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Rod damping
Moderator: Torsten
Rod damping
Now that the thread on “rod unloading during acceleration has diverged from its original topic, maybe we can move the ongoing discussion into a new thread to discuss rod damping. The damping has been identified with a record:
Vince provided a link to a paper dealing with the grip topic for tennis rackets, but it is not so easy to get the full paper. I could do that from HAL Science web site but the access to the paper does not work every time. I saved a copy on my PC if one is interested.
Just in case you want to have a go:
https://hal.science/hal-01440222/document
The conclusions of that paper do not appear consistent at first sight, just because the reference taken is the free-free mode of a racket, not the clamped free one which is more practical when one considers a flyrod. The authors refer to a rather fast mode (free-free), undamped, and do not vary conditions up to the point where the rod is fully clamped, undamped again. Bad luck since it is likely that there can be a kind of optimum grip, neither fully clamped, neither fully free, providing the possibility to nearly critically damp a rod. Another drawback is the lack of damping factor values in the paper, so we do not know how critical damping factors were in that study.
I tested a body interface for my SDM model (torsional spring with damper) and even if I can mimic a rebound/hump, this had no effect on the rod itself. I had to introduce a damping function for the rod to mimic a critical damping for the rod, which incidentally influenced the rebound shape.
The internal damping of rods is just very small, Noel did a test by 2007 and calculated a value for the damping factor of a graphite rod, but I cannot find it in my paper files. Orvis produced the Trident series years ago, which had increased internal damping, without great success. I talked about such possibility with a research center of a WW Automotive company, and the conclusion was that one would double the weight of a rod with a system hidden into the handle. The only mean is just the caster himself, and it is not yet clear to me which methodologies are in use among the casting community.
Merlin
Damping takes place from MCF apparently, and could involve both the rebound of the rod which has to spoil its remaining kinetic energy after RSP1, and the rod itself, hence the mention of the role of the grip.Vince provided a link to a paper dealing with the grip topic for tennis rackets, but it is not so easy to get the full paper. I could do that from HAL Science web site but the access to the paper does not work every time. I saved a copy on my PC if one is interested.
Just in case you want to have a go:
https://hal.science/hal-01440222/document
The conclusions of that paper do not appear consistent at first sight, just because the reference taken is the free-free mode of a racket, not the clamped free one which is more practical when one considers a flyrod. The authors refer to a rather fast mode (free-free), undamped, and do not vary conditions up to the point where the rod is fully clamped, undamped again. Bad luck since it is likely that there can be a kind of optimum grip, neither fully clamped, neither fully free, providing the possibility to nearly critically damp a rod. Another drawback is the lack of damping factor values in the paper, so we do not know how critical damping factors were in that study.
I tested a body interface for my SDM model (torsional spring with damper) and even if I can mimic a rebound/hump, this had no effect on the rod itself. I had to introduce a damping function for the rod to mimic a critical damping for the rod, which incidentally influenced the rebound shape.
The internal damping of rods is just very small, Noel did a test by 2007 and calculated a value for the damping factor of a graphite rod, but I cannot find it in my paper files. Orvis produced the Trident series years ago, which had increased internal damping, without great success. I talked about such possibility with a research center of a WW Automotive company, and the conclusion was that one would double the weight of a rod with a system hidden into the handle. The only mean is just the caster himself, and it is not yet clear to me which methodologies are in use among the casting community.
Merlin
Fly rods are like women, they won't play if they're maltreated
Charles Ritz, A Flyfisher's Life
Charles Ritz, A Flyfisher's Life
Re: Rod damping
Hi Daniel
The reference on the tennis racquet that you quote is one of several I suggested, this one is probably the most informative:
https://www.sensorprod.com/news/white-p ... 009-08.pdf
Having reviewed both baseball bat and tennis racquet literature, I don’t think that there is any value in trying to read across those sports to fly casting because the impact time of the ball is short compared to the rod going into counterflex and recovery. This is evident in that multiple studies find that gripping the bat/racquet tightly increases the transfer of vibration to the hand/forearm, which is the polar opposite of advice given by experienced casting instructors to students.
In terms of your modal analysis, I would suggest that you consider a damped/free mode as being active from MCF rather than clamped or free/free.
Regards
Vince
The reference on the tennis racquet that you quote is one of several I suggested, this one is probably the most informative:
https://www.sensorprod.com/news/white-p ... 009-08.pdf
Having reviewed both baseball bat and tennis racquet literature, I don’t think that there is any value in trying to read across those sports to fly casting because the impact time of the ball is short compared to the rod going into counterflex and recovery. This is evident in that multiple studies find that gripping the bat/racquet tightly increases the transfer of vibration to the hand/forearm, which is the polar opposite of advice given by experienced casting instructors to students.
In terms of your modal analysis, I would suggest that you consider a damped/free mode as being active from MCF rather than clamped or free/free.
Regards
Vince
“Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius — and a lot of courage — to move in the opposite direction.” — Ernst F. Schumacher
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- gordonjudd
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Re: Rod damping
Merlin,Damping takes place from MCF apparently,
When we were varying parameters in your finger/spring/model trying to fit the tip deflections measured in the Paradigm cast I think we changed the damping factor and mass term for the model starting a RSP1 not MCF.
