Position Capture Compute Failure

[mda]

I've got an assembly with dozens of parts, bodies, and/or sub-assemblies.  I made a small dimensional change to an extruded drawing feature on a linked part outside the assembly, then updated my assembly to reflect that change, but when I did this it caused another part in the assembly to move, breaking its own joint to do so.  When I say it broke the joint what I mean is that the part moved despite being joined.  The joint was still there but was for some reason being ignored, so I deleted it, repositioned the part and re-jointed it where it had previously been.  When I applied that joint I got the usual capture position query message and selected to capture position but after the joint had been applied I got a warning for that position saying compute failed: Capture position cannot move grounded component occurrence.  Can anyone shed light on what this means?  The parts involved in the repositioning and joining procedure described above are not grounded components within the current assembly.  There is however a linked sub-assembly that contains a grounded component in it.  I thought this might be the issue so I opened that assembly on its own to unground that one part, then saved and updated the larger assembly it is contained in but sill the compute failure on the position capture is there.  Can I just ignore this?  The assembly doesn't seem to be suffering in any way from this failure.

[paul.clauss]

Hi @mda

Thanks for posting! I've seen some residual errors fail to clear with joints before - does the warning clear if you perform a Modify > Compute All?

I'm happy to have a look at your file if you'd like to share a downloadable link of the assembly with me. Please let me know if you have any questions.

[mda]

Thanks for your reply. I tried the modify-compute all, but it didn't have the desired effect of eliminating the compute failure.  I've attached a video from today where I experienced a similar issue as described in my first post.  I start the video showing you a couple changes I made to an assembly which exists as a linked sub-assembly in my primary assembly model.  Then I go to the primary assembly to update it, which it does but with the additional effect of breaking the assembly, disregarding applied joints.  I have already dealt with this now by deleting the joints on the affected parts, repositioning them and re-joining them, like I did when the same issue occurred yesterday.  This seems to have resolved things but I would still like to know why this is happening and I would still like to get my head around the capture position compute failures which you'll be able to look into via the link I've shared below, which will require a password.  Is there a way I can PM you the password so only you can access it?

https://a360.co/2PFn19C

In the video, you can skip from around 2:12-4:12 in the video.  This is time waiting whilst the update computes.

[TrippyLighting]

I'd have to see a model (I am not an AD employee) to fully answer the question.

However, looking at your timeline it looks like you have a good number of position capture features right before you apply a joint.

Usually these are created because you pull the component out of its original position so you have access to the geometry you want to pick for the joint location. Once the joint is completed, you can delete that position capture feature as it's not needed anymore.

While it does not explain it that might inherently also take care of the warning message.

[paul.clauss]

Hi @mda

Thanks for posting the video. I agree with @TrippyLightings points on position captures above and am happy to have a look at the model. You can direct message me a password by hovering over my forum handle and selecting "Send Private Message" as shown below:

You may need to turn on private messages in your site preferences to do so:

The position capture flag in the timeline is only a warning (not a failure, which would be shown in red), and I would think that, with the changes to the sub-assembly (the addition of the joint), that capture position command is either redundant or not allowed by the joint, which is why it is be flagged. I would try deleting it from the timeline.

Its hard to comment too much on the joint issues without seeing the behavior firsthand, but the resources below may help explain how Fusion handles large assemblies:

• Master Assembly Class Fusion 360
• Large Model Management in Fusion 360
• Large Assembly Example: Marble Machine

Hopefully this helps! Please let me know if you have any questions.

[mda]

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@TrippyLighting wrote:

I'd have to see a model (I am not an AD employee) to fully answer the question.

However, looking at your timeline it looks like you have a good number of position capture features right before you apply a joint.

Usually these are created because you pull the component out of its original position so you have access to the geometry you want to pick for the joint location. Once the joint is completed, you can delete that position capture feature as it's not needed anymore.

While it does not explain it that might inherently also take care of the warning message.

---

Im relatively new to Fusion, having previously been trained in Inventor so there's a lot I don't know/understand.  So, what is the necessity of a position capture?  When should I use them or not?  If I understand what you're saying correctly, the joint that is made does not rely on any data from the position capture once it has been made and the position capture can be deleted.  So when is it important not to delete the image capture?  Sorry, a lot of questions there.  If you or anyone knows of an Autodesk tutorial that covers this specifically, please point me to it.  Thanks for your help.

---

[paul.clauss]

Hi @mda

Thanks for sending the file over! I had a look today and found that I saw no joint warnings in your design. Its possible that the deep recompute required when creating a new copy of the file resolved whatever was preventing the warning from being resolved in your original file.

I did notice that running a Compute All in the file triggered a warning in Sketch8 - I believe this has to do with a projection failing to close a profile. The model seems to be rebuilding just fine using cached geometry so, as much as it pains me to see yellow in the timeline, you probably could just ignore either this or the position warning in your file. I believe that breaking the link of the projected geometry and using Extend to ensure the profile is closed would work too, but it may require you to reselect the profile wherever it is used downstream.

The other "band-aid" solution would be to kill the design history and work in direct modeling from this point on - this will resolve any errors in the timeline as the timeline will be completely removed. 

As you seem to be seeing different errors with the position capture, I would try simply deleting the position in your file.

With all of this said, I was able to:

1. Open the file and capture the position (pending).
2. Run a compute-all.
3. Observe the warning in Sketch8.
4. Align the "Bottom Deck Suction - Rotalock to Header Pipe" components XZ plane to top level assembly Plane 12. This straightened out a tiny rotation that appears to have occurred.
5. Observe this did not resolve the Sketch8 warning. 
6. Delete Sketch8, as it did not appear to be used elsewhere.
7. This triggered a warning for Body>Component1 feature as the source was lost - there was no body to select in the top level design to create a component from.
8. Delete the Body>Comp1 feature.

This will mess with the browser hierarchy a bit, but I believe the assembly stays in place in there are no timeline errors. I've sent you a PM with a link and password to download this file. 

This video may help you understand the basics of Capture Position in Fusion 360.  I would also recommend having a look at RULE #1 to avoid the Body>Component command, as well as considering using a Point to Point move when inserting components and following that by creating rigid groups rather than many rigid joints. The videos in my previous post explain this in detail.

I apologize that I can't give more perspective on how the file got to this state - this is one of the larger assemblies I've worked with in Fusion and it is relatively clean with all things considered. I hope this helps!