Is it possible to monitor check on an erg?
Charles Carroll
Anyone who followed the thread on the Accelerometer may be interested to
know that yesterday morning UPS delivered ours. I will offer a more
extensive report on them in a couple of days.
Chris Dadd, however, offered an initial comment that I found intriguing. I
am curious to know what others might think.
Chris, by the way, is the rowing coach for Berkeley High School, and also
coaches at my Club in Sausalito and several other Clubs in the San Francisco
Bay Area. Chris is also an active and very fine sculler. And I can tell you
from person experience that he is an excellent sculling coach.
So anyway Chris was with us when we opened the package and were going
through the Accelerometer's six modes. The Clock, Rate, various Start Modes,
etc., were all interesting, but not particularly unusual.
"It would be really cool if it had a Check Boat Mode," said Chris.
"It does," I answered. "That's why I ordered it."
Then Chris said something that surprised me.
"I've always thought that this is the one important function missing in the
C2's monitor. The erg would be so much more useful to people who row on
water if the Performance Monitor could analyze how much you were checking."
So I am curious. Could you build a check analysis factor into the
Performance Monitor? Is this feasible?
Cordially,
Charles
sjgid...@aol.com
wrote:
I am not sure how you would measure "check" on an erg, as it is
stationary. Check implies interfering with the forward motion of the
boat, either at the finish or at the catch.
Ted van de Weteringe
> I am not sure how you would measure "check" on an erg, as it is
> stationary. Check implies interfering with the forward motion of the
> boat, either at the finish or at the catch.
As I understand the concept, 'check' is kicking the stretcher before the
blades are locked. Because the erg doesn't move (no accelerations),
it'll require force sensors on the stretcher and a way of comparing and
timing the difference between force on stretcher and force on handle.
It think it may be rather difficult to automatically calibrate add-on
foot plate pressure pads.
Charles Carroll
> stationary. Check implies interfering with the forward motion of the
> boat, either at the finish or at the catch.
I wondered about measuring check on a static erg. Ewoud's idea of "force
sensors on the stretcher" sounds awfully complex.
But what about an erg on slides?
Cordially,
Charles
Ted van de Weteringe
> But what about an erg on slides?
Same easy accelerometer as in the boat, I guess.
kda...@kidare.com
wrote:
Does this make sense on an erg? In a boat the trick is to lock the
spoons in the water before the pressure goes on the stretcher, and the
spoons and stretcher are disconnected bits of kit. On an erg, the
chain is physically connected to the stretcher via the wheel and
machine. So put pressure on the stretcher and you can't do anything
but engage the chain, or alternatively, engage the chain and you can't
do anything but put pressure on the stretcher. So I think check is a
boat-specific phenomenon.
Kit
Ted van de Weteringe
> So put pressure on the stretcher and you can't do anything
> but engage the chain, or alternatively, engage the chain and you can't
> do anything but put pressure on the stretcher. So I think check is a
> boat-specific phenomenon.
Completely logical, yes. (Not taking into account the bum-shoving
phenomenon perhaps, but that isn't check.) Excuse my earlier confused
post, Charles.
John....@googlemail.com
> sensors on the stretcher" sounds awfully complex.
We make the ActiveTime (it is not actually called The Accelerometer!)
and have tried it on a Rowperfect as somebody asked if it would work
on one.
It didn't, presumably because the changes in speed of the flyweel
assembly are too gradual. We have not investigated this further but I
suspect that it would have the same problem on a C2 on slides.
In rowing you typically see boat speed changes of 25%+ within each
stroke and these are unavoidable as they are primarily caused by the
body changing direction relative to the boat.
Interestingly Dr. Valery Kleshnev has shown that the very best rowers
generate larger checks, but over shorter periods, so overall they
check the boat less. This overall effect is what the ActiveTime
measures.
Charles Carroll
I didn't have any time yesterday to reply to your post. This was the reason
why I have had time to think about what you said. Imagine thinking before
writing! What a novel idea!
