Grounded Imported Components Still Move

[Anonymous]

Hi, was just curious if I'm missing something with this one.  In the screencast I try creating a joint between two components, and to align the components to satisfy the joint, Fusion moves some of the components, even though they're suppost to be grounded.  Wondering if being imported has anything to do with it. 

Here's the screencast:

https://knowledge.autodesk.com/community/screencast/9d7aa5cd-398a-452d-bf1c-11218e57d769

Thanks for any help!

Jesse

[jeff_strater · Accepted solution]

Hi @Anonymous,

This is the "grounding the sub-assembly does not ground the leaf parts" problem.  There are a bunch of threads on this.  I'll find a few and add them.  But, for now, just know that grounding a sub-assembly is not sufficient.

Jeff

[jeff_strater]

This is probably the most complete thread:  ground-in-fusion-360-will-not-work.  Take a look and see if it makes sense to you.

Jeff

[Anonymous]

That's right, I totally forgot about that, thanks Jeff!

Jesse

[Anonymous]

And being imported it comes with a subcomponent inside of a component.

Jesse

[TrippyLighting · Accepted solution]

It does make sense and it does not.

I just was trying to help a user in another thread and came across this problem as well. It is really tedious when one want's to work with assemblies that are imported from step files such as the vise in the other thread.

Is there any other recourse than going down to the sublevel and start rigid-grouping all the subgroups and then the upper level groups and so on ?

[TrippyLighting]

Also, what does the "Include Child components" check box in the Rigid Group joint do ?

One would assume that when you select two subassemblies or one component and one subassembly that it creates a gigid groub including all parts including the child components in the subassembly. That however does not work.

The second thig I notices that theUI for the rigid group is inconsistenct with many areas of Fusion 360 with similar selection UI's. It does not allow deletion and re-selection of the components. If you misselected a component you cannot delet the selection, you have to start from scratch.

[jeff_strater]

Hmm... that's a really good question, @TrippyLighting.  It sure seems like it was intended to include child components, but it also doesn't seem like it does this.  so, I need to do some research.  Is this thing broken, or is it just poorly named?

I'll get back to you...

Jeff

[jeff_strater]

I think it's just buggy.  I was able to get it to work one time out of 3.  I think the intention is to do exactly what it says, but for some unknown reason, it just doesn't work all the time.

Here's a screencast:

Jeff

[TrippyLighting]

Thanks for the update!

[Le_Bear]

If I may add my 2 cents, it does not seem to work as it should for me:

I am designing a CNC machine in different sub-assemblies, and I have a design where all sub-assemblies are imported into. I want to ground the base assembly. I made sure it is a rigid group, and ground it on the upper level, making sure sub-elements is checked.

But I can still drag it around, just as if it was not grounded at all.

Now, if I go ahead and select every single component part of this assembly, then ground them all, it works as expected.

To test more, I ungrounded the assembly at the upper level. it is STILL grounded.

So, basically, it works as if grounding/ungrounding at the higher level has no effect at all.

Let me know if a screencast would help here.

Thanks,

Bernard

[Le_Bear]

Want to add a screencast, but I have not seen how to edit my message. Sorry. Anyway, here it is:

[Phil.E]

This is as expected.

An assembly is just a container for components. When you insert an assembly it is assumed to be "flexible" meaning that any degrees of freedom it has will be available to the assembly.

For instance, you wish to insert a hinge to attach a cabinet door to a cabinet.

• The hinge has joints that make it work before you insert it.
• After inserting it you want the hinge to open and close, which it does.
• But also after inserting it, you need to add joints to the hinge to get it positioned in the door frame.
• So you start Joint command, and pick a face on one of the hinge halves, join it to the cabinet.

What you have done is join the hinge half to the cabinet, not the entire Hinge assembly.

What you are doing in the video is the correct workflow.

1. If there are no joints, make a rigid group out of the inserted assembly.
2. Then attach one of the parts to the assembly you inserted it into.
3. In your case you are grounding one of the elements of the rigid group inside the recipient assembly, which is attaching the rigid group to the recipient assembly.

In the real physical world, this is very much like bringing your CNC machine into your shop, setting it on the table (as a rigid group) then clamping it to the table. When you clamp it to the table, you are only clamping one of the parts at a time. You simply cannot clamp the entire CNC machine, there is no clamp that does that! So you clamp only one leg or two, now the CNC machine will not slide off the table.

In this way, Fusion 360 assemblies act very much like physical objects. In your case, the top level assembly is not an object, but rather an idea. It is an abstract thing, the rigid group is "real" and can be bolted down.

I hope this helps.

[Le_Bear]

It does help, and make sense.
Thanks you!

Regards,

Bernard