Concept2 Forum

I'm very sorry if the answer to my first question as a noobie is self-evident, but I am frankly stumped as to what is happening, and I'm not even sure if it is at all important.

I read all the articles and posts I could explaining about the setting the drag factor setting with the damper. Then I went through a few drills recommended by an Aussie coach as to how to determine which damper setting worked the best for me as a function of said drag factor, that is, where I felt the most comfortable. This turned out to be around df 130-135 on my very recently-purchased C2 as displayed on the "Row to display drag factor" screen on the PM5. Then I started to sign into ErgData and do the daily WOD. Knowing that I'm going to be named (or shamed) on the board for all the world to see makes me work harder from start to finish and hopefully will help to improve.

The data for each workout includes the drag factor.....this is consistently around 116-119, despite showing 133 on the "display drag factor screen". During the workouts I'm rowing as hard as I can while still making it to the finish, and my 500 splits are relatively steady. Also, I have the display set to show the power curve and it shows the strokes to be fairly smooth and uniform, and not conical.

Please explain to me what I am doing incorrectly. Thanks very much.

There is some variation expected, so a drag factor is set using the screen, it deviates one or two points maximum from your training.

However, the change you describe is quite big. Could something disrupt the airflow (for exampke a T-Shirt or towel on the cage)? Did you pull a good set of strokes?

iahoka wrote: ↑

August 9th, 2022, 10:31 am

The data for each workout includes the drag factor.....this is consistently around 116-119, despite showing 133 on the "display drag factor screen".

Neat.

You are setting drag factor correctly using the only procedure. Good. Downloaded workouts can't change the drag factor. Your drag factor is 133 as long as you don't move the damper or interfere with the fan cage (e.g. hang a towel over it, blow a fan at it, move a box next to it, etc)

Where are you reading the 116-119 value?

What drag factor shows up in the log entry for the workout after you upload to the C2 log ?

iahoka wrote: ↑

August 9th, 2022, 10:31 am

I'm very sorry if the answer to my first question as a noobie is self-evident, but I am frankly stumped as to what is happening, and I'm not even sure if it is at all important.

I read all the articles and posts I could explaining about the setting the drag factor setting with the damper. Then I went through a few drills recommended by an Aussie coach as to how to determine which damper setting worked the best for me as a function of said drag factor, that is, where I felt the most comfortable. This turned out to be around df 130-135 on my very recently-purchased C2 as displayed on the "Row to display drag factor" screen on the PM5. Then I started to sign into ErgData and do the daily WOD. Knowing that I'm going to be named (or shamed) on the board for all the world to see makes me work harder from start to finish and hopefully will help to improve.

The data for each workout includes the drag factor.....this is consistently around 116-119, despite showing 133 on the "display drag factor screen". During the workouts I'm rowing as hard as I can while still making it to the finish, and my 500 splits are relatively steady. Also, I have the display set to show the power curve and it shows the strokes to be fairly smooth and uniform, and not conical.

Please explain to me what I am doing incorrectly. Thanks very much.

If your preferred drag factor is 130-135 as shown on the PM then it doesn't matter that it shows something else on Ergdata. If your damper hasn't been changed the drag factor will remain the same. It's just numbers. The actual drag did not change just the reporting of it.

kini62 wrote: ↑

August 9th, 2022, 4:02 pm

If your preferred drag factor is 130-135 as shown on the PM then it doesn't matter that it shows something else on Ergdata. If your damper hasn't been changed the drag factor will remain the same. It's just numbers. The actual drag did not change just the reporting of it.

Sorry,

You couldn't be further from the truth here. ErgData reports the actual drag as calculated through the entire rowing session, which is the basis for all displayed metrics on the PM5 during that session: ErgData reports the average of the per-stroke drag across the session. So when there is a serious conflict between the drag displayed on the PM5 prior to rowing and ErgData during the session, ErgData is in fact leading.

There are several factors that could explain such a big difference: obstruction of the airflow (moving the rower closer to a wall, towels over the cage) is the most likely one. Another is that the strokes that were used for displaying it on the PM5 were quite explosive where the session was quite relaxed. As the C2 isn't a 100% perfect, you get some deviation there due to mechanical en electrical effects, although this big is surprising.

JaapvanE wrote: ↑

August 9th, 2022, 4:58 pm

kini62 wrote: ↑

August 9th, 2022, 4:02 pm

If your preferred drag factor is 130-135 as shown on the PM then it doesn't matter that it shows something else on Ergdata. If your damper hasn't been changed the drag factor will remain the same. It's just numbers. The actual drag did not change just the reporting of it.

Sorry,

You couldn't be further from the truth here. ErgData reports the actual drag as calculated through the entire rowing session, which is the basis for all displayed metrics on the PM5 during that session: ErgData reports the average of the per-stroke drag across the session. So when there is a serious conflict between the drag displayed on the PM5 prior to rowing and ErgData during the session, ErgData is in fact leading.

There are several factors that could explain such a big difference: obstruction of the airflow (moving the rower closer to a wall, towels over the cage) is the most likely one. Another is that the strokes that were used for displaying it on the PM5 were quite explosive where the session was quite relaxed. As the C2 isn't a 100% perfect, you get some deviation there due to mechanical en electrical effects, although this big is surprising.

