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Sub-assemblies registering as 0 mass in top assembly?

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Sub-assemblies registering as 0 mass in top assembly?

I'm trying to run a dynamic analysis using a servo motor and just gravity for a landing gear, but everytime I try I get an error message stating parts have zero mass. I know it's the sub-assemblies that are causing this because when they are removed, the dynamic analysis works just fine. Unfortunately the subassemblies are a requirement for the project. Material files are assigned to every part, all part files and assembly files are in the same units and the sub-assembly files give mass measuremtns for the parts contained in the subassembly. It's only when I go to the top assembly that the analysis fails, and mass analysis of the top assembly says the two sub-assemblies have unknown material and masses. I have no idea how to fix this and would appreciate any and all help!

11 REPLIES 11

Re: Sub-assemblies registering as 0 mass in top assembly?

Based on general debugging (not so much with dynamics package) it is referring to bodies, not parts or assemblies. I know the analysis package puts items together as bodies, so look at the mechanism explorer to see if the bodies make sense.

Re: Sub-assemblies registering as 0 mass in top assembly?

I'm really new to this and taking an intro course so could you explain a little more in depth if possible? thank you!

Re: Sub-assemblies registering as 0 mass in top assembly?

You will never get this error if each and every part has a density. By therory, only individual "bodies" need to have a mass, as David mentions. I have found that I never have issue if I am as formal as possible with MDO rules.

Re: Sub-assemblies registering as 0 mass in top assembly?

Is there any extra step I'm missing somewhere? All the parts are assigned materials in the part files and all the material files contain the density for each respective material.

Re: Sub-assemblies registering as 0 mass in top assembly?

This may be one of those issues that is not possible to help diagnose unless we have your set of parts and assemblies. Do you have a "skeleton" part that you connect others to in a sub-assembly? If so, you'd likely need to give a mass to this "ground", or skeleton part of the sub-assembly.

Re: Sub-assemblies registering as 0 mass in top assembly?

Here's a zip folder containing everything, the only thing is it's the educational edition so I don't know if it'll be accesible. And no I don't believe I have any "skeleton" parts. Thank you for your help!

Re: Sub-assemblies registering as 0 mass in top assembly?

Yes - you are correct, commercial versions of Creo cannot read educational version files. Sorry, but it looks like we cannot help much more than guess at root cause.

Re: Sub-assemblies registering as 0 mass in top assembly?

Even if read only, commercial version of Pro/Creo should be able to open student versions for just this reason:

http://communities.ptc.com/ideas/2842

Thanks, Dale

Re: Sub-assemblies registering as 0 mass in top assembly?

Hi,

Does the attached help?

It works with assmblies with subassemblies for us.

True skeleton parts should be ignored. by mechanisms. 'homemade' skeletons will need to be made part of ground or attached in some other way.mechanism+mass+props.jpg

You will have to pedantically work your way through every component whether its this way or o set up mass properties before going to mechanisms.

Regards