Accelerating a fly rod - constant or constant increasing

[Eugene Moore]

Excellent job Gordon.
When I go through the numbers I get different results but I'm viewing it as a rigid body.

Given
displacement 100 degrees rotation
duration .38 seconds

Assume
9' 8 weight rigid rod grip at 8" ; 100" radial length
Displacement @ 110 degrees rotation 192"
Line carry 60' weight 420 grains ; .060 lbs ; 27.22 grams

Using proposed acceleration diagram
Max velocity 823"/sec ; 20.90 meters/sec @ .266 sec
Max acceleration 4862 in/sec^2 ; 12.58 G's @ .133 sec
Weight @ acceleration .755 lbs ; 342.4 grams
Torque required @ rod tip for line acceleration 75.4 in lbs

Additional torque will be required to rotate the rod inertia.
Velocity will be lowered due to rod flex.
Max acceleration at .133 seconds give .247 seconds for some rod recovery. Max velocity at .266 seconds give .114 seconds for recovery and decel. That's 30% of the event duration. I felt decel could be very abrupt as the only thing to slow was the rod inertia.

Please correct me if I've erred.
The torque is higher that a constant accel, but quite acceptable for a person of modest strength.

[Merlin]

Eugene

I'm sending a graphic to Gordy who will add it to this post (thanks again, Gordy). It illustrates an acceleration then deceleration profile and you can see the individual contribution of elbow (in blue) and wrist (in yellow).

If the more or less linear acceleration needs the lowest torque, why (and how) would we try to learn casting a cycloid?

Merlin

[Eugene Moore]

Merlin,
This thread is about accelerating a fly line.
Applying as much power as possible, as long as possible is not an effective way of gaining velocity in a flexible shaft.
I presume the data shown was the velocity curve of a measured cast. If so, that is not representative of a constant acceleration curve, which would be a straight line from zero to it's peak followed by a straight line to it's end. What you have shown is very close to what I've proposed. There's no need to learn anything new. The difference is how the load is felt and adjusting to it since you now have a model.
Granted calculation is much easier with a constant acceleration. I don't however believe that's how our muscles work.
The total arc at 110 degrees. Was a portion of that created through translation ?? Elbow rotating wrist ??

[Merlin]

Eugene

Yes, this is the rotation velocity. Don't misunderstand my point, I am not arguing if favor of a theoritical perfect cast. This illustrates the fact that our natural motion is a progressive acceleration. The purple curve and the yellow curves are the results of measurements made by gyros, then the blue curve is calculated by difference and allocated to the elbow, assuming the shoulder has not been used. I think I have a document on javelin casting which shows another set of rotation (all joints separatly). I shall try to find it for another illustration.

Then I do not see how we could produce a constant speed profile for a period of time.

If you want to look to the global motion, you need to define a "casting robot" on your computer, with shoulder, arm, elbow, forearm, wrist and hand. If you input the rotations, you will be able to identify the translation of the rod handle. I can do that with one of my models, but is is time consuming.

Merlin

[Eugene Moore]

Merlin,
I felt , maybe incorrectly that the constant velocity would be the easiest of all to pruduce.
No shock, no torque required, just continue the speed and allow the rod time to respond. We must stop accelerating prior to decel of the rod. This just placed a time between without added torque.

[Merlin]

Eugene,

That is what I thought when I used the sinusoidal accel and decel: smooth start, fast accel, smooth stop, and smooth start again, fast decel, ending in a smooth stop.

But as you can see on the records, we are able to change from accel to decel at once.

Merlin

[Eugene Moore]

Merlin,
The actual wave form is smooth start, smooth accel, thru max back down to zero accel, continue velocity, rapid decel.
The reason we can accomplish the rapid decel is that we only require to stop the rod blank. The line weight is not part of the decel as it's actually overunning the rod tip.