Find balance point of weight on a rod : Calder sculpture type

Grasshopper Kangaroo
1

Hello,
I want to determine the center balance of weight with different density suspended to a rod.
I can’t achieve it on Kangaroo.
Herei is a picture and a GH definition.

balance-analysis
balance-analysis1547×646 53.2 KB

kangaroo-test.gh (28.9 KB)

Thank you for the help.
Skkratch

2

You don’t need Kangaroo just to determine the center of mass - for that you can just average the centers for the different parts, weighted by their masses.
What are you trying to do?

There’s an example for a simulation of Calder like sculpture here:


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3

In regular Rhino there is not need to separately average the centers of the different parts if the density is the same for all parts. Just use VolumeCentroid and select all the parts. The result will be the volume/mass averaged centroid.

4

Hi Daniel,
Thanks for sharing your definition.
I understand that RigidPointSet takes a set of points and returns a plane with the origin at the centroid of those points. In your Calder example, the Load component then uses that point cloud centroid as the input for the center of mass of the load.
If I am understanding correctly, it works in the Calder example because of its symmetry and relatively simple geometry. That definition does not seem to work on geometries with a center of mass different from the centroid of its vertices.
Am I missing something here?
Is this where it would be more appropriate to use RigidBody?

Thanks for your help on this and for all the thousands of helpful posts you’ve made through the years!

H

5

Hi Helena,

The RigidPointSet component creates a Kangaroo goal (the ‘RB’ output), and it also outputs (from the ‘P’ output) the plane it is using as the frame for the rigid object, to make it easier to identify it and apply other goals (such as loads) to the same object.
If no ‘Plane’ input is supplied, this frame will default to the centroid of the points.
However, you have the option to specify a custom plane to use here.
Yes, if you have a more complex shape, and want a more accurate center, then it makes more sense to use the center of mass (found with the standard ‘Volume’ component, or Area if it is a thin surface-like object) instead as the Plane input.

If you already have a closed solid, then indeed it is probably easier to use RigidBody(which defaults to the center of mass as its frame).
RigidPointSet was intended mainly as a way to simulate rigid geometries which aren’t closed solids, such as treating wires as curves, or thin shells as open surfaces, without always having to thicken them into a closed mesh (which generally means more points to simulate so slower).

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