Inncorrect interation between contact set, joints, and motion joints.

[Anonymous]

I have a model of a cylinder head with an intake and and exhaust valve.  The valve slider joints have limits set with a rest position defined so the valve returns to the closed position after being depressed.  I have a rocker-arm with a contact set between the arm and the valve.  I can move the rocker arm to actuate the valve and then the valve rest returns it to the closed position.  When I add a cam to actuate the rocker arm there seems to be a conflict between the cam-rocker arm contact and the valve rest limit.  If the cam stops in a position where the valve is open, the valve rest limit over-rides the contact set and snaps the valve back to the closed position.

I also run into some problems when I drive the cam through a motion. link.  I added a flywheel assembly to the model which consists of a hub revolutely joined to the cylinder head and a flywheel rigidly joined to the hub.  If I grab the flywheel to turn the cam the cam-rocker arm contact set doesn't work.  If I grab the hub to turn the cam the contact set works.

Finally if I select the flywheel hub revolute joint and use it to animate the model the cam-rocker arm contact set doesn't work.

Thanks

Jim

Fusion 360 2.0.2026 Windows 10

Screencast will be displayed here after you click Post.

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[Anonymous]

Looks like your screencast didn't come through. Can you post it again?

[Anonymous]

This looks very similar to an issue that I (and loads of other people) are encountering since the latest update. Apparently Autodesk is working on a fix.

[jeff_strater]

@Anonymous - it's possible that this is related to a joints issue we are chasing now.  Is this something that started recently?  Would it be possible for you to share your design with us?  We can do it privately, if you don't want to share it publicly. 

The other possibility is that this is a long-standing behavior with contact sets.  To be perfectly honest, contact sets are not all that useful in Fusion.  In fact, I'm impressed that they work as well as they do in your video.  The way contact sets work, it is possible sometimes for each incremental step in the animation to go too far, and actually violate the contact limit.  I've seen this before, which makes me wonder if it might not be related to the issue that @Anonymous is referring to.

[Anonymous]

@jeff_strater  thank you for your reply.  I just started using Fusion 360 , so I don't know if this is something that has started recently.  The model is based on copyrighted drawings, so I don't think I can share the models publicly without violating the copyright.  How do I share the model privately?  I've seen the recent problems mentioned by  @roach374 in a higher level of this assembly, but I think the problems here are different.

I've tried to get rid of the rocker-arm/valve contact sets by using a motion link between the rocker arm and the valve, but that causes the valve slider joint rest limit to stop working.  With the motion link I tried moving the joint limits from the valve slider to the rocker arm revolute joint, but that did not work either.  I think I have read about the motion link/joint limits problem elsewhere.

Also the contact sets in the intake and exhaust valve sub-assemblies are not being transferred to the top level assembly and I have to redo them.  However this may be a problem with my modelling rather than a bug.

You probably already have thought of this, but could you improve contact sets by assigning them at the surface level rather than the component level?

Another feature that would help in the situation I have is a non-linear motion link.  Then I could motion link the cam to the rocker arm and valve and get rid of the contact set.

Thanks.

Jim