Rod unloading during acceleration

[Bernd Ziesche]

Nils,
I have been thinking (whatever that means ):
I move my rod hand along a (nearly) straight path. And I start with velocity to be zero. At the end velocity is again zero. My goal is to have a constant increase in velocity to as close the end as possible. So I aim to use the shortest possible section of the path for decelerating back to zero.
The slower I move my hand (the less I accelerate), the closer I position max velocity to the end. I can then use a high rate of decel. compared to the rate of accel..
Seems pretty logical, because as I said, more max velocity means longer path of deceleration.
Taking this to my casting I think I can go like 70/30 in an avg. cast, but will end up 50/50 in a distance cast.
That does make sense to me.
Maybe with the broomstick I get so much less speed, that I get away with a shorter distance for decel.. I dont know and I yet don't know about matching the time for straightening of a fly rod into this. But we obviously are doing well. Sometimes...
Maybe some weird thoughts. Well, I am trying to understand this!
Regards
B

[Paul Arden]

I don’t know Bernd, I work the other way. I suspect it’s probably an impulse. But I can tell you it’s a weird question to ask me In flycasting, physics always comes after the fact.

[NM]

I move my rod hand along a (nearly) straight path. And I start with velocity to be zero. At the end velocity is again zero. My goal is to have a constant increase in velocity to as close the end as possible. So I aim to use the shortest possible section of the path for decelerating back to zero.

Bernd, I guess that fixed-available-arc-for acceleration and deceleration starting point may be what makes you so hang up on the Stop, and what may be taking you down the wrong reasoning path (and that is good, because the stop hang up is associated, I think, with this idea that you have to stop the rod to force it to unload (and that loading and unloading the rod is all that matter)). We are not moving our rod hand in a straight line, and the arc we have available for moving the hand from zero velocity to zero velocity could be as much as 200-220 degrees. Ignoring for the time being the haul, then want to have the line tip pulling the line as fast as possible in the direction of the cast when the loop is formed. The arc we have available for that is much less (in the examples we looked at, 90-135), and is determined by the rod position at the start of the cast and the line trajectory we want. What happens to the rod tip after the loop has been formed is for a shooting head tournament cast like T38 and ST27 of little or no importance (it matters slightly more for MED5 because of the thicker shooting line). You can use all of the remaining arc until the rod tip hits the ground to stop the rod if you want, and as noted before some of the German tournament casters in the 70s and 80s did literally have it hit the ground using a hand path similar to Henry’s (it is not possible with my hand path). So, we are trying to accelerate the rod tip as fast as possible until the loop has been formed—and no, we do not want/need a constant acceleration at any point during the cast. To increase he rod tip speed as much as possible we try to rotate the rotate the rod handle as fast as possible until line release. Interestingly, and unfortunately, the measurements we now have show that we for some reasons that still needs to be explored, are only able to increase the angular velocity of the rod but during the earlier part of the stroke and that we are de fact decelerating it during the latter part when we think, and it feels like, we are applying an increasing force. As discussed earlier in this tread, this must have a lot to do with resistance to rotation increasing as the rod bends during that early part of the stroke, and possibly also as it unbend/unload during the second phase. There’s a many interesting differences between the distance casting stroke we have measured, but the measured “deceleration” phase has nothing to do with the Stop. We are all rotating as hard as we can past RSP1 and (until) line release.

The slower I move my hand (the less I accelerate), the closer I position max velocity to the end. I can then use a high rate of decel. compared to the rate of accel..

Interestingly, Paul and I have the same MAV position in those casts, but Paul is slide loading while I am not. So, while I start accelerating the line (and for T38 and ST27, as fast as possible), from the very start, Paul does not. MAV is slightly later for Chris and Henry. I am not sure why, but it could be because they start the haul much later, or….

And, no I don’t think I am explicitly aiming “to position RSP1 where we want it to happen.”
RSP1 just happens somewhere during the latter part of the rotation of the rod butt.

[John Waters]

Thanks a lot, Nils (and Gordy)!
I looked into those vids and played them back and forth trying to get the numbers for accel. and deceleration.

Nils
14:30 to 12:30 = 60 deg RSP0 to MAV
12:30 to 10:00 = 75 deg MAV to RSP1
135 deg arc, 44% accel. and 54% decel.

Paul
14:30 to 12:15 = 67,5 deg
12:15 to 10:00 = 67,5 deg
135 deg arc, 50% accel. and 50% decel.

Matthias
14:30 to 12:00 = 75 deg
12:00 to 10:30 = 45 deg
120 deg arc, 62,5% accel. and 37,5% decel.

Mittel
14:30 to 11:45 = 82,5 deg
11:45 to 10:00 = 52,5 deg
135 deg arc, 61% accel. and 39% decel.

I think we aim to position RSP1 where we want it to happen. For most distance casters I saw this to be around 10 in the delivery shot. Then the rod needs time to straighten. So maybe 40 to 50% of the arc for decel. is needed to match straightening with the desireded RSP1 position.

