Center of Mass definition

I'm a grasshopper newbie looking to create a definition that will help me find the center of mass/center of gravity of a group of objects.

I have a scene of a room that includes ceiling, walls, floor, objects etc and I know the weights of each of these items.

This is how I think things should go: I would find the Volume Centroid of each of these objects and then assign weights to these Centroid points in grasshopper. Then I could use the Maths functions or Expression Editor to do the maths to find the center of mass for all the objects (using a formula similar to here). Is that right?

If so, I'm a bit baffled about the best way to do it in GH. I'm not sure whether I need to do calculations for x,y,z separately or whether I can do it all in one hit.

Any help would be appreciated. Once complete I'd be happy to share the definition for anyone to use as it would be a pretty useful tool!

Replies to This Discussion

Permalink Reply by yehezkielwm on September 29, 2016 at 7:58pm

Is it like this? The center point is the center of all in terms of location. But Im not very sure if it's same if u need to involve calculation of material density or etc.

Permalink Reply by Andrew Chan on September 29, 2016 at 8:38pm

Hi yehezkielwm - Thanks for your reply!

Your definition would be ok if all the objects were the same weight. But lets say the object on the bottom left was 4 times heavier than the other objects. Then the center of mass will be much closer to that object.

That's what I'm trying to achieve.

Permalink Reply by yehezkielwm on September 29, 2016 at 8:51pm

https://www.youtube.com/watch?v=E1OACDnfY00

I see, looking at this video, I think what u want to achieve can be done in grasshopper through some vector multiplication etc. I would do it smtime later if u are not rushing it.

Permalink Reply by David Rutten on September 30, 2016 at 2:44am

Merging mass properties is a difficult process. Rhino has ways to compute the centre of mass of multiple objects, but I did not expose this in Grasshopper. It could easily be accessed thriugh a C# component though. I'm not quite sure how to deal with different densities though.

Permalink Reply by Andrew Chan on October 1, 2016 at 12:04am

Hi David,
Luckily for my current task I don't need material densities. All the objects are made up of multiple materials so I've been given weight estimates for each object.
That being said, I think i found a solution that works for my current task:
Using the maths components I recreated the formula for center of mass and it worked!

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image.png, 116 KB

Permalink Reply by Andrew Chan on October 3, 2016 at 6:31pm

As promised, I'm sharing my Center of Gravity / Center of Mass definition.

It uses the simple maths formula of x_c = m1x1+m2x2 / m1+m2

My definition includes 21 bodies, but you can delete as needed. I'm sure there's a simpler way to do this, but I needed to make it graphically easy for me to organise my data.

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