Full calibration every time?

[johnlvs2run]

Recently the BE has been requiring a full calibration for every ranking piece.
May 29th - I did a full calibration for a ranking piece.
June 6th - Another full calibration was required for a ranking piece!

June 9th - I did a full calibration so it would be fine the next day.
June 10th - Another full calibration was required for a ranking piece!

Why is this happening?
Does the pm5 have a malfunction?
Is the most recent firmware to blame? Let me know what you think.

[Dutch]

I get asked every time I do a piece, I am sure it is some glitch with the update as well, waste of time if you ask me, I never do them.

[johnlvs2run]

Dutch, thanks for the confirmation.
Ironically, it didn't ask again before another time trial the same day.
Thus, I'll try a full calibration earlier in the warmup, and maybe that will work better.

[Rower972]

Same thing here. It’s been behaving like this from the start.

[ppollard83]

I get asked to confirm calibration every time I ride a distance/set time that can be registered as a "ranked workout". I recently did a full calibration, yet next day it was way out and needed a full calibration again (drag on my iphone said it was 49, yet the physical level was at 1, so should have been 37).
Normally I don't bother to calibrate, I train with power and as long as I can get reach the session numbers and the effort seems correct, I'm happy.

[Nomath]

I am not a BikeErg user, but I have often wondered how the BikeErg is able to compute power accurately without a pause in the application of power (as happens on the RowErg during each recovery). The drag factor is a key parameter in the calculation of power (and distance).

I think all BikeErg users should be glad that C2 requires them to calibrate before entering a ranking piece. This keeps the rankings clean from simple tricks and manipulations (although not from changing the drag during the ride).

[johnlvs2run]

I think all BikeErg users should be glad that C2 requires them to calibrate before entering a ranking piece. This keeps the rankings clean from simple tricks and manipulations (although not from changing the drag during the ride).

That's not true for 3 reasons.

#1- C2 allows workouts to be ranked. For example, 10x400m with 5' recoveries can be ranked as a 4k. I pointed this out to C2 when they first started with verifications and thought they had corrected that mistake long ago. However, recently the rank button showed up next to a workout of mine that was coincidently a ranking distance. I thought, what?, clicked rank and the workout was ranked. I immediately removed it but first discovered that the workout could be both ranked and verified! Both couldn't be done at the same time, but perhaps they could be on Ergdata or some other programs.

The point is that only single ranked AND verified pieces should be accepted for the rankings, although even that criteria might be bypassed with other software. Of additional note and concern is that C2 calls ranking events "ranked workouts" in the log book, apparently encouraging people to rank workouts.

#2- The drag factor is separate from calibration, thus changing the drag factor during a ranking piece would be perfectly fine. The drag factor doesn't even need to be set, and many people don't bother to check it.

#3- The calibration itself is done at settings 1, 10, 8, 6, 3 and 2 on the fan cage. Thus any single one of those and any settings in between them are not specifically calibrated. Rather, the settings are calibrated as a whole, another reason why moving the setting during a ranking piece makes no difference.

[Nomath]

....#2- The drag factor is separate from calibration, thus changing the drag factor during a ranking piece would be perfectly fine. The drag factor doesn't even need to be set, and many people don't bother to check it.

Measuring the drag factor is the essence of calibration!

On a BikeErg there are only very small variations in the speed of the flywheel during a pedal turn.
Except for the first few pedal turns, the relation between measured power P and the angular speed of the flywheel ω is quite simple : P = DF * 10^-6 * ω³ .
So power depends linearly on drag factor DF.
What the PM does is to measure ω continuously. It cannot measure the drag factor unless you stop pedalling for a few seconds. This is called calibration. The drag factor is not only determined by the damper setting but also by the cleanness of the flywheel and its enclosure, on the air circulation outside the enclosure, on the actual temperature and air pressure and on the elevation. All these conditions affect the DF. If one of them changes significantly, the power measurement will not be accurate.

I am not a user of the BikeErg so I went looking for confirmation. Here is what C2 says in their manual :

Calibration
The BikeErg will prompt you periodically to confirm the calibration, including whenever you program a distance that is part of
our Online World Ranking. The process is simple and the PM5 will guide you through it. To confirm the calibration or start a
full calibration at any other time, press More Options > Utilities > Calibration Utilities.
After moving the BikeErg to a different location, confirm the calibration to ensure accurate results.

