Kangaroo Chain question (incomming newbie warning)

Hey guys, I'm fairly new to Grasshopper and Kangaroo and I am slowly figuring things out but there are a few things that I am stuck on. I am basically trying to recreate the catenary chain that is in the first 10 seconds of the kangaroo Video (link also at bottom).

My problems are:

how do I move the points in rhino and have them effect the points in grasshopper?

And

Generally how i make the chain, my assumption is that it is a poly-line with the endpoints set as anchor points, with a uforce or spring force on each of the points?

Thanks,

Kevin

Video: http://vimeo.com/8706003

Replies to This Discussion

Permalink Reply by Daniel Piker on February 5, 2011 at 12:08pm

Hi Kevin,

The curve must be split up into multiple segments, and each segment becomes a spring.

Unary forces applied to the division points give weight to the chain.

To be able to move points in Rhino and have them affect the simulation they must be set as anchor points.

When you start the simulation (by setting reset to false and turning on the timer) the chain will stay attached to these points as you move them.

Note that if you want to reset the simulation after moving it around, you must move the rhino points back to the ends of the line, otherwise they will not be attached to the chain when you restart it.

Hope this helps

Attachments:

simple_catenary.3dm, 42 KB
simple_catenary.ghx, 106 KB

Permalink Reply by Kevin Pazik on February 5, 2011 at 4:12pm

Wow that was fast!

Thanks. The issue was resolved, it seems that I was trying to do the same but with a different method. By the way this kangaroo this is great, just keeps getting better and better.

Permalink Reply by Anabela Popovici on February 9, 2012 at 9:20am

Hello Daniel,

I am trying to achieve the same movement and I recreated your set-up exactly, but the "Kangaroo Physics" return an "Invalid curve" message in the "GeometryOut" position. Do you have any idea why this is happening and how it could be fixed?

I also replaced the line tool that was supposed to rejoin the shattered elements with join, as the line inhereted no values from the source, allthough the shatter tool did output planar curves.

Thanks!

Anabela

Permalink Reply by Hannes Löschke on February 10, 2012 at 7:24am

Judging from your error messages you are feeding spline curves into the definition. Kangaroo can only work with straight lines. Make sure each of your input lien segments is a line and only a line.

If you need to use slines as input curves, I'd use the endpoints of the division results and connect them with a 2PointLine.

Permalink Reply by Anabela Popovici on February 11, 2012 at 2:05am

Thanks a lot...that was the problem with the output geometry....that i was feeding a spline.

However, i think i am also setting my anchor points wrong, cause it just doesn't look right and the chain doesn't have that gravity effect. i guess i have to keep trying :)

Thanks again!

Permalink Reply by Anabela Popovici on February 11, 2012 at 9:03am

ok...got it! works now....thanks for the help

Permalink Reply by Muhammad Zharif Rafiq on August 2, 2015 at 6:35am

Hey guys, relating to the same simple problem, I'm having problem with using polyline. The point force are not in order. Any ideas?

thanks,

zhaff

Permalink Reply by Daniel Piker on August 2, 2015 at 8:53am

You can use the Geometry/GeometryOut instead of reconstructing from the ParticlesOut. It accepts lines and polylines. In your image it looks like the segments are straight, but if you had curved segments you might need to first make straight lines between their endpoints.

Permalink Reply by J K on June 21, 2016 at 6:15am

Hi everyone,

I am trying to hang down a cube, as if it is going to fall down, but it's then connected to a rope. I simply don't understand, why Kangaroo automatically creates a line between the starting and end point of the initial curve, so this line restricts the full free fall of the cube.

Anyoune some ideas?

Thanks!

Attachments:

Falling Cube.gh, 18 KB

Permalink Reply by Daniel Piker on June 21, 2016 at 10:50am

Hi - In your definition you have a show component for the polylines, but also another connected to the original NURBS curves. This is why it is showing the line from start to end of the curve.

Permalink Reply by J K on June 21, 2016 at 11:03am

Thank you Daniel,

I put the show component there in order to see where the problem comes from. Even if you delete this component, you will see that only the line is not shown,but the physics don't change.
These lines from the start to the end of the original NURBS are also restricting the movement of the object because they are shorter than the polyline and the cube can't completely hang on these polylines. As you see the two upper polylines are not completely tensioned.

I hope this explains it more or less.

Best,
G

Permalink Reply by Daniel Piker on June 21, 2016 at 11:28am

I don't follow what you mean by 'not completely tensioned' - The cables are not straight, but sagging slightly because you have also applied some self weight to them.

As it is set up now, all vertices have the same weight applied, so each vertex of the cable has as much weight as 1/8th of the box. Perhaps this is why it appears a little strange - it is a heavy cable/light box.