Constant Acceleration

[John Waters]

What happens if the acceleration is not constant, but increases through the stroke?

John

[Paul Arden]

My thoughts too James. I think that slow rate of acceleration at the beginning is critical in avoiding tails. Don’t we have a read out of acceleration from a 170 cast of mine that showed acceleration increasing not just during the first part of the stroke but right through?

And yes it’s because Bruce states this that I read it in the CCI training email list for example. I have brought it up with Bruce a number of times.

Here is a graph he sent me..

Cheers, Paul

[Dirk le Roux]

Here you go:

https://www.sexyloops.com/articles/perfectloop.shtml

Quest for the Perfect Loop
by Bruce Richards

"- The rate of acceleration of the rod butt must be as close to the same at the beginning of the stroke as it is at the end. Yes, the rod will be going much faster at the end than the beginning, but the rate of acceleration should be constant in getting the rod from slow to fast. I know this goes counter to what many have said and written, and even to what many of us think we do, but ALL the best casters we've analyzed had very constant acceleration, regardless of what they thought they were doing."

Torsten.

Accuracy is required with terminology, lest confusion accelerates, constantly!

From Bruce's article referenced in the one Torsten quoted: "The butt acceleration can be either linear or exponential, although exponential is better". What now?

Then, the velocity/speed plots he shares show no straight (velocity) lines but rather parabolic curves, which means the acceleration magnitude definitely does not stay constant:

So, just guessing here, I think what Bruce meant by "the rate of acceleration" must be the rate at which acceleration increases (a slope plot for acceleration) and his reference to exponential refers to velocity, not acceleration.

All the best,
Dirk

[gordonjudd]

but ALL the best casters we've analyzed had very constant acceleration, regardless of what they thought they were doing."

Torsten,
I would like to see that list of "best casters" and also know what distance they were casting.

The data I have seen shows that elite casters such as Chris Korich and Steve Rajeff have anguar acceleration profiles that are increasing when casting longer distances. Here is a typical angular acceleration plot for one of Chris Korich's accuracy casts.

korich_omega_accel.jpg (41.79 KiB) Viewed 1134 times

I think that the "constant angular acceleration" concept that Bruce Richards proposed was something that represented his own style when casting shorter distances. Even the acceleration profile that Bruce measured in his "expert 50" cast had a linearly increasing acceleration profile.

expert_50_accel.jpg (31.52 KiB) Viewed 1134 times

I don't think there is any "magic" to having a constant angular acceleration of the butt rotation. Certainly from an energy standpoint it is the last thing you would want to do in a distance cast. Constant acceleration would burn up a lot of of the available rotation angle while applying a relatively small amount of force to the line.

Gordy

[gordonjudd]

Don’t we have a read out of acceleration from a 170 cast of mine that showed acceleration increasing not just during the first part of the stroke but right through?

Paul,
Here is a plot of the angular acceleration of your butt angle rotation for the "a1" cast data you produced years ago.

paul_a_1_10_accel.jpg (33.41 KiB) Viewed 1134 times

As expected you really increased the acceleration rate at the end of the cast. Waiting to "hit" the rotation at the end of the cast will apply a much larger bending force from the rod over a much longer rotation angle than if you had used a constant acceleration throughout the cast.

Gordy

[Torsten]

Thanks Gordy,

actually I fail to see in any of the above plots something that's close to a constant function.

Maybe another case of an unverified myth?

Perhaps Paul could ask Bruce or Sage for a dataset that really shows a constant (angular) acceleration.

Torsten.

[John Waters]

I don't want constant acceleration in my casts. It generally reflects an arm-centric technique.

John

[Paul Arden]

Thanks Gordy. That was along time ago. One of the challenges posed by the analyzer is the requirement that it rotates in plane. Torsten did you finish your 3-dimensional measuring device? And the graph I posted above was one apparently showing constant acceleration vs one with Creep.

Cheers, Paul

[Dirk le Roux]

If you focus on the apparently straight top leg of parabolic plot it looks straight, but it is more likely a mere continuation of the bottom curvy part.

James is right.

To instantly start at a target constant* acceleration requires a huge jerk, a jack rabbit start. There's no such thing as constant acceleration in initiating any human movement. Further, in fly casting smoother is better

*Constant as in remaining at a fixed m/s², if I correctly understood James'

[James9118]

To instantly start at a target constant* acceleration requires a huge jerk, a jack rabbit start. There's no such thing as constant acceleration in initiating any human movement. Further, in fly casting smoother is better

*Constant as in remaining at a fixed m/s², if I correctly understood James'

Correct. If you differentiate a perfectly linear increase in velocity you obviously get a step function as the acceleration. If you then differentiate the acceleration (the step function) you get something that is sometimes referred to as 'jerk', as you state above. The differential of the step function has a huge initial 'jerk'.

This is fairly academic though - the human body cannot just jump to an acceleration rate.

James.