Merlin wrote:Hi everybody
The results were always the same: the rod continues rotating, because it has a significant kinetic energy.
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When I talk to that to casting pros (accustomed to fine tuning rod designs), they just do not understand how a rod could stop by itself.
Merlin,
I can not remember anyone saying that the rod can stop it's rotation all by itself.
What some (including me) are saying is that the rod will unload without any significant retarding moments from the caster. And that the rapid decrease in angular velocity (between max rod load and RSP1) measured at the butt of the rod is (mainly) due to the rod unloading.
These two things are not at all the same, and I don't understand why you keep insinuating that someone is claiming that "the rod can stop it's rotation by itself".
Cheers,
Grunde
"Essentially, all models are wrong, but some are useful."
George E. P. Box
I can not remember anyone saying that the rod can stop it's rotation all by itself.
Grunde,
This is the claim that started this thread.
"Fortunately, it can be easily shown that prior to RSP the caster never exerts retarding moments//torques on the rod and this fact is intuitively consistent with everything most people would believe about fly rod behavior during casting."
As far as I can see there is no qualifier that says the caster does not need to exert "significant" retarding moments to get the rod to unload by itself.
What some (including me) are saying is that the rod will unload without any significant retarding moments from the caster.
If that is what you were referring to in regards to stopping the rod, then no wonder we had a disconnect. I would agree the rod will unload on its own once a deceleration torque is applied to reduce the angular acceleration that was being applied. You can obviously see that in Tom's and Sakke's video.
If the acceleration could be continued long enough the rod would still unload by itself as predicted by the your model, but as noted in the first post:
The loaded frequency of the rod/line for the Paradigm cast was 1.2 Hz. As discussed here if the caster did not put on the brakes to stop the acceleration of the rod rotation then the time for the rod to unload by itself would be .5/1.2=.417 sec.
However, Grunde’s measurements found the actual unloading time was .122 second. Thus to get the fast stopping time we see in casting you would expect that some additional reversing torque must be applied to stop the rod more quickly.
But the fact that the rod will unload on its own without significant retarding moments is much different than saying the caster never applies negative torque prior to RSP.
Merlin and I took never to mean never, so in terms of cancelling out the KE in the rotating rod that made no sense.
I am relieved that you and I were talking about different things and that is the reason we were saying diametrically different things.
Gordy
"Flyfishing: 200 years of tradition unencumbered by progress." Ralph Cutter
What some (including me) are saying is that the rod will unload without any significant retarding moments from the caster.
I share this point for some milliseconds, but no more. There is a time when the caster "brakes" to lower the rotation speed of the rod, mainly due to its KE, and that gives a negative torque, but not to the point that there is a pullback. The casters I talked to could not understand that there was no stopping action from their part.
And that the rapid decrease in angular velocity (between max rod load and RSP1) measured at the butt of the rod is (mainly) due to the rod unloading.
This is what I interpret as "stopping by itself": if the butt velocity decreases without any action from the caster, the rod "stops by itself". I rely on someone speaking better english than mine to moderate this point.
These two things are not at all the same, and I don't understand why you keep insinuating that someone is claiming that "the rod can stop it's rotation by itself".
Again I may not express myself correctly in english (I'm not native), So I do not insinuate, I interpret (badly maybe).
To close my criticism about the theory from Server, a last one "he (the caster) is trying very hard to load the rod during unloading". That may be worth a thread, but I'm kidding this time.
Merlin
Fly rods are like women, they wont´play if they're maltreated.
Charles Ritz, A Flyfisher's Life
For that matter does the second statement even make sense?
Magnus,
I hope it does to Grunde, as I was agreeing with his premise that the rod will unload on its own after the initial negative torque is applied to slow down the rotation rate of the rod.
In Tom's video the primary source of that negative torque was applied by stopping the rotation rate of his elbow as described here.
Is the deceleration rate of the elbow shown below significant to you? As far as getting the rod to start unloading it was:
If that does not make sense to you, I am sorry that I cannot explain it more clearly.
Merlin,
Just as a check, did that wording make sense to you?
Gordy
"Flyfishing: 200 years of tradition unencumbered by progress." Ralph Cutter
You were and are saying rather more than "You're right Grunde"
Are you are saying the caster applies a negative torque to the rod which then begins to unload?
In Sakari's clip I see the rod unloading as it comes away from the side of the cup. So, as far as I can see, the rod begins unloading before it reaches the other side of the cup.
The rod unloads anyway, even if we could keep on accelerating. We need to stop it because it has a significant kinetic energy that cannot disappear by itself.
The mechanical characteristics of our rods are fit to our casting capabilities, so most of the time, the unloading takes place more or less at the time the deceleration of the rotation speed starts. As the rod starts unloading, we do not need a lot of torque to decelerate it, but we need some afterwards, because it has KE.
This is what the cup is doing: stop the rod rotation definitively. Then it counterflexes sharply.
