Low Cost PowerMeter for cycling trainers

What about when somebody stands on the pedals? Pedal force isn't going to be such a good measure.

I've seen altimeters for bikes; seems like you could do a simple power meter based on work, by adding the actual power on the system (ie, mass times change in height) to a factor that adds in drag from wind, road, and mechanical linkages (which is probably close to linear with velocity.) Using GPS might make it a bit more accurate than pressure altitude, since you only care about differences, not absolute altitudes.

However, calibration will be required, such as entering total mass, drag coefficients, and that sort of thing. It might be possible to auto configure the main drag coefficients using terminal velocity on a glide. At terminal velocity, the power going into drag equals the power being obtained by a decrease in altitude.

Isn't there some kind of transducer that can measure the torque being applied to a shaft? X ft-lb * S mph = power, or something like that, isn't it? Just put one of those on the hub, at the sprocket. Measuring RPM is trivial.

Thanks, Rich

Measuring the real force is going to be a *lot* better than trying to estimate aerodynamic drag. Drag is approximately a * v^2 + b*v + c where a,b,c are set by the geometry. But on a bike the geometry is nowhere near constant - standing up / sitting upright / bent over in full racing position / clothing all make a huge difference. To say nothing of trying to estimate the wind effects on the actual velocity.

Un bel giorno Bob Monsen digitò:

Why? I don't see the difference.