#3- The calibration itself is done at settings 1, 10, 8, 6, 3 and 2 on the fan cage. Thus any single one of those and any settings in between them are not specifically calibrated. Rather, the settings are calibrated as a whole, another reason why moving the setting during a ranking piece makes no difference.

I didn't know this feature. So 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.

[MartinSH4321]

----
I didn't know this feature. So 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.

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.

[Nomath]

..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.

Interesting observation! It should be easy to check by BikeErg users whether throwing a towel on the fan cage changes the DF. It would also throw light on how far the calibration is upheld.

[gvcormac]

I am not a BikeErg user, but I have often wondered how the BikeErg is able to compute power accurately without a pause in the application of power (as happens on the RowErg during each recovery). The drag factor is a key parameter in the calculation of power (and distance).

I think all BikeErg users should be glad that C2 requires them to calibrate before entering a ranking piece. This keeps the rankings clean from simple tricks and manipulations (although not from changing the drag during the ride).

The BikeErg (unlike the RowErg and SkiErg) has an angle sensor on the damper, and (like the RowErg ans SkiErg) a velocity sensor on the axle. From these two numbers it can calculate resistance and hence power. I have seem claims (which I've been unable to verify -- can somebody help?) that it also measures and corrects for temperature and pressure. In any event, every million metres (and more often for competitition setup) it asks you to pedal and coast so that it can recalibrate.

For comparision, since the RowErg and SkiErg inherently coast as part of each stroke, the PM can simply measure the coast-down rate to determine precisely how much work was done on each stroke. Concept 2 has a patent (presumably now expired) for this method.

[Nomath]

An angle sensor on the damper would not detect what MartinSH4321 suggested as an easy trick to lower the drag factor on a 'calibrated' BikeErg : throw a towel on the fan cage while pedalling.
Is there no interested BikeErg user on the Forum who can check whether the erg can handle such a cunning deception ?

... I have seem claims (which I've been unable to verify -- can somebody help?) that it also measures and corrects for temperature and pressure. In any event, every million metres (and more often for competitition setup) it asks you to pedal and coast so that it can recalibrate.

The drag factor measured while no power is applied (hence during the every recovery on the RowErg or in the calibration procedure of the BikeErg) automatically corrects for temperature, pressure, dusting of the fan cage, air flow restrictions outside the fan cage such as towels on the fan cage, etc.

[gvcormac]

Yes, the towel trick spoofs the power reading. I have verified that. Since I'm interested in a good faith estimate of power, not spoofing a competition, that is not a problem for me. That said, there will inevitably be at least one coast period, and the PM could do some spoofing detection.

Can you provide me documentation on the temperature/pressure correction?

[gvcormac]

On re-reading your post, I think we may be at cross purposes.

Granted, if you do a calibration, it accounts for current temperature, pressure, and towel presence. My question is: Assuming no towel presence, does PM5 adjust for temperature and pressure without recalibration?

[Nomath]

Can you provide me documentation on the temperature/pressure correction?

It is in the physics of an air-braked flywheel, as explained in http://eodg.atm.ox.ac.uk/user/dudhia/ro ... meter.html
The basic equation is : P = C * ω³ + ω * J * dω/dt
P = input power to the flywheel [W]
ω = angular velocity of the flywheel [radians/s]
C = drag coefficient [kg m²]
J = moment of inertia of the flywheel [kg m²]

With no power input (i.e. during the recovery of a rowing stroke or free-coasting on the BikeErg) this simplifies to : d(1/ω)/dt = C/J
The PM sensor measures the angular velocity during the zero-input phase and the moment of inertia of the flywheel is a constant and manufactured within very narrow tolerances by C2, so the actual drag coefficient can be determined very precisely. This drag coefficient accounts for the actual temperature and pressure, and for air flow inside and outside the flywheel cage, including the damper setting.

Regarding your last post: the calibration accounts for the temperature and pressure that existed during the calibration, not during the exercise. That's why C2 recommends to redo the calibration when you move the erg to a different location, e.g. closer to a wall.