Search Members Help

» Welcome Guest
[ Log In :: Register ]

Page 1 of 3112345>>

[ Track This Topic :: Email This Topic :: Print this topic ]

reply to topic new topic
Topic: Fulcrum< Next Oldest | Next Newest >
 Post Number: 1
Alejandro Search for posts by this member.

Avatar



Group: Members
Posts: 106
Joined: Nov. 2003
PostIcon Posted on: Nov. 22 2011,14:13  Skip to the next post in this topic. Ignore posts   QUOTE

I bring to a new topic the debate of the last pages of Excellent Double Spey Video (http://www.sexyloops.co.uk/cgi-bin/theboard_07/ikonboard.cgi?act=ST;f=14;t =13975) because it was different to the initial matter of the thread, and I believe that it is really interesting.

I am beginning to get ready for THCI, and I am reading some strange things in the texts that I am studying. One of those things is the use of the term fulcrum, that doesn't seem to have any relationship with the rotation center for some instructors.

For me, to cast with a two handed rod implies to accelerate the rod with both hands, and if we make this is impossible to maintain the rotation center in the superior hand.

By definition the fulcrum is the point that support a lever. In the real case of a two hands rod we would have two fulcrums: the upper hand is fulcrum of the force exercised by the inferior hand, and vice versa.
To “see” these fulcrums we should transform into observers inside the system, traveling in one or another hand. But in this case we lose the perspective of our own movement, as it happens to a passenger inside a vehicle. It seems that some can take this trip in a hand, but not in the other.

If we take a look to a conventional spey cast we won't see any fulcrum, only a rotation of the rod around an imaginary axis whose position changes throughout the cast.

Therefore, in my opinion or we speak of two fulcrums or of a rotation axis. Only one fulcrum I don't see the sense,

If we have a video and we want to know where this axis is we don’t need to know any speed. It is only necessary to superimpose two frames and to draw two lines that unite the positions of a couple of points of the rod.  We mark the half point of those lines and trace in that point a perpendicular line. The rotation center is where both lines cross.
In high-speed videos and among successive frames the rotation center is near the instantaneous center of rotation, but if the movement of the rod is very small it can be difficult to make the drawing to find it.

In connection with this, some instructors defend that a lever of first class is, for cast with a two handed rod, more efficient than a lever of third class. In my opinion to cast moving only the lower hand is as ineffective as to cast only moving the upper hand.
I understand that when we teach the handling of a two handed rod we insist in the importance of the lower hand, because the fishermen accustomed to the handling of one hand rod forget it. But is it necessary to invent a physics to make it?

Alejandro
Offline
Top of Page Profile Contact Info 
 Post Number: 2
gordonjudd Search for posts by this member.

Avatar



Group: Members
Posts: 2215
Joined: Jul. 2006
PostIcon Posted on: Nov. 22 2011,16:26 Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

QUOTE
One of those things is the use of the term fulcrum, that doesn't seem to have any relationship with the rotation center for some instructors.

Aitor,

To get the upper hand to be the fulcrum for a two handed cast you would just  strap the  forearm so the rod would rotate about a fixed wrist while the rotation torque was applied by pulling the butt of the rod back with the lower hand.

That would produce what people were talking about in in terms of the upper hand serving as a fulcrum for the cast in  the other thread but as you know that is not the way most casters  rotate the rod in a two handed cast.

The combination of translation and rotation that we use in casting causes the effective instant center of rotation to vary throughout the cast, and I do not know if it would ever migrate to the upper hand.

QUOTE
If we have a video and we want to know where this axis is we don’t need to know any speed. It is only necessary to superimpose two frames and to draw two lines that unite the positions of a couple of points of the rod.  We mark the half point of those lines and trace in that point a perpendicular line. The rotation center is where both lines cross.


Here is an example of doing just that for the Anderson video you showed in the other thread with measured velocity vectors.


You can see the instant center of rotation you get from the intersection of the perpendiculars to the velocity vectors (the white circle) is nearly the same as the one I get using  the geometry of the rod butt  movement (the red circle)

At that point of time you can see Anderson was producing a rod rotation about a rotation center near his chest,  I do not think the instant center would ever go the upper hand with his casting style.

Gordy


--------------
"Flyfishing: 200 years of tradition unencumbered by progress."  Ralph Cutter
Offline
Top of Page Profile Contact Info 
 Post Number: 3
Alejandro Search for posts by this member.

