Managing DoF in subassembly

[thomasfla]

Hi, thanks for this super tool!

I'm wondering it is possible to have some DoF defined inside an assembly which is itself included inside a global assembly multiple time.
I guess this will lead to naming issues, but maybe could be fixed by adding a suffix?
At the moment, onshape-to-robot detects 0 dof.

It this is not doable, I can of course simply make a big assembly.

[Gregwar]

Hello,
I agree that it might be easier, but it would require deeper rework of the logic
Actually, some current constraints can be lightened by refactoring/rewriting onshape-to-robot, hopefuly I will have some time to do that someday

[Gregwar]

Just for the detail; currently the problem is also that non-dof relation (like two parts being fastened together) don't work on top-level assembly (that could also be improved)

[thomasfla]

Thanks for the fast response, I'll then do a separate flat "link level" assembly for the URDF export.

[Achllle]

This is a pretty important feature to have. Most complex assemblies will have DOFs defined in a subassembly.

@Gregwar, you wrote

it would require deeper rework of the logic
Actually, some current constraints can be lightened by refactoring/rewriting onshape-to-robot, hopefuly I will have some time to do that someday

Curious if that day will come soon? Alternatively I can try to tackle this one issue if you could share high level steps on how this is easiest accomplished - preferably without requiring a big refactor.

[Gregwar]

Big refactor happened recently
However there are still some work to be done if we want to reach that feature 🙂

From my current understanding on how I would implement that, there are underlying hard problems to tackle. Mostly, considering features in all the sub assemblies would mean that all the parts present in the robot would become candidates to be their very own link. In that case, it become less clear what is actually a body, it would need an analysis of all the features to understand which bodies are "weld" together and what can move.

[Gregwar]

Here are the questions that needs to be addressed:

1. How to decide the name of links ?
2. How the DOFs would be named ?
3. Some extra fancy features should be supported, like assembly patterns. Else the parts created by pattern for e.g. would not be associated to the proper rigid body
4. Fastened mates would make two parts the same body. But we would need to "understand" that a planar mate + a slider mate is equivalent to fastening and then merging the bodies into a same rigid bodies.
5. Variables (/variables) can't be accessed with microversion
6. Mate values (/matevalues) can't be accessed with microversion. Moreover, mate values don't seem to reflect the values of mates in subassemblies anyway

[bogumat]

This is an important feature for me. This is obviously not a trivial issue but for question 2 to be addressed I imagine that the naming convention onshape has for replicated/duplicate subassems is subassem<1>, subassem<2> etc could be used. You could make the dof revolute joints inherit the name of the subassembly that they are part of.

[hartikainen]

This would be really valuable for us too. Happy to test things if anyone gets to implementing something around this.