## Accelerometers just might work

Tuesday, February 17th, 2015 at 11:15 am

The green is the raw plot of the accelerometer vector which was aligned with the crossbar of my bike on the ride. The red is the altitude, the yellow is my speed — clearly slower going up hill than going down as time advances from left to right. We stopped for a bit at the top of the hill.

This is smoothed with an exponential decay factor of 50/51 on a time sample rate of 0.1seconds, so a sort of 5 second time window.

This is applying the exponential smoothing filter backwards as well, which is a trick I heard about a few days ago. I haven’t worked out of the maths of it yet, but it looks good.

Here are some vertical lines showing periods of ascent and descent with the second white horizontal line denoting the overall average accelerometer reading that you can think of is approximating how much the bike cross bar is pointing up or pointing down from the horizontal. I can convince myself that it is negative on the uphills and positive on the downhills where it is tending to point more in the direction of gravity.

Here’s a zoomed-in section of where we peddled down the hill and then heaved our way back up the other side. Because the rates of descent and ascent are about the same it means the slope down must have been shallower as I don’t peddle up hills very fast.

Unfortunately I’m not competent enough to overlay this on a map to see these places on the contour lines, and I don’t have a bike wheel trip magnet to measure distance travelled properly.

Anyway, it’s not really for my bike; it’s for putting on my hang-glider. The bike is just a good way to test things till I can get out flying again.