Odd mate behavior in multilevel assembly.

douglas_clark

Referring to the picture below.  Of the 4 blue elbows 2 (1 and 4) of them are in the wrong position.  You can see that they are part of the Cooling System sub-assembly.
If I attempt to drag the elbows about in the workspace then they will not move.



If I go through to the Cooling System sub-assembly the parts are in the correct place.  As shown in the picture below.  The elbows are held in place by mates to the radiator but the radiators are held in place by a group mate to a fixed part.  I do not think it is a version thing as if I insert another part into the sub-assembly and then go to the main that is shown directly without rev-ing up the version.


I've found if I modify the offsets in the mates to move the parts in the sub assembly then that has no effect on the main assembly but when I deleted the 2 parts and replaced them and recreated the mates as before then they came through correctly into the upper level assembly.

so I am at a loss to know why it wasn't working the first time, any ideas?

konstantin_shiriazdanov

check if you have group mate applied on any level of subassembly, except the part level?

douglas_clark

konstantin_shiriazdanov said:

check if you have group mate applied on any level of subassembly, except the part level?

So in the sub-assembly there's 2 groups "Radiator parts group", that's the highlighted parts in the second picture above and "Expansion tank parts group" which is 2 more parts.  The elbows belong to neither of those groups.

In the higher level assembly "Drive Train" the "Cooling system sub-assembly" is part of a group that contains that sub-assembly and all the other parts in the assembly.  

Does that help explain it?

konstantin_shiriazdanov

douglas_clark said:

In the higher level assembly "Drive Train" the "Cooling system sub-assembly" is part of a group that contains that sub-assembly and all the other parts in the assembly.  

I think this is the case, in onshape i don't reccomend to use group on subassemblies. It blocks the rebuild of all other mates of subassembly.

douglas_clark

Thanks I've been able to unlock the sub-assembly by taking it out of the group and then adding mates in a higher level assembly to pull the part back into the correct location.

How do you do multilevel assemblies where each sub-level is fixed and then rolls up to a higher level with more parts and sub-assemblies which is again fixed and so on.... I mean fixed as in it doesn't move when brought into the next level up assembly?

BTW In SolidEdge whe you Fix or Ground something you have the ability to force its location and orientation, I don't see that in Onshape.  Is it not there or am I missing something?   At the moment I'd drag something to where I want it then fix it.  Normally I'd not see this as an issues as mates shown be built as the project evolves but I'm dealing to a large extent with modifying imported parts an assemblies and I don't want to spend days rebuilding relationships for parts that are in the right place and are not to move.

douglas_clark

Now I've confused myself again.
In the picture below the pipe on the right is built from imported parts and uses mates to connect it together and determine the orientation and it cant move.

Now when I go up a level in the assembly the pipe is facing some random direction and is free to move in ways it was not in the sub-assembly...
I'm confused.

konstantin_shiriazdanov

can't guess whats going on, but seem like you use some exessive amount of mates. if you provide a link to document somebody could be more helpful

romeograham

Mates in Onshape can be quite a bit simpler than some other systems: a single Mate is all that's required to fix a part relative to another part or mate connector. It looks like you are using a combination of cylindrical and planar mates for the elbows - requiring several mates per joint. You should be able to use a single Fasten mate for each joint. This will simplify the model a lot....and might make it easier to troubleshoot the larger issue. It's almost certainly related to using Groups in subassemblies.

In Onshape, All Assemblies are "flexible" so all movable parts in sub assemblies will move freely in higher-level assemblies. While groups are tempting to use, they can interfere with mates, especially with sub assemblies etc. Best practice is to fully constrain parts with as few mates as possible in sub assemblies - that way they'll behave more predictably in higher-level assemblies.

As @konstantin_shiriazdanov mentioned - if you can share a link with the forum, someone may be able to diagnose the issue more easily.

Good luck!
Romeo  

douglas_clark

Thanks for the replies, I'll investigate the fastener mate further.
The thing about assemblies being flexible when put into higher level assemblies still bothers me clearly I'm not getting something.  For (silly) example if you have a motor assembly, rotor, stator, nuts bolts etc. so the only freedom left is for it to spin.  Then you put it into a higher level assembly and all that is lost and the parts are free again which makes no sense to me at the moment.  Which is why I was doing the group thing as per this discussion: 

https://forum.onshape.com/discussion/9158/fixed-components-on-an-assembly-still-move

Anyhow I'll keep plugging away at it hopefully a light bulb will come on for me.

romeograham

Your example above (that you have everything mated in a Sub Assembly and then the mates are lost in the higher-level assembly) sounds like a bug or something. That is not the way Onshape should work. I have found that once mates are set up with the proper degrees of freedom, it's actually more predictable in higher-level assemblies than I was used to in SolidWorks before I switched to Onshape.

Again, if you can share a link for others to review, we might be able to see what's going on.

You can also contact support for help from within the troublesome document: