Rod Loading - Spring v Lever

[Merlin]

I think you have a few, it is called a fly rod (with line)

Merlin

[Stoatstail50]

Well either way it should be possible to do the calculation.

[gordonjudd]

Did you mean the brick will take off at maximum car velocity?
and
Yes Walter, thanks for correcting me

Merlin,
Shouldn't that be the maximum spring velocity? As I remember the maximum car velocity was around 16 m/s for the Paradigm cast while the maximum spring (and hence brick velocity) was around 21 m/s.

It is getting a bit confusing going back and forth between a casting example and Aitor's proposed experiment but in the example you showed in post #415 for the spring connection it appears to me that shows a maximum lead weight velocity of 4.4 m/s while the maximum brick velocity was around 6.3 m/s.

But the same principle applies in that the brick will launch with the maximum spring velocity that in the model (no losses) happens when the spring deflection goes to zero.

In the real world the maximum tip velocity will be a bit before RSP1 and the line does not start to go ahead of the tip until some point between RSP1 and MCF.

Gordy

[Stoatstail50]

There isn't a spring between the car and the brick Gordy. Velocity Car = Velocity Brick.... and we're a bit loose on specific numbers at this stage, certainly not talking about the paradigm cast anyway.

[Hal Jordan]

Yes Walter, thanks for correcting me

You are welcome. I know you know what you meant so I apologize for being nit picky but somebody has to do it.

[Merlin]

Sorry for the confusion Gordy,

We were talking about the no spring case and Marc was thinking about achieving the same speed than with a spring by introducing more energy at some moment.

Introducing Aitor experiment model is also somehow confusing because it is not exactly the simulation of a cast, although we can show the usefulness of a spring with it.

Merlin

[Stoatstail50]

I was just wondering, hypothetically, how much kinetic energy would be transferred to the line, must be a very difficult sum though...

Aside from that, if the model is not taking into account energy losses due to the spring then it's going to show all the upsides but none of the down isn't it ?

[VGB]

Introducing Aitor experiment model is also somehow confusing because it is not exactly the simulation of a cast, although we can show the usefulness of a spring with it.

Merlin

With all due respect, I am not sure that any of the examples are an exact simulation of a cast, nor is the brick/lead and brick/spring/lead a fair comparison of a rod and a broomstick. The main advantage of Aitors proposal is that it maintains the effects of the length of the rod/broomstick on velocity.

Vince

[VGB]

As a result of ruminations that are more interesting than what I should be doing, I thought it might be use to take the discussion back to basics.

Grundes original spring model was used to discuss the effects of the stop not the lever/broomstick:

http://www.sexyloops.co.uk/cgi-bin....ry96037

So it is not really applicable to the original statement of this thread which is:

"Numerous threads over the years. Ian Walker was the first to mention it. Torsten calculated spring energy as 15-20%, leverage 80-85%. Grunde measured it. Gordy graphed it. Leverage is the significant factor in casting, rod bend helps us apply this force in a straighter line"

I think there is general agreement that the rod is 3rd class lever, so we can look at the attributes of a 3rd class lever.

Firstly Mechanical Advantage (MA) where:

MA = Load/Effort

3rd class levers operate at a mechanical disadvantage compared to 1st and 2nd class levers in that their MA is always less than one. However, if we compare the broomstick to the flexible lever the broomstick generally has a greater MA than a flexible lever. This I think is Aitors and Sakkes sticking point

if MA is not the reason, then we should look at the Velocity Ratio (VR) where:

VR = Distance Mover by Effort (caster)/Distance Moved by Load (Line)

The situation is the inverse of MA and our flexible rod enjoys the advantage providing the load is within its capabilities. This is why we use a 3rd class lever, it enables you to move loads quickly not move large loads.

When we have resolved MA and VR, we can talk about efficiency, where:

Efficiency = MA/VR

In all instances we need to include the effects of the lever when making comparisons of broomstick vs flexible lever and our model selection should reflect that need.

Vince

[gordonjudd]

I think there is general agreement that the rod is 3rd class lever,

Vince,
I think that we can agree that the broomstick functions as a third class lever, but because of the more complicated dynamic response of the spring in the rod to external forcing accelerations the rod (even to first order) does not.

Merlin's and Grunde's model does give a reasonable simulation of the complicated response of the rod to a given external forcing acceleration of the butt rotation. The static-related equations you gave in your post do not.

Grundes original spring model was used to discuss the effects of the stop not the lever/broomstick:

The simple harmonic oscillator (SHO) ordinary differential equation (ODE) is a simple one dimensional model of a much more complicated three dimensional problem, but it gives very good estimates of how the deflection in the rod is going to vary in an actual cast, including the impact that different stopping functions will have on the line velocity.

