Create joint to a component having sub-components

[tinglett]

I've been experimenting with different ways to do things, and ran into this one that I expected to work, but came up confused instead.  I suspect the answer is "you can't do that," but am interested also in alternatives.

So my example may seem goofy, but I wanted to make it real simple.   Here is a link that hopefully works for anyone willing to have a look:  https://a360.co/2UjdTtF

What I did was create a component called "Stuff" that has a child component "MyBox" which is a simple 1-inch high box.  I then used Create>Pattern>Rectangular Pattern to replicate this box vertically so I had a stack of 5 of them.  Thus, the component "Stuff" has 5 child components named "MyBox:1" through "MyBox:5"

Now I activated the entire model and created a sibling component to Stuff called "TopThing."   This component is also a box, albeit smaller.

Now I want to join TopThing so it rests on top of component "Stuff."   I'd like to join TopThing with Stuff, but can't figure out how to interactively select component "Stuff."   I can trivially create a joint between TopThing and MyBox:5.   But if I do that, things go bad with the joint when I edit the pattern and reduce the number of "MyBox" components.  Now MyBox:5 doesn't exist anymore and the joint goes red in error.

If instead I create an as-built joint things look better at first because I can select both TopThing and Stuff via the the browser.  But now if I edit the pattern and reduce the number of replicated "MyBox" components, I get a different error.  This time the box for "TopThing" has a yellow warning with this message "BoxPrimitive1  1 Reference Failures  Failed to get target occurrence transform."   I'm not sure how to parse that one :).

My thinking was that if I join "TopThing" to the parent "Stuff" component, the joint wouldn't need to worry about the content of "Stuff."  It would just adapt to however "Stuff" comes out -- from a bounding box point-of-view, I suppose.  But things don't seem to work this way.

Todd

[TrippyLighting]

You have run head first into one of Fusion 360's many  incomplete tools, the pattern tool.

What the pattern tool should let you do when patterning components is to automatically create a rigid group between the seed component and the patterned instances. Then when you change the instance counter that joint would auto automatically update. 

Unfortunate in this semi-parametric tool when you decrease the counter the rigid group joint will complain about a missing instance. You can simply edit the pattern feature and then click ok and it'll correct the count.

When you increase the counter you'll be left with a free-floating instance, which will not cause anything to fail and is more dangerous.

Having said all that, creating a rigid group selecting the "stuff" component, right clicking on it and selecting "rigid group" is still the best solution. You then need to ground the "Stuff" component/assembly.

Then you can create a "normal" joint between the last instance of "myBox".

If you always want the TopThing to float on top of the last instance, regardless of how many instances you have then that can also be done, but it requires a different approach.

[tinglett]

Thanks Peter!

What I'm really trying to do is have a way to model a cabinet with drawers with shelves above the drawers.  For practical purposes this is a cabinet on top of another cabinet, and I was hoping there would be a way for me to design the "top cabinet" without having its design be dependent on the inside details of the bottom cabinet.

I'm sure I could create parameters and such, but I'm not really trying to make this design be programmable to that degree.  I just wanted to learn how to "do it right" so things adjust correctly if I go back and change things.

Maybe someday the pattern tool will grow up a bit :).  Or perhaps a parent component can be more "real" than it is today.  I suppose if the parent component had an actual body (box of "air") it might work better...but it would still be a manual process to adjust the size of that box of air against the size of the stack of drawers it contains.  I'll just live with some manual editing for these types of design changes for now.

Todd