Rotational KE in the rod - How do we increase angular velocity

[Merlin]

Thanks Sakke, your answer came in before my (provocative) question, this is a miracle of editing. The brain connections are working again now (you shall see when getting older). Thanks also to Walter/Gordy for reminding me my important role on the earth, at least by comparison to a fly rod. I consider the forces issues as “classified” now, in my personal case.

If I jump to the original problem which was the evaluation of the torque produced by the caster (in another thread) by any means (body, shoulder, elbow, wrist, fingers), then it necessarily has a component linked to the stiffness of the rod and another one due to its inertia. To make it short, the spring unloads itself, although the time in which it does it is influenced by the cast, but ones need to do something more to reduce the kinetic energy of the rod (the line will make its life on its own after the launch). This is where there is a need for a negative torque / retarding torque / decelerating torque at some time, I know this wording may be confusing, to stop or nearly stop the rod. It is also in line with the fact that a caster just does not feel the bending in the rod, but also its inertia (swing weight). The beginning of the reduction in rotation speed does not need effort thanks to the unloading of the rod, but there is some effort needed to stop it afterwards. All that is done in the blink of the eye.

So even if models can be considered as b… by some people in the forum, I think they give a fair (but not exact) idea of what is happening. We do not need models to learn casting, but just to understand a little bit the complexity of the fly rod mechanics (that helps for design sometimes). I hope I contributed to this understanding somehow; my objective is not to convince everyone that I have the truth, but to bring a piece of work that can help finding it. I am human, so I make mistakes; the last one about forces makes me laugh of myself.

Paul

I do not think the original purpose of the forum is to constitute “clans” of “pros and cons” or “gentles and villains”, but to exchange ideas with respect to each other. Maybe I unintentionally offended some people in writing my posts. That came back with some more or less aggressive ones recently, and I was not used to, but that’s life. My apologies anyway for those who are concerned.

I chose “Merlin” as a nickname because I liked very much the cartoon from Walt Disney when I was young. I like the way this old sorcerer takes things in the life. If you know the story, do you remember what Merlin does when he is disappointed by people around him? He takes his magic wand and touches himself to become invisible for a while (but he keeps listening).

Bing!

[gordonjudd]

I do not think the original purpose of the forum is to constitute “clans” of “pros and cons” or “gentles and villains”, but to exchange ideas with respect to each other.

Merlin,
Cooler heads prevail. Thank you.

I feel the same way, and will try to focus on the data not on personality clashes in the future.

And Magnus, I did get very upset with your quibbling over details, and trying to discount everything I had said about how rotational energy is produced. Your guess on angles was just that, and yet you had to point out that my guess was way off the mark. (The actual angle measured by putting a friend into the position shown in that frame grab was around 75 degrees by the way.)

I felt (rightly or wrongly) you were doing more than just quibbling over actual angles but in fact were implying that you do not need to use big rotation angles of the elbow to get more energy into the cast because the angle used by in that video was much smaller than what I was saying.

I took that to mean that you were discounting the physics behind the torque over angle concept, and thus you felt it necessary to find some different casting styles trying to show that the rotational energy produced by the elbow must not be a big factor in casting as I was claiming.

To clarify that you understood the concept, I even asked:

You do understand that the bigger the angle range the torques from our rotating joints are applied means you will produce more rotational work energy don't you?

just to make sure you did understand the basic physics involved.

Rather than saying, "Of course I understand, it is the same concept as force over distance." you could not let your example go, and came back a second time with what I took to be an insulting question:

This guy looks like pretty good caster to me, and those look like sound and really rather stylish 'fishing distance' casts. You want to tell him his "1/2*moi*omega^2 energy" is lacking because the angle at his elbows doesn't change a lot?

That pushed me over the edge, because it implied to me that you were saying the torque over angle concept was not important because here is someone who cast very well without doing it. That question came after I thought I had pointed out there will always be style differences in the way we cast, but from an energy standpoint some casting styles are better than others in a previous post.

Rightly or wrongly, I took your question to be saying in a backhanded way that what I was saying was B.S. and you had an example to prove it.

Anyway, if I insulted you I do apologize, but please realize that all your quibbling over values and examples is an irritation to me as well.

I would prefer to focus on the physics, and hope that most people now understand where the rotational energy comes from in casting. Looking at Alejandro's thread on forces from the hand, I do not think that was the case beforehand.

Gordy

[Paul Arden]

Well I'm pleased that's all sorted out now.

[Magnus]

Rightly or wrongly, I took your question to be saying in a backhanded way that what I was saying was B.S. and you had an example to prove it.

Wrongly

Look - you know I am a layman in this stuff and hopefully you know I'm working (hard) to try and get to grips with the concepts involved. I'm certainly not dismissing them - nor am I trying to challenge them. At the same time I am trying to get some handle on the consequences of this method of investigating things.

So - please - expect some questions ('what ifs' or 'what abouts') which seem dumb or insulting - if interpreted that way - it's in the nature of the beast.

Now, specifically, there are effective styles of DH casting where it looks to me like the elbow is not where energy for the cast is produced. My elbow extends mainly because my triceps contacts - that's a small muscle compared with my biceps or the muscle groups across my chest for example. From that perspective I'm not convinced that DH casting SHOULD (sorry for shouting) or at least needs to be focussed on producing torque at the elbow - even if the physics implies something else.
That reasoning - right or wrong - also leads me to wondering about how we apply force (term used for a reason ) at the upper and lower grips. Pulling my lower arm so the angle at the elbow decreases uses my biceps. Pushing the rod around a curve with a straight upper arm uses muscles on my torso and shoulder.

Anyway I'm sure you get the idea - quite possibly half-baked - I am fully aware of that

Merlin
If I gave the impression that I thought modeling was b.... I'd like to apologise.

[Bobinmich]

Wow, this thread is a trip. I don't see a real problem in trying to understand the dynamics of a rod down to the casters hand. As you know, I have long been a fan of getting to the actual forces in the hand as a method of quantifying rod characteristics. I have been harping on that for some time now and I am refining a piece-wise linear model that does just that. Down to the hand, rod dynamics can be characterized quite easily with Newtonian equations in either cartesian (rectilinear) or polar (rotational) mathematics. You don't need to worry about frequency or energy or anything else. you can also use the Energy balance approach with the same free body diagrams and get the same answer.

But you guys tried to blow right past the hand (the part you can feel) and wade straight into biomechanics. I would be surprised if anyone on this board is capable of engaging in a meaningful conversation on this.

The statement was made that internal forces have no ability to generate work. The attempt to regulate the forces applied to the handle of the rod by the hand as internal is pure poppycock. The argument as to what generates these forces is where you get into biomechanics and fly past most of our ability. Even though this is where the energy is generated for distribution into the rest of the process, knowledge of the generation process is required to progress further. I think it is a noble exercise bound to fail because of the skill sets of the participants. Or is there a biomechinical engineer or scientist here?

Bob