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The Stop

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gordonjudd
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The Stop

#101

Post by gordonjudd »

When I get time, I'll shoot a better one,
Lasse,
When you do it would be better to position the camera directly in the path of the line on the forward cast. That might present a problem in the line hitting the camera, but would get rid of the oblique angle that will affect the angle measurement for the casting plane.

Better yet would be to have a 6 degree of freedom sensor attached to the rod so you could get real time 3-D measurements of the butt path like they do for golf swings.

It appears to me that you bring the rod more in line with the casting direction at the end of the cast and that would make the rod appear to be longer when viewed from a camera positioned perpendicular to the casting direction.

The result that is giving Merlin problem in the measured cord length values is that the cord length at MCF appears to be longer than it was at RSP1 when the cast was viewed from the side.

Hard to tell when the rod was vertical in your video and the oblique camera angle will affect the tilt measurement, but it appears the plane tilt in that cast was around 30 degrees
Image
That would produce a foreshortening factor of cos(30)=.86 (36 degrees would be .81) which gives Merlin problems in comparing measured data with the predictions of his 2-D model.

Gordy
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Lasse Karlsson
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#102

Post by Lasse Karlsson »

Paul Arden wrote:Stefan is vertical. I'll shoot some 170 this week. Mine can be a pretty mixed bag depending on how much training I'm doing, but if you take slide out of the equation I think my very best casting is very close to vertical. The forward cast will never be completely vertical however - not if you want to turn the rod butt through past the forearm. I'll try to have a distance session on Thursday and will keep my rod handy :)

Cheers, Paul
Hi Paul

Stefan isn't vertical, at least not when I cast with him :D

Cheers
Lasse
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Flycasting, so simple that instructors need to make it complicated since 1685

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Lasse Karlsson
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#103

Post by Lasse Karlsson »

Hi Gordy

Just send me that sensor, and I'll be happy to cast with it attached :)

Cheers
Lasse
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Flycasting, so simple that instructors need to make it complicated since 1685

Got a Q++ at casting school, wearing shorts ;)
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gordonjudd
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#104

Post by gordonjudd »

This shows the unexpected angular velocity measured for Paul's 170 "stopless" cast. We knew there had to be a stop in a "stopless" cast, but I was not expecting that there would be two distinct deceleration phases.



You can playback the full size video at https://vimeo.com/189803106

The first phase may be showing the deceleration of the angular velocity of the butt rotation related to the self deceleration mechanism (SDM) that Merlin has analyzed. The second deceleration phase was timed after RSP1 (t=0) and finally brought the rod to a full stop at an angle near the horizontal.
Image

I was surprised to see that the butt angle of the rod was nearly vertical in this cast just as it was in the cast using a regular pull back to stop the rod. The SDM also produced a higher deceleration value (-4381 deg/s.^2 than I would have expected since Paul was only casting around 9 m of line in this cast as shown below.
http://imageshack.com/a/img924/2383/G2HV60.jpg

It is a bit muddy to compare deceleration rates of this cast compared to the values measured for the pull back cast since this cast had a much larger maximum angular velocity (627 deg/sec) than in the pull back cast (354 deg/sec). But you can see the deceleration rate produced with the pull back was -4564 deg/s.^2 which is quite close to the -4381 deg/s.^2 value measured for the first deceleration phase of this "stopless" cast. I was expecting the deceleration rate in a stopless cast to be much less than when using pull back to quickly stop the rotation of the rod.

Interesting result indeed.

Gordy
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Paul Arden
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#105

Post by Paul Arden »

Thanks Gordy. Quick question, would it be self-deceleration mechanism or unloading as the force moves away from the angle of the flyline? And can you let us know what thoughts the results of this experiment lead to?

Very many thanks,
Paul
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Paul Arden
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#106

Post by Paul Arden »

Oh and what was the deceleration of the normal "hard" stop? Thanks.
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gordonjudd
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#107

Post by gordonjudd »

Oh and what was the deceleration of the normal "hard" stop?
Paul,
I don't mean to be rude, but it was not so hard.

Here is the video for that "squeeze" stop cast:


You can play back the full size video at https://vimeo.com/189873314.

Its deceleration rate (-2750 deg/s.^2) and duration was not sufficient to stop the rod rotation before RSP1. Thus the remaining angular velocity after RSP1 bled into the angular velocity normally associated with the rebound hump. This is somewhat similar to the two deceleration phases observed in the "stopless" cast. As a result the rod did not come to a full stop until some time around RSP2.

Image

You reached your maximum angular velocity just after the rod was vertical in this cast (95 deg), and thus that relatively slow stop still produced a nice tight loop as shown below.
Image

Gordy
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Paul Arden
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#108

Post by Paul Arden »

Fascinating! Thanks!
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Merlin
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#109

Post by Merlin »

Gordy

Is the plot for the pulled-back cast available? One thing interesting to know is that a rod under self deceleration is suject to its "free-free" vibration mode, which is very close to the second mode of the "clamped-free" rod, the mode which one can make appear when making a pull back with the wrist. This is about 3 times the fundamental "clamped-free" mode.

To me, rebounds are the mark of self deceleration. Their position in time depends on casting parameters, like the weight of the carry.

Merlin
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Paul Arden
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#110

Post by Paul Arden »

I remember Aitor shooting a video of my backcast which showed S-shape curvature on the 170 prior to "hand stop". Merlin, that's a hell of an interesting email you sent this morning. Is it possible to post it here?

Many thanks,
Paul
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