topic Re: Flexible components and outdated mass properties in 3D Part & Assembly Design

Flexible components and outdated mass properties

Ralph_W — Tue, 30 Apr 2024 15:35:42 GMT

We use the PRO_MP_MASS parameter for our weight calculation and as a value on our drawing.

To ensure everybody is executing the mass calculation the setting mass_property_calculate is set to report_outdateness_only (or check_upon_save). A warning

For normal assemblies these settings are ok.

But in assemblies where we use flexible component (e.g. a spring or a folded flexfoil) the mass properties of the assemblies keep outdated every time the assembly is opened.

Even a bottom up mass calculation of all parts and finally the assembly will not help. Because after closing and re-open the assembly, the assembly shows "outdated mass properties".

How to solve, or block this?

Re: Flexible components and outdated mass properties

BenLoosli — Tue, 30 Apr 2024 16:06:28 GMT

I'm not sure you can prevent this due to the flexible part being 'modified' when brought into the assembly.

A hose assembly modeled as 12 inches as a standalone part, when in the assembly it is now 15 inches as it follows the flexible path, it has a new mass due to the longer length. Not sure how a sping 'stretches' as a flexible part (add coils or changes spacing) but the add coils would also change the mass.

Re: Flexible components and outdated mass properties

kdirth — Tue, 30 Apr 2024 16:16:39 GMT

You may need to use User Defined Mass Properties for any part that you intend to flex. Even stretching a spring by changing the spacing will change the mass calculation as the diameter of the spring is not collapsing as it would in real life.

Re: Flexible components and outdated mass properties

Ralph_W — Wed, 01 May 2024 08:11:30 GMT

The strange thing is that I already brought the flexible component into the assembly and adjust the length or folding angle. I updated the mass calculation of the assembly (and this one is correct).

But after closing and opening the assembly again (no changes made) the mass property of the assembly is outdated.

Somehow the mass is not stored in the assembly if flexible component is in.

Re: Flexible components and outdated mass properties

kdirth — Wed, 01 May 2024 12:14:37 GMT

Using flexibility does not change the part file. It still has the unflexed mass properties. A flexed part in an assembly loads the original part file into memory then modifies it based on the flexibility settings, changing the mass properties calculation.

Re: Flexible components and outdated mass properties

Ralph_W — Wed, 01 May 2024 13:31:21 GMT

Clear, and there is not even a hidden setting to avoid this?

Re: Flexible components and outdated mass properties

Chris3 — Thu, 02 May 2024 11:33:00 GMT

We have the same setting and have experienced the same issue without a solution. If you make an idea for maybe people will vote it up.

Re: Flexible components and outdated mass properties

Chris3 — Fri, 24 May 2024 13:45:48 GMT

@kdirth wrote:

It still has the unflexed mass properties.

This is not true. The mass property parameter is not updated but if you run the mass property report (Analysis -> Mass properties) it is updated.

This is part of the reason that we don't rely on the mass properties parameter to get mass properties out.