It will be interesting to see if I actually have understood anything.
OK! So you are on an erg. Isn't the flywheel at the release moving at its
fastest?
From then on, as you slide the erg underneath you on the recovery, isn't the
flywheel decelerating?
And doesn't the change in rate of deceleration of the flywheel remain
constant all through the recovery to the release?
It seems to me the answer is yes to all these questions.
Now, if you come to the entry while erging and just stop, what happens to
the change in the rate of deceleration of the flywheel?
I just tried it, and nothing happens. The change of rate of deceleration
still remains constant.
Now try the same thing in a shell. Come to the entry, lock the spoons in the
water, and stop. And what happens? Don't you bring about an abrupt change in
the rate of deceleration of the shell?
Of course the answer is yes to that question, isn't it?
Hence my favorite definition of Check: "an abrupt change in the rate of
deceleration caused by pressure on the stretcher without a simultaneous
pressure on the pin." ("A Short History of American Rowing," Thomas
Mendenhall. P. 1)
So if I have understood you correctly, you are saying that on an erg it is
not possible to affect an abrupt change in the rate of deceleration of the
flywheel, and therefore impossible to produce any meaningful measure of
check.
Of course you have said it more simply and clearly than I have. What you
wrote was just beautiful.
I have one other note to add. Steve Fairbairn says in "Chats on Rowing" that
"coupling the drive and the draw . is the foundation of all rowing." In more
modern terminology, isn't this what Thomas Mendenhall suggests, if I am
permitted to extrapolate? In trying to row well, aren't we all seeking to
apply simultaneous pressure to the stretcher and the pin? Or, in slightly
different words, aren't we all trying to keep boat check to a minimum? This
leads me to think that the fastest rower will be the person who can apply
the greatest pressure to the stretcher and pins at the highest rate while
keeping boat check to a minimum.
Or anyway I thought so, until I read John Ewans' post saying that "Dr.
Valery Kleshnev has shown that the very best rowers generate larger check,
but over shorter periods."
So once again I think I have understood something, only to learn that I have
understood nothing.
I'm going sculling.
Cordially,
Charles
Dave Sill
>
> Now, if you come to the entry while erging and just stop, what happens
> to the change in the rate of deceleration of the flywheel?
>
> I just tried it, and nothing happens. The change of rate of deceleration
> still remains constant.
>
> Now try the same thing in a shell. Come to the entry, lock the spoons in
> the water, and stop.
Ah, but isn't the analogous thing in a shell to pause at the catch
*before* dropping the blades?
> Hence my favorite definition of Check: "an abrupt change in the rate of
> deceleration caused by pressure on the stretcher without a simultaneous
> pressure on the pin." ("A Short History of American Rowing," Thomas
> Mendenhall. P. 1)
If the blades are in the water, there's going to be pressure on the
pins, one way or the other, unless the oar handle is moving at precisely
the right speed--which is pretty unlikely. I think he's saying that
jamming the stretcher before the catch is what causes check.
> So if I have understood you correctly, you are saying that on an erg it
> is not possible to affect an abrupt change in the rate of deceleration
> of the flywheel, and therefore impossible to produce any meaningful
> measure of check.
On fixed ergs, which is all we have, I think check causes the whole
erg/rower system to slide in the direction the rower faces. We have a
smooth concrete floor, and we have to use weights to keep machines from
creeping across the room.
-Dave
Charles Carroll
Sorry that I missed the correct name. I will use ActiveTime from now on.
I wasn't able to go sculling for two days, so this morning was the first
time I saw the ActiveTime in use. I think you may recall that I purchased
one for a friend. He has been using his for two days.
The first question is what do the numbers mean for boat check? At lower
ratings he scores in the very low 20s. At higher ratings, however, his
numbers go up into the low to mid 30s. He thinks this means that at higher
ratings he is producing more boat check, that is, rowing less smoothly. Is
this correct?
