Wednesday, November 30, 2011

Apple iPod Nano 6g v1.2 (Part 2)

Back in early October, I gave a favorable report on using the internal accelerometer on the Apple iPod Nano 6g (when updated to v1.2), see here. I decided to test it again on the treadmill.

This morning, I was too fatigued to do the Al Corniche run I did two days ago (see here). (I was suffering perhaps too much from a skin allergy condition that has recently flared up again.)

As a result, I decided to simply run with the iPod Nano on the treadmill in cool air-conditioned comfort at the Mövenpick Towers hotel (see left) for about 30 minutes. The gym there does have a spectacular view of the Gulf from the 25th floor. Better than feeling sorry for myself and doing absolutely nothing I suppose.

But instead of setting a steady, fixed pace (like last time), I varied the treadmill speed up and down. In fact, I ran for the first 10 minutes at 12.5 km/hr (7.8 mph). Then bumped up the speed to 13.5 km/hr (8.4 mph) for 5 minutes, and dropped it to 10.0 km/hr (6.2 mph) for 5 minutes to recover. Finally, back to 12.5 km/hr for the reminder of the run.

So what would one expect the device to report? Well, one would expect something like the red line shown below (possibly shifted slightly vertically, modulo speed calibration of the treadmill).

I can report that the blue data points seem to track the red line fairly well. Though it's not clear there is much difference in the data recorded between the 12.5 km/hr and 13.5 km/hr sections...

(Note: I downloaded the raw data points and directly plotted it in Excel myself. For those interested, you can find them in the directory /Volumes/iPod Nano Name/iPod_Control/Device/Trainer/Workouts/Empeds/nikeinternal/synched when mounted on a Mac. )

This ridiculously heavy-handed smoothing is potentially a huge problem that renders the device useless under non steady state conditions.

(Ignore what I said above. In a previous edition of this post, I said the iPod Nano smoothed away the speed changes. Mea culpa. I screwed up. There was a mistake in my Excel formula.)

From my treadmill speed settings, I should get an average pace of 7'54" min/mile, assuming the treadmill was calibrated perfectly. The internal accelerometer gave me a 7'25" min/mile average or about 6.5% off the treadmill settings.

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