Help Error "rigid body modes in the system"

I am a student learning Rhino7 and Grasshopper and I have some issues with my project.

The final aim is to compute some Maximum stress, forces, displacement etc but before that, I have to make a structure (and fix it thanks to supports, which are 2 points per pentagon’s base).

I encountered an error at this step when i did the Assemble ! The error is:
1. There are 573 rigid body modes in the system. This means some parts can move freely without causing deformation. Try to use the ‘Eigen Modes’-component and activate the display of local coordinate axes: The first eigen-mode will be the rigid body motion. If this does not help, check whether you have a pinned support directly attached to a hinge. A hinge introduces an extra node which may cause the problem. When analyzing a flat shell structure one has to lock the rotation perpendicular to the plate in at least one node.

It leads to strange behavior when I look to the displacement (what is normal due to the error i guess).
An illustration is given just below.

I tried to resolve the problem by removing the duplicated points/lines, but it was not enough apparently … My set up is probably not the most optimized for my purpose, I apologize for that, it is my first “big” project.

Here is the grasshopper file: (49.8 KB)

If someone can help my, it would be great,


use the ConnectedParts component to see if your model is connected properly.
You have multiple branches meaning that parts of your model are not split at their intersections.

Hi Matthew,

I am not sure i understood what is the problem and how to solve that…
So some branches are not well connected to the pentagon shape here ?

Which kind of component can be used to connect everything ?
Thank you for your first answer

After using the component “ConnectedParts”, i think i understand the problem, so some paths exist which means that some lines are continue (and thus not “split”) at the intersection with the pentagon shape ?

But on my model, I do a “merge” between the line groups (one group of line = the lines between two choosen pentagon shapes). So i guess it is the main problem ?
I would say that, by removing the “Merge” component and immediatly connect the lines to the “linesToBeam” component, the problem would have been resolved but i still have the issue.

What is wrong with my development ?
Thank you and sorry for the many questions !

this has nothing to do with how you organise your data. It is a geometric issue.

You should have rebuilt the polygons as polylines and not as curves and you can remove the pt input in the Assemble Model component. Now the script is calculating properly, but you have to check your cross sections.

Star_Idea - (57.9 KB)