Merlin
Fly rods are like women, they wont´play if they're maltreated.
Charles Ritz, A Flyfisher's Life
Yes, the negative torque is for the inertia of the rod, not for the unloading.
Our torque is positive until the point the grip leaves the cup edge in my video just before RSP. This was what I expected to see in the video before making it and was happy to see my assuption was right.
You can put negative torque (pull back) in before that and the indication, if done more than slightly, is S-curve in the rod.
I think we should not use term deceleration torque as it is confusing - at least it initially was for me, until I read it in my mind as negative torque (positive is in the rotation direction of cast).
I'm here just for the chicks.
President of The Village Idiots of Vantaa Rapids
President of The Casting Federation of Finland
Yes, the negative torque is for the inertia of the rod, not for the unloading.
We share the same view
Our torque is positive until the point the grip leaves the cup edge in my video just before RSP. This was what I expected to see in the video before making it and was happy to see my assuption was right.
You can put negative torque (pull back) in before that and the indication, if done more than slightly, is S-curve in the rod.
The confusion might be that we interpret “negative torque” as a pull back only because the rod goes backwards (in a forward cast) with the pullback. But we do can produce “negative torque” and the rod keeps on going forward. It moves forward, but with a lower and lower speed until it stops. If we keep on using a negative torque after the stop, then it goes backwards. So the problem of understanding is in the fact that a negative torque (or a deceleration, which is a negative acceleration) can be applied and that the rod keeps on moving forward. Just like when you use the brakes in your car: your car decelerates, but is still moving forward until it stops. The torque exerted by the brakes is negative by comparison to the direction of rotation of the wheels. If you want to "pullback" your car, you need to use the gear box in rear position to generate a negative torque by comparision to the former direction of your car.
The S curve during the pullback is due to a sharp motion that excites the second NF. Use your arm instead of your wrist and the S curves should not pop up.
I think we should not use term deceleration torque as it is confusing - at least it initially was for me, until I read it in my mind as negative torque (positive is in the rotation direction of cast).
But for me this is the point: a decelerating torque is negative by comparison to the direction of the motion.
Merlin
Fly rods are like women, they wont´play if they're maltreated.
Charles Ritz, A Flyfisher's Life
You can put negative torque (pull back) in before that and the indication, if done more than slightly, is S-curve in the rod.
The confusion might be that we interpret “negative torque” as a pull back only because the rod goes backwards (in a forward cast) with the pullback. But we do can produce “negative torque” and the rod keeps on going forward. It moves forward, but with a lower and lower speed until it stops. If we keep on using a negative torque after the stop, then it goes backwards. So the problem of understanding is in the fact that a negative torque (or a deceleration, which is a negative acceleration) can be applied and that the rod keeps on moving forward. Just like when you use the brakes in your car: your car decelerates, but is still moving forward until it stops. The torque exerted by the brakes is negative by comparison to the direction of rotation of the wheels. If you want to "pullback" your car, you need to use the gear box in rear position to generate a negative torque by comparision to the former direction of your car.
Hi Merlin,
Actually, as can be seen from my cup video the point on which we can apply negative torque (deceleration) is very close to RSP (unless we move so fast that the rod inertia becomes important and we get the second node). Had I tried with the cup cast to get negative torque, the handle would still have followed the back edge until there was little enough bend in the rod so that its own inertia wins the that force coming from the bend (which is pretty close to RSP). So, if we try apply negative torque, our movement needs to be fast so that rod inertia becomes significant - otherwise we are just "letting bend out" from the rod.
I get S-curve without pullback. The part above my top hand is rotating forward the whole time and it still appears. It must be so evident as the 18' has so much moment and thus inertia up in the rod.
I'm here just for the chicks.
President of The Village Idiots of Vantaa Rapids
President of The Casting Federation of Finland
The "negative torque" period of time is really short, just before/around RSP (0.15s max maybe). In your experiment, this role is devoted to the cup which stops abruptly the forward motion of the handle. In this case, the "negative torque" is likely high and extremely short.
S curve: you are speaking of DH rods dont'you? For SH rods, that can be controlled by minimizing the wrist rotation. For a DH rod, I'm afraid the control is much more difficult. Both hands, elbows and likely shoulders are part of the game. Try to be less sharp in your motions (I can see that in the videos, the stopping action of DH rods is really sharp).
Merlin
Fly rods are like women, they wont´play if they're maltreated.
Charles Ritz, A Flyfisher's Life
Regarding the braking of the car, you need to think of two cars. One car tows (rod handle) and tows another car (tip/line) with bungee rope. Consider that the first one accelerates first very much and the bungee is stretched, the towed car has started to move. The towing car decelerates but the bungee is still trying to pull both cars towards each other. Thus, no negative torque.
I'm here just for the chicks.
President of The Village Idiots of Vantaa Rapids
President of The Casting Federation of Finland
I'm getting more confused by the clarifying explanations as they evolve.