Revolute joints randomly freeze up

[Noah_Katz]

I have a machine design with many revolute joints that sometimes work and sometimes don't.

Sometimes exiting and reopening the design frees it up.

One time I got it to work by grounding one of the components, which is itself attached to a grounded component, but that won't always be possible without violating the design intent.

Sometimes if I redefine the joint limits to a position that it's not currently in it will force it to move and free it up.

Right now that's not working and I'm pretty fed up with the whole situation as it's frequent and time-consuming (for recalculation).

Are there some guidelines I should know about?

Link to model: https://a360.co/2r2hlvZ

Right now I'm wanting to pivot the red roller down but I can't.

[Anonymous]

@Noah_Katz

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@Noah_Katzwrote:

Are there some guidelines I should know about?

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Hint: for a stable model it is a good idea to avoid warnings and errors.

I did a "Compute All" and got this:

Especially warnings for joints are not helpful for clean kinematic calculations.

Example:

[Noah_Katz]

Easier said than done 🙂

I'll try deleting and recreating them first, as it could take many hours going through and fixing them all.

I know it's not good practice, but this is a one-time design that I'm almost finished with and I want to get to making parts.

Would it be correct to assume that rigid joints between components other than the ones with troublesome revolute joints are unlikely to be part of the problem?

Thanks, @Anonymous

[Anonymous · Accepted solution]

@Noah_Katz

Just my personal opinions:

1) Don´t ignore warnings, do something immediately to correct the model/sketch. If you ignore them, it´s getting worse and worse.

2) If you apply a workflow assembling parts with joints only, there should be no reason for any "capture position" oder "move" operations left in the timeline. I might capture a position to create a joint - but after joint creation my next step is to delete the  "capture position".

3) rigid-joints part of the problem? Maybe. I suspect that the Fusion solver algorithms don´t like rigid joints with missing joint-origins for both components.

for example:

[Noah_Katz]

I now (I started the design with much less experience) try to delete Capture Position operations, but sometimes that causes a lot of other features to turn yellow or red.

Rather than spend hours trying, and perhaps failing,  to fix them all, I leave the Capture Position.

Speaking of Capture Position, do you know why it pops up when I edit sketches?

It's annoying to have to chase the sketch all over the screen if I say Continue.

Good point about those rigid joints, I'll investigate.

What drives me crazy is that the joints seem to go bad without provocation, like when I edit a sketch of an unrelated component.

[Noah_Katz]

Hmm, perhaps deleting the Capture Positions causes problems because the joints are bad...

[Anonymous]

Sorry, obviously I used the wrong wording regarding "capture position" - causing a misunderstanding (English is not my native language). 

My intention was not to suggest that you should delete them in your specific example. It requires a workflow where you position all the components with joints in a "clean" (proper?) way. That was meant as a hint for a future project - not for the current one.

Sorry again.

[Noah_Katz]

No problem.

I'm working on fixing the joints now, and so far five were not really bad.

What I mean is that the warning said a reference was lost and to edit the joint, but when I did there didn't seem to be anything wrong.

So I exited the form and the yellow warning shading went away.

I wish we wouldn't have to fix things that aren't broken.

[Noah_Katz]

Interesting, starting at the beginning of the timeline and fixing joints made later ones go from bad to good.

Revolute joints are working nicely now.

[Noah_Katz]

The cure is not quite complete.

No joints show warnings now, but as shown in the screencast, I cannot move the tensioner pivot unless I lock the main pivot joint.

Even before fixing the joints, sometimes I was able to do this.

@Manfred.Steinbach, any idea what the problem could be now?

[Noah_Katz]

let me try inserting that screencast again

[Anonymous]

@Noah_Katz

I can only guess because I have no access to your current model.

In my user-experience the "drag components with mouse" mode has its limits if the kinematic relationsships (kinematic model) are getting more complex. The use of "drive joints" gives you a better control - if the model then shows the expected movement, your joints should be ok.

Maybe you can try to control the (complex) kinematic movement with motion-links?  Or use motion-study, where you can alter the values of several joints for an (controlled) animation?

[Noah_Katz]

Link to model: https://a360.co/2r2hlvZ

I don't really want or need to relate the individual motions.

[Anonymous]

it appears to be the same model that you posted before, same warnings and errors

[Noah_Katz]

@Anonymous

Oops, sorry, forgot about this.

I thought the link was live; when I made a new one, it was the same.

Maybe it just looks the same but isn't.

Anyway, everything works fine after cleaning up the warnings.

Thanks again.

[Anonymous]

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@Noah_Katzwrote:

@Anonymous

Anyway, everything works fine after cleaning up the warnings.

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Great! Glad to hear it worked. Thank you for the feedback.