Subassembly and Mechanism Dynamics

[TedJ1]

Hello,

I'm having a problem with the Student Edition of Pro Engineer Wildfire 4.0 and Mechanism analysis with the dynamic analysis option on. If I have an arbitrarily simple subassembly (containing one part that is just a simple cube) within a top level assembly containing only that subassembly, I get the error message:

"The mass of one or more bodies in your mechanism is zero. Dynamic analyses require nonzero mass for all bodies. Please review mass properties using Info, Mechanism, Details."

The problem doesn't occur if the top level assembly contains only the nested part and no subassembly. The problem doesn't occur if only the subassembly is being analyzed with no top level assembly. Nested subassemblies seem to be the problem. Can anyone help me with this? You can download a small zip file containing the part and assembly files here:

<A href="http://www.afafa.org/Unlinked/Mechanism_Dynamics_Problem.zip" eudora="autourl" target="_blank">http://www.afafa.org/Unlinked/Mechanism_Dynamics_Problem.zip

</A>Any help would be appreciated. Thanks.

Ted

 

[Ankarali]

Sorry but i coudlnt open the files because they're from the Studentversion of WF4.


Really sorry.....

 

[TedJ1]

No problem, Ankarali.I was way too primitive in my understanding of the mechanism model tree and constraints as they relate to mechanisms. I just needed to rigidly constrain (coord system) at least one part in the subassembly to the subassembly itself, which I had overlooked. Page 7 of this link helped lead me in the right direction:


[url]http://www.sdcpublications.com/pdfsample/978-1-58503-431-4-1 .pdf[/url]


Basically, all bodies in the tree (other than the ground body)need to include some part(that hasmass). Another fellow suggested a kludge of putting an arbitrary partin the top level assembly (which defines the ground body) and rigidly attaching it. My explanation may be a little rough, but I hope it's sufficient. Thanks.