watts and damper setting

[gvcormac]

Watts (e.g. work per unit time) gives you a linear, much more interpretable, reading of effort than "distance" or "pace" or "speed"

My work as a person isn't accurate anyways as a huge energy expenditure is omitted in C2's calculations: me constantly accelerating and decelerating about 100Kg up and down a slide.

Sure, you waste some energy in recovery. I alluded to that as an advantage of using a lower drag factor: You have more time for recovery, which means you don't need to accelerate (and decelerate) your body as hard, which is what wastes energy. My understanding from the literature is that this is less than 10% of total work.

"distance" or "pace" or "speed" which are often speciously equated with stroke rate, or flywheel rotational speed.

I hate to bring it to you, but everything you do on a PM5 (or any rowing monitor) comes down to one variable: angular velocity of the flywheel. That is the only thing actually measured. Rest of the metrics depend on it, including dragfactor. When you can accurately calculate angular velocity and dragfactor, the rest of the metrics is a given.

This is misleading. It comes from the angular velocity as a function of time. Or, to take it to more basic quantities, angular position as a function of time. From this measurement, we can take the second derivative to calculate deceleration during recovery, from which (combined with the known moment of inertia of the flywheel) we can calculate drag. Not just the first erivative, which is velocity. Once we know drag, we know how much energy is dissipated by the flywheel, and hence how much energy is added by the drive.

Strokerate is just a means to produce average angular velocity in a specific way. From a metrics perspective, strokerate (and thus stroke detection by the PM5) is only relevant as it provides a convenient way to present metrics (and allows for drag calculation as that needs a recovery). With ORM we actually designed algorithms to be robust against missed stroke detections, aside from some lack of update of specific metrics, it doesn't make one iota difference.

This is gobbledegook. The amount of work you impart to the flywheel is force times distance. You increase force by pulling harder. You increase distance by using a longer stroke and/or by using a higher stroke rate. As you noted above, you also do work in recovery, which is not accounted for by the erg. But that work is a fairly small part of the total work you do, and that fraction doesn't vary all that much--but does vary some--depending on the combination of force, stroke length and stroke length that you choose.

[iain]

This seems like a debate between engineers!

To me a do an action (pull a stroke) and the PM converts the mechanical work I do into something easier to comprehend - how far a particular boat would travel in real time if I did a similar effort pulling an oar in it. The conversion may be arbitrary, but for a given efficiency of stroke there would be a boat that would indeed perform like that given the variation between the drag of boats.

As for the inefficiency, while I( suspect that at least for someone as inefficient as me this is much more than 10%, this happens in all physical actions. As I see it, what is measured is the "useful" physical work not the kinetic energy generated by the rowers muscles. In any event the inefficiency of converting chemical potential energy into motion is much higher than that not recorded for moving the rower!

[JaapvanE]

My work as a person isn't accurate anyways as a huge energy expenditure is omitted in C2's calculations: me constantly accelerating and decelerating about 100Kg up and down a slide.

Sure, you waste some energy in recovery. I alluded to that as an advantage of using a lower drag factor: You have more time for recovery, which means you don't need to accelerate (and decelerate) your body as hard, which is what wastes energy. My understanding from the literature is that this is less than 10% of total work.

You realize you have the same mass up a slide on the drive as well? Because my body does not magically appear on the end of the slide, it has to be pushed there (and accelerate quite a lot to reach a decent pace). It actually starts to add up quite badly if you do the math....

This is misleading. It comes from the angular velocity as a function of time. Or, to take it to more basic quantities, angular position as a function of time. From this measurement, we can take the second derivative to calculate deceleration during recovery, from which (combined with the known moment of inertia of the flywheel) we can calculate drag. Not just the first erivative, which is velocity. Once we know drag, we know how much energy is dissipated by the flywheel, and hence how much energy is added by the drive.

I know. I literally have designed, built and validated the open source counterpart of the PM5. You can read about the physics here in the primer I wrote three years ago: https://github.com/JaapvanEkris/openrow ... monitor.md Any comments are welcome, although several physicists have looked at it already (scientific validation has its challenges).

This is gobbledegook. The amount of work you impart to the flywheel is force times distance.

That is what is translated into. In the end, the PM5 seems to measure one thing, and one thing only: flywheel velocity. I am not certain if the current sensor package does position reports to be honest. I'd be surprised if they took that approach. With OpenRowingMonitor, we indeed use an electrical circuit to translate the C2's sine-wave into a blockwave, and we treat the individual upgoing flanks as position reports from the flywheel. However, we see that the sine contains frequency modulation, where we actually detect it in ORM's position reports. It is deliberate, as we tested many flywheels, and even got one from C2 directly to test, all containing the exact same signal. This approach is an indication they use an continuous measurement of angular velocity instead of a discrete approach used by ORM.

As you noted above, you also do work in recovery, which is not accounted for by the erg. But that work is a fairly small part of the total work you do, and that fraction doesn't vary all that much--but does vary some--depending on the combination of force, stroke length and stroke length that you choose.

For a lightweight, perhaps. For a 100 Kg guy, it starts to be a significant part of the exercise.

[gvcormac]

You realize you have the same mass up a slide on the drive as well? Because my body does not magically appear on the end of the slide, it has to be pushed there (and accelerate quite a lot to reach a decent pace). It actually starts to add up quite badly if you do the math....

In recovery, you accelerate your body to a certain velocity, and then decelerate to zero. The kinetic energy that you impart to your body rises with the square of the velocity; that is, with the inverse square of the recovery time. So a faster recovery requires more kinetic energy. Where does that kinetic energy go at the end of your recovery? Almost entirely into heat. Maybe a tiny bit is recovered from plyometric elasticity, but not much. So faster recovery wastes more energy.

This is gobbledegook. The amount of work you impart to the flywheel is force times distance.

That is what is translated into.

No. That is the definition of work. The Erg measures work indirectly, but reasonably accurately. If you increase work; i.e. force times distance, the Erg will show it.

For a lightweight, perhaps. For a 100 Kg guy, it starts to be a significant part of the exercise.

Reference, please. I think it is reasonable to estimate that the force on your drive is of the order of nine times higher than the force of your recovery. They involve the same distance. Ergo, recovery is 10% or less of the work.

I'm a bit perplexed by why you're attacking what I'm saying.

All I am saying is that force times distance is much more readily observable than what the PM uses to measure work, and the "watts" display is easier to interpret within this context. If you want to increase watts, you need to increase how hard you pull, or how far you pull, or how often you pull.

We agree that there is some work involved in recovery, which is not measured by the PM. We disagree, it seems, on the magnitude of that work.

[jamesg]

The energy used to accelerate a mass equals the kinetic energy gained or force x distance, the result is the same.

If when erging our max cg speed is 1m/s during the pull, ke is mV²/2 so at 80kg, 40Nm.

Doing this at rate 20 is 20*40/60W = 13W.

At the finish we then do work on the handle with the arms, which stops our travel and cancels ke, so avoiding a crab if our feet are out of the straps.

[jamesg]

During recovery, all the work done to come off the backstop becomes kinetic energy, which is then cancelled by the work done by the legs to stop us at the catch.

We don't bounce, but keeping the leg muscles contracted when reversing travel direction, it all happens very quickly. Coaches call it feeling the weight on your feet; and it's one of the first things we hear.