These two companies, and several others have claimed to be making a power meter that measures straight from the pedal. There are some obvious benefits to this, including but not limited to: Power before mechanical drag, and individual leg power. It isn't that simple though. Each pedal sees a complex loading which is very hard to reduce. Sure accounting for the bearings will eliminate the torsion the pedal axle sees, but there is still much more. Cycleops measures the torsion of the hubshell, and multiplies that with the radial velocity of your pedals (read: Cadence).
Here is what Garmin and the other folks have to take into account:
-Position of the Crank/pedal
-Angle of the Pedal
-Centripital effect of the pedal. (It should be noted that the effect due to the Coriolis acceleration is reduced to zero)
-Deflection of the pedal axle
-Cadence
-Crank Length
-Speed
Here is what that requires:
-Potentiometer (Easy)
-Multiple Accelerometers
-Multiple Strain Gauges
-A fairly complex computer to make sense of all the data.
Building it is what I am guessing is not going to be a problem. Validating the equations is where things get messy. For example, pedaling very fast (over 150 rpm), will make the accelerometers read essentially trash.
The complex computer would require a fast (with respect to other brands running at 2-3 Hz) processor running at around 60Hz, and a large medium for storage, 16gb should do. It will also have to process all the data. I am pretty sure that all the companies will be using the dynamic equation of motion (EOM) in conjunction with the Stokes equations of vector calculus. (See: http://en.wikipedia.org/wiki/Stokes%27_theorem#General_formulation for more information). I am hoping to have the equations written out an simplified over spring break, but to be honest that probably won't happen. Anyway, I hope this is some insight about how complex these little power meters are.
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