On Friday, September 3, 2021 at 6:57:03 AM UTC-6, carl wrote:
> On 03/09/2021 09:46, Andy McKenzie wrote:
> > On Thursday, 2 September 2021 at 20:09:40 UTC+1, Bob wrote:
> >> On Thursday, September 2, 2021 at 3:14:19 AM UTC-6, Andy McKenzie wrote:
> >>> On Wednesday, 1 September 2021 at 23:17:25 UTC+1, Bob wrote:
> >>>> On Wednesday, September 1, 2021 at 11:26:06 AM UTC-6, carl wrote:
> >>>>> On 01/09/2021 17:32, A. Dumas wrote:
> >>>>>> Bob <head...@gmail.com> wrote:
> >>>>>>> More to the point is your statement that a flywheel moving air is more
> >>>>>>> complex than the relatively simple
> >>>>>>> relationships I'd use to calculate the power curve from flywheel speed.
> >>>>>>> I don't see how ergs can be
> >>>>>>> accurate enough for comparison purposes given all the variables like
> >>>>>>> stoke rate, temperature, humidity,
> >>>>>>> air pressure etc. that influence flywheel speed. I know they measure the
> >>>>>>> rate of slowdown of the flywheel
> >>>>>>> order to compensate for the conditions but how accurate is that?
> >>>>>>
> >>>>>> They re-calibrate (calculate the drag factor) every stroke. See
> >>>>>> http://eodg.atm.ox.ac.uk/user/dudhia/rowing/physics/ergometer.html#section7
> >>>>>>
> >>>>> Correct. But still inaccurate as the flywheel's energy-dissipation vs
> >>>>> time on slow-down & vs angular velocity are not log-linear, & fan energy
> >>>>> consumption is affected by flow transients, so that power consumption
> >>>>> during acceleration differs from that during run-down. And when the fan
> >>>>> moves with the feet of the rower, e.g. RP, then the intake vortex formed
> >>>>> in the vicinity of the fan is being dragged to and fro - which is also
> >>>>> suboptimal.
> >>>>>
> >>>>> And the intake geometry of other machines is scarcely ideal. Fans are
> >>>>> turbomachinery (of a kind) & intake design is a key part of the overall
> >>>>> system - just as hull design really matters for racing boats
> >>>>>
> >>>>> I guess (blindly) that it would not be too hard to program a form of
> >>>>> magnetic induction resistance to replace the fan and flywheel with a
> >>>>> resistance that better matches real-life boat dynamics. But we can use
> >>>>> a sculling boat to settle those arguments, & it's a lot more fun ....
> >>>>> Cheers -
> >>>>> Carl
> >>>>>
> >>>>> --
> >>>>> Carl Douglas Racing Shells -
> >>>>> Fine Small-Boats/AeRoWing Low-drag Riggers/Advanced Accessories
> >>>>> Write: Harris Boatyard, Laleham Reach, Chertsey KT16 8RP, UK
> >>>>> Find: tinyurl.com/2tqujf
> >>>>> Email: ca...@carldouglasrowing.com Tel: +44(0)1932-570946 Fax: -563682
> >>>>> URLs: carldouglasrowing.com & now on Facebook @ CarlDouglasRacingShells
> >>>>>
> >>>>> ---
> >>>>> This email has been checked for viruses by AVG.
> >>>>> https://www.avg.com
> >>>> A.
> >>>>
> >>>> The link you provided led to the article I planned to use to calculate my own curves hence the need for the
> >>>> flywheel inertia.
> >>>>
> >>>> Carl,
> >>>>
> >>>> I believe the Hydrow uses magnetic resistance. The thing weighs and costs a lot but at least you can turn the TV down when you erg!
> >>>>
> >>>> https://www.fitrated.com/hydrow-vs-concept2-model-d/
> >>>>
> >>>> The non-steady state fan effects you mention have me concerned. It might be easier to put a strain gage on the handle chain and measure
> >>>> force directly. The distance moved by the chain (old RowPerfect) might be hard to measure. However, I LEARNED MY LESSON AND LOOKED
> >>>> at my RowPerfect and saw that the nut on the flywheel spins with it. This would lend itself to an optical encoder. The force and distance
> >>>> over time sounds like work to me.
> >>>>
> >>>> Thanks,
> >>>>
> >>>> Bob
> >>> I use a WaterRower for my winter sessions of self torture when light and weather preclude sculling. The water rower's split calculation is well known to be more generous than that of a Concept 2, by about 10% at 'normal' paces. You can now equip a WaterRower with a 'Smartrow', which is a strain gauge inserted between handle and flywheel (actually a replacement of one of the pulleys). These measure force and stroke length, and have been programmed to match Concept 2 results more directly.
