Pendulum rigging

[wiley_p]

Angus or Graeme, I have a question. When I do this it's always with much lighter weights, or very small angles. In the work situation you were in, there was opportunity for a large increase in force on one rope as that line angle becane greater. When moving blocks around, the angle on one high block would be around 70 degrees? maybe more, the angle on the "close" block would be less than 45 degrees.

Is the the extra force imparted on the far block negated by the higher capacity gained as the angle decreases on the "near" block, or does the far block and line bear more force?

[Angus]

Is the the extra force imparted on the far block negated by the higher capacity gained as the angle decreases on the "near" block, or does the far block and line bear more force?

 

Both statements are not mutually exclusive.

 

By definition the overall vector forces must cancel out in order for the load to remain static. If there was no negation of force in pre-calculations, the block would dynamically load the system and shift to a position where it was in equilibrium.

 

In answer to the second part, the block with the highest line angle will have the most weight.

I might whip up an application tonight for opposing pendulums so you can have a play with some numbers.

[Angus]

Its not finished by any stretch, but here is an implementation of Opposing Pendulums that will eventually be able to generate a graphical interpretation of the system from the user's input.

 

Download Opposing Pendulums Basic

 

 

You will need the .NET framework to make it work.

[Angus]

I've just put some numbers into the program... I've coded something incorrectly. I'll post an updated version sometime soon.

[Angus]

Fixed a few problems...

 

Opposing Pendulums Example RC1

 

Have fun!

[Tony Croft aka hamadryad]

Am i not understanding this right?

 

if i enter load as 1000kg the blue line at 90deg andf the red line at 45 deg it says the load on the blue line is 1000kg and on the red it is 1414.21kg

 

is this suggesting that it will require 1.4 times the load wieght in force to move the load via a force applied to the red line?

[Angus]

Hrm. No its the way the program deals with the inputs.

 

The program forces itself to use two ropes. In reality when you input 90degrees, you should be told all the weight is on one rope.

However the program can only do as its told, and so it treats the second rope as a pole, rather than a rope.

 

I left the option open to enter ANY value, however it is confusing to allow users to enter non-standard parameters. I'll adjust some stuff.

[Angus]

Doh. Can't edit my post.

 

Adjusted some things. It still puts out some crazy numbers under certain conditions.

If I get some time over the next little while I'll put some formula restraints on. All real world situations should work no problem, odd systems like 500l89r89b, 500l90r45b etc. Won't throw errors like its supposed to... yet.

 

Opposing Pendulums RC1.1

Edited January 10, 2010 by Angus

[Tony Croft aka hamadryad]

I asume the idea with this is that we will be able to work out the loads on each rope in a pendulum rigging scenario, as in as the angles change etc.

 

if the two lines being equal in angle the load should be distributed evenly between the two lines?

increas the angle of one and the load share increases in its uneven distributions?

[Angus]

Yep, its all about knowing what tensions will leave your load in equilibrium.