do a post-ride calibration using the Issac software, it fixes the data. But the next time I ride, the problem comes back.

Screen Shot 2016-01-17 at 5.25.06 PM by Joe P, on Flickr

[Velocomp]

During the first 7 minutes of a new ride, PowerPod adjusts its internal settings to compensate for any changes in its mounting position.

You'll notice that, after the 7 minutes, the two units are essentially identical.

This problem will be minimized if you're VERY CAREFUL to mount the PowerPod in exactly the same angular position each time you attach it.

[Morocco Mole]

Joe, I am curious, are you removing the powerpod after each ride to download the data? When you re-attach the powerpod to the mount are you being careful to place it in exactly the same position eg push the back of the unit down until the square edge is flush and tight against the mount? In your chart the difference in the power between the powerpod and the powertap is significant until the auto calibration has corrected things, to me this indicates the powerpod has moved in it's mount a substantial amount between rides which is what I am having difficultly in understanding. I remove my unit regularly and as John indicated there is minimal or no calibration required.

Thanks
Jim

[qrasco]

To piggy back on this thread about taking the PowerPod regularly to sync with my computer...I would prefer to leave it on so I don't have the issue about the auto correction, however I am afraid to leave it on my bike in the garage. It gets awfully cold in there and like any electronics, I am afraid of what the cold will do to the PowerPod...thoughts?

Thanks.

[Velocomp]

PowerPod won't be hurt by cold. You'll need to charge its battery once a week.

[Musiker]

I noticed the same on my two rides today..
A couple of suggestions:
1) Would it be possible (And a good idea) to start tilt calibration when/if you select to calibrate Powermeter on your head unit? This morning I knew that the tilt would be wrong, but I diden't do a reset prior to my ride (Just switched mount type for that bike profile)
2) Is there a way to clean up the ride files, If not maybe consider making it possible? I can't sustain 800-1000W for several minutes .... And maybe the pod could even indicate that it is working furiously on auto-cal

BR
Henrik

[Velocomp]

There is an easy way to lop-off the first few minutes of your ride:

1) Download your ride in Isaac

2) Click in the graph window, where you want to separate the ride file

3) Use the command File/Combne-Split/Split Ride File at Cursor...

4) Save the last part of the file

[joep]

During the first 7 minutes of a new ride, PowerPod adjusts its internal settings to compensate for any changes in its mounting position.

You'll notice that, after the 7 minutes, the two units are essentially identical.

This problem will be minimized if you're VERY CAREFUL to mount the PowerPod in exactly the same angular position each time you attach it.

I'm aware that I have to put it back in exactly the same position as before. I push down on the back so that the unit is flush with the stops on the mount. This particular time though I turned it on between rides to check whether it would sync to a new computer, but I didn't mount it to the bike when I turned it on. Maybe that's the cause of the re-calibration. Thanks for your reply.

[joep]

I noticed the same on my two rides today..
A couple of suggestions:
1) Would it be possible (And a good idea) to start tilt calibration when/if you select to calibrate Powermeter on your head unit? This morning I knew that the tilt would be wrong, but I diden't do a reset prior to my ride (Just switched mount type for that bike profile)
2) Is there a way to clean up the ride files, If not maybe consider making it possible? I can't sustain 800-1000W for several minutes .... And maybe the pod could even indicate that it is working furiously on auto-cal

BR
Henrik

The Issac software actually fixed the erroneous data from the first 7 minutes when I opened the file and chose Analyze->Check Calibration.

[Velocomp]

I noticed the same on my two rides today..
A couple of suggestions:
1) Would it be possible (And a good idea) to start tilt calibration when/if you select to calibrate Powermeter on your head unit? This morning I knew that the tilt would be wrong, but I diden't do a reset prior to my ride (Just switched mount type for that bike profile)
2) Is there a way to clean up the ride files, If not maybe consider making it possible? I can't sustain 800-1000W for several minutes .... And maybe the pod could even indicate that it is working furiously on auto-cal

BR
Henrik

The Issac software actually fixed the erroneous data from the first 7 minutes when I opened the file and chose Analyze->Check Calibration.

Yes, that works too!