I used to say one advantage of rod flex is the tip still accel. during decel. of the butt section. Maybe the advantage of a non flexible tool is, that we need less percentage of arc for deceleration?
Regards
Bernd

Hi Bernd,

I'm not the fastest rod in the rod rack, so I may be drawing incorrect conclusions from your excellent data but may I clarify the following,

All are forward casts in the Trout Distance event
Do the arc widths measure the rod tip, or some other part of the rod?
Do the acceleration %s reflect the acceleration of the rod tip or some other part of the rod?
The dataset of each cast reflects (approximately) both the behind the shoulder and front of the shoulder stroke

Is it possible to separate the stroke into behind the shoulder and in front of the shoulder segments as defined by the position of the elbow in respect to the shoulder, and produce the same data?.

Thanks in advance,

John

[Paul Arden]

And, no I don’t think I am explicitly aiming “to position RSP1 where we want it to happen.”
RSP1 just happens somewhere during the latter part of the rotation of the rod butt.

Me neither. I don’t stop the rod, it just happens.

[John Waters]

And, no I don’t think I am explicitly aiming “to position RSP1 where we want it to happen.”
RSP1 just happens somewhere during the latter part of the rotation of the rod butt.

Me neither. I don’t stop the rod, it just happens.

I don't either now Paul.

John

[Bernd Ziesche]

And, no I don’t think I am explicitly aiming “to position RSP1 where we want it to happen.”
RSP1 just happens somewhere during the latter part of the rotation of the rod butt.

Me neither. I don’t stop the rod, it just happens.

I don't either now Paul.

Hello guys
Thanks for your thought provoking comments.

Some years ago I checked the RSP1 positions for the delivery shots on all distance videos (quite a lot) I had from the WC. The RSP1 position was positioned at 10 by nearly all casters. Pretty small variation.

As Nils said:

You can use all of the remaining arc until the rod tip hits the ground to stop the rod if you want, and as noted before some of the German tournament casters in the 70s and 80s did literally have it hit the ground

I agree all those experts could have stopped the rod in a much lower position and thus positioning RSP1 in a lower position, too.
But no one did!
In my opinion this was not, because the rod did straighten all by itself precisely at ten, but because the arc was matched to the best outcome for the cast.
RSP1 doesn't happen anywhere, but in the position I want it to.
We all put the rod in an acceleration and then we decelerate it. It's us staying in the final line shooting "eagle position" (as I call it), while the rod is in our hand and we force it to pause it in it's movement. If we don't apply force to stop the rod, it would obviously fall down following gravity.

I agree, that eventually we haven't nailed down to perfectly describe the decelerational process of stopping the rod yet. But this doesn't mean we don't stop the rod. In every cast the movement of the rod comes to an end. It's us constantly applying force (not a constant level of force) to the rod in order to accelerate and decelerate it.
Well, that's how I understand Newton's laws.

Daniel said:

There is no advantage to cast a broomstick, and stopping it certainly takes more degrees compared to a flexible rod.

I had a look into the footage Aitor and I made 13 years ago. Resolution is a bit low, but the broomstick positions and the start of loop formation was captured perfectly.

Comparing to the other percentages for flexible rods provided in this thread, the deceleration of the broomstick was done in a relatively small fraction, I think. Why was that possible with such a heavy tool?
I believe due to much less max angular velocity as we can achieve it with the flexible rod.
I believe, the faster I move something, the more distance I need to stop it.

I am wondering what percentage of arc we need to decelerate the rod butt when simiulating the movement of a distance cast. Could we keep the percentage much smaller compared to this Broomstic cast and compared to casting the whole rod and line?

If all the factors we came up with in those threads Nils linked in this thread (like air resistance increases in square to the speed and so on) end our deceleration at some "early" point, then we should be able to use a very small fraction of arc to decelerate a pure butt section, right?

Worth a test?

John,
those percentages were taken from RSP0 to RSP1 being the arc. MAV was taken by Gordy on the lowest part of butt section where our input is applied.
Regards
Bernd

[Merlin]

Hi Bernd

Some years ago I checked the RSP1 positions for the delivery shots on all distance videos (quite a lot) I had from the WC. The RSP1 position was positioned at 10 by nearly all casters. Pretty small variation.

For the record of Paul’s competition cast I have, RSP corresponds to 63 degrees from vertical, that is to say just after 10 o’clock (60 degrees). The difficulty with such cast (and record) is that it is not possible to see exactly when rod butt is stopped, since deceleration ceases before the end and then a more or less constant rotation speed follows. Bad luck, the exact end of the rotation was not recorded.

The following graphic illustrates the situation. Tip path is “not so flat” which is partly due to the slightly too stiff modeling of rod bending (too much non linear).

Given the nearly symmetry of rotation speed pattern (acceleration slightly longer than deceleration which is aborted rather soon), it seems that all rotations (elbow/wrist/fingers) are approximately in synch at their maximum, which corresponds to MAV. The shoulder rotation manages rod butt path I guess, and trunk rotation is likely at play.

Merlin

[Paul Arden]

That seems like a very early peak haul velocity, Daniel.

[Merlin]

Peak haul velocity is just after MAV which is fine, Paul.

Merlin