F360 Interference Glitch

[dkorchagin]

I come across an issue with interference analysis. I have two components in two separate models, each assembled of a number of parts, also stored in separate model files. When I do interference analaysis in each of those sub-components F360 shows pretty fine detection of interferences. However, when I try to do the same on the final assembly, containing those two, analysed well in separate, I get a very strange picture.

Even without any move, as I insert second component having the first one grounded, I get a picture that I cannot understand. Please take a look at the attached screenshot.

Can you explain this behaviour?

Then, as I positioned and joined components together as they should be, I get yet another strange picture, shown below:

I remember when I was working with the first assembly I inserted the part, which created the red colored interference, and slightly moved it to the position of then created interference. The correct, and actual, position of the part is depicted with the grey color. So in place, where F360 shows the interference, there's no what it thinks interfers with the second sub-assembly (inserted in the first one, T-shaped).

Is it possible to work around this, or what are hygiene rules I might have violated assembling those two?

Still, the first screenshot looks very strange to me..

[dkorchagin]

I am now pretty sure the strange behaviour I observe has the only reason: it "remembers" the original position at which a component was inserted regardless of how you move it afterwards. The test steps:

1. Create a component, e.g. a bar in one model
2. Create another bar in a separate model
3. Create an empty model where you would "assemble" those two bars
4. Add the first bar and ground it
5. Add the second bar and move it around so it would not interfere with the first bar
6. Create a rigid joint between the two (e.g. set the second bar by one of its sides to a side of the first bar)
7. Create a third bar in a separate model
8. Create an empty model where you would assemble the final model
9. Add the previously assembled model created on step 3, and completed on step 6 and ground it
10. Add the third bar and move it around to the place where the second bar was on step 5 (it's expected it wouldn't interfere with anything else, because the second bar is expected to be settled on the first bar.
11. Now run analysis->interference on the model created on step 8, and select sub-assembly component added on step 9, and the third bar
12. See the magic of having second bar interfering with the third one, despite it's resting on the first bar and has nothing to do with the position where the third bar is located.

Screencast is coming..

[dkorchagin]

Here's the screencast..

[Phil.E]

@dkorchagin

Thanks for the post. This is a known issue.

(Internal reference FUS-32035)

Regards,

[dkorchagin]

@Phil.E, thanks for letting me know. Is there any way for me to access your internal bug tracker to see details, or can you tell when the fix is going to be released please?

[Phil.E · Accepted solution]

Sorry but no we don't expose the bug tracking system. Also, it's not clear when this will be fixed at this time.

I put the reference number so that when other community members find this and enter comments we can link it back to the bug report.

Sorry for the inconvenience, I have asked for a higher priority on this bug now.

Regards,

[dkorchagin]

I also observed that if I break the link of the referenced component which was causing the issue, it's gone. Not sure if it helps but anywise.

[dkorchagin]

Thanks for raising priority as the issue makes interference analysis completely useless on complex assemblies. And complex assemblies is where it is supposed to bring most value.

[dkorchagin]

Yet another observation, seems obvious, but I post it just in case. If you place all the components in one flat assembly, i.e. no sub-assemblies inserted as components into another sub-assembly, etc., the interference analsysis works fine. However, making flat assemblies just to eliminate the issue, also eliminates the value of assemblies 🙂 sort of repeating myself..

[dkorchagin]

@Phil.E, sorry for bombarding you, but I've also accidentally discovered that components' origins remain in initial position where they were inserted despite the component moved to a joint position. I think this is related issue, i.e. analysis logic considers coordinates of the origin, which remained intact, however bodies were moved.

I think it can be easy fix if the only problem is to move the origin along with the bodies, i.e. capture new position, so the logic then would correctly understand where the component is located. Please see the screenshot illustrating the issue (I forgot to turn off the origin in the component model and that became apparent):

[Phil.E]

What you are seeing is the assembly origin, after you have moved a sub component with a joint. This is expected. All assemblies are "flexible" in Fusion, and thus if you insert an assembly that is not fully constrained you can see the individual components move relative to the inserted assembly origin.

In your source assembly you can try using an As-Built joint between the parts and the root component. This should lock the parts to the assembly origin when you use them as inserted assemblies.

Thanks for all the info, we are looking into the problem with interference preview and will report back here when we think it's fixed.

