Excellent Double Spey Video - Good explanation of the technique

[Aitor]

I was typing an explanation of the .gif and the meaning of the velocity vectors for each hand... but I will get the same results by keeping silent.

Ciao.

[Ben_D]

how do you tell if a car is front or rear driven?

Thanks, Paul

Find a roundabout with some diesel on it and put your foot down :p

[Juergen Friesenhahn]

O.K....Look...

If a wellknown person would be nailed to a speyrod with the tophand and he moves bottomhand only with a fixed tophand in relation, we all would agree, that the fulcrum of the framework rod/caster is in the tophand, right? (or does Mr. I.C flow Computer say something different)

But if this person of the past drives on a skateboard on a bumpy road doing the same movement as above flmed by the camera sideways, where would the misterious I.C flow red fulcrumdot of truth, seen by the computeranimation be?
Where would be the red dot If the camera faces the caster?
Where would it be, if the caster is filmed from above?
...in an angle...

The fulcrum of the framework caster/rod is clearly in the tophand.
But the fulcrum moves in relation to the camera.
So the seen fulcrum of the framework caster/camera can be somewhere else.

Relativity of the framework.

BTW... Did the have skateboards down in Nazareth? Or speyrods?

J.

[gordonjudd]

I would need to know and understand a lot more about how the analysis worked Aitor. Ive asked for this info but so far its not forthcoming.

If you are interested in how the instant center of rotation flow is calculated there are more than enough details here that describes how the instant center of rotation can be calculated for a rigid body such as the butt of a fly rod.

The concept is also described in Wikipedia here so you should be able to get some more examples of how the the I.C. is applied in that article.

How can this be done on a DH rod without having any measurement of force applied by either hand?

As noted in the Wikipedia article is is not about force. Simply (or not so simply if you are not an engineer) put the I.C. is determined by the velocity of different points on the body at any instant of time.

It may be easier to see how this works in casting using a stickman representation where the rotation results from idealized rotations about the shoulder, elbow, and wrist as described in the evaluation of angular velocity thread..

As noted in that thread:

The point of this analysis is that casting does not necessarily have a proximal to distal kinetic linkage as it does for most throwing motions. The wrist may or may not be the joint that provides the most angular velocity depending on the caster's style.

As long as the rod rotates about a reasonably horizontal axis the rotation center calculation should point to the joint that is providing the most rotation at a given point in time. You can see that rotation center flow effect in the "Gumby cast example". In the distance casting styles I have measured, the rotation center is generally near the elbow at the point of maximum angular velocity so it would be interesting to see if that is the case for your style as well.

.

Gordy

[Juergen Friesenhahn]

So the method is about measuring and comparing speedvectors of certain measuringpoints from a certain point of view in 2D.
Nice toy.

It simply can't measure thrust/force. You remember the front/reardriven car?

BTW: the main sense in relation to twohaded casting is about applying force/thrust w. bottom or tophand, not speed alone.

And last but not least, as we also all know about twohanded casting, that force applied is separate from the tempo of the cast, because we are not takling about a stick, we are talking about a flexible rod and a line in different mediums (water/air).

I also repeat: let the guy cast a twohander bottomdriven casting unbelievably nice V-loops on a slowly rolling skateboard downhill an uneven road and measure it from different angles!

...search the fulcrum....search ;-)

Best

J.

PS: being German could somebody please translate me the word "mullocking"?

[Juergen Friesenhahn]

The results of this measuringmethod are also a great teachingtool.

"Hey student, rotate this twohander around an axis two feet behind your ass!"

[Aitor]

:O :O :sick:

[sms]

It simply can't measure thrust/force.

It doesn't need to. We can calculate the force from the bend (or acceleration of the line), from the distance of the hands, length of lever and direction of force by the hands.

Movement is not important to force. You can push a wall to your heart's liking and it won't budge. But you are still applying force to it. So, one more time, it does not matter if it moves or not.

[grunde]

But if you are after power application rather than just force it does matter :p

What I don't get is this obsession with the fulcrum thing...

Cheers,
Grunde

[Juergen Friesenhahn]

It simply can't measure thrust/force.

It doesn't need to. We can calculate the force from the bend (or acceleration of the line), from the distance of the hands, length of lever and direction of force by the hands.

Please... no whole rod, line, bend and so on...

We were discussing, to judge, if a caster drives the rod top- or bottomhanded, seeing hands and rodhandle only, like in the video presented by the spanish gent. Post 46 in this thread.

I simply said no.

And you can't judge out of this kind of video, where the "fulcrum" of the lever is, because this is a question of the framework and in this case of measurement of perspective to the object, that should be captured.

But this is a discussion, that has nothing to do with the sourcethread and I apologize being part of the misuse.

Cheers

J.

[gordonjudd]

What I don't get is this obsession with the fulcrum thing...

Grunde,

We can easily understand where the rotation point of a lever or a see-saw is since it is always at a fixed point in space. Our intuition leads us to misapply that simple understanding of how a object rotates in the static case involving a lever and think that it must apply to a dynamic situation as well. That leads us to see the top hand serving as a fixed rotation point in casting or that the rod is being rotated about the midpoint of the hands as I thought would be the case for a two handed cast.

Since we use a combination of joint rotations (torso, shoulder, elbow, and wrist) in casting the rotation center of the rod butt changes considerably during the cast. When those movements result in more translation than rotation, the instant center of rotation can move to a point that is some distance from any specific point on the body.

I think that the way we really rotate the rod is much more interesting than the old concept I had that we rotate about the wrist in single hand casting and at a point between the hands in two handed casting. The actual case is much more elegant, and requires the coordinated rotation of many different joints to make a good cast.

Where would be the red dot If the camera faces the caster?
Where would it be, if the caster is filmed from above?
...in an angle...

Juergen,
If you did the I.C. calculation in 3-dimensions then you would get a red dot that showed how the rotation center moved in x,y, z space.

I am only doing this calculation in 2 dimensions (since you can only get x,y information from a single camera). Thus it only shows a reasonably accurate 2-D I.C. point when the camera is positioned at a point that is perpendicular to the rotation plane of the rod. That is why it is important to take the video from the side of the caster, and not at an angle from the front or the back.

Gordy

[easterncaster]

i'm thinking this top-hand vs. bottom-hand contest requires a strain gauge.

craig

[sms]

Jurgen, the framework must be fixed to the ground as that is the framework were casting in.

[Juergen Friesenhahn]

To sum up...

There is phyiscally nothing "wrong" with a casters saying, that his tophand is the fulcrum of his doublehanded rod and driving with the bottomhand, because of the framework he's judging this - his moving body, he lives inside.

And the measurements of Gordon, which work I highly respect , are totally correct with the point of rotation somewhere else, because of the framework, the perspective and the twodimensional measurement; simply of the restriction of the method.

And I clearly see the use of this method to compare and optimize caster and castingstyles in a new way. Great idea!


What I do not appreciate are short pseudophysic explanations that include sayings like "I know, that you are wrong...", without explaining it explicit.
This is kind of a halfknowledge sniffy approach.


Anyway the truth is found on the water with the rod in the hand and we surely can tell, if somebody is mullocking...

All the best

Juergen

[Aitor]

What I do not appreciate are short pseudophysic explanations that include sayings like "I know, that you are wrong...", without explaining it explicit.
This is kind of a halfknowledge sniffy approach.

I totally agree!