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Lock up or lock down - which type of real seat?

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Bernd
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Post by Bernd »

https://vimeo.com/42259632
It looks to me that the cf makes my rod hand move forward and then the movement can last til rebound takes place.
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Bernd
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gordonjudd
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Post by gordonjudd »

I have always wondered why the rod butt goes forward as the tip is coming back towards the caster after counterflex.
and
I would want to see a CA graph synchronized, with a slow mo to back that up in detail

Bernd,
I think you have probably seen this example for the Paradigm cast before.

The angular velocity in that video came from taking a derivative of butt angle data rather than the CA so there is no error that might arise from trying to determine how to synchronize the data in a CA file to a video file. I know the relative timing shown in this plot is correct since the velocity data was derived from the video data, and thus they have the same time base.

You can see that in this case the maximum angular velocity of the rebound hump is reached just after maximum counterflex as shown below:

Image

They way you relax your hand after RSP1 appears to give a different shape to the deflection profile of the rod tip during counterflex. You can see that in Mathias case (which has a more typical deflection profile) the deflection during counterflex is a fairly symmetrical sinusoid as shown in the red curve below.
Image

The way you kill the return from MCF I think your deflection curve would fall off much more quickly than it rose from RSP1 to MCF.

If you can upload the original of your file to Dropbox I will run a velocity profile for it, as I think it will be different than what we have seen in Grunde's videos.

Gordy
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Bernd
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Post by Bernd »

Hi Gordy,
after watching that slomo of Matthias several times frame by frame it looks to me that cf means increasing force acting on his rod hand. After inertia is overcome by these force the rod hand starts to move forward. Since it takes time to deccelerate the rod hand again this happens during rebound. The max peak as you pointed out happens very short after mcf. I think that is just a very short delay of the rod hand reaction to the force that has just being pulling up on it.
If the force moving the rod hand does not come by cf then I don't understand where it should come from and why.
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Bernd
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gordonjudd
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Post by gordonjudd »

After inertia is overcome by these force the rod hand starts to move forward.

Bernd,
There is some translation going on with the hand throughout the cast as tracked in the blue curve shown here so I am not sure what you mean by "inertia".

But the relative movements I am talking about has to do with rotation not translation therefore so I am looking for sources of torque not forces.

The simple explanation would be that the wrist acts like a one way torsional spring with no ability to store PE. Thus as long a there is some bending torque at the butt of the rod that is related to the tip deflection during counterflex that torque will increase the rotation of the wrist. But unlike a true torsional spring there is no PE build up in the wrist that would return the rod angle to the equilibrium angle it had at RSP1.

That is a quasi-static argument (bending moment at butt is proportional to the tip deflection) that I do not know holds when there is also a moving mass component going on in the spring. Hence the speculation the dynamics that cause the butt to rotate forward while the tip is coming back from counterflex could be a signature of the free-free mode that Merlin talked about.

At least I think you can see that the rod continues to rotate forward as the rod goes from RSP1 to RSP2.
Gordy
"Flyfishing: 200 years of tradition unencumbered by progress." Ralph Cutter
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Bernd
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Post by Bernd »

Was it Newton's second law? "An object being motionless wants to stay motionless..."
I understand this means my rod hand wants to stay motionless after stopping it. But than there is torque acting on it caused by cf of the rod.
It starts to be very little torque and then it increases. At some point it will be enough to make my hand move, make the rod butt rotate further.
In the very next moment the torque will end with mcf. Well, actually am not sure but would there be a little delay from tip to butt maybe?
However my hand will not stop immediately. It first has to deccelerate. And that takes time while the rod tip runs thru rebound.
For sure there would be differencies from caster to caster about how much torque exactly it needs to make the rod hand move again.

Btw I may forward the original file but I think it would be better to simply understand what we see in the file of Mathias! :D ;)
If we can't really explain what happens there in detail, I think we will be lost in all files?! :p

When I hold my rod and put the tip in mcf position I feel the torque working on rod hand. If I let the tip go the resistance ends.

