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Finding poorly constrained parts?

S1monS1mon Member Posts: 2,246 PRO
edited October 2023 in General
I'm running into an issue which is turning out to be more painful than necessary. I have some reasonably complex assemblies with 100s of parts and several levels of subassemblies. It's great that the indicators were added which show fixed, grouped etc, but when a fastener is free in a lower level assembly, it's not immediately apparent. I'm only finding these issues now because I'm making an even more complex assembly with these other assemblies as subassemblies and the floating parts are becoming apparent.

I've also found that sometimes these icons are out of sync with the mates in an assembly.

In the past I would usually drag select everything in the assembly, and try to move it. This would usually quickly make it obvious if something wasn't tied down at a lower level. This is not so successful for me these days. Onshape just pretends that everything can't move, at least when there are too many parts to think about (my theory of what's happening).

If I unfix (or unmate from the origin) the one key part, and then drag the assembly, the unmated parts will be left behind. Why is dragging all the parts not doing the inverse any more?

Are there other techniques to find parts or subassemblies which aren't fully constrained? This seems like a good opportunity for a search filter which highlights things which are not fixed.

Why don't folders of instances have icons like assemblies do which show if all the instances inside are fixed?

I can see a few potential improvement requests here, but I'm trying to figure out if I'm just missing something.


  • eric_pestyeric_pesty Member Posts: 1,395 PRO
    Yeah it would be nice to be able to find parts that might "fly off" when you move things around in a higher level... I'm not aware of a good way of doing this other than manually checking the various assemblies from the bottom up or inserting the assembly in an "unconstrained" higher level and looking for anything left behind when dragging. The problem is that it can be hard to see in a physically large assembly that contains small parts.

    The tricky part from the software perspective is to differentiate between intentional degrees of freedom and unintentional ones...
    Basically we need a way to highlight any items that have "infinite" freedom (so that anything with limits or that only spins in one place is "ok") in an assembly structure.

    It would be nice to have a "strong wind" analysis feature that would try to move things around in every direction and highlight the can "fly off the screen".
  • S1monS1mon Member Posts: 2,246 PRO


    I'm looking for parts or subassemblies which have no mates, or no mates to anything in the current assembly. I want something almost as glaring as how failed features are in part studios. Those warnings roll up to the top (they show at the feature level, the folder and the top of the tree) and they're hard to miss.

    As a corollary to this, I would also ask that importing assemblies would not default to everything being unconstrained. That wasn't the issue in this particular case, but it is also a recipe for disaster. See this IR: https://forum.onshape.com/discussion/16515/import-and-group

    I'm fine if this is some sort of toggle, if it really freaks some people out to see a bunch of errors, but the current state of trying to find parts which are unconstrained is challenging. It's too easy to mistakenly have parts which have no mates, especially when there are a bunch of configurations of subassemblies. Maybe one config is fine, but another is missing mates due to lack of checking all the configs. When an assembly first gets dumped into another assembly, it isn't always obvious that mates are missing until something gets moved in certain directions, or as you mention, far enough to see that the part is out in space.
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