Components moving and losing joint/alignment positions

[adwarbinek]

Hello

This has happened a few times over the past months and I am trying to figure out why. 

Issue 1:

Components in this project are moving after opening Fusion 360. The components each have multiple jointed parts within them and are linked into a main project file. The linked components are aligned together and also jointed in certain cases. When opening Fusion I find that the sub-components within many of the linked components have moved around and are not maintaining their alignment/joints. 

The image shows how massively confusing this problem is. It is making it nearly impossible to work on the main project file. Does it have to do with versions of linked components and updates to Fusion? There was one instance where I only worked on a single component over a day and when I opened the main project file where that component was linked into the main project looked similar to the image attached below. After removing the component from the main project file all the other linked in components went back to their intended joints/alignments.

Issue 2:

The timeline shows new compute fail warnings in red when Issue 1 occurs. Last night the main project file was in great shape and the timeline was all clear. Saved it, closed Fusion, shut down computer, and then this morning when I opened it all up Issue 1 and Issue 2 all appear.

How does all of this happen when I have saved and closed fusion? My only guess right now is it has to do with the automatic updates that occur in Fusion which break the timeline? Some server side computing of the project file that breaks the timeline? 

Images:

There are two images attached. What I saw this morning and a few times over the past months, and a render I did a week ago of the exact same file with no real changes since then. 

I would appreciate some explanation as to why this happens and how to fix/avoid it.

Thank you kindly.

[Phil.E · Accepted solution]

If you open one of the linked components, one of the ones that shows the problem, do you see this icon in the toolbar?

This looks like what happens when there is a pending capture position in a linked component. Those are ignored where the component is inserted, because they are pending.

[adwarbinek]

This was not the case for all objects. I found that other linked components would lose joint positions if there was a grounded object within that linked component. 

It seems to be a mix but for me the most common issue I found was having a grounded component within a linked component.

The main body of a component file was grounded with other parts having joint connections. When inserting these component files into another file the join positions would lose reference and move to other locations. Especially after aligning/jointing that inserted component file to another object.

[Phil.E · Accepted solution]

This could be related to the grounds. 

• Grounded parts are not grounded when inserted into other assemblies. 
• Ground is only in effect in the design where it is applied. 

Before inserting an assembly:

1. Ensure there are no pending capture position commands on it. Save it.
2. Un-ground any grounded components and drag them.
3. If the assembly comes apart, it will also come apart in the destination design where you intend to insert it.
4. If everything stays jointed as intended you can close without saving, it's ready to insert.

Please let me know if this helps.

[rwpinto763BC]

Hello,

I am having a similar problem. I do not have any pending position captures nor are any of my components grounded. The linked assembly contains 3 joints; one of the joints fails when inserted into a new design. I am attempting to add a joint between the linked assembly and a component in the new design. Any thoughts?

[Phil.E]

It's difficult to say without looking at the design. Can you possibly share it?

[jeffwPP4JQ]

Fusion 360 throwing away grounds from assemblies when inserting them is now the new dumbest thing I've discovered Fusion 360 doing. Was there some challenge given to the team(s) responsible for coordinate frames/joint/grounding to make those features as unintuitive as possible?

[TheCADWhisperer]

@jeffwPP4JQ 

Actually it can be demonstrated relative to the real world that the behavior makes logical sense. 
Attach your assembly here if you can’t figure out the logic. 

[jeffwPP4JQ]

I disagree. There's no case I can possibly think of where you would make an assembly and say "This part(s) is fixed relative to its coordinate frame/each other in this assembly" and then when you inserted that assembly as a subassembly you wouldn't want that relationship maintained or need those parts to change their position relative to their original coordinate frame in a meaningful way.

Instead, if a joint or motion in the parent assembly moves one of the "grounded" parts then the coordinate frame of the child assembly should move with it in the parental assembly as well to maintain the "grounded" position relationship designed in the child assembly.

Take railroad tracks as an example. They are a known standard fixed distance apart. You could make a rail part with the proper profile and length. Reuse it all over the place. An assembly of two rails makes perfect sense. Place the first rail, ground it, place the second rail, ground it. Great. Use that as a subassembly all over knowing that nothing can move... Oh, wait... when you insert the subassembly into a railyard parent assembly all the rails can move independently of each other and now you wonder why trains are falling off the tracks. Nope. stupid. Keeping the designed fixed relationships in assemblies is smart, intelligent, and intuitive. If you can think of real world example where the positions make sense to change then you shouldn't be grounding/fixing those components relative to each other in the assembly in the first place. "Place the rails with a joint you say". Well, great, what do I need grounds a feature at all then? Any ground can be done with a rigid joint to the coordinate frame or another rigidly jointed component.

I'll give you a challenge to present me with a counter example. I think you won't succeed simply for the fact that SolidWorks functions exactly as described here, and I've never seen a situation where that didn't work as expected. If you do present something, I suspect it will be highly artificial and a more intuitive solution exists if grounds were retained as described above or that you can't solve the problem more generally by just eliminating the ground from the subassembly to start with.

Fusion 360 suffers badly from a chronic case of "Oh no, we can't do it the same way SW does for certain features. So, we need to change 'fix' to 'ground' and 'mates' to 'joints'". And in doing so they provided far, far less intuitive features.

But here you go any ways: SillyGrouding, a simple parent assembly consisting of a DRO scale unit where the head unit can move as a slider relative to the glass scale unit (The subassembly: SinoKA400_120mm_Internal works perfectly). Ground whatever in the parent assembly you want, and it doesn't work right. Parts can be moved away from each other in manners they shouldn't be able to do with their intended grounds/joints. It gets even worse when you try to joint this subassembly to anything else within a more complex multi-component parent assembly. There are two problems going on here 1) There's yet another bug in Fusion 360 where it doesn't handle joints for internal components correctly, and 2) discarding grounds from subassemblies is stupid.

[IRONGUS__]

Autodesk, stop making fusion bad. Thank you.

[jhackney1972]

Do you have a Fusion issue and model to back up your meaningless statement?