Dynamic vs Stationary

[NavigationHazard]

I too am mystified by the proposition that a properly maintained, properly rowed C2 erg has "20-30 cm" (i.e. ~8"-12") slack at the catch before the sprocket engages fully. You sure you have your units right? Measured rather precisely with ErgMonitor, 2 cm on my erg (and on my club's ergs) is more like it on a typical drive. That's maybe 0.02 seconds' elapsed time. Here's a screen shot from a veteran LW rower illustrating the point:



The saddle-shaped green curve is handle speed against time. The 'catch slip' as he engages the sprocket (on a quite sluggish drive) is visible as the gap between the vertical axis and the left topside of the handle-speed curve. Here it's about 0.01 second as the sprocket engages. If you look at the blue force curve, you'll see a bit of a corresponding 'kink' at the left-hand base of it. That's a sign that he's 'feeling' for the catch with his hands and arms - even though he's actually got the handle going back fast enough to engage the sprocket, he doesn't really begin to lay on the force until roughly 0.04 into the drive. That is, there's a slight hesitation while he waits to feel fully engaged even though he already is sufficiently locked in. But 1) it's in the rower, not the machine; and 2) it involves nothing like 20-30 cm of chain being pulled.

If you propel the handle up the slide faster than the shock cord wants to retract it on the recovery, you can generate corresponding slack in the chain at the catch. This problem is easily solved: slower recoveries and/or adjustment of the shock-cord tension such that the handle retracts more quickly.

[jamesg]

The zero on the abscissa is (probably) where the flywheel starts to accelerate, so after the slack has been taken up.

2 cm to reach say 2m/s handle speed implies a handle acceleration of around 10g, somewhat unlikely, from v2=u2+2as.
1g acceleration to 2m/s needs 20cm; plus any mechanical slack.

When sculling, I've no slack at all; which is a problem too, for me, because it makes the stroke very long and so with much more work in it.

[jamesg]

Anyway, I had a another go on both Oartec and Dynamic at Goldie boathouse yesterday, and must correct my impression of less slack; both show it, albeit limited by Newtonian effects (less mass to accelerate, so it's quicker and hence shorter). It's less noticeable, because the stretcher moves rather than us, but there all the same.

As usual, the first pull from stationary has no slack at all.

I set drag low so that I get a smooth transition into the pull, which implies it is longer that strictly necessary, in my case. But I never had any type of injury from erging, and don't wish to find new ways to get one.

[johnlvs2run]

James, thanks for those updates. I agree the slack is much more than 2cm on the erg.

Here is lightweight Sebastian Baes rowing 20:01 for a 6k on a modelD erg. It is readily visible that the flywheel is not engaging until the handle has moved back to his feet, a distance of at least 20-30cm from the catch. Even so, he manages to keep his arms straight through that movement, quite an impecable style, though it is probably hard on his ribs.

In comparison, the empty space likewise shows up greatly at 45 spm in the latter part of this video of Joe Sullivan on an Oartec Slider, where he is trying to make up for the space by contorting his body and twisting his arms. Notice again the handle had moved from the catch to over his feet before finally engaging. The space was not evident at the beginning of the video because the movement at 18 spm was too slow. This well demonstrates the differences in empty space between rowing at different ratings, and also the height of the rower.

I've not yet found a Concept2 dynamic at higher ratings. If someone finds one please post it. Here is one at low rates, which of course doesn't show anything.

[johnlvs2run]

Anyway, I had a another go on both Oartec and Dynamic at Goldie boathouse yesterday, and must correct my impression of less slack; both show it, albeit limited by Newtonian effects (less mass to accelerate, so it's quicker and hence shorter). It's less noticeable, because the stretcher moves rather than us, but there all the same.

As usual, the first pull from stationary has no slack at all.

I'm very interested to see results between these two machines. That's a good point about the first pull not having any slack.

I set drag low so that I get a smooth transition into the pull, which implies it is longer that strictly necessary, in my case.

Yes, I think that is always the case, as the fan is going much faster at low drag and therefore the empty space will be greater.

[slwiser]

I've not yet found a Concept2 dynamic at higher ratings. If someone finds one please post it. Here is one at low rates, which of course doesn't show anything.

Try this one on for the Concept Dynamic: http://www.concept2.com/us/indoorrowers ... c_home.asp

Over on the right are links to several examples of rowing and one is at "race speed" of 36 spm.

