Today was the first day where I got some good data skiing to and from work using my data logger. There’s a photo of it in it’s protective box on the right. The Arduino and data logging shield (with the sensors soldered to it) is sitting on top of a battery pack holding six AA batteries. The accelerometer is the little square board that is sticking up on the left side of the logger, and you can see the SD card on the right side. The cord under the rubber bands leads to the external temperature sensor.
This morning it took about four minutes for the sensor to go from room temperature to outside temperature (-12°F), which means I need to pre-acclimate it before going out for a ski. A thermocouple would respond faster (much less mass), but they’re not as accurate because they have such a wide response range (-200°C to 1,350°C). A thermistor might be a good compromise, but I haven’t fiddled with those yet.
Here’s the temperature data from my ski home:
When I left work, the temperature at our house was 12°F, and I figured it would be warmer almost everywhere else, so I used “extra green” kick wax, which has a range of 12 to 21°F. I’ve highlighted this range on the plot with a transparent green box. In general, if you’ve chosen wax that’s too warm for the conditions, you won’t get much glide, and if the wax is rated too cold, you won’t have much kick. The plot shows that as I got near the end of the route and the temperature dropped below the lower range of the wax, I should have lost some glide, which is pretty much exactly what happened. Normally this isn’t a big issue on the Goldstream Valley Trail because it’s often very smooth, which means that a warmer wax is needed to get a grip, but this afternoon’s trail had seen a lot of snowmachine traffic, it wasn’t very smooth, and I didn’t get as much glide as earlier in the ski.
The other interesting thing is the dramatic dip marked “Goldstream Creek” on the plot. This is where the trail crosses the Creek on a small bridge designed for light recreational traffic (nothing bigger than a snowmachine or four-wheeler). It’s probably the lowest place in the trail. Our house is also on the Creek, so the two coldest spots on the trail are exactly where I’d expect them to be, right on the Creek.