Those plots are probably on the old board somewhere.
Gordy
- gordonjudd
- Posts: 1860
- Joined: Sat Jan 19, 2013 11:36 pm
- Location: Southern California
Re: Rod damping
Vince,This is evident in that multiple studies find that gripping the bat/racquet tightly increases the transfer of vibration to the hand/forearm, which is the polar opposite of advice given by experienced casting instructors to students.
I agree but then there is also the opposite example shown in Alejandro's tests without a line where the vibrations with a firm grip were damped much more quickly than with a loose grip.
I don''t know what you mean by a damped/free mode. There is damping involved in both the clamped/free and free/free mode shapes. Unfortunately the real situation is much more complex as there are multiple mode shapes that contribute to the bendform of the rod as it goes from MCF1-MCF2.In terms of your modal analysis, I would suggest that you consider a damped/free mode
I don't know what you would call the bending mode shape that was captured in Lasse's cast with a glass rod. Gordy
Re: Rod damping
Gordy, only one person in the world knows how firm that grip was. How would you measure it, what scale of firmness do you use?Alejandro's tests without a line where the vibrations with a firm grip were damped much more quickly than with a loose grip.
Vince
“Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius — and a lot of courage — to move in the opposite direction.” — Ernst F. Schumacher
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Re: Rod damping
We have been through this before and you have yet to offer a shred of evidence to support your position. A fly rod being cast does not meet the definition of free free, I gave you the Ansys definition for this. Daniel also told you that the higher modes are sporadic and trivial, so where’s your modal analysis showing him to be wrong?I don''t know what you mean by a damped/free mode. There is damping involved in both the clamped/free and free/free mode shapes. Unfortunately the real situation is much more complex as there are multiple mode shapes that contribute to the bendform of the rod as it goes from MCF1-MCF2.
Yes there is damping in clamped free. When does clamped free exist in a real cast and what is the outcome when you have a rod in a vice? A good cast?
Fred seems a nice name what shall we call this one?I don't know what you would call the bending mode shape that was captured in Lasse's cast with a glass rod.
Vince
“Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius — and a lot of courage — to move in the opposite direction.” — Ernst F. Schumacher
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- gordonjudd
- Posts: 1860
- Joined: Sat Jan 19, 2013 11:36 pm
- Location: Southern California
Re: Rod damping
Vince,We have been through this before and you have yet to offer a shred of evidence to support your position.
Doesn't that overlay of the complicated bendforms shown in Lasse's count as a shred of evidence that the rod is recovering from MCF1-MCF2 show that the rod is not recovering in a simple clamped-free or free-free mode?
Neither do I, but I think it is evidence that there is a complicated combination of different types of modes involved in the return from MCF1.I don't know what you would call the bending mode shape that was captured in Lasse's cast with a glass rod.
I don't know what that shape came from but with a frequency of 138 Hz it probably did not come from a flyrod.Fred seems a nice name what shall we call this one?
Gordy
- gordonjudd
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Re: Rod damping
Vince,what is the outcome when you have a rod in a vice? A good cast?
No.
The casting robot used rigid bands to attach the butt of the the rod the rotating robot arm as shown below. According to Bruce Richards they could not get the robot to make good loops and sustain false casts until they added a rebound hump to the angular velocity profile they input to the robot. That addition did not change the damping applied at the butt because the attachment did not change but the it did make a big improvement on the loop shape it produced.
Gordy
Re: Rod damping
Gordy, you took the overlay from the only stroke in about 5 minutes of glass videos, where the cast either did not settle at RSP2 either immediately without a visible MCF2 or with a little overshoot. Graeme dropped a major hint when you initially posted it by complementing Lasse on a sublime backcast, you probably missed it. Your overlay is taken from a failed cast if the aim was to damp the tip quickly.Doesn't that overlay of the complicated bendforms shown in Lasse's count as a shred of evidence that the rod is recovering from MCF1-MCF2 show that the rod is not recovering in a simple clamped-free or free-free mode?
If you are now moving away from saying that the rod is not clamped free or free free then I would suggest that you have changed horses and I’m pleased to see that you are joining the active damping fan club.
Why?Neither do I, but I think it is evidence that there is a complicated combination of different types of modes involved in the return from MCF1.
It is a fishing rod with a lower frequency than a baseball bat or tennis racquet.I don't know what that shape came from but with a frequency of 138 Hz it probably did not come from a flyrod.
Vince
“Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius — and a lot of courage — to move in the opposite direction.” — Ernst F. Schumacher
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Re: Rod damping
It is good that we are in agreement that clamped free is a poor damping mode. How was the angular velocity added, by varying the motor speed? If so that is an operator adjustment, not the rod causing the operator to change its input.gordonjudd wrote: ↑Mon Aug 28, 2023 11:04 pm According to Bruce Richards they could not get the robot to make good loops and sustain false casts until they added a rebound hump to the angular velocity profile they input to the robot.
Vince
“Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius — and a lot of courage — to move in the opposite direction.” — Ernst F. Schumacher
https://www.sexyloops.com/index.php/ps/ ... f-coaching
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