Sunday, March 17, 2013

Step 2 - Break prototype

Step 1) Calculate calibration adjustment based on Powertap and upload to microcontroller
Step 2) Break off the USB connector promptly after uploading
Step 3) More testing - To be posted soon
Step 4) Leave the house, get coffee with plans on attempting to solder it back on sometime in the evening

pb = V3 prototype, pw2power = Powertap G3

Not major, but annoying. I've got the calibration close but now my version is over predicting power. This might technically be okay because of drivetrain losses but I have no basis for the calibration now. The whole point was to bring it in line with the powertap. To subjectively look at the graphs I'd say they are similar, but breaking it down there is about a 7 watt offset with now.

Around the 286 samples mark you'll notice something. I stopped pedalling  My prototype doesn't detect a stopped condition yet. It therefore does not update the transmission. This goes to how the chipsets work. When I tell an ANT+ chipset to transmit data it does it continuously until I update it again. Really this is a few lines of code, but it'd be quite annoying to anyone familiar with power meters. It'd artificially increase or decrease average power. You can see it doesn't make much of a difference anywhere else except around 7981 samples. otherwise it's pretty similar. More to come.

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