Walter & Group :
This is a really instructive message from Bruce Richards. He has taken Server's detailed message and helps interpret it for us by making comments in Shane's text delimited by ***** marking and as I've highlighted in red.
I've learned a great deal from this, and I hope you do, too.
Gordy
Hi Shane, Gordy and all,
I've just been reading the technical musings without remarking because it
would take so long to remark. Shane, virtually every detail you mention in
your paradigms of rod structural dynamics is bipolar (opposite of real
behavior). Don't be in despair because I suspect you have no real
expertise in Structural Dynamics. I'll just mention one or two things to
get you and anyone else in the right direction. Acceleration is easy when
the speed is low and takes great effort and energy as the center of mass of
object is put into motion.
****He's just saying that it is easier to accelerate something that is
moving slowly than something that is already moving fast.
The idea of increasing acceleration at will is simply unrealistic and
would even be hard for a machine to produce let along a human.
*****Most casters, even inexperienced casters throwing very hard,
accelerate the rod in a fairly linear fashion, except for moving too slowly
at first. What Server is saying is that our period of acceleration is short
and to attempt to accelerate at an increasing rate would be very difficult.
Velocity increases, yes, but the rate of acceleration is quite steady. Many
casters think that the "right" acceleration is slow at first, fast at the
end, the classic "speed up and stop". In reality, good acceleration is
marked by a constant rate, that is what allows a straight tip path.
It is better to think in terms of the torques which can be applied to the
rod -- a number of things effect the torque which can be applied to a rod
and it isn't long into the casting process when the torque can no longer be
increased and the rod begins unloading. The acceleration of the tip at RSP
is zero --i.e., tip speed at this instant is not changing while velocity
direction is changing so a minor acceleration is connected with direction
change.
*****Again, many might read this confusing speed with acceleration. Tip
speed is max at RSP, but acceleration is zero.
The acceleration of the tip is greatest at maximum rod deflection which
occurs long, long before rod straightening.
*****True, the rod tip is accelerating at its fastest when the rod is bent
most. The tip continues to gain speed all the way to RSP, but at a lesser
rate than at max deflection (max rod bend). This must be the case, we know
that tip acceleration is zero at RSP, and it can't go from max accel. to
zero in an instant.
As the rod straightens the acceleration must decrease -- this occurs
monotonically. That one is very easy to understand and anyone with
competency in basic college physics can understand this statement. It is
no different from the behavior of a simple oscillator -- this behavior
always demonstrates accelerations proportional to spring deflection which
are comparable to the rod deflection. One last note is that from high
speed infrared photography images (and understanding rod structural
dynamics) about (my estimate) 25% of rod unloading occurs after the flyline
is flying and the loop begins forming. RSP is symbolic of the end of rod
unloading but the rod has stopped accelerating the bulk of the line earlier
(except for a little line near the tip which it is in fact trying to throw
into the ground and this accounts for the details of loop formation).
****We know that rod unloading continues beyond RSP, we see that in the
counterflex. Tip direction during counterflex is downward and this does
largely determine where the loop bottom leg will be.
I hope this helps make some sense of Server's engineer speak!
Bruce