The second question is what is a good number? I know my friend. What he is
asking is what numbers do the fastest, smoothest scullers produce? Is the
low 20s a good number? Or should he try for lower numbers? Could you give us
a target number?
The third question is that the ActiveTime doesn't seem to work very well at
20 spm or lower. Could there be a problem with his unit? Or is this just
what is?
If later on I get some time I am going to take mine downstairs to the erg
and tape it to the arm. My erg, a C2, is on slides. I am curious to see if I
can generate numbers, and if so what they look like.
By the way, for an initial comment my friend thinks that the ActiveTime
gives much better rating in rough water than anything else he has seen.
Oh, also he made another comment. He said he had to play a bit with how the
ActiveTime was angled before it worked correctly. This was not a criticism.
He theorized that the ActiveTime is sensitive to how it is set up, and that
if it seems not to be working correctly, don't get discouraged, just play
with it until you have it angled correctly.
Mike, if you happen to see this post and are curious about the ActiveTime,
you are welcome to borrow it any time you feel like it. I can leave it at
the desk and you can drop by on your way to Palo Alto on a Monday, keep it
for the week, then drop it off Friday on your way back to Clear Lake. Let me
know.
Cordially,
Charles
Charles Carroll
I found 15 minutes this evening to test the ActiveTime accelerometer on a C2
on slides. Very brief test!
I angled the arm of the C2 towards the bow so that the arm was parallel to
the floor.
I then attached the ActiveTime to the arm.
The ActiveTime was set in Clock Mode
When I began erging it took a few seconds for the ActiveTime to begin
registering.
Interestingly enough ActiveTime displayed a rate identical to the rate on
the C2's Performance Monitor.
After a few minutes I switched the ActiveTime to Check Mode.
At first nothing happened-The ActiveTime didn't register at all. But I gave
it time.
Suddenly the ActiveTime began to display check numbers . . . 23 . . . 25 . .
. 27 . . . 29 . . . 33 . . . 31 . . . 25 . . . 31 . . . 23 . . . etc.
What are these numbers? Where do they come from? What do they measure?
Cordially,
Charles
kda...@kidare.com
wrote:
> Kit,
>
> I didn't have any time yesterday to reply to your post. This was the reason
> why I have had time to think about what you said. Imagine thinking before
> writing! What a novel idea!
And sorry I haven't replied to yours. I was on an office Christmas
lunch, and, well, hey ho.....
You give me way, way too much credit. Actually, the deceleration of
the flywheel didn't come into my thinking. Consider this: in a boat,
imagine I draw the feet/stretcher up to me for the catch, but don't
put the blades in. If I then push with the feet, the boat will shoot
back because it is not being locked in place by the blades, which are
not in the water. So the boat checks, and hence the importance of
timing the blade entry before the work goes on the stretcher.
On an erg however, there is no concept of not having your 'blades' in
the 'water'. The handle is permanently attached to the chain, which
will always engage more or less straightaway. Hence, push with the
feet / engage the handle, and vice versa.
Following that train of thought, an interesting engineering exercise
would be to build an erg wher the rower has to 'engage' the handle in
the drive chain at front stops in order to take a stroke. Not sure
what it would look like, but if it could be done on a sliding erg then
you could definitely measure proper check on an erg.
> I have one other note to add. Steve Fairbairn says in "Chats on Rowing" that
> "coupling the drive and the draw . is the foundation of all rowing." In more
> modern terminology, isn't this what Thomas Mendenhall suggests, if I am
> permitted to extrapolate? In trying to row well, aren't we all seeking to
> apply simultaneous pressure to the stretcher and the pin? Or, in slightly
> different words, aren't we all trying to keep boat check to a minimum? This
> leads me to think that the fastest rower will be the person who can apply
> the greatest pressure to the stretcher and pins at the highest rate while
> keeping boat check to a minimum.
>
> Or anyway I thought so, until I read John Ewans' post saying that "Dr.
> Valery Kleshnev has shown that the very best rowers generate larger check,
> but over shorter periods."
>
> So once again I think I have understood something, only to learn that I have
> understood nothing.