The function of a simple harmonic oscillator is not so simple (especially when it has an accelerating forcing function) so it is difficult for non-technical people to understand its operation and concepts. I certainly did not understand it when Grunde first presented it several years ago. However it is a good first step in understanding the impact of the non-linear spring characteristics of a rod and its related operation as a forced harmonic oscillator has on the dynamics of casting.

Gordy

[Stoatstail50]

I think that we can agree that the broomstick functions as a third class lever, but because of the more complicated dynamic response of the spring in the rod to external forcing accelerations the rod (even to first order) does not.

Really..??!!!.. Blimey..thats going to set the cat amongst the pigeons...so when I rotate the rod I get no benefit from it as third class lever ?

[VGB]

I think there is general agreement that the rod is 3rd class lever,

Vince,
I think that we can agree that the broomstick functions as a third class lever, but because of the more complicated dynamic response of the spring in the rod to external forcing accelerations the rod (even to first order) does not.

Merlin's and Grunde's model does give a reasonable simulation of the complicated response of the rod to a given external forcing acceleration of the butt rotation. The static-related equations you gave in your post do not.

Grundes original spring model was used to discuss the effects of the stop not the lever/broomstick:

The simple harmonic oscillator (SHO) ordinary differential equation (ODE) is a simple one dimensional model of a much more complicated three dimensional problem, but it gives very good estimates of how the deflection in the rod is going to vary in an actual cast, including the impact that different stopping functions will have on the line velocity.

The function of a simple harmonic oscillator is not so simple (especially when it has an accelerating forcing function) so it is difficult for non-technical people to understand its operation and concepts. I certainly did not understand it when Grunde first presented it several years ago. However it is a good first step in understanding the impact of the non-linear spring characteristics of a rod and its related operation as a forced harmonic oscillator has on the dynamics of casting.

Gordy

Gordy

Do I really have to quote every time?

I agree that the SHO allows you to calculate VR and MA for a flexible rod and from that you can derive the Efficiency for a rod. However, there is no need to turn the SHO into voodoo.

The model consist of a car, brick and a spring. If I am correct in assuming that the brick is the load (line) and the spring is the spring constant of the rod. Then the car has the driver and lever as a combined entity.

But to make a fair comparison, you cannot just throw the spring away and say that this is the broomstick, the driver/car must increase to account for the additional length of the broomstick compared to the flexible lever length otherwise it is not a fair comparison.

[VGB]

I think that we can agree that the broomstick functions as a third class lever, but because of the more complicated dynamic response of the spring in the rod to external forcing accelerations the rod (even to first order) does not.

Really..??!!!.. Blimey..thats going to set the cat amongst the pigeons...so when I rotate the rod I get no benefit from it as third class lever ?

No mechanical advantage as I mentioned it is a mechanical disadvantage. If you wanted to lift a heavy weight you would not use a fishing rod or a broomstick held in your hand.

However, you do get an improved velocity ratio with a fishing rod and the SHO is useful to calculate that. Fortunately , it is much easier to calculate the VR of a broomstick

[gordonjudd]

Do I really have to quote every time?

Vince,
If it bothers you that I added:
I certainly did not understand it when Grunde first presented it several years ago.
(notice the itallics)
to my original post to indicate that unless you think in terms of integrating differential equations in your head, Merlin's and Grunde's SHO model is not so simple to understand, then I guess you must.

But to make a fair comparison, you cannot just throw the spring away and say that this is the broomstick, the driver/car must increase to account for the additional length of the broomstick compared to the flexible lever length otherwise it is not a fair comparison.

If you understood the model (it is not voodoo as you seem to think), then you would realize it is a fair comparison. As Merlin noted you can simulate the impact of a non-flexible broomstick (or an inextensible string) in his model by using very high spring constant in the model.

Gordy

[Stoatstail50]

No mechanical advantage as I mentioned it is a mechanical disadvantage. If you wanted to lift a heavy weight you would not use a fishing rod or a broomstick held in your hand.

Yes, I completely understand your point.

It's one of the issues I have had in understanding this model with respect to the benefits of a bendy rod. It has been historically explained as generating a mechanical advantage and I don't understand how it could, not in the conventional sense of levers and pulleys anyway.

I can see perfectly how it mediates with respect to the acceleration at the butt v the tip and I can see how it generates a biomechanical advantage but thats different.

Rotate the rod, tip travels further than the butt in the same time and therefore faster...completely get that. True if its rigid...not true if it's bendy apparently... I don't get that at all... :oh:

If the model doesn't account for system energy losses and doesn't account for the reduction in lever length due to the bend then the output data, whatever it may be, is going to be overstated isn't it, or am I going mad ?.