Avatar



Group: Members
Posts: 106
Joined: Nov. 2003
PostIcon Posted on: Nov. 23 2011,08:37 Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

Hi Gordy, I am not Aitor, fortunately :-)

Yes, we can find the instantaneous center of rotation from the vectors of speeds. But for it we should have a software that calculates those vectors, and to know how to manage it (small errors when marking the points can make big changes in the vectors). We could also calculate IRC if we know the data of v and w of a point, and a good knowledge of mathematics.

I proposed an alternative method to calculate the rotation center with two frames of a videotape. It is a simple and useful system for know the absolute center of rotation during the phase of maximum rotation of a cast.
We unite the same point (butt and end of the handle, red lines). On the center of those lines (yellow point) we draw the perpendicular (blue lines). Where the lines cross the rotation center is.

Placing a translucent paper on the screen of the computer or of the TV we can make this in a moment, at least in an approximate way, for any videotape.

I think that the rotation center is not in the superior hand in any casting style, at least in none that is effective.

Alejandro


Attached Image
Attached Image
Offline
Top of Page Profile Contact Info 
 Post Number: 4
gordonjudd Search for posts by this member.

Avatar



Group: Members
Posts: 2215
Joined: Jul. 2006
PostIcon Posted on: Nov. 23 2011,17:54 Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

QUOTE
Hi Gordy, I am not Aitor, fortunately ':D'

Alejandro,
I am sorry for not paying more attention to who started this thread.  You are not the first to point out my error, and I apologize for giving Aitor the credit for starting the discussion of  what I think (apparently few others would agree considering  the activity in this thread)  is an important concept in casting.  I.e. we do not rotate the rod about the wrist of the rod hand as most people believe.

I had been having some e-mails back and forth with Aitor on the same subject, and had a bit of a slip in my salutation.  I hope Magnus will straighten that out for me.

QUOTE
I proposed an alternative method to calculate the rotation center with two frames of a videotape. It is a simple and useful system for know the absolute center of rotation during the phase of maximum rotation of a cast.
We unite the same point (butt and end of the handle, red lines). On the center of those lines (yellow point) we draw the perpendicular (blue lines). Where the lines cross the rotation center is.

That is the way I am computing my instant center flow (the red dot in post #2) as well.  The process I use is discussed in mind numbing detail here.

Usually the change in the movement of different points on the rod can be quite small, so I use a smoothed fit to the x,y paths of those points to get a more stable I.C. point that comes from a wider range of sample values.  I also take the average of the 3 I.C points you get with three different points in the rod to smooth out some of the fluctuations you get in finding the perpendicular bisector of just two points on the rod.

Regardless of you find it (velocity vectors or perpendicular bisectors) I think you will find the true instant center of rotation in a cast is not where you might think it would be.  A little translation can move the effective I.C. to points that are some distance from the hand (or hands) that are holding the rod.

It appears from your overlay that the I.C. at MAV in that cast would have been near the elbow of the right arm, just as I saw in Aitor's cast as shown below.


Gordy :blush:


--------------
"Flyfishing: 200 years of tradition unencumbered by progress."  Ralph Cutter
Offline
Top of Page Profile Contact Info 
 Post Number: 5
Alejandro Search for posts by this member.

Avatar



Group: Members
Posts: 106
Joined: Nov. 2003
PostIcon Posted on: Nov. 24 2011,08:43 Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

I agree completely. To know the approximate point around  the rod rotates in one cast is important, at least for an casting instructor.

I also believe that a good system to find the instantaneous rotation center is to find the bisector of the perpendicular speed vectors of two, or better three, points of the most rigid area in the rod. I have also used this system (only with two pints), and I regret not to have read the technical forum before, but I don't have time to follow it.

The method that I propose, and that you also know, it is not good to find the instantaneous rotation center, but is good for find the global rotation center for a certain movement. If the rotation doesn't have translation, and I suppose that also if the traslation is uniform, both centers coincide.

In the many videotape analyses that I have see the last weeks, most of expert casters with two handed rods, I have seen that the rotation center is near the elbow in shorter cast, and goes away toward the shoulder in longer cast.

I have applied this to my cast and I have checked that it is a good help. I find simpler to adjust the impulse knowing around what area the rod really rotate. For me, trying to transform into fulcrum the superior hand has never worked, without a doubt because my fulcrum idea is not the same that for those that defend this concept. I don't criticize those who achieve good results thinking that during their cast the superior hand is the fulcrum, although in fact it is not certain, simply for me this doesn't work and it looked for an alternative form to teach to those to who the same thing happens.
Offline
Top of Page Profile Contact Info 
 Post Number: 6
gordonjudd Search for posts by this member.

