Eneroth Center of Mass


I’ve just published a new extension: Eneroth Center of Mass. As the name suggests it finds the center of the mass for the selected entities. Well, that was a short description, but conceptually it really is a quite simple extension.



Excellent! Thank you.

You’re welcome!

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What do you find it most useful for, and what entity info needs to be added first?

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Finding the center of mass or center of gravity can be useful in determining how stable something would be. I’ve used TIG’s CofG extension for checking the stability of furniture. It is more sophisticated and can take into account the volume of the groups/components and their density. It can also indicate a composite CofG.

I think Christina’s extension is nice for quickly identifying the center when you don’t need the extra info provided by TIG’s extension.

An example using TIG’s extension. To keep it simple, I assumed all parts of the model have the same density. The box has a mass of about 20 Kg. If the CofG is outside the base of the table so the table would tip over.


Right now I’m working on a laser cut scaled up model of my first house in architecture school from all those years ago. Hopefully, if I can get the balance right and find a dense ballast for the bottom of the column, it can stand without any additional base plate.

I’m not sure what you mean by this. So far it doesn’t support density so there isn’t really any information to add. Just select some stuff and runt it, and the center of mass gets highlighted.

This tools also kind of supports composite center of mass, except it doesn’t call it that and there is no special command for it. You just select everything you want to check and run it; it doesn’t matter if the geometry is nested in groups or components or even lose in the active drawing context. It’s all supported right out of the box.

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I used to use center of mass to locate lifting points on prefabricated concrete building panels.


What are you going to make the house out of? Paper? What about the column? It’ll be interesting to see if you can get the center of gravity low enough to keep it inside the column if the stand gets bumped. Do you know where you can get a hunk of spent uranium for ballast? :smiley:

It’s a paper model and paper tube. I’m thinking of using sand or maybe scrap metal as ballast. Worst case scenario I’ll just add a base plate. but it would be fun not to have to.

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I have a stockpile of re-claimed lead flashing, that I cut into strips [with scissors] and roll into cylinders…

I used them for counterweights but you could easily put one in the bottom of a tube…


I seem to recall being taught, at any given point in masonry construction, that the load from (i.e. center of mass of all that stuff) must fall within the middle third of the cross section at that point or else tension forms at the outside extreme edge. I think our teacher derived a proof, but that was a long time ago and I don’t recall it.

That sounds like a lovely material. My dad recently started working at a company making mechanical inventions so maybe he can find some useful scrap metal pieces there.

I think I’ve read something similar once but can’t fully remember. I’ve however drawn a few diagrams of how far the model would need to be tilted for the center of mass to reach the highest point and begin going downwards again. It depends on its height, and the horizontal distance to the closest end of the base. If I manage to get the center of mass low enough, so the model would need to be tilted quite a lot before it starts to fall, I think it could be safe.

FWIW, I tried Googling it, and, yes, it is a “rule”, just as I remembered (wikipedia, quora, illustrated example)

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Hi Christina,

I do. And thank you for extension !
It creates a new group with three edges(intersecting but interestingly not breaking (like in the early days)). But they are black, default.
Would it be possible (yes), and/but are you willing to make a little change to the group’s result. To always give the group (thus the edges) a color, say purple.
With the style set to ‘Color by: material’ the new group would stand out more prominently.


The problem with this is that the model would suddenly have a purple material that the user doesn’t know where it came from. It can be really quite annoying to have things happening to your work without your knowledge or concent. I prefer to not have extensions do anything silently in the background, but do only one thing and do it completely transparently.


Not my view at all but I do have to respect yours.
Thank you for the extension as is. It’s an interesting tool for some piece of art I’m thinking of. Makes it more fun to experiment.


COG is fundamental in calculating proper suspension geometry in vehicles.
There are empirical ways of calculating this with a good approximation, however the possibility to calculate it within a CAD software is certainly a plus.
All the data relative to the various components (such as the motor or transmission) must be taken into account though. This a tedious and fairly time consuming process within CAD applications due to various parts and materials which constitute each component.
I wonder if it is possible with this “TIG” extension - which I didn’t know existed - to simply assign a known mass to a given SK component in order to simplify the overall vehicle COG calculation and component placement.

For what you want you might find MSPhysics useful.
Here’s a quick demo with a balance beam.
The default materials are the same but change to another material and away it goes.
There are many other settings.

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Thank you for you suggestion Box, nut no, the COG of the vehicle is a specific parameter required for the necessary calculations - for which a specific calculator exists.
Also the components are not “solids”, they can be designed (or found in the SK warehouse) and the mass is known for each one of them, so no need to calculate the weight of the solid by changing the material.
Simulating the variations of the COG of the vehicle as a set of components, depending on placement, size and mass of said components is what would be very interesting.

Christina, Very cool. Thank you for sharing. This is going to be shared in the Trimble SketchUp Group right now.

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