Damper setting - I don't get it

[Bob S.]

@ Jack. Did you check out the "physics of rowing?" I have not spotted it there myself, but that does not mean that it isn't in there. I have looked at that page a lot, but did not specifically hunt for that item. A direct post of enquiry to one of the C2 techs that post here fairly often might be the best why to find out.

Bob S.

[jackarabit]

From Concept 2|

"Between each stroke, the machine measures how much your flywheel is slowing down to determine how sleek or slow your “boat” is. This rate of deceleration is called the drag factor. The erg uses the drag factor to determine from the speed of the flywheel how much work you are doing. This way, your real effort is calculated regardless of damper setting".

Sounds to be something like:

df = RPM of fan @ finish - RPM of fan @ catch plus the usual Newtonian rate of change perspective. I don't know the range of RPM generated by average to exceptional ergers so don't know if the range of deltas/whatsit/whatsit would be a good fit with quantification by ~90-210? You're the Physics teacher, Bob. Give us a clue here! Jack

[maestroak]

So if this is how it works, why does the "towel trick" that was discussed a few months back work? Is it just a matter of it being at an extreme so these calcs breakdown?

-Steve

[Bob S.]

You're the Physics teacher, Bob. Give us a clue here! Jack

Sorry, Jack, but my field was organic chemistry. Or were you referring to another Bob? I had the usual 2 years of lower division physics required for engineers and physical scientists in those days, but that was completed before 1950. I did try an upper division course in analytical mechanics, but bombed it.

Bob S.

[coastline]

The unit of the drag factor is given in http://www.atm.ox.ac.uk/rowing/physics/ ... l#section7

"The calculated 'Drag Factor' k can be displayed on the Concept monitor (units 10^(-6) N m s^2)"

The unit can also be expressed as Ws^3, equation 3.3, or kgm^2 (mass moment of inertia), equation 7.2.

Note the scaling factor of 10^(-6).

The displayed drag factor equals the power dissipation (in Watts), at an angular velocity of the flywheel of 100 rad/sec.

The corresponding handle speed, with a 14 tooth sprocket, 1/4" pitch, is 1.4 m/sec.

[lindsayh]

The unit of the drag factor is given in http://www.atm.ox.ac.uk/rowing/physics/ ... l#section7
"The calculated 'Drag Factor' k can be displayed on the Concept monitor (units 10^(-6) N m s^2)"
The unit can also be expressed as Ws^3, equation 3.3, or kgm^2 (mass moment of inertia), equation 7.2.k
Note the scaling factor of 10^(-6).
The displayed drag factor equals the power dissipation (in Watts), at an angular velocity of the flywheel of 100 rad/sec.
The corresponding handle speed, with a 14 tooth sprocket, 1/4" pitch, is 1.4 m/sec.

Thanks Bjorn but I am still thing "catspaws" as Jack has suggested!
That is one serious equation.

[Citroen]

So if this is how it works, why does the "towel trick" that was discussed a few months back work? Is it just a matter of it being at an extreme so these calcs breakdown?

-Steve

The towel trick worked on old performance monitors that didn't recalculate drag factor on every stroke, but only did it on every sixth stroke.

[jackarabit]

I'm having a moment of inertia after tracing Coastline's glyphs with my finger while drooling down my front. Wow, got to be careful what you ask for! A mere bagatelle to be sure but I couldn't help noticing: Would the expression Kgm^2 be more properly expressed as Kg m^2? Just kidding folks! Jack

[speedy]

Huh? What????

From Concept 2|

"Between each stroke, the machine measures how much your flywheel is slowing down to determine how sleek or slow your “boat” is. This rate of deceleration is called the drag factor. The erg uses the drag factor to determine from the speed of the flywheel how much work you are doing. This way, your real effort is calculated regardless of damper setting".

Sounds to be something like:

df = RPM of fan @ finish - RPM of fan @ catch plus the usual Newtonian rate of change perspective. I don't know the range of RPM generated by average to exceptional ergers so don't know if the range of deltas/whatsit/whatsit would be a good fit with quantification by ~90-210? You're the Physics teacher, Bob. Give us a clue here! Jack

I like the Concept2 explanation better. You guys were way too technical that I was totally lost; felt like but in 95 when I was in calculus class and I was ...HUH? Yet I got an A+ in College Algebra. Go figure!

