C2 Erg Prototype

[bloomp]

John,

I think you're overlooking the benefits of having a moving seat. Think of there being a 'wall' you hit because the seat doesn't move. By having the seat and footplates move there is 'give' in both directions.

[DUThomas]

I think a moving pitching mound is somewhat different in that the movement of the mound would directly affect the speed of the pitch. The C2 prototype (or any erg) essentially captures the energy expended in unfolding oneself. The seat movement would be caused by imbalances between the pushing force with the legs and the pulling with the arms and back, but the amount of "wasted" energy (i.e., energy not being measured by the erg) would likely be small.

People who actually know something about physics can correct everything I said.

[johnlvs2run]

Paul,

With or without the seat fixed, the feet move and the erg is dynamic like on slides.

However, the seat is moving rather aimlessly on the prototype.

[johnlvs2run]

The seat movement would be caused by imbalances between the pushing force with the legs and the pulling with the arms and back,

One should balance the other.

Currently there is way too much movement of the seat.

[NavigationHazard]

If you fix the seat then you have to have a longer rail than the prototype so that tall ergers don't slam into frontstops every drive when they try to extend their legs.

The prototype that was at HOTC had a relatively unforgiving seat. Since it didn't go back, I could bang into frontstops every stroke without trying too hard. There are rowers out there taller/longer-legged than I am (cf. Sjoerd Hamburger, Pavel Shurmei, Jamie Schroeder) who would find that unworkable no matter how they adjusted their technique.

The more forgiving seat on the revised model at Crash-Bs largely eliminated the problem. I could still hit front stops on the drive but as JonW will testify I had to try to do it.

I don't see how you can keep a small footprint for the machine with a fixed seat. C2Jon may have a professional opinion, but in my present view the two are fundamentally incompatible.

[johnlvs2run]

Nav,

I agree the railing is too short, though that is a problem with the railing not the seat.

If the seat were fixed and the railing longer, the erg would still be much shorter than a modelCDE.

For example if the railing were 4 or even 5 feet long, then no one would hit the footplates to the end.

The modelCDE is 7 feet 11 inches in length.

[NavigationHazard]

FWIW here's a force curve off the prototype:



Photo courtesy of Mary Van Buren.

The herky-jerk bit in the catch is from unfamiliarity with the prototype as opposed to a grounded erg, and from seeing what would happen if you were to try to 'gorilla' the stroke.... In my defense I was in street clothes....

[Rockin Roland]

A fixed seat strays too far away from the ideal of the feel of a boat on the boat. A doubt that Warren would have much in the way of OTW rowing experience to know what to look for in designing a dynamic erg.

A moving seat is essential for the new C2 prototype. Both the Oartec Slider and new Rowperfect have moving seats however the amount of travel is quite contrasting between the two.

The Oartec Slider allows you to move the seat the length of the rail which is a considerable distance. I noticed that experienced rowers with good technique only needed 1-2 inches of travel on the Slider whereas gym junkies with poor technical form ran into difficulties because they used way too much seat travel. In contrast the new Rowperfect combats this problem for novice rowers by having an upward bend in the rail and a restraining bungee cord from the back of the seat to the end of the rail. In this way you are guided into rowing with correct technique.

The first C2 prototype has limited seat travel but doesn't seem to need such aids because it has a tendancy to operate more like a leg press than something closer to a boat on the water which is a little bit dissapointing.

[johnlvs2run]

Warren has quite a bit of rowbike experience, plus his design of the fixed seat rowing ergometer in 2000.

Here is a clip of Warren on one of his rowbikes.
http://www.rowvelo.com/video/both_hill.mov

[eldberg@cstone.net]

Folks,

Glad to see that there is lots of interest in the design.

doubt that Warren would have much in the way of OTW rowing experience to know what to look for in designing a dynamic erg.

It is true that I have never rowed a shell, but I have many thousands of miles OTR, most in the mountains over the last ten years.

I went through the same iterations C2 did.

From my notes: 12-31-00 22 minutes rowing, 116.5 watts ave., 55spm, free seat

That was my first row of any length on the prototype. The seat slid just as on the original C2 prototype. It felt vague, or herky jerky.