Thinking about the issue of slack at the handle during the early part of the stroke makes me wonder....

Aren't we supposed to be pushing with the legs with the arms/hands straight out during this portion of the stroke? So what then is the issue with slack in the handle during this period? I don't see this issue with any of the examples in the post above.

[johnlvs2run]

Try this one on for the Concept Dynamic: http://www.concept2.com/us/indoorrowers ... c_home.asp

The video at upper right shows a guy just standing there talking, not rowing.
The one showing Dick and Peter on the screen comes up blank. At least Oartec shows a guy rowing at 45 spm.

The issue is that (1) the energy from the first part of the drive is not being applied to turning the fan, and (2) that part of the drive length is used up with none of the length being applied to turning the fan.

Discerning eyes can see where the handle engages the fan. It's where the handle flies out, then stalls above the feet, as the energy starts being applied to the fan at THAT point, not at the beginning of the catch.

[Bob S.]

Try this one on for the Concept Dynamic: http://www.concept2.com/us/indoorrowers ... c_home.asp

The video at upper right shows a guy just standing there talking, not rowing.
The one showing Dick and Peter on the screen comes up blank.

Personally, I had no trouble finding the proper video. I checked his strokes against my watch and it looked to me to be right on 36spm. Did you try clicking the button labelled 36spm? It was a guy erging - not talking.

Bob S.

This is what the site shows:
Advantages of the Dynamic Indoor Rower
Steady State @ 21 spm
Effective Start Sequence
Race Pace @ 36 spm
Try that 4th button

[johnlvs2run]

Did you try clicking the button labelled 36spm? It was a guy erging - not talking.

Yes, that one also comes up blank.

[slwiser]

Did you try clicking the button labelled 36spm? It was a guy erging - not talking.

Yes, that one also comes up blank.

You need a new edition of flash for you browser I think.

BTW, I obviously do not have "Discerning eyes" that can see where the handle engages the fan.

[johnlvs2run]

You need a new edition of flash for you browser I think.

Perhaps, though I tried with two different operating systems, both of them new within the last couple of months.
Everything on youtube works well for me, and c2 is on youtube but not any c2 dynamic 36-45spm video.
Maybe they don't want me to see it.

I'm interested to compare the c2 dynamic with the Oartec Slider.

[slwiser]

Maybe they don't want me to see it.

They are smarter than the usual website to target you personally...

[johnlvs2run]

Maybe they don't want me to see it.

They are smarter than the usual website to target you personally...

It is very crafty on their part.

[Tinus]

The zero on the abscissa is (probably) where the flywheel starts to accelerate, so after the slack has been taken up.

2 cm to reach say 2m/s handle speed implies a handle acceleration of around 10g, somewhat unlikely, from v2=u2+2as.
1g acceleration to 2m/s needs 20cm; plus any mechanical slack.

When sculling, I've no slack at all; which is a problem too, for me, because it makes the stroke very long and so with much more work in it.

In order to determine the force you don't necessarily measure where the flywheel starts to accelerate but instead where it stops to decelerate. This happens already at a fraction of 2 m/s handle speed. The chain doesn't need to move at the speed of the flywheel in order to apply force. I don't know the exact cut-off value but I am sure it can be expressed as a fraction. 20 cm is also silly it would be visibly by the naked eye very clearly. 20 cm may be apparent in those cases when the rower is not keeping the hands at the proper height and starts the drive before the arms and chain are aligned (e.g in the foreground of this vid http://www.youtube.com/watch?v=FjY3eKNvzug).

[johnlvs2run]

The chain doesn't need to move at the speed of the flywheel in order to apply force.

Please explain how this works.

I don't know the exact cut-off value but I am sure it can be expressed as a fraction. 20 cm is also silly it would be visibly by the naked eye very clearly. 20 cm may be apparent in those cases when the rower is not keeping the hands at the proper height and starts the drive before the arms and chain are aligned (e.g in the foreground of this vid http://www.youtube.com/watch?v=FjY3eKNvzug).

You can see this in Rob Smith's drive too, where there's a hesitation when the handle gets right over his ankles.
At the end when his stroke length is less, the glitch moves forward and is very close to the catch. This might indicate the empty space is as much from a delayed chain return as it is from the chain catching up with the fan.