Can there be "easy" and "hard" ergometer

gcanyon · Post by **gcanyon** » April 7th, 2006, 10:08 pm

John Foy wrote:Does the tension of the shock cord on an erg change the pace that a given effort will produce? I hope not. That would really mess things up in terms of racing.

I think it does, but hopefully only in a very slight way. During the drive you are doing two things:

1. Accelerating the flywheel.
2. Stretching the shock cord.

During recovery, the shock cord contracts, drawing the handle back in. The shock cord gets the energy to do that from step 2 above -- i.e. from you. It doesn't need much energy to do that, which is why I think it's not a big deal.

But imagine if there were twenty shock cords inside the C2. The recovery wouldn't be any different, except that possibly the handle would pull you back instead of you using your legs

But the drive would be much harder. Stretching out twenty shock cords takes a lot of work -- and that's work that's going into 2 above instead of 1. Hence the shock cord is robbing you of a small bit of performance. As I said, hopefully not much in the first place, and likely not enough to change much if one shock cord is a little different than another.

And in response to Citroen, remember that the C2 monitors the flywheel. Any energy that is used for 2 above is not available for 1, and the C2 is completely unaware of it.

Finally, consider a thought experiment: detach the chain from the flywheel altogether. Pull on the handle. Is it going to resist you? Yes -- the shock cord is going to resist you, and the C2 records nothing, because the flywheel isn't moving. Pile on another twenty, thirty shock cords and even Xeno would have a hard time pulling the handle for full strokes, but the C2 still records nothing.

c2jonw · Post by **c2jonw** » April 10th, 2006, 2:00 pm

Good Topic- The bungees sole purpose is to return the handle to the catch position and do so quickly enough to avoid slack in the chain. The bungee is a closed system that essentially stores energy as you stretch it during the drive and gives that energy back to you during the recovery- ie, it aids in returning your body to the catch position.
Certainly there is a small amount of energy lost in the friction of the bungee turning over pulleys and internal fiber movement. But as long as we are talking about a similar order of magnitude (4-8 pounds, not 40-80), this will be a very small amount and it will be very consistent between machines.
I would guess that the biggest potential source of wasted energy on a given machine would be a rusted or poorly lubricated chain. The monitor doesn't measure this and it's a common situation.
C2JonW

ancho · Post by **ancho** » April 11th, 2006, 4:13 am

I have my own model D at home since january.
I have the sensation that my own erg feels "harder" than those in our club or in the gym.
And by harder I mean that my splits use to be 2-3 seconds below the pace on "other" ergs.
I don't know if it's the machine, or if it's because at home I use to row at "strange" times (eraly in the morning or late at night).
Fact is that in 3 minths I only have managed to make 1 PB (6k) on my own erg, and the other day I did my 10k PB without pretending it.
Polaco has tested my erg and he says it's fine, but I'm somehow concerned about equilancies between different ergs.

gcanyon · Post by **gcanyon** » April 11th, 2006, 2:31 pm

ancho wrote:I have my own model D at home since january.
I have the sensation that my own erg feels "harder" than those in our club or in the gym.

Have you checked the drag factor? It's possible the ones in the club are very dusty and thus a setting of 4 on your new erg could be equivalent to a higher number at the club.

ancho · Post by **ancho** » April 12th, 2006, 5:51 am

gcanyon wrote: ...
Have you checked the drag factor? It's possible the ones in the club are very dusty and thus a setting of 4 on your new erg could be equivalent to a higher number at the club.

I always use to row at "confirmed" DF of 120-125.

gcanyon · Post by **gcanyon** » April 12th, 2006, 1:23 pm

ancho wrote:I always use to row at "confirmed" DF of 120-125.

Beats me then. The only other possibilities I can think of are a very stiff chain, very strong shock cord in the return mechanism, the environment is different (your home is warmer than the club, or the airflow is less).

Or maybe it's psychological.

Or your new D model really is harder.

johnlvs2run · Post by **johnlvs2run** » April 12th, 2006, 2:03 pm

c2jonw wrote:The bungee is a closed system that essentially stores energy as you stretch it during the drive

It takes strength and energy to stretch the bungee. A new and tight bungee takes more strength and energy to stretch. Try the experiment of snugging up the bungee another 18 inches, then row and see if there is any change in your time or effort.

charlesrwells · Post by **charlesrwells** » May 10th, 2006, 12:25 pm

I think that there can be easy and hard ergs, sometimes when you have older ones the chain can get somewhat rusty and be harder to pull.

staehpj1 · Post by **staehpj1** » March 6th, 2007, 9:33 am

Citroen wrote:RTFA I refered to; you total BOZO.

the article wrote:Things that are not compensated are:

* Changes in the chain friction
* Changes in the tension of the return mechanism
* Manufacturing variations flywheel moments of inertia (probably negligible)
* Changes in flywheel moments of inertia (unlikely with the solid flywheels)

Pardon me if I am dense, but that means that a tigher than necessary shock cord reduces your measured output, right?

PaulS · Post by **PaulS** » March 6th, 2007, 10:31 am

staehpj1 wrote:
Citroen wrote:RTFA I refered to; you total BOZO.

the article wrote:Things that are not compensated are:

* Changes in the chain friction
* Changes in the tension of the return mechanism
* Manufacturing variations flywheel moments of inertia (probably negligible)
* Changes in flywheel moments of inertia (unlikely with the solid flywheels)
Pardon me if I am dense, but that means that a tigher than necessary shock cord reduces your measured output, right?

Pardon granted. Technically yes, but since the Bungee is about 10' long and on a multi-pulley system, it is only being stretched 1/4 of the handle travel, so the tension at the release is very similar to the tension at the catch, and it would take a very large change to make what one might call a "significant" difference. Though perhaps we should argue that the shorter rowers have an advantage since they don't stretch the bungee as far.

ErgMonitor was verified for accuracy in it's calculated handle forces, and it was off by a near constant that turned out to be the bungee tension. So basically, the bungee tension costs us all something, the PM does not account for that cost, and as a percentage of total power that cost would be more for the weaker rowers.

johnlvs2run · Post by **johnlvs2run** » March 6th, 2007, 12:23 pm

As Paul has stated, the resistance in the bungee makes more of a difference when it's a greater percentage of the rower's strength and/or weight.

Another factor is that a rower with a lighter stroke for the pace is going to perceive a resistance more easily, whereas a rower with a heavy stroke will likely not notice any difference at all, even though the difference in resistance is the same for either of them.

Thus the percentage difference a tight bungee makes is a matter of one's weight and strength, though the amount of difference is the same, and whether this is noticed is a matter of the rower's type of stroke and perception.