Rigid Joint not Maintained

[neljoshua]

Lots of posts from me today...hopefully this is not an indication of how the entire day is going to proceed.

I created a plate design and added some features to it using rigid joints.  I then inserted it into another design and tried to join the plate to the frame.  Unfortunately the brackets are joined while the plate itself is not.  It seems that the design that I inserted the plate into is not paying attention to some of the joints.  I say "some" because the two brackets and pipes seemed to be joined to some phantom geometry.

I created the plate using a form, but when finished (and before applying any joints), I made it into a component.

[neljoshua]

This is also happening in other models.  It is to the point that I am not able to continue working on assemblies.

[neljoshua]

For what it is worth, all the joints in question reference construction planes, lines, or points.  Am I incorrect in assuming that construction geometry should be kept with what it is referencing?  If so, that severely limits its usage!

This seems related to the issue I was seeing with another model (in this post).

[paul.clauss]

Hi @neljoshua,

Do you have any of the components in the plate design file grounded? If not, please try grounding a component to see if this problem still occurs.

If it does, would you mind sending your Fusion 360 assembly files over to me? I'd like to have a look into what may be the root cause of this issue...

Thanks,

[neljoshua]

@paul.clauss,

Thanks for the reply.

Yes, everything is properly grounded.  I will share the designs with you later this morning.

The work-around is to remove all construction geometry (Fusion seems to be having issues with this in general right now) and re-join components via other means.  This is not my preferred method, as it means I will have to re-edit these joints if any changes are made to the designs.

[Beyondforce]

Could you please attach the file?

[paul.clauss]

Hi @neljoshua,

Thanks again for posting!

 It looks like this issue is due to the position of the main "Body" component in your design not being defined in relation to the other components. While the position of the brackets and inlet-outlet pipes are fully defined in relation to one another through construction geometry, none of them are joined directly to the main "Body" component. While the "Body" is ground to be in the correct position in the x-referenced file, its position is not defined in relation to the other components (as there is no direct link to them via joints or a rigid group).

To clarify - the joints in your model only create a link between the brackets/ inlet-outlet tubes and the construction geometry. There is no joint that positions the main "Body" component in your model with respect to the construction geometry or the other components.

Component groups inserted into new designs in Fusion 360 are not automatically converted to rigid groups. Because of this, a singular component in a component group must have its position fully defined in relation to the other components in the group in order to maintain its relative position when inserted into a new design. While the "Body" component was ground in its correct position in the "Draft_Plate" design, it was not related to the position of the other components through that grounding command. To create this relation, I made all the components in the "Draft_Plate" design into a rigid group. I have illustrated this in the screencast attached below:

Hopefully this helps resolve your issue and move forward with your designs! Please let me know if you have any other questions or anything need clarification - I'm happy to help!

Thanks, 

[neljoshua]

@paul.clauss,

Ok; I see what you are saying.

I still have a question regarding construction geometry.  If I base the geometry on a component that is grounded, why can that geometry and the component move with respect to each other when the component is inserted into another design?  This seems wrong to me, but I may be thinking about it incorrectly.

Take this example: I wanted to define the inlet and outlet based on the center of the plate so that if the size of the plate changes the inlet and outlet will move accordingly.  This should happen with correct construction geometry, as the geometry I used was based on the edges of the plate.  If I use a rigid group, however, this would not happen and I would need to edit the group any time a change is made to the plate.

You mention in your Screencast that the construction geometry is based on the origin.  I guess I am misunderstanding something here--I thought that construction geometry was based on the body or component it references (I created the axes using the corners of the plate).  If this is not the case, I am struggling to see how construction geometry can be helpful--it is no longer linked to the body or component it was originally referenced to.  If it no longer references that body or component, how is it different from a plane placed in space only referencing the origin?

Am I expecting something that cannot be done in Fusion?  Is there, perhaps, another way to do this?

[paul.clauss · Accepted solution]

Hi @neljoshua,

Thanks for the response! 

When you insert a component group into a new design, the ground from original file will not be honored. If it was, you would not be able to move the new component group in the higher level assembly design at all - because it would still be grounded in space relative to the origin. However, if you include the grounded component in a rigid group, its position will be defined in relation to the other components in its group, and the entire group will be allowed to move together in the new assembly file.

In your example, you say you want to define the inlet and outlets based off the center of the plate, so they will update if the size of the plate changes. But, if you look at the joints you set up in the design, you can see that they define the position of the inlet/outlet with a 900mm offset from the XZ plane, which happens to be at the center of the plate. This offset distance is not linked to the size of the plate - it will always be 900mm from the XZ plane. I have attached a screencast to this post, in which I illustrate how to create a link between the position of the inlet/outlet and projected geometry from the corner of the plate, which allows the joints to update correctly when the plate is resized. This method does not require you to edit the group when changes are made to the plate because the joints define the position of the inlets/outlets in relation to the corner of the plate and the rigid group ensures that each component maintains its spatial relationships to the other components in the group.

I hope this helps clear up some of the questions you have relating to joints and assemblies in Fusion 360. Please let me know if it does not - I'm happy to help!

Thanks,

[neljoshua]

@paul.clauss,

Yes, I see that the rigid joints are just a set distance from the XZ.  I changed them because what I was doing originally was not working; they originally were based on the construction geometry.

So, the take-away for me is that I should not be using construction geometry to hold spatial relationships between components.  Personally, I see this as limiting and would prefer it not to be the case, but now I know how to work with it.

Thanks again.

[jeff_strater]

Hi @neljoshua, I would like to address the work geometry/component position issue.

The problem is that all these operations in Fusion are history-based operations.  The reason why the work geometry won't move with component position is that the move happens after the work geometry is created.  If you do the move before the work geometry, then edit the move, the work geometry will update as you expect.

Here is a screencast:

Jeff

[neljoshua]

@jeff_strater & @paul.clauss,

Thanks for the clarifications.  This information helps; I am still learning.

[timkrins]

I had a similar issue today, where a sub-assembly rigid group was not maintained when imported into a larger assembly.

Now, the interesting thing here was that everything was grounded - the sub-assembly did not move.

I determined that the issue I was having was related to the timeline order in which the sub-assembly grounding had taken place.

If anyone else is having issues, try moving the 'Ground Component' action in the timeline to just after you imported your base component.