Spring Effect on Timing - effects of the spring on time constant

VGB · Post by **VGB** » Sat Nov 03, 2012 4:34 pm

I'd like to pitch a question to the board that came up during a discussion with Mark Surtees at the recent AAPGAI open day.

We were discussing the effects of the spring/lever combination on tip path and line tension based on Grundes excellent spring/car/brick analysis. We came to a sort of conclusion that in addition to the studied effects on tip speed, the spring constant also had an effect on timing and how the application of power at the butt was seen felt at the rod tip.

The long and short of it was that it appeared that a fast action rod did less to aid the caster with smoothing out the force application than a moderate action rod and that would be bad news for a thudnut caster like me. Additionally, a very slow action rod would not maintain the line tension unless the butt was translated very quickly.

Is anyone aware of any study into the time constant of various action rods using Grundes model?

grunde · Post by **grunde** » Mon Nov 05, 2012 7:51 am

Hi Vince,

I'm glad you like the model, but you know in physics, the harmonic oscillator is one of the most used/abused models so it's not very original or anything :p

Also, I'm not entirely sure what you are after?

In this model it is relatively simple to measure different times (unloading time, time to max load etc.) and force as function of time for different spring stiffnesses, "strokes", etc. It is also easy to update the model to include non-linear springs and arbitrary casting strokes (I only did linear springs and constant acceleration/deceleration of the car).

If you want you can have my code to play with. It's written in/for Matlab but I'm pretty sure it will also run in GNU Octave (http://www.gnu.org/software/octave/) which is a free and good alternative. Also , rewriting the thing in Python (using NumPy) have been on my todo list for quite a while, but until now I've just not found the time and/or motivation to do it...

Cheers,
Grunde

VGB · Post by **VGB** » Mon Nov 05, 2012 9:10 am

Thanks for your reply Grunde.

For me the words Python and Octave are things my eldest son used to talk about before I made him tidy his bedroom. Now he is over 6ft, I tidy his bedroom for him, it saves time :p . However, I can always get a grown up to help me if I have a problem.

I know that the question was badly phrased but there are 2 properties I am interested in:

1. For the slow action rod, the phase change or time delta from start of input to the start of the output. It seems to me that as a rod gets slower there comes a point where it becomes more difficult to maintain line tension or even that the line hits the ground before the rod pulls it forward.

I recall that the phase is set by the initial conditions but if we are pausing between strokes, aren't we re-setting the initial conditions?

2. For the fast action rod, my understanding is that as the action become faster, variations in input accelerations will start to be seen in the output. Therefore, the smoother the input acceleration rate is the faster rod a caster can use? It would be nice to show it graphically as it is difficult to put into words

Not sure if the above helps, I'm sure it made sense when we were discussing it a only coffee was involved at the time.

regards

Vince

Hal Jordan · Post by **Hal Jordan** » Mon Nov 05, 2012 2:13 pm

I looked at Octave a couple of years ago and it wasn't worth the effort to try and use it then. Maybe things have improved. I'll take a look. It would be nice to have some analysis using open source tools so we could all share them and use them.

I think your spring/brick model would be a great place to start Grunde. Your model has already shown us a lot of interesting things and I think it still has more to teach us. Adding in non-linearity and perhaps tip path could be fun.

grunde · Post by **grunde** » Mon Nov 05, 2012 2:35 pm

For number crunching and modelling Octave is really good. The only important areas where it's behind Matlab is imho only documentation an plotting.

Hal Jordan · Post by **Hal Jordan** » Mon Nov 05, 2012 4:15 pm

Grunde - I'll give a more careful look then. In the past there were some serious incompatibility issues.

Python is actually more intriguing.

There might be some short term pain but it would be truly awesome if we were all able to share stuff using open source tools like Octave and Python.

grunde · Post by **grunde** » Mon Nov 05, 2012 7:50 pm

The reason I would like to go for Python (and NumPy/SciPy) is that there is a good selection of PDE packages/solvers available for Python

and Python is a more of a real programming language than Matlab/Octave...

Cheers,
Grunde

Hal Jordan · Post by **Hal Jordan** » Mon Nov 05, 2012 8:11 pm

I prefer the real programming language aspect as well but the best part has to be:

By the way, the language is named after the BBC show “Monty Python’s Flying Circus” and has nothing to do with reptiles. Making references to Monty Python skits in documentation is not only allowed, it is encouraged!

Can't go wrong with software and Monty Python.

grunde · Post by **grunde** » Mon Nov 05, 2012 8:35 pm

There are _many_ rhings I hate about Python (significant white space is a really bad idea), but Python also have many good libraries... The naming of the language is also a +

Hal Jordan · Post by **Hal Jordan** » Mon Nov 05, 2012 8:51 pm

I can also overlook the fact that it is an interpreter if it has the useful libraries and Monty Python... :laugh:

We have a strong propensity in the computer industry to not only argue, but to argue about what we’re arguing about. Most meetings are, in fact, meta-arguments, which explains why everybody loathes them.

Not only do we argue with one another, we argue with our customers, or at least our potential customers: If you don’t think our product is awesome, you must not be smart enough to appreciate it!

VGB · Post by **VGB** » Wed Nov 07, 2012 11:47 am

it appears to me that both of you need to go and tidy your bedrooms.

James9118 · Post by **James9118** » Wed Nov 07, 2012 2:05 pm

I coded the basic model in MS Excel if that's of any use to anyone.

VGB · Post by **VGB** » Wed Nov 07, 2012 3:01 pm

Thanks James but I'm knee deep in models now, my thanks to everyone. I might have a shoot out and see which one casts the furthest :kungfo:

Hal Jordan · Post by **Hal Jordan** » Wed Nov 07, 2012 4:26 pm

James9118 wrote:I coded the basic model in MS Excel if that's of any use to anyone.

I could use it to compare results to what I come up with...

ennio · Post by **ennio** » Thu Nov 08, 2012 6:18 pm

Please will someone share a link to Grunde's excellent spring/car/brick analysis (assuming it is written somewhere).

Ta, Andrew

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