topic Re: Sub-assemblies registering as 0 mass in top assembly? in 3D Part & Assembly Design

Sub-assemblies registering as 0 mass in top assembly?

ptc-5250221 — Fri, 04 May 2018 15:19:21 GMT

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

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

dschenken — Tue, 10 Dec 2013 04:09:57 GMT

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?

ptc-5250221 — Tue, 10 Dec 2013 04:16:35 GMT

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?

ChrisKaswer — Tue, 10 Dec 2013 14:19:27 GMT

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?

ptc-5250221 — Tue, 10 Dec 2013 15:29:18 GMT

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?

ChrisKaswer — Tue, 10 Dec 2013 18:27:47 GMT

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?

ptc-5250221 — Tue, 10 Dec 2013 18:33:43 GMT

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?

ChrisKaswer — Tue, 10 Dec 2013 18:48:04 GMT

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?

Dale_Rosema — Tue, 10 Dec 2013 19:56:23 GMT

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?

346gnu — Wed, 18 Dec 2013 17:03:44 GMT

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

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

vzak — Wed, 18 Dec 2013 23:29:17 GMT

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

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

jhansson — Mon, 12 Jun 2017 09:10:22 GMT

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

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

CG_2960659 — Wed, 12 Mar 2025 20:46:23 GMT

It's 2025 (on Creo 10) and this is the only thread at all that I can find on this subject anywhere. If anybody is even still around.

I have the same issue with a sub-assembly that shows up as a body with 0 mass. Kinematics work, but the Dynamic analysis will not. It's not any of the sub-components causing it. "Exclude From Mechanism" sounds like the perfect solution and I managed to find the command under RMB > Customize, but it's grayed out. I added it to the top ribbon and it's still grayed out.

Is this a defunct ghost command? Is there any other way to remove sub-assembly top-levels so they don't show up as bodies? Thanks!