Sub-assemblies registering as 0 mass in top assembly?

[ptc-5250221]

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!

[dschenken]

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.

[ptc-5250221]

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

[ChrisKaswer]

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.

[ptc-5250221]

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.

[ChrisKaswer]

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.

[ptc-5250221]

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!

[ChrisKaswer]

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.

[Dale_Rosema]

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

[346gnu]

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.

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

[vzak]

As already mentioned by people here, the problem is in that you have subassemblies that are bodies by themselves - hence have zero mass. Have you had few parts in these subassemblies belong to same body as subassembly this will give mass to the body and resolve the problem.

But given you need such subassemblies by design structure, try this : after entering Mechanism go to Body Tree / find this Body that only has such subassembly / select it and RMB > Exclude Fom Mechanism. Check if analysis run now.

Regards

- Vlad

[jhansson]

Hi,

I have the same problem as stated above since I have a subassembly with parts of which none of them can be rigidly attached to the ground.

The Exclude from mechanism solution seems very conevient but when I RMB click a body in the mechanism tree I can only choose Info. Is it possible to find it in some other way? I am using Creo 2.0.

Kind Regards

-Jimmie