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Bernd
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Post by gordonjudd »

In the very next moment the torque will end with mcf. Well, actually am not sure but would there be a little delay from tip to butt maybe?

Bernd,
As you have seen with your static test the bending moment from the deflection in the rod will reach its maximum at MCF and then start to decrease as it goes back to RSP2.

I think there will be a delay for the changes at the rod tip to impact the movement at the butt.

Btw I may forward the original file but I think it would be better to simply understand what we see in the file of Mathias!

A Simple understanding of rebound may be beyond us!

Do you have some CA files that shows the shape of your rebound hump? Generally that hump is reasonably symmetrical, but just looking at your video I don't know if that would be the case for that cast at least.

Gordy
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Merlin
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Post by Merlin »

Hi Gordy
This is a bit of speculation, but I am wondering if the reason the rod butt rotates forward and produces the rebound hump as the rod goes through counterflex is because the rod has a strong free-free mode as it returns from counterflex.

It may rather come from the "free" motion of the rod under its center of gravity as we release the grip. My point with NF2 is about controling and dampeing extra vibrations coming from NF2.

Merlin
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Post by gordonjudd »

It may rather come from the "free" motion of the rod under its center of gravity as we release the grip.

Merlin,
Could you expand on what the "free" motion of the rod means in that statement? Does it have something to do with the concept that "An object will ALWAYs rotate, free in the air, about an axis that passes for the center of mass."

My point with NF2 is about controlling and damping extra vibrations coming from NF2.

If that is the case I do not understand what the location of the first node of the free-free first mode near the butt has to do with the location of the first node of the second clamped-free mode that is at the x=0 position. If you assume the first node for all of the clamped-free modes are at the center of the hand, why would the location of the free-free mode node have an effect on how they are damped?

I can see that the second node for those modes are located at about the same 80% point on the rod, but I do not see why node locations that match at the far end of the rod will impact something at the butt end where they have different node positions.

Gordy
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Merlin
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Post by Merlin »

Hi Gordy
Does it have something to do with the concept that "An object will ALWAYs rotate, free in the air, about an axis that passes for the center of mass."

Yes, that's it.

I start again from the beginning: the second "clamp free" mode frequency is similar in value by comparison to the first "free free" mode. They both have a node in the tip at approximately the same place, the difference lies in the butt. The "clamp free" has no node (a node means there is a change is curvature on each side, this is not the case here, there is no curvature around the butt end point). The "free free" mode has one (a real node).

To get rid of the potential appearance of the butt node in "free free" conditions, the caster can either: grip the handle as hard as he can (then there is no node anymore, it is back in "clamp free" conditions), or control the node as much as he can from the grip (damp the second mode vibration, which is not huge).

The point is that if the second node appear as we relax the grip, he may give an uncomfortable feel as it tends to move the system away from our hand. A simple rule of the thum is: keep the center of gravity just above your hand grip, or at the top of it.

Merlin
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Post by gordonjudd »

A simple rule of the thum is: keep the center of gravity just above your hand grip, or at the top of it.

Merlin,
Thanks for all your explanations and explaining what a node is. I had the understanding that a node was a non-moving point on the vibrating beam.

I like your rule of thumb and will check out how my heavy reels work out on your center of mass chart.

Gordy
"Flyfishing: 200 years of tradition unencumbered by progress." Ralph Cutter
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Post by gordonjudd »

A simple rule of the thumb is: keep the center of gravity just above your hand grip, or at the top of it.

Merlin,
Thanks for all your explanations and explaining what a node is. I had the misconception that a node was a non-moving point on the vibrating beam.

I like your rule of thumb and will check out how my heavy reels work out on your center of mass chart.

Gordy
"Flyfishing: 200 years of tradition unencumbered by progress." Ralph Cutter
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