Re: Will Polar make a good power meter someday?
Originally Posted by Alex Simmons
Hmmm. I'd go with that except at lower powers it seems OK, it's only when power goes up that it looks wrong.
Well...at a given cadence, a higher power will mean a higher chain tension. This also will mean a low chain vibration amplitude as well. If the "environment" is too "quiet", the chain isn't getting "excited" enough to vibrate at a larger amplitudes. The inductive sensor can't tell the difference between changes due to the chain going up and down vs. changes due to things like the pins of the chain passing the sensor. The circuitry just does it's job and locks on to the largest signal...if it happens to not be the chain vibration...well, things will be off.
Take a string or a rubber band and stretch it between your 2 hands. Pluck it to get it vibrating and then increase and decrease the tension and look at what happens to the amplitude of the vibration and you'll see what I mean.
On the road, the random inputs of the road surface keep the chain vibrating at a sufficient amplitude so that this isn't a problem (random and impulse inputs tend to excite ALL frequencies equally in the range encompassed by the random input). This is why I speculate there's a difference between "on road" and trainer performance with the Polar.
Now...with the fact that the Polar unit actually has a chain speed sensor already, I would think it would be somewhat trivial to design the circuitry to reject any signal that's the same frequency as the chain speed. But, then again, I'm not a signal processing engineer and it may not be that easy...
|Maybe an endless reel of the Dr Who sound track pointed at the cockroach
If the input energy was high enough, that might work. However, I have no idea what effect it would have on the sanity of the rider forced to listen to the "loop"
Hmmm...I know that there are white noise CDs available...I wonder if I can rig up an experiment to prove/disprove my theory? First, I'll need to make sure that the noise is in the same frequency range as my expected chain vibrations and then I'll have to figure out how to get the energy into the chain....