I'm not wrong. What I said is that if he prefers the drag with the PM showing 130-135 then it doesn't matter if that is right or wrong. It is what it is, his preferred amount of drag, no matter what ergdata says.

kini62 wrote: ↑

August 9th, 2022, 6:12 pm

I'm not wrong. What I said is that if he prefers the drag with the PM showing 130-135 then it doesn't matter if that is right or wrong. It is what it is, his preferred amount of drag, no matter what ergdata says.

Until someone touches the slider or you use a machine in another gym, you can't find your optimal setting back. Or the machine is now at a suboptimal setting due to a change in airflow. As a rower it is an important number to get right, as it allows you to get back to a setting even when someone touched the dial, temperatures/humidity changes or obstructions occur.

ErgData only records what the PM5 calculates, based on the exact same calculation used for the "Display dragfactor", but then across hunderds of strokes instead of just two. The PM5 recalculates the drag for each recovery phase during a session, and adjusts the dragfactor for that stroke. This is structurally reported through the Bluetooth interface to ErgData.

The PM5 software has plenty of flaws, but miscalculating DF certainly isn't one of them (as I am the lead developer of OpenRowingMonitor's physics engine, I systematically compare every stroke in every session with our own algorithm). Worst variation for me was at DF 222, with +/- 3 across a 6K. At DF 133 the worst variation I've seen is +/- 2 points across a session. As it happends to be close to my DF setting for the 2K and 5K, it has been tested a lot. Over 10 point either the dial moved or the airflow is obstructed somehow.

When there is a conflict between the two with this much variation, one of them has to be wrong somehow. So either the determination of the 133 was wrong (not a big issue, just redo the test or accept the 119 value if the session felt good) or the 133 was right and the machine is now at a suboptimal setting due to some circumstance.

I too see discrepancies between PM DF and ergdata V2. But no others, so evidently the sums haven't changed, must be still the PM that does the math, not ergdata which just copies. No explanation yet. Feel is same as before, so haven't moved anything.

jamesg wrote: ↑

August 10th, 2022, 12:50 am

I too see discrepancies between PM DF and ergdata V2. But no others, so evidently the sums haven't changed, must be still the PM that does the math, not ergdata which just copies. No explanation yet. Feel is same as before, so haven't moved anything.

There are, typically you get one to two points deviation in my experience. I blame subtle mechanical properties as I typically do the initial PM5 DF on three or four strokes. Thus the flywheel isn't a 100% on speed, and some types of drag (mechanical from the bearings, electromagnetic from the generator/sensor) scale linear instead of quadratic (like the air) with the flywheel speed. So when you speed up the flywheel further during training, the drag mix changes slightly, and the dragfactor follows.

During a training, you see subtle fluctuations in the drag as well, probably due to the same effect. Both the PM5 and ORM fluctuate. As we know the inner workings of ORM, and that it reports a very high 0.97 match with the data, we think it is mechanical in nature. When the dragsetting increases the stroke-by-stroke difference in DF becomes bigger. Our hypothesis here is that due to the high drag the flywheel slows down more, and thus subtle timing issues result in a lower flywheel speed, and thus subtle drag changes (of +/- 3). But given enough strokes, you get a decent average.

Thanks very much to all. I just now looked at the replies and haven't had a chance to look at each workout to see the difference between the "set" df and the "calc'd" df (which show up in the logbook on each workout towards the bottom of the data page).

But I'll get back to you all with specific numbers. Sufficed to say, I've not moved the rower nor have I laid towels, etc, over the cage, so at least obstruction is eliminated.

Again, thanks for the thoroughness of your answers.

I am unfortunately old enough (in my very late sixties) to remember the good old days when help desks for anything electronic were staffed with actual humans at the other end of the line. Two of their most common help questions were "have to checked that it is plugged in" and "did you try turning it off and back on?" I'm reminded of this more and more often nowadays.

When I work out on any gym machine I don't wear the contact lenses needed to correct the corneal ectasia I suffer from due to sweat running down into my eyes. This is particularly true on the C2 because it causes me to sweat like crazy and the lenses become instantly clouded and very hazy.

Which explains why I've been reading a df of 133 when it actually displays 122. This became obvious when I sat down today to check everything and saw both the reading of df 122 and the damper set in the middle of 4 rather than the middle of 5. After resetting the damper and displaying df 133 I did a workout and at the end it showed measured df 133.

Again, thank you all, and especially JaapvanE for the thorough explanations, and I assure you that I do in fact feel really dumb right about now.

My DF on Ergdata matches the PM5. Not much help I know. I’m on iPhone 11 version 2.03, firmware version 171 on pm5.

iahoka wrote: ↑

August 10th, 2022, 11:49 am

Which explains why I've been reading a df of 133 when it actually displays 122. This became obvious when I sat down today to check everything and saw both the reading of df 122 and the damper set in the middle of 4 rather than the middle of 5. After resetting the damper and displaying df 133 I did a workout and at the end it showed measured df 133.

Again, thank you all, and especially JaapvanE for the thorough explanations, and I assure you that I do in fact feel really dumb right about now.

You're welcome, glad that I could help you!

And we all have these days. A couple of weeks ago I grabed my towel after the workout, just to discover it was my oilrag (used to lube the chain) after I tried do dry my face.

Well, at least you have oil on your face......I've got egg all over mine. But I will admit I really enjoyed the comments on how it works, and how it applies to the erg as if it were rowing on water. The feel is indeed the important thing. It's interesting to learn how this machine really works, and how to keep the main thing in the forefront.