Assemblies are really just kinematic simulations?

OpenR2

Had my first chance to play with Assemblies this weekend....after a couple of hours of frustration it came to me.
In Onshape ...

A Document is a Project.
A Part Studio is an Assembly
Parts are Parts
An Assembly is a Kinematic simulation

Sort of dissappointed that we dont have our own secret term for Parts. Can we call them widgets or gadgets. Anything but an industry standard term? :P

traveler_hauptman

The way I think of it is:
Part Studio -> In-context design (layout assembly or multi-body part depending on where you are coming from).
Assembly -> Grouping of parts and subassemblies that you actually stick together during manufacture.

If you dig in the forum you'll find some long discussions on onshape mates (specify degrees of freedom) vs the dual which you see in Solidworks & Creo (specify degrees of constraint).

OpenR2

I thought that was true too until I actually went to try to use the assembly and none of the features for assembly modeling were there.

I wanted to model the first in context design of each detail in the part studio, and then do all the patterning and mirroring in an assembly, I couldn't find any of the patterning or mirroring tools and was answered by Onshape that they only exist in part studio.

So I don't immediately see what can you do in assembly besides setting up kinematics?

florian

Another quick remark why a part-studio is not always an assembly: When your tree is long and your parts are complex, changing a dimension at the top of the tree takes time to regenerate. Up to a coffee break.
I hope Onshape will overcome this with shear computing power, however: The tree isn't a tree but rather linear, an thats hard to split up into parallel processes… isnt't it? Who got the idea that we need more cores for faster computing?

Anyway: An assembly is there to assemble parts. For me it's clear: when I'm assembling my real bike/car/Mac I don't expect to be able to mirror parts 

OpenR2

I think if there is more than one part in your part studio, then it is an assembly.

I am curious to see how the multiple parts in a part studio works once Onshape start to think about lifecycle. Will you be able to version and release each part in a studio separately?

i think to say the differentiation between when to use a part in a part studio and a part/part studio in an assembly is determined by spec tree regeneration time...I don't think that's a well thought out long term data model.

Ar this point im struggling to see how an assembly is anything beyond a kinematics workbench.

lougallo

@OpenR2 A Part Studio is a place to model and build parts.  Multiple parts can be built in context, share features and be built on the history of the Feature List.  What assemblies bring besides mating and kinematics is instance counts.  A part studio treats a new part as a new part and does not care about the seed or duplication of the seed.  When you insert a part into as assembly, you are mating it to other parts and positions in context of that assembly.  We don't insert a Part Studio into an assembly, we give you a shortcut to drop all the parts from a studio at that instant into as assembly.  Those parts will update, as you would expect, but subsequent parts would not show up in the assembly since they have not been explicitly inserted.  You can imagine things like BOMs will need good instance counts and currently a BOM of a Part Studio would be a long list with every part showing a quantity of 1.

In general, many companies will avoid doing too much in-context assembly modeling since it can be pretty volatile since the assembly composition can change with new inserted parts or when motion has changed the environment that the in-context part was created.  That is not to say we are not looking into implementing in-context assembly modeling in the future.  

Part Studios provide a very stable birthplace for parts, even when designed in context.

brucebartlett

OpenR2 said:
I wanted to model the first in context design of each detail in the part studio, and then do all the patterning and mirroring in an assembly, I couldn't find any of the patterning or mirroring tools and was answered by Onshape that they only exist in part studio.

@OpenR2 I'd really like to think that at some stage we will see patterning and mirroring in the assemblies for quick repeatable instances of parts. We already have the replicate tool which is an absolute dream when instancing things like bolts. I have a lot of symmetry in the things I design and will find it really painful and time consuming without some form of mirror tool for assembly. I am sure it come only a matter of time

brucebartlett

I really love the in context part studio modelling setup rather than modelling in context assemblies. Although took me a while to warm to it after coming from a very ordered way of doing things with assembly layout sketches however my experience so far has been extremely stable models built in-context in Onshape. What I love about the part studio is you only have 1 instance of a part is you know this is the driving part and you can not mixup your parametric links and you are less likely to have bits move breaking links. I think Lou's statement  sums it up well.

lougallo said:

Part Studios provide a very stable birthplace for parts, even when designed in context.

OpenR2

Lou. Bringing up the instance/reference topic....most CAD/PLM systems support three objects. Instance. Reference, and Occurrence. Most BOMs are generated off the Occurence graph...opposed to the Intance/Reference graph.

A skate board would have 2 wheel instances under an axle reference. It would have 4 wheel occurrences. So the BOM would need four wheels...generated by traversing all paths of the instance/refernce graph...which is the occurrence graph. 

In CATIA/Enovia they have part editor that sets up Instance/Reference graphs and effectivity expressions They have the product editor that sets up the Occurrence graph and solves effectivity based on the product and filter requirmrnts.

When we are in the Onshape part studio there are no instances so everything is references? And then when we go to the Onsgape assembly are we looking at an instance/references graph? Or are we looking at an occurrence graph?

billy2

OpenR2- you're spot on!

What if you controlled body positions in a part tab with a series of translations & layout sketches? Do we really need assemblies?