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Tailing Loops vs. Rod Action?

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VGB
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Re: Tailing Loops vs. Rod Action?

#121

Post by VGB »

I’m looking forward to this control systems engineering was my favourite module but converting critical damping ratios derived from models into caster movement is an interesting topic. I looked at it in 2013 with a basal accelerated SHO model but got the application wrong because I thought a hard stop was key to distance casting due to listening to bar talk.
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Re: Tailing Loops vs. Rod Action?

#122

Post by Merlin »

Vince

I guess there can be interferences in between rods. If I remember well, the Berkley and Sage rods were taped together to ease their holding. That could end up in a mass damping effect (for each rod the other one is an extra mass), and there may be flexural waves transmission / reflection impact at hand level as well. I'm looking forward to your findings.


Paul

I did some work on damping in the past (considering the arm of the caster as a mass+spring+damper system) to mimic the rebound of a rod, and it worked fairly well, but I never looked at a dual outfit casting issue like in Lasse's amazing experiments.

Merlin
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VGB
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Re: Tailing Loops vs. Rod Action?

#123

Post by VGB »

Merlin wrote: Fri Feb 04, 2022 7:46 pm Vince

I guess there can be interferences in between rods. If I remember well, the Berkley and Sage rods were taped together to ease their holding. That could end up in a mass damping effect (for each rod the other one is an extra mass), and there may be flexural waves transmission / reflection impact at hand level as well. I'm looking forward to your findings.
Daniel

There could be interferences between rods but Paul made 2 videos with the same set up and entirely different results. Any decent caster can take a set up and make it counterflex a lot or just a little by changing nothing but combinations of the rise time, tightness of the grip and deceleration into the stop to vary the overshoot and damping ratios. Add factors such as Fitts Law and the Law of Practice to accommodate the human response into your model and a whole new world will open up. You will need a lot of subjects in a large scale trial to validate your model though.

Vince
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Re: Tailing Loops vs. Rod Action?

#124

Post by Torsten »

Hi,

I think it's very likely the damping ratio depends on the grip of the caster.

I've checked Lasse's first video:
Lasse_bendy_stiff.png
Lasse_bendy_stiff.png (118.96 KiB) Viewed 1436 times
There is almost no difference of the rod bend!
I'd guess: if the line weights are the same, the rods have at this configuration a similar stiffness. I don't think we're comparing here really "a bendy vs. a stiff" rod.

--
Lasse_bendy_stiff2.png
Lasse_bendy_stiff2.png (156 KiB) Viewed 1436 times
After RSP one rod shows more counterflex, one possible explanation is a different mass distribution of these rods.

--
Lasse_bendy_stiff3.png
Lasse_bendy_stiff3.png (100.9 KiB) Viewed 1436 times
This is from Lasse's 2nd video and something that seems to be more plausible if the rods have a different overall stiffness.

Greetings,
Torsten
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Re: Tailing Loops vs. Rod Action?

#125

Post by VGB »

Without damping, any joint would tend to oscillate following movement but the details of what actually goes on in the motor control system to produce variable damping coefficients are beyond me. Nevertheless, it’s far more likely that Paul is struggling with fine control of the tip because of the higher swingweight of his set up and the shortness of his tip path compared to Lasse. Both of those factors would tend to increase the overshoot as shown in his 2nd video.


I had the same discussion about the relative stiffness of the rods in the bendy/stiff video with Lasse a couple of years back. I can’t remember the details but it ended in him casting a rubber chicken in the snow.

I’ve got to finish rewiring my living room before the weekend or I’m toast.

Regards

Vince
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Re: Tailing Loops vs. Rod Action?

#126

Post by Paul Arden »

When I was visiting Bruce Richards, a long time ago now, he had casting robot which Noel had built. At first they tried to compute it to cast and failed. So they plugged in the read-out from one of Bruce’s casts into the robot and it worked. The fascinating thing however was the stop. Instead of a stop, it went stop..stop cast stop..stop. Which looked nothing like how Bruce cast. However that second movement must be what happens below the hands.

When Jon Allen built Rodney, “to see how far a cast could really go”, which was a cruder version of Noel’s robot, we couldn’t get good loops at all, until we replaced the hard stop with a cushioned stop.

Unfortunately I only have photos and not a video of Noel’s machine. But I’ve asked Bruce to see if there is any video.

Very interesting to see this problem occur here. On the video the HT4 clearly starts to reverse direction when the HT10 reaches RSP2.

Cheers, Paul
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Re: Tailing Loops vs. Rod Action?

#127

Post by VGB »

Very interesting to see this problem occur here. On the video the HT4 clearly starts to reverse direction when the HT10 reaches RSP2.
Hi Paul

I think that you are chasing a red herring. The video shows waves in both rod legs that don’t occur when you cast the rods individually, so carrying 2 rods together appears to effect your normal casting stroke. Once you sort that out, it will be worth looking at any artefacts that remain. The reversal could be an issue with a lack of damping but not because of where Lasse is holding it but because you have the 2 rods touching each other but if you don’t have significant counterflex, it may not occur.
Instead of a stop, it went stop..stop cast stop..stop. Which looked nothing like how Bruce cast. However that second movement must be what happens below the hands.
My recollection is that the casting analyser had some limitations that may have meant that what was measured was not actually fully representative of the forces applied at the rod handle.

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Vince
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Re: Tailing Loops vs. Rod Action?

#128

Post by Paul Arden »

Hi Vince, I think I can hold them separately so that they don’t touch and this should minimise the problem. If so I’ll be able to launch both casts from the ground position and should have no problems tailing one and not the other.

Cheers, Paul
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Re: Tailing Loops vs. Rod Action?

#129

Post by VGB »

Morning Paul

If you don't have a woman's hands, you can try isolating them with a piece of wood or cloth,
f so I’ll be able to launch both casts from the ground position and should have no problems tailing one and not the other.
Looking forward to seeing it :p

Regards

Vince
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Re: Tailing Loops vs. Rod Action?

#130

Post by tinpusher »

Is there a rod database that quantifies rod action or are we left to the each manufacturers subjective opinion?
What is CCS and CRN?

Thanks
Doug
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