Concept2 Forum

After using ErgData for a few weeks I was curious to know if the drag setting of the rower is used at all?
You'd think that power calculations and calorie calc's would need to know what drag you are set at. In fact, almost every statistical output would be affected by changing the resistance setting wouldn't it?
I can't see an entry box to manually enter it and it doesn't seem clear whether the drag setting is somehow being transmitted from the machine. I find the latter suggestion hard to believe since I am using a Concept2 model C from the 90's.
Anyone got any ideas?
cheers

The current drag factor is available in the CSAFE API (which is used by all client programs).

jhoweld@gmail.com wrote: ↑

February 20th, 2023, 9:54 am

I can't see an entry box to manually enter it and it doesn't seem clear whether the drag setting is somehow being transmitted from the machine. I find the latter suggestion hard to believe since I am using a Concept2 model C from the 90's.

See
http://eodg.atm.ox.ac.uk/user/dudhia/ro ... meter.html

Long story short: the monitor can see the velocity of the flywheel decelerate, and thus it can calculate the drag factor. Please note that the drag setting and the numbers on the rim are only loosely related: due to aging the drag for a given number on the rim can shift. As the dragfactor is calculated using physical properties if the flywheel, it is always spot on. In newer monitors (PM3 and PM5), you can even display the dragfactor.

You can display the drag factor on the PM2 as well.

Drag factor is a calculation derived from the rate of deceleration of the flywheel during the recovery.

jhoweld@gmail.com wrote: ↑

February 20th, 2023, 9:54 am

You'd think that power calculations and calorie calc's would need to know what drag you are set at. In fact, almost every statistical output would be affected by changing the resistance setting wouldn't it?

No.
Search the forum, there are innumerable threads about drag factor. On the rower, the DF only changes the feel (like a heavier dory or lighter racing boat), not the metrics that are displayed on the monitor. DF is a personal preference, so set it where you like it. The power, calories, pace are all dependent on YOU, the rower.

I don't have ErgData for my rower, so don't know if it displays DF, but again, it wouldn't make any difference in the metrics, it would be an information readout only.

You can display drag factor on ergdata and it is pushed to your logbook by ergdata, so - yes, ergdata knows your drag factor.

if the drag setting of the rower is used at all?

It's us that needs to know the drag factor, not the machine, when we get on a different one. Can also go by feel.

Drag is Impedance: High impedance means high force low speed; Low impedance the opposite. The machine sees the flywheel speeds at each catch and release, so already knows enough about its energy status, given the Inertia.

Set it so that you can row a full length stroke at any rating without using excess force, which could cause injury and/or stop you before the end of the race.

The pull/recovery time ratio is what makes us feel comfortable or not. We are essentially rhythmical if not musical beings, and the waltz is amazingly beneficial if prolonged. It needs us to work at UT1 level: seeming effortless once we know how and have done enough of it.

jamesg wrote: ↑

February 21st, 2023, 2:32 am

if the drag setting of the rower is used at all?

It's us that needs to know the drag factor, not the machine, when we get on a different one. Can also go by feel.

The monitor needs to know the dragfactor as well. It is an essential part of the transition of rotational metrics (angular postion, angular velocity and angular acceleration) into linear metrics (distance, speed, power).

Could be, according to how complex your approach is. But once we know the speeds and times of the flywheel, of known inertia, and can determine the peaks, we know the power and the only conversion is W=kV³.

There is no rotational data to convert: all the PM gets is an impulse train.

jamesg wrote: ↑

February 21st, 2023, 4:38 am

Could be, according to how complex your approach is. But once we know the speeds and times of the flywheel, of known inertia, and can determine the peaks, we know the power and the only conversion is W=kV³.

There is no rotational data to convert: all the PM gets is an impulse train.

Nope. I am responsible for the physics engine of Open Rowing Monitor, I actually made software that replicates the PM5 behaviour to 0.05% accuracy. For all linear metrics, you need the dragfactor, see https://github.com/JaapvanEkris/openrow ... ar-metrics

The BikeErg (but not the RowErg or SkiErg) has an angle sensor on the damper. From time to time you need to calibrate it, to figure out the drag factor at various damper angles.

The RowErg and SkiErg measure the rate at which the flywheel coasts down during recovery. More coast-down, higher drag factor. The BikeErg can't do that as you pedal continuously for extended periods.

jhoweld@gmail.com wrote: ↑

February 20th, 2023, 9:54 am

I can't see an entry box to manually enter it and it doesn't seem clear whether the drag setting is somehow being transmitted from the machine. I find the latter suggestion hard to believe since I am using a Concept2 model C from the 90's.

As others have said, the Perfomance Monitor determines the drag factor from the decrease in the flywheel speed during the recovery. You don't have to enter it ; it is measured very precisely while you prepare for the next stroke.

jamesg wrote: ↑

February 21st, 2023, 4:38 am

Could be, according to how complex your approach is. But once we know the speeds and times of the flywheel, of known inertia, and can determine the peaks, we know the power and the only conversion is W=kV³.

There is no rotational data to convert: all the PM gets is an impulse train.

You are wrong. With a steady stroke, the power in the stroke is proportional to the drag factor and to the average radial velocity of the flywheel to the power 3 : P = DF * ωavg³.
Of course the radial velocity of the flywheel is not constant but increases during the drive. A good approximation is : ωavg = (2*ωmax + ωmin)/3.
ωmin is the radial velocity just after the catch and ωmax is the radial velocity slightly before the finish of the drive.

Note : the drag factor displayed on the PM has the physical units [mg m²] ; in the above equation the DF should be entered in [kg m²], hence a factor 10^-6 .

Cyclist2 wrote: ↑

February 20th, 2023, 11:16 pm

...On the rower, the DF only changes the feel (like a heavier dory or lighter racing boat), not the metrics that are displayed on the monitor. DF is a personal preference, so set it where you like it. The power, calories, pace are all dependent on YOU, the rower.

As explained above, the DF not only changes the feel but also the calculated power, pace, calories. What happens when you increase the DF and keep the power input the same, is that the average flywheel velocity drops. Flywheel velocity and handle speed in the drive are directly proportional. To keep the power constant at a higher DF, the handle speed drops but the force pulling the handle has to increase.