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Rod deflection and acceleration

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Paul Arden
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Re: Rod deflection and acceleration

#11

Post by Paul Arden » Thu Aug 29, 2019 9:37 am

It’s also worth remembering that while the relationship of spring/lever is something like 17/83% [Torsten] the springy rod allows us to put in something like twice the amount of work [Gordy].

The Bow and Arrow certainly works but not too well with a distance carry!

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Merlin
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Re: Rod deflection and acceleration

#12

Post by Merlin » Thu Aug 29, 2019 10:27 am

Lou

I run another example: same line/carry and three rods of different stiffness. The rule of the thumb for speed is applicable: stiffer/faster rod give more speed (assuming you are not limited by caster's power).

The result in terms of peak acceleration is now the opposite: the larger the maximum deflection is, the lower the peak acceleration is during unloading.

There is no universal rule, things are depending on two many parameters. :sorcerer:

Merlin
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Re: Rod deflection and acceleration

#13

Post by Merlin » Thu Aug 29, 2019 10:38 am

Paul

I though you read the paper on Swing, Spring and Whip :)

The figures which one use to quote are based on a convention, which is that the energy coming from the spring is only linked to its deflection. It is the same thing than considering that the rod is a bow, a paradox, isn't it?

You cannot completely split functions, Here is an updated split where I extract the "pure lever" energy, for a modern SH rod:
55% pure lever / 15% lever-spring / 17% pure spring / 3% spring -whip / 10% pure whip

Pure lever is obtained from calculating the leverage during the cast (shorter than the rod length)
Pure spring is energy linked to rod deflection (bow)
Pure whip is the net inertial contribution

There are unbreakable combinations. A fly rod is a combination of lever, spring and whip and you cannot separate them completely. You get advantage from the flexible lever thanks to the other functions and vice versa.

For Esa, the same estimate for a (long) DH rod:
30% pure lever / 10% lever-spring / 30 % pure spring / 10% spring-whip / 20% pure whip

Paul, do you still stick to the 80/20 legend?

Merlin
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Re: Rod deflection and acceleration

#14

Post by Paul Arden » Thu Aug 29, 2019 11:16 am

Ah yes I’d forgotten about the whip! :D Thanks Merlin. I’ll reread your paper.

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Re: Rod deflection and acceleration

#15

Post by Lasse Karlsson » Thu Aug 29, 2019 3:45 pm

Merlin wrote:
Thu Aug 29, 2019 10:27 am
Lou

I run another example: same line/carry and three rods of different stiffness. The rule of the thumb for speed is applicable: stiffer/faster rod give more speed (assuming you are not limited by caster's power).

Merlin
Hi Merlin

Have you tried that experiment? And if yes, what was the difference?

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Re: Rod deflection and acceleration

#16

Post by Lou Bruno » Thu Aug 29, 2019 4:20 pm

Merlin

Is it because fly rods bend we say they function as a spring...no bend-no spring?

Lou

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Re: Rod deflection and acceleration

#17

Post by Lasse Karlsson » Thu Aug 29, 2019 8:25 pm

They spring back to their original shape, once force is released.

🙂

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Re: Rod deflection and acceleration

#18

Post by Merlin » Fri Aug 30, 2019 9:01 am

Hi Lasse,
Have you tried that experiment? And if yes, what was the difference?
I do know that this virtual experiment does not fit with your video. Let’s look for the reason why. In my virtual casting model rods are described by many physical parameters. In the case I mention, they all belong to the same series (same family of design, same material, etc.). So basically they have a different loaded speed which translates into the launch speed given by the model.

In your video, rods are different and of different material (one graphite, one glass). I do not remember if they have the same length but for sure they have different basic characteristics. If we can see that they perform in a similar way (counterflex apart), then we can assume that they have similar stiffness and similar speed of recovery (which contains a spring part and an inertial part). Even if the glass rod is likely slower, other characteristics can compensate for this:

• The “action” of the glass rod is more on the butt side (material influence), and when loaded, the loss in frequency is less than the one for the graphite rod: their “speed” is closer that we might think from their non loaded frequency.

• The mass of the glass rod which is heavier (I speak of the shaft) generates more inertial effect, and the “speed of recovery” of the rods may be pretty close.

The only way to check that is to get technical parameters from the rods (not ERN and the like): their actual frequency curve with load, their MOI and their actual stiffness. That would not give all necessary information for the model, but it would support (or not) the assumption about their speed characteristics. If I was living close to you, I would come and measure that with my tools.

The problem we face with a single experiment (your video) is that it is used as an universal law. There is nothing like that in rod dynamics IMHO. I could also try to make an educated guess of the characteristics of the rods and run the model to check if launch speed is similar and counterflex different, but I need a starting point as close as possible to the rods you have used. The difficulty is pretty large: rod design is included indirectly in the model. I could start with an average graphite rod and try to design a glass rod that would fit the video, but I’m afraid it would take a very long time.

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Re: Rod deflection and acceleration

#19

Post by Graeme H » Fri Aug 30, 2019 11:42 am

Hi Merlin,

Can I ask what family of rods your virtual one belongs to? If Lasse was casting a carbon fibre rod and 'glass rod and neither matched yours, how well does your model fit his reality? What sort of rod would Lasse need to cast to fit with your model? Could he even do it in this physical universe? Is Lasse casting with universal laws similar to Newton's ones?

;)

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Graeme
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Re: Rod deflection and acceleration

#20

Post by Lasse Karlsson » Fri Aug 30, 2019 1:46 pm

Hi Merlin

I know its just two videos with the same rods, However it is a stable part of my demos now since those vidoes, and I tend to use whatever is handy if I don't have my own rods 😉 and results stay the same... But I have found out that no matter what, only by handing the rods over to skeptics and have them cast them themselves have they had a lightbulb moment.

I asked if you had done the experiment, and your answer is a no, outside the virtuel world. You also makes quite an amount of requirements for your experiment to unfold like you want. Would you be happy to have three different rods from the same manufactures series in what said manufacturer would give different line weight designation like 6, 8 and 10? Same line on each and all pulled back the same distance before released, marked so we can measure the velocity of each line? Or do we need a bigger jump than those designations?


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