The Board

Merlin wrote: ↑Tue Jun 11, 2019 10:13 am Beside that, rotating above 900 deg/s needs a pretty high torque. We have little data to analyze on that point.

Merlin

Rotating above 900 deg/s requires very little torque, accelerating the angular velocity up to 900 deg/s is where you require torque. Sorry to be pedantic, but I know you're a stickler for pulling up people on such basic mistakes. If you want to get to 900 deg/s with a short stroke it's going to take more torque than if you spread the input over a bigger angle i.e. a 170.

Paul Arden wrote: ↑Tue Jun 11, 2019 9:50 am So maybe the advantage of the stiffer rod is not line speed but rather tip path, James?

Thanks,Paul

I'd go with line velocity because of tippath

Cheers
Lasse

I thought you said there was no advantage?!

James

Good point if the torque was only due to rotating the rod, but you have to pull on that damn line and max torque is not when you think it is. The following information comes from the simulation of one of Paul's 170 cast.

First, the "active" part of rotation is not 170 deg, it it around 120 deg followed by a stopless rotation which brings the angle closer to 170 at some more or less constant speed. In fact I never saw a full 170 record up until now. 150 yes.

Peak acceleration for the rotation is obtained after 150 ms of rotation, for a rather small angle (35 deg). So the maximum acceleration (180 rad/s2) is produced along a very small angle, and not along a 170 angle. This peak occurs slightly before max rotation speed which takes place at 75 deg. The total active rotation takes 350 ms.

Maximum torque at handle level occurs when the rotation speed is close to maximum, and that means that the acceleration of the line peaks too at that time and dominates the torque requirement. Line speed keeps on increasing up to slightly before RSP, as the rod decelerates strongly (-220 rad/s2) up to 120 deg.

A basic mistake you said?

Merlin

Merlin wrote: ↑Tue Jun 11, 2019 1:37 pm
A basic mistake you said?

Of course it was a basic mistake which you've now corrected in your above post by linking angular acceleration to torque. Your original statement read that high torque is required to rotate at 900 deg/s with no mention of acceleration - that was your basic mistake.

And I'll point out again that max torque for any given cast is just a measurement - it is not the max torque which the caster is able to produce.

James.

Read my post again James, max torque is not linked to max rotation acceleration, but rather to max line acceleration.

Merlin

Merlin wrote: ↑Tue Jun 11, 2019 10:13 am rotating above 900 deg/s needs a pretty high torque
Merlin

This is the statement that I'm pulling you up on - until you can acknowledge this is wrong then I can't see any point going further with this. If you'd have said 900 deg/s/s (or some other acceleration figure) then I'd have no problem. What you actually said was equivalent to me saying I need a lot of force to move an object at 30mph. F=ma, a=0, therefore F=0. Wriggle all you want.

My sentence includes the full picture, that is to say line acceleration, since I know that max torque is close to max rotation speed thanks to modeling.

I can understand this brings some confusion since there is a shortcut, and if you want to stick to the characteristics of a simple rotation, feel free to do it but I shall not spend more time on it.

Merlin

Merlin wrote: ↑Tue Jun 11, 2019 10:13 am The necessary coordination of the body likely creates a torque constrain, which might well be below the maximum torque that a caster can produce. That does not change the global picture when comparing rods, there is an optimum somewhere. Beside that, rotating above 900 deg/s needs a pretty high torque. We have little data to analyze on that point.

Merlin

This is your full post quoted - point out the word 'acceleration' to me.

Paul Arden wrote: ↑Tue Jun 11, 2019 12:29 pm I thought you said there was no advantage?!

Never said that! I said there was no free lunch and a magic two meter increase from just picking up a stiffer rod!

Cheers
Lasse