>
> I'm going sculling.
>
> Cordially,
>
> Charles
As a sliding erg man, you might have noticed another factor which I
think contributes to check. I find that as I lean forward from the
finish, the erg moves back under me as Newton decrees. As I draw the
feet up to me for the catch, this movement continues. However there is
a moment between the end of the sliding phase and the push with the
legs when the erg changes direction and moves backwards. In a boat
this would be check. Since you cannot stop sliding and then push with
the legs with zero delay, this check is inevitable (*on an erg*). But
it is made much worse by the movement of the body off the finish. With
a sharp movement, the body has a momentum back towards the start line
and this is preserved until that moment when the sliding finishes,
when that momentum causes your body to push against the stretcher and
check the boat. I find that if I control the movement of the body off
the finish (mainly by not leaning back too far at the finish) I get
much less 'check' at the catch.
In a boat, you can counter this check partly by getting the blades in
the water while the last bit of the slide is still happening, giving
you the option of engaging the drive using the arms/pecs before the
legs start driving. That's the theory anyway. Good luck trying to do
it in practice!
More helpful stuff only available on a sliding erg...
Kit
(PS the Google captcha requires me to enter "Row NSUBC". Intriguing)
john....@googlemail.com
>The first question is what do the numbers mean for boat check?
The number is an average (over time) of the amount that you are
slowing the boat as you approach, and take, the catch. There is some
compensation built in for rate as at higher rates there is no way of
avoiding higher boat decelerations.
>The second question is what is a good number? What he is asking is what numbers do the fastest, smoothest scullers produce? Is the low 20s a good number? Or should he try for lower numbers? Could you give us a target number?
From what we have seen so far, good scullers achieve numbers in the
low 20s when paddling and numbers in the low to mid 40s when flat
out.
>The third question is that the ActiveTime doesn't seem to work very well at 20 spm or lower. Could there be a problem with his unit? Or is this just what is?
The units are designed to gives rates from 17 to 55 strokes per
minute. However we have had a few units where one axis of the (three
axis) accelerometer is not properly connected to the PCB and this does
create problems at very low rates. We have introduced tests to pick
this so it should not now occur but perhaps you could compare the two
units to see if they behave the same? If there is a problem we will
obviously replace the unit ASAP.
>By the way, for an initial comment my friend thinks that the ActiveTime gives much better rating in rough water than anything else he has seen.
A lot of work went into the algorithm that works out the rate. It is
very easy to calculate rates in flat water but becomes extremely
difficult when you get significant waves.
>He said he had to play a bit with how the ActiveTime was angled before it worked correctly.
The ActiveTime should operate at any ‘sensible’ angle. However it does
work out the angle it is mounted at over a 60 second period so if you
change the angle with the unit turned on it can take up to a minute to
give rate and check readings. If your friend finds that it does work
better either almost horizontal or almost vertical this might indicate
that one accelerometer axis is playing up as near these extremes of
angle one axis of the accelerometer is dominant.
>I found 15 minutes this evening to test the ActiveTime accelerometer on a C2 on slides. When I began erging it took a few seconds for the ActiveTime to begin registering.
Because we have to time between strokes you have to take two strokes
before the unit registers a rating in a boat. On the erg it might take
even longer if the first strokes do not register high enough
decelerations.
>After a few minutes I switched the ActiveTime to Check Mode. At first nothing happened-The ActiveTime didn't register at all.
This must because either the initial strokes were not generating
decelerations above the sensing threshold or because the angle of the
unit had changed. Having it in check mode does not affect how soon
ratings are displayed and once ratings are being read there is always
an associated check figure (even if it is not being displayed) as this
is recorded, as an average, in the timing modes.
>But I gave it time. Suddenly the ActiveTime began to display check numbers. What are these numbers? Where do they come from? What do they measure?
Clearly they are measuring the level of decelerations of the erg/rower
combination. However to find out if these readings are of any
practical use on an erg a fair amount of work might be needed……