Mass and CG Location from Digital Models

[DrJB]

This question came up in a thread in the Technic Forum. I was then advised to ask it here. So, here it is:

Is there a way, with any of the digital tools, to calculate the total mass and location of the Center of Mass (CG) of a given assembly?

Edited February 11, 2015 by DrJB

[Alasdair Ryan]

This question came up in a thread in the Technic Forum. I was then advised to ask it here. So, here it is:

Is there a way, with any of the digital tools, to calculate the total mass and location of the Center of Mass (CG) of a given assembly?

Autodesk inventor or Solidworks can do that,if you go to college and do a HND in CADD you will get taught CADD analysis.

This kind of feature will not be appearing in Lego software you need to remember that the Lego software is really only used for as a hobby and not in industry.

Edited February 12, 2015 by Alasdair Ryan

[DrJB]

Thank you, but my question was about whether the existing lego tools had such functionality. I know that professional tools (AutoDesk and others) do have such functionality, but importing Lego geometry in them might be a real challenge. I was hoping that, with the amount of engineers we have on the forum, maybe someone has already figured out a way to do this. As for going to college and learning CAD, well, ... suffice it to say that after several graduate courses in Solid Modeling and a PhD, if I were to go back to college, it'll be for teaching, as I might be too old to be taking courses.

Edited February 12, 2015 by DrJB

[EdmanZA]

I'm not aware of any of the LEGO tools having this functionality. To get an accurate measure, the programs would need to know the centre of mass and mass of each individual part. Professional CAD calculates this based on part volume and density, while LDRAW etc. would either need to calculate the volume and mass of each part on the fly, or this data would need to be included in the part files.

If you just want the total mass, you can import the parts list into Brickstore or the like and you should get a mass.

To get an estimate of the CoM, you could assume that each individual part's CoM lies at its origin. You could then read the LDRAW file into Excel to get the origin location of each part. Combine this with mass data from Brickstore and some lookup functions and it's fairly trivial to treat the model as a system of particles and calculate the CoM location.

To get an accurate CoM calculation, you will need to know the CoM location of each part, relative to its origin. You will then need to perform transforms in Excel to work out the part CoM location from its origin location and rotation. With that data available, the CoM calculation is, again, trivial.

[DrJB]

Thank you. This sounds like a very promising lead. I was not aware Brickstore had the mass information. Once the total mass is calculated, I agree, it's fairly trivial to 'approximate' the moments of inertia as the structures I'm after are relatively simple geometric shapes. Cheers.