01-04-01 11 minutes rowing overhand, 120.6 watts ave., 40-45 spm
11 minutes rowing underhand, 113.1 watts ave., 40-45 spm, seat bungee, feels great!

That was with the seat restrained by bungees, as on the latest C2 prototype.

Fixing the seat would demand a longer rail so that tall rowers could extend their legs fully. It's incompatible with the present prototype's small footprint.

Not so. The rail needs to be as long as the distance from the back of the seat to the tips of the toes of the tallest rower...period. If you want the seat to have some room to move back and forth, you must make the rail longer to accommodate any backward movement of the seat.

I decided to try a fixed seat to reduce length, and complication. It worked fine. There was a little tendency to wiggle your bottom on the seat, but the vast majority of erg users are "gym junkies with poor technical form", as someone on here condescendingly said, referred to those of us without the good breeding to row a shell!

01-13-01 another 22 min., this time with an almost rigid seat on rubber blocks

This is how I left it. The rubber blocks under the seat allow it to feel tippy side-to-side to simulate sitting in a boat.

Either way, it is great exercise. And almost as much fun as swinging on a swing...still one of the greatest body rushes you will ever have!

Warren

[eldberg@cstone.net]

Folks,

I have been told that the moveable stretcher assembly on the prototype weighs about 30 pounds

I can see that I was on a different track than the C2 people. I was trying to reduce the strain on my knees and back as much as possible. It never would have occurred to me to strap the equivalent two car batteries to my feet.

They are obviously trying to simulate the feel of a shell. I suspect that by experimenting with the masses they can do that.

By getting my fat butt out of the loop, and only having to move the mass of my extremities, and a light stretcher and row bar, I was able to get more power to the flywheel too. Being an old hotrodder, this appealed to me.

On 03-24-01 I did the first Annual C2 Marathon. 3:28:38.4 for 42,200 meters, 138 watts ave., 41 spm ave., low gear, and one of my homemade damper rings.

This doesn't sound very impressive I know. But I would not have finished, let alone in this time, on a stock C2. My joints wouldn't have taken it.

Warren

[johnlvs2run]

Warren,

Thanks for posting on the forum and sharing your insights.

I have been told that the moveable stretcher assembly on the prototype weighs about 30 pounds

30 pounds?

The prototype chain attachment is quite low under the seat, and could be much closer to the railing.
Ditto the lower pulley in front, and the higher pulley looks too high (compare with Warren on previous page).
Warren, you're the expert in these things. I am thankful for your comments.

[eldberg@cstone.net]

John,

30 pounds?

Yes. They may have been referring to the one on the first prototype. The latest one doesn't look that massive.

The prototype chain attachment is quite low under the seat, and could be much closer to the railing.

Doesn't matter a wit. They needed to get the cord in line with flywheel under the seat. Logical location. I had thought the ultimate setup on a production version would be to have it under the seat, maybe on its side, with the air directed up on the user. I get some air flow on my back with mine.

the higher pulley looks too high (compare with Warren on previous page).

No. I think they are about the same. They have matched mine pretty closely. Even down to the hook on the stretcher for holding the rowing handle!

Warren

[johnlvs2run]

Warren,

Thanks for your reply.

What do you think is the case of the herky-jerky on the prototype?

John

[eldberg@cstone.net]

John,

"What do you think is the case of the herky-jerky on the prototype?"

You need to be attached to something to work from. That is why astronauts have so much trouble using a ratchet in space.

In a shell your feet are attached to the hull, which has some mass, plus the drag of all that water. Not as easy as sitting on the ground, but probably a better anchor than a seat and stretcher on rollers. By attaching bungees, and in C2's case replacing the rollers with plastic skids, you are able to reduce the float as much as you like. Playing with that, and the mass of the stretcher, you should be able to get a feel that approximates the "loose" connection you'd have in a shell.

Notice I got through that without using the terms "static" or "dynamic". Manufacturers throw those terms around the way motivational speakers like to use the term "quantum".

Warren