> >>>
> >>> However I think there is a bit of over pessimism about the 'accuracy' of the Concept calculations. The fact that rowers in gyms don't tend to care which erg they sit at and don't get all superstitious about only producing their 'best' times on a particular machine seems to be empirical evidence of consistency.
> >>>
> >>> Andy
> >> A. Dumas
> >>
> >> That is a very interesting link! They discuss how the errors increase as the effort and SR change on the CII erg which supports Carl's statement that transients affect flywheel energy dissipation. There is one thing about their graphs that I don't understand. I think they scatterplot the instrumented vs CII Power values and create
> >> an average line. That is fine but the plotted values are all over the map so to speak with significant outliers. This seems surprising to me. Can anyone enlighten/correct me? I'm also curious about the authors surmise that there is an intentional error in the power reading - "It can be supposed that the manufacturer has modified the C2D with the main objective to reproduce the speed of the boat rather than to assess the actual power developed by the rower".
> >>
> >> Your comment about gym ergs and consistency makes sense but different damper settings can result in differing variations in flywheel speeds which induces errors
> >> according to the paper and Carl. That cumulative error could depend on stroke rate so I wonder how it all works out or if there is some innate faith in the CII Model D
> >> as a tribute to CII marketing? In some ways, it doesn't really matter what the readout says as long as the CII is consistent from unit to unit and under all conditions and settings which, I think, is a tall order. I know I can't help taking a childish pleasure in beating someone's split by even a second! As an engineer, I'm not astute enough to know what that says about me and human nature but it probably isn't good.
> >>
> >> Andy,
> >>
> >> Can the Smartrow be programmed to yield power directly and, if so, how does it compare to the original WaterRower display on a stroke by stroke basis? The paper mentions that CII underestimates power so is the fact that the Smartrow needs to be scaled down to match CII, the reality of a gold standard that is not pure gold?
> >>
> >> Thanks,
> >>
> >> Bob
> > I haven't got a Smartrow myself. The original WaterRower display gives distance/speed, rather than any attempt to display power, so direct comparisons would be hard, but users have posted a fairly consistent 10% difference between pieces, even at differing intensity. From my perspective it doesn't really matter as I'm racing myself and no one else.
> >
> > Andy
> >
> And, of course, no ergs precisely simulate a boat, & (though RP comes
> pretty close on the dynamics) none of them teaches you about blade-work,
> or those other trying aspects of technique. So there's an element of
> sales hype in promotions that tell you otherwise, or kidology in telling
> ourselves that erg performance can represent on-water performance. The
> erg is a land-training device which can help you to develop strength &
> fitness, as can weights & body-weight circuits, running etc. But it
> will not make you into a rower.
> Cheers -
> Carl
>
> --
> Carl Douglas Racing Shells -
> Fine Small-Boats/AeRoWing Low-drag Riggers/Advanced Accessories
> Write: Harris Boatyard, Laleham Reach, Chertsey KT16 8RP, UK
> Find: tinyurl.com/2tqujf
> Email: ca...@carldouglasrowing.com Tel: +44(0)1932-570946 Fax: -563682
> URLs: carldouglasrowing.com & now on Facebook @ CarlDouglasRacingShells

I want to thank everyone who contributed to informing me on the nuances of my little project to measure erg power.
I've abandoned the flywheel measurement approach and ordered an optical encoder from ebay and a pull pressure load cell from Amazon?!.
Despite the fancy names they were surprisingly inexpensive. I still plan to pursue making a precision measurement of power in
comparison with the numbers from my original RowPerfect.

The real takeaway of this discussion is just as Carl said. Ergs can make you stronger but if you want to become better, you need to get on the water.

Many Thanks,

Bob