PDA

View Full Version : Environmental factors which influence calibaration of foot pod?



HAPPYRUNNER999
09-24-2009, 04:39 AM
The foot pod calculates speed/distance and sends a signal to the watch. I am wondering whether environmental factors influence accuracy. In other words, if you calibrate in one environment, is it accurate in another?

Speed? If you calibrate when running 9:00 miles, is it accurate when racing at 6:00 miles?

Pod Shoe angle: If you calibrate on one shoe, is it accurate on a different model?

Temperature? If you calibrate at 30 degrees, is it accurate at 90 degrees?

Altitude? If you calibrate at sea level, is it accurate in the mountains?

Terrain: If you calibrate on flat terrain, is it accurate on hills?

Air Density: If you calibrate in low humidity, is it accurate in high humidity?

Linear: If you calibrate on a round track, is it accurate when running straight?

It got me thinking because one day I calibrated and got 103%, in different conditions 99%, which is a pretty big difference.

t_smit
09-24-2009, 08:36 AM
The factory calibration of the footpod sets the scale factors and offsets for the accelerometers, including temperature compensation. This eliminates almost all unit-to-unit variation and in most cases this will give runners less than 3 percent error out of the box. The user calibration then allows the runner to dial in a distance scaling factor so that you can compensate for individual stride characteristics such as pronation and other slight differences due to shoe mounting.

My own calibration characteristics:
I've done tests on our local indoor track (232 meter track, tight corners) and I get different calibration factors on each foot, and also depending on if I run clockwise or counterclockwise. So in practice, I always put the pod on the same shoe, to eliminate at least one variable.

If I run 5:00 kilometers or slower (about 8:00 miles) then the factory calibration is very close. As I speed up the pod gets optimistic and when I'm at 4:00 kilometers the pod is out by about 5 percent. This is a characteristic that is common to all the pods I've run with so I just compensate in my head.

Running up or down hills does affect the calibration although it will come reasonably close to canceling out on any out-and-back or loop run. If your course has very tight turns (or if you're running on a track) then you might find that affects the distance reporting.

If you're calibrating on a track, make sure you warm up thoroughly before doing calibration laps. Take at least one complete lap around the track before doing a cal...

I've found the pods to be fairly transportable from shoe to shoe (from a calibration perspective), so long as you make sure that the pod is aligned reasonably well on the lace bed and it's snugly mounted.

The pods are not affected by temperature, altitude, or humidity.

TRYING2GOFAST
11-18-2009, 09:25 AM
I've found the pods to be fairly transportable from shoe to shoe (from a calibration perspective), so long as you make sure that the pod is aligned reasonably well on the lace bed and it's snugly mounted.

This actually scares me to death, because unlike the mount on the 705 - which I'm sure to know when the mount wears out and the computer goes flying into the weeds or the hard asphalt :( - I might not be aware when the mount on my footpod wears out until I take my shoes off and find it's not there.

My experience with the 705 handlebar mount is that it's good for about 6 to 8 months - which would translate into roughly 150-200 mount/remove cycles.

Can you estimate how many times you've taken your footpod off?

ALAALA
11-18-2009, 09:40 AM
This actually scares me to death, because unlike the mount on the 705 - which I'm sure to know when the mount wears out and the computer goes flying into the weeds or the hard asphalt :( - I might not be aware when the mount on my footpod wears out until I take my shoes off and find it's not there.

I always secure the pod by wrapping the whole package in (electrical) tape.
I wouldn't trust that mount one second (better safe than...).

t_smit
11-18-2009, 10:24 AM
I might not be aware when the mount on my footpod wears out until I take my shoes off and find it's not there.

My experience with the 705 handlebar mount is that it's good for about 6 to 8 months - which would translate into roughly 150-200 mount/remove cycles.

Can you estimate how many times you've taken your footpod off?

The current oval footpod's clip is pretty resilient and I haven't broken one so far (in about 18 months of testing off and on) but I don't generally remove the pods from my shoes except when I transfer a pod from one pair of shoes to another. I might have removed and installed the pod into the clip about ten times total. Since more shoe manufacturers are including a pod slot or pocket in the sole of their shoes, you might not need the clip at all on your next pair of shoes.

ridera
11-18-2009, 05:07 PM
Running at the same speed, both right shoe, same lace position, 2 runs of 1600m on a good high school track.....

The calibration factor for my racing shoes: 91.0%
Training shoes: 97.8%

t_smit
11-19-2009, 08:24 AM
Running at the same speed, both right shoe, same lace position, 2 runs of 1600m on a good high school track.....

The calibration factor for my racing shoes: 91.0%
Training shoes: 97.8%
In our testing we consistently observe a warmup effect where the first couple of laps around the local indoor track produce a different calibration value compared to the next six to eight laps. Have you noticed the same? Or equivalently, does the calibration value between your two pairs of shoes change depending on which set you test first?

I have a pair of Asics DS Trainers that I've used for races the last couple of years. They are about 2 oz. lighter, per shoe, than the Kayanos I use for distance runs, and they feel completely different especially when I pick up the pace. I wouldn't be surprised at all if switching shoes changed my gait enough to affect the calibration factor.