But in short it's exactly what I thought it was. The distance it covers after you do the stroke. So each stroke can change the drag factor up or down depending on the damper setting as well as how much pull/force is used. In terms of being on the water for there are technically more things involved in a boat sense including current which the damper in a way represents as much as the boat itself. Also, the direction of the current you are following for if I follow the current it requires less effort where if I go against the current it requires more effort then there is the force of the current to consider, then again the boat/floating device you are on. For instance I just did SUP this past Sunday and less effort and I still was going faster than when I was on a kayak.

But in the end, even if I get a boat down the road I still won't bother with the numbers. I am more about learning from doing. But I get the just of the drag now. Note for future reference, the other explanations will go over the average person's head that doesn't have a in-depth knowledge of the topic in hand sort of speak. Not sure if you did that on purpose but I have my answer now.

[jackarabit]

A lot of fellers would like to see the boat coast 220m after they pull the sticks out out of the puddle, Speedy. Same on the erg. When I stop stroking, accumulated distance number on monitor never increases by more than 10-15m before freezing. Fan/flywheel may continue to move but has no further influence on the calculation. 15 is not in the range of df numbers.

?

[Bob S.]

So it all comes down to:

10exp-6 N m s2 = 1 catspaw.

The only thing that bothers me about it is the unit N, which was defined sometime in 1946, about the time I completed the semester of basic mechanics, Physics 1A. I believe that it replaced what we called kg of force, i.e. the force exerted by 1kg of mass under the pull of standard gravity, AKA a kg of force to distinguish it from a kg of mass. I can see why the new (as in Newton) unit since using 2 different kinds of kg could be confusing. It was quite a while later that I heard about the new unit and, until now, never bothered to find out what it was all about.

Bob S.

[speedy]

A lot of fellers would like to see the boat coast 220m after they pull the sticks out out of the puddle, Speedy. Same on the erg. When I stop stroking, accumulated distance number on monitor never increases by more than 10-15m before freezing. Fan/flywheel may continue to move but has no further influence on the calculation. 15 is not in the range of df numbers.

?

Well I never calculated nor guessed a number, but one coasting can be determined by a current. I am not saying the numbers will be high or low but depending on what the person is on can determine that. For instance, when I took my SUP class there was a part where the current at the opposite direction was so strong we had to paddle stronger for at the current stroke speed/power we weren't even moving, just staying in place. Then same spot going with the current the SUP took off like a bullet to the point I almost dropped to my knees to avoid falling into the water.

As far as the fly wheel not having a effect, well isn't that by design?

[sekitori]

I have been told by those at C2 that the maximum and minimum drag factors decrease as the rower ages. C2 states the following. Notice the words "brand new rower":

"A brand new indoor rower will have a drag factor of about 90–100 at a damper setting of 1 and about 210–220 at a damper setting of 10."

My C2 Model D is now close to 12 years old and this fact seems to be true. My maximum damper setting is now about 185 and my minimum is around 80 when the cage is completely clean.

Why is this true? I would think that as long as the rower is working properly, those numbers should not change no matter how old it is. On the other hand, I doubt if they are really that important. I assume that most people row in the 120-140 range and if those drag factors can easily be attained, very high maximums and very low minimums mean very little.

One interesting note. After I remove the perforated band between the two cage halves and wash it with a detergent, the range increases considerably. Apparently, dust inside the cage can also affect the band and simple cleaning with Windex or something similar won't get rid of it.

[Balkan boy]

"A brand new indoor rower will have a drag factor of about 90–100 at a damper setting of 1 and about 210–220 at a damper setting of 10."

There's a 15 years old Model C at my gym that gives out exactly those drag numbers.
It's been cleaned once, on my insistence, in the past 4 years, it screeches and grinds, chain has never been lubed and it's misused by many.

So not brand new is what I'm saying.

[Carl Watts]

One interesting note. After I remove the perforated band between the two cage halves and wash it with a detergent, the range increases considerably. Apparently, dust inside the cage can also affect the band and simple cleaning with Windex or something similar won't get rid of it.

You are correct, just a brush doesn't actually end up cleaning out the holes, as you pointed out you need wash it with detergent as the dirt and dust really sticks in the outside area round the holes. The water gets pretty dirty. Compressed air helps a lot through the holes to dry and remove everything and get it back to brand new condition. The leading edges of the fan also get quite a build up, in the end I remove the flywheel/fan to enable it to be cleaned properly and also add a tiny amount of grease to the clutch/one way bearing and reassemble it.