Regards,

[dkorchagin]

Hello @Phil.E,

Just to make sure we are on the same page. Below is the full picture showing the origin of the main assembly, and origins of the inserted sub-assemblies, which I expected to move along with their respective components. Am I not right to expect that the origins of inserted sub-assemblies should be expected to move with the components as they change their position because of joints and other movements?

What's the intention of not moving the origins? It doesn't seem logical to me..

[Phil.E]

The reason for this is called "flexible assemblies". In other CAD applications it is always assumed that inserted assemblies are "rigid". In Fusion 360 they are assumed "flexible".

Think of this example:

You wish to insert a hydraulic ram into your design in several places. It should be the same assembly in each case, but the parts will be in different positions (sliding in and out) in each instance. Flexibility allows this.

This concept includes the origin of your inserted assembly. Unless your parts are tied to it in the source assembly, the origin is flexible relative to the parts.

Open the assembly you are inserting (the source assembly), turn on the root origin visibility.

• Can you drag the parts relative to the origin?

There is one exception:

• Grounding is only honored in the source assembly. Grounding can't be honored where the files are inserted.
• Using a As-Built (rigid) joint to tie the part you would normally "ground" to the root component is preferred.

See if any of this helps.

Article:

http://help.autodesk.com/view/fusion360/ENU/?guid=GUID-83CC75E4-B382-4C29-9352-F6E662BB8CB8

Autodesk University Master Assembly class

http://au.autodesk.com/au-online/classes-on-demand/class-catalog/2016/fusion-360/pd19577#chapter=0

Thanks,

[dkorchagin]

Thank you very much for the explanation.

I understand the concept of flexibility, how parts move related to each other and so on. However, I am not quite convinced that it's right to have the origin of assembly resting a few meters away from all of its parts moved because of alignments and other manipulations.

Parts of the hydraulic ram you were referring to likely have limits applied to restrict their movement within construction boundaries, and there's normally some grounded component, very likely aligned to the origin of the ram assembly. In that case, it seems much more logical for the origin of the sub-assembly to move along as you pull it around. Think of a real world, in which when you receive an assembled ram from a manufacturer, you look at it and know its coordinates right before you, not at the plant it was first inserted in the world, right? 

I already had a few confusing cases, where I was puzzled of where the origin had gone and then found it far far away from the place I expected it to be. Also when you assemble parts in a different model without taking care of where the origin is relative to the parts you insert, when you then insert that sub-assembly in another model you can be surprised that it's visually aligned not to the origin of the assembly you are making but floating somewhere outside of the camera sight. Then you drag it closer to the place you want, align it, and voila you instantly create a mess so that you cannot tell where all those origins of all the parts you inserted are because they start to live their own lifes.

Anywise, I see now that the origin of the sub-assembly has nothing to do with how interference is computed, but still I think it's worth paying attention to keeping origins aligned with the grounded part of the component as in the original model, so when you pull any part of the subassembly (except for those flexible, i.e. not joined) the origin of the sub-assembly should follow the grounded part to keep original alignment.

I hope you know what I mean, sir.

[Phil.E]

Thanks for the feedback. That is why you should, if desired, tie the source assembly components to the source assembly origin. That solves the problem instantly.

Thanks,

[dkorchagin]

Yeah, that's what I learnt. However still, if the origin of the subassembly won't move along with the sub-assembly (its rigid part(s) at least), eventually it may be lost, especially, if you make a relatively large assembly, and decide to shufle stuff around.

[Phil.E]

Actually, perhaps you misunderstand me.

If the assembly you wish to insert has one part tied to the root origin with a Rigid - As - Built joint:

When it's inserted into another assembly, the root origin will travel with the parts if you move them. Are you finding this is not the case?

[dkorchagin]

Are you saying that instead of "grounding" the part I should rigid as-built-joint it?

[Phil.E]

Yes. Sorry, I should have been more clear. This advice is for assemblies that you intend to insert into other assemblies.

• Grounding is only honored in the source assembly. Grounding can't be honored where the files are inserted.
• Using a As-Built (rigid) joint to tie the part you would normally "ground" to the root component is preferred.

This is all covered in the assemblies master class from Autodesk University, it's one of the links above.

Regards,

[dkorchagin]

That is a great advice, thank you very much! I've just tested - worked like a charm! 

Unfortunately, it didn't magically solve the interference problem so looking forward to seeing interference solution soon! 

Rushing to watch the master class right away..