Full calibration every time?

[gvcormac]

I think our posts crossed in the mail. I understand how to calibrate for the present conditions. I also understand that an angle sensor allows the PM5 to adjust for deviation of damper setting from calibration conditions. My question is whether it also able to sense pressure and/or temperature so as to compensate for them deviating from the calibration conditions.

[Nomath]

No, as far as I know the BikeErg is not able to sense and compensate for the pressure and temperature during the exercise if they deviate from the calibration conditions.

[gvcormac]

Thanks. I suspect the effect isn't large, at least indoors. Mainly confined to barometric pressure changes due to weather. That would be no more than a couple of percent pressure difference. I'll have to scratch my head a bit about how much that would affect calibration, but probably less than that.

Anyway, it ends up being very simple -- it calibrates using a pre-arranged coast-down, with an adjustment for damper angle.

[johnlvs2run]

probably C2 included on the BikeErg a sensor for the damper setting, which interpolates the DF when you change the damper setting during the exercise.

Tossing a towel over the air intake makes the pedaling very easy but does not change the drag factor.
The drag factor is not determined by resistance, and thus has no correlation to any change in resistance.
This is because, depending on the calibration process results, the drag factor is determined by position.

But wouldn't this mean I can easily cheat by just putting a towel over the fancage (or something similar) after calibration to reduce the DF at the same damper setting? Hopefully there are other features that prevent this.

Yes, people could easily cheat that way, also because Concept2 allows "workouts" to be ranked and verified.

[Cyclist2]

the drag factor is determined by position.

That caught my attention. I did a couple experiments with my Model C and the BikeErg: I set the DF to a number, then threw a towel over the flywheel blocking all the external airflow. On the Model C, the rowing got easier, AND the DF number displayed on the monitor went way down, too. On the BikeErg, I did the same thing. This time the pedaling got much easier but the DF number displayed did not change (as was noted).

So, the DF on the two machines is calculated differently, or at least displayed differently. Did C2 do it this way because of the inherent differences between rowing and cycling? i.e. In a boat, the resistance of the water is constant and steady, but on a bike the resistance changes when you go up or down a hill, for example.

I looked around the C2 web site, but found nothing talking about this difference in displayed drag factor. Do you have any further insight?

[Nomath]

Did C2 do it this way because of the inherent differences between rowing and cycling? i.e. In a boat, the resistance of the water is constant and steady, but on a bike the resistance changes when you go up or down a hill, for example.
...

No, the Performance Monitor of C2 can only determine the drag factor when there is no power input to a spinning flywheel.

On a RowErg, this condition happens in every stroke during the recovery. So the drag factor on the RowErg reflects the actual air flow conditions (e.g. damper setting, room temperature changes, a fan blowing near the flywheel cage, a towel on the mesh grid impeding air flow, etc.)

On a BikeErg during steady pedalling no such zero power condition exists and the PM is blind to internal or external changes in air flow, except for changes in the damper setting which is monitored by separate position sensor. It uses the drag factor as measured during the last calibration. So it is possible to fool the power measurement, for example by putting a towel on the flywheel cage. With a towel the air flow is impeded and for the same physical effort the rotation speed of the flywheel goes up. The PM then 'measures' a higher power input because P = DF * 10^-6 * (angular speed)^3. The drop in the actual DF is not taken into account.

[Cyclist2]

Got it. Thanks!

I've put small, more visible markers on the flywheel cage so I can "shift gears" with a little more accuracy. It will be interesting to see the drift in damper position for those as-new DF marks as the cage slowly clogs up. I guess that will be a indicator that I need to clean it!

[Nomath]

The clogging of the cage goes very slowly. From what I understand about the calibration procedure (item #3), regular calibration will compensate for clogging.

However, day-to-day variations in room temperature and barometric pressure will not be compensated if you do not renew the calibration. Barometric pressure may change by 20 mbar from one day to another, i.e. 2%. Air drag is proportional to air density, so to barometric pressure. On a RowErg such variations are compensated automatically.

[JaapvanE]

However, day-to-day variations in room temperature and barometric pressure will not be compensated if you do not renew the calibration. Barometric pressure may change by 20 mbar from one day to another, i.e. 2%. Air drag is proportional to air density, so to barometric pressure. On a RowErg such variations are compensated automatically.

On my RowErg I structurally record DF (ErgData does that as well for a row). At DF 80, i get a variation of +/- 2 point due to changing environment, which sounds consistent with wat you are saying.

I strongly suspect that callibration determines the df at a certain measured angle, allowing the PM5 to extrapolate the df at other angles. Having built identical software to the PM5, and applied it to dozens of machines, I'm fairly certain there is no other way to reliably determine df than through the coast-down behaviour of the flywheel.