Fly casting robot / 3 SLP's ! / Great website

Al,

What an ambitious project it was to build a casting machine!! It is too bad that the human-fly rod-fly line system is so complicated. One way to begin examining the complications for humans casting is to put your hand palm upward on a desk or table surface and take the smooth end of a writing pen and press down on the fleshy part of your palm. I would guess it is easy to move the pen downward 1/2 inch and not impossible to move it 3/4 inch. Similar, as well as other effects, when holding a rod are unavoidable and they cause a number of behaviors we care about

1) the soft connections create time delays and the system acts slower - it takes time to do things to the system and when the faster part of the system reacts (as in rod unloading) it acts against slow stuff (I'm thinking ahead to further//future explanations of why a caster can determine the maximum rod loading but that subsequent behavior is pretty much programmed in and cannot be influenced or changed).

2) your machine system was probably much faster reacting because it did not deflect//deform much when load was applied. Depending on exactly how loads are applied or changed on a machine without gaps//play, loads can be changed rapidly. This can cause what are called higher modes of vibration to be excited (language that may be used is -- "the second, third, and fourth modes we excited when we did that" or "we generated multimodal response". If you placed your hand on the rod in your machine my guess is you'd have no trouble feeling the vibrations.

3) it is quite common for folks (I have had these conversations with qualified engineers in the past who had become brainwashed by terms they have seen in their textbooks) to talk about damping. In fly casting their is no//little damping in the sense that damping is defined in textbooks. To fit the texbook definition the rod blank would have to absorb the energy - the rod blank is almost incapable of absorbing energy and the only part of a rod with the ability to absorb significant energy is the cork handle (An easy demonstration is to press a strong fingernail into the cork - you do work in that process of pressing. Almost all that energy is probably lost when you let-up on the pressing load and in fact you can see the indentation that is associated with the energy which was lost.)

4) Most energy has to be absorbed by the human body in the hand and the limb muscles. This is actually a process of performing negative work where the rod's kinetic energy does work on the caster//is absorbed by the caster.

All this specialized intrinsic cushioning and energy absorption separates a rod in a human's hand from a rod controlled by a machine with metal components.

I hope we cross paths because it would be so interesting to hear about your machines!!

Regards - Server

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From Ally Gowans:

Hi Gordy,

Knowing how talented and particular Al Buhr is I would have said that he had as good a chance of building a successful casting machine as anyone. It is not surprising that the result was less than perfect because all the scientific knowledge we have does not come close to understanding the behaviour of the human body.

I like the 500fps video published by Jason Borger (http://jasonborger.com/the-rod-the-cast/) showing Grunde Løvoll (Ph.D) casting complete with the rod tip track indicated. This illustrates the difficulty of applying detailed science to fly casting. You see the “stop” RSP then another RSP as the angler controls rebound and then after “follow through” the final “RSP” if you like. At the first RSP the rod parts still have momentum which forces the tip into counterflex, at counterflex the blank fibers either side of the curved blank are in compression or tension and are storing energy that causes rebound and this counterflex/rebound energy interchange might sustain for a time but for the damping effect of the line and the human body because when a good caster “stops” the rod grip is relaxed and often the rod butt is moved to minimise disturbance. If you clamp a section of rod blank solidly at one end, deflect it and release it quickly you will see these harmonic vibrations decaying over time as the friction and windage effects dissipate the energy, not what we want during a cast! We often observe the affects of counterflex in a poorly executed cast but rebound is not so prevalent because it is smaller and the dampening effect of the body and line are effective. If you want to see these effects while you cast just grip the rod very tight during and after delivery and observe the sine waves in the line. Al’s machine would have suffered similarly. I have attached some sketches taken from the video referred to which illustrate the movement of the rod tip. Sketch 1 shows RSP, 2 shows max counterflex, 3 shows max rebound by which time the caster has the rod under control hence it is straight and 4 shows the adjustment made by the caster during line flight (follow through). It’s also worth noting how the line path is very similar to the rod path as expected.

An aspect of casting that we have not yet thought about is harmonics or resonance during casting. For every rod/line combination, for every cast made there is a “most efficient” method of delivering energy to the rod to get the most from it. We can’t do it every time but just occasionally we “get it right” we “hit a sweet spot” and a cast goes exceedingly well for what appeared to be little effort. Using resonance or vibration as it was called about a hundred years ago optimizes performance and the secret is to tune your cadence to the rod, question is how?

Best wishes,

Ally Gowans

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Ally.... Fascinating ! To think we now have 3 SLP'S.

The more we study this stuff, the more we learn .... yet, at the same time, the more we need to learn. I hope we never completely fathom all the complexities of fly casting, just as I hope and pray we never find the one perfect fly !

I've included your attachments.

Gordy

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WEBSITE - Loop connections

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Let me emphasize something from Lefty's message: Dan Blanton's website, www.danblanton.com . This presents a wealth of information of all kinds, especially for those interested in salt water fly fishing.

I've already made some of the braided hollow core nylon fly line loops and will soon put them to the test .... not simply with the line tester, but with shock tests and (best of all) use in actual fishing situations. I doubt I'll find anything different than that reported by Lefty.

One question will be whether or not these connections using soft pliable woven material will effect casting or loop turnover. That will be important for me to find out especially when pin point accuracy and careful layout are needed when fly fishing for permit. (Probably wouldn't make much difference when making short casts with very large flies to billfish. )

One omission so far in our discussions on fly line loops, is the welded loop which Airflo has placed on the ends of some of their fly lines. I have field tested them and find they are very smooth and don't catch on the tip top or guides. They test at almost the tensile strength of the fly line core itself. Bruce Richards has discussed the pros and cons of using those welded loops on the ends of some of the SA fly lines.

Gordy