Avatar



Group: Members
Posts: 2215
Joined: Jul. 2006
PostIcon Posted on: Nov. 24 2011,16:57 Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

QUOTE
The method that I propose, and that you also know, it is not good to find the instantaneous rotation center, but is good for find the global rotation center for a certain movement.

Alejandro,
I think that looking at the perpendicular bisector over a many high speed frames still gives an "average" rotation center that would be quite close to the one I get looking at the smoothed points on a frame by frame basis.  Therefore it is still a useful way to see how someone is actually rotating the rod and does so without a few hundred lines of computer code. (I am a very inefficient user of MATLAB).
QUOTE
For me, trying to transform into fulcrum the superior hand has never worked, without a doubt because my fulcrum idea is not the same that for those that defend this concept.

I do not think that basing your instruction on invalid concepts is a very fruitful way for a student to learn how to cast.  The idea of pulling back on the bottom hand to rotate the rod about a rotation axis fixed at the top hand is not the way people actually cast, and therefore I would not want to teach that technique to a student either.

Gordy


--------------
"Flyfishing: 200 years of tradition unencumbered by progress."  Ralph Cutter
Offline
Top of Page Profile Contact Info 
 Post Number: 7
Alejandro Search for posts by this member.

Avatar



Group: Members
Posts: 106
Joined: Nov. 2003
PostIcon Posted on: Nov. 27 2011,15:26 Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

QUOTE
I do not think that basing your instruction on invalid concepts is a very fruitful way for a student to learn how to cast.


I think the same thing, but they have told me at some time that they are not mistaken concepts, but a poetic use of the technical words.
I am not contrary to the use of metaphors, or analogies, to explain technical concepts, but in this case it is necessary to give the keys so that all can understand us.

If we don't give the key, then it happens like with "fulcrum" and also with "tempo (and better not to speak of "momentum" :-)

Alejandro
Offline
Top of Page Profile Contact Info 
 Post Number: 8
gordonjudd Search for posts by this member.

Avatar



Group: Members
Posts: 2215
Joined: Jul. 2006
PostIcon Posted on: Nov. 27 2011,16:22 Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

QUOTE
they are not mistaken concepts, but a poetic use of the technical words.


That must be a "poetic" Spanish translation for "Bullshit", just as Merlin's characteristic of "vetran" is the polite  French word for "old fart" (at least in my case).

Gordy


--------------
"Flyfishing: 200 years of tradition unencumbered by progress."  Ralph Cutter
Offline
Top of Page Profile Contact Info 
 Post Number: 9
Hal Jordan Search for posts by this member.

Avatar



Group: Members
Posts: 604
Joined: May 2011
PostIcon Posted on: Nov. 27 2011,20:14 Skip to the previous post in this topic. Skip to the next post in this topic. Ignore posts   QUOTE

Alejandro - a wise person once told me that there are very few absolutes in fly casting. We use a lot of anecdotes like, "You have to stop the rod", or "the line follows the rod tip", or "Don't use the wrist" because they help people understand a concept and seem to work well for other instructors - not because they are correct from a scientific standpoint. Most people learning how to fly cast (single or double hand) don't want to spend a lot of time hearing about fulcrums and lengthy discussions about where the point of rotation is throughout the stroke any more than a person learning to ride a bike wants to hear about the gyroscopic affect of the wheels and air resistance.

From reading many of your posts I'm sure you will have no trouble with any questions you face on the test. Just keep it simple.

Trying to change the way the various organizations teach fly casting before you become certified isn't going to work. You will have better success when you are a thci.


--------------
Casting Definitions
Offline
Top of Page Profile Contact Info 
 Post Number: 10
Aitor Search for posts by this member.

Avatar



Group: Members
Posts: 2074
Joined: Jan. 2005
PostIcon Posted on: Nov. 27 2011,23:45 Skip to the previous post in this topic.  Ignore posts   QUOTE

Alejandro, let me paraphrase Johnny Cash:
But I forgot more than you'll ever know about her...


--------------
Aitor is not like us, he is Spanish, and therefore completely mad.
Cheers
, Paul

No discutas nunca con un idiota, la gente podría no notar la diferencia.
Immanuel Kant

Videos for casting geeks
Offline
Top of Page Profile Contact Info 
304 replies since Nov. 22 2011,14:13 < Next Oldest | Next Newest >

[ Track This Topic :: Email This Topic :: Print this topic ]


Page 1 of 3112345>>
reply to topic new topic

» Quick Reply Fulcrum
iB Code Buttons
You are posting as:

Do you wish to enable your signature for this post?
Do you wish to enable emoticons for this post?
Track this topic
View All Emoticons
View iB Code