djconnel wrote:Another factor: acceleration-based cadence is challenging if you don't have a way to separate centrifugal acceleration from the bike bouncing up and down. I wonder how they make that work and how well it works, especially at lower cadences (for example, 40 rpm) on rough roads, especially since their accelerometers appear to be on an intermediate radius of the crank arm (where centrifugal acceleration is less than on the outer radius, for example at the pedal).
There is a pretty easy way to calculate this. If you place two accelerometers in the crankarm at a known distance (very little if possible) and you substract the two readings, you can calculate the radial component of acceleration. Neglecting the difference of acceleration between these two point due to the rotation of the bicycle as a whole and applying some sort of filtering you can get a pretty accurate value.
I'm impressed by the weight. Full strain gauges bridge with temperature compensation, accelerometer/s, Bluetooth chip and battery. There must be some sort of electronics WWism