Joint compute warnings

[Anonymous]

Hi all,

I'm having a hard time with reconciling joint compute warnings in my design.  After digging around on the forums, I locked my sketches which weren't previously fully defined (all black lines, not sure why they weren't presenting as fully defined), tried redefining various joints in the design, and suppressing individual joints to see if I could identify the offending joint, no joy.  Something about the interaction of the "retention link to base pin-slot" joint has caused all of the joints to fail, even when I apply constraints for the sliding movement range of that joint.  This feels to me like I'm just missing something about how joints need to be implemented, maybe I'm using the wrong kind of joint somewhere?  I'd welcome anyone's recommendations as to where to go digging next, and if it looks like I've missed some major block of Fusion360 training, I'd love recommendations on which courses I should complete.  I've attached my design export for reference, and have done my best to abide by rules 1 and 2, pardon the probably bad terminology as MechE isn't my primary discipline.  The intended function of the design, in case it's not clear, is the movement of the lever component moves the catch and catch-hook in and out of the base, and once the catch-hook component has been pushed beyond the base, the retention link pulls the catch-hook vertically.

[jhackney1972 · Accepted solution]

I really do not know what your intended motion is, you seem to not know exactly either.  Take a look at the Screencast.  I suppressed two joints that were tying up the assembly motion.  I also added a Pin-Slot joint to the pin in the slot.  I also added limits to this joint, you will see in the video, to make the piece at the end either flip up or down with the lever motion.  I think the slot is way too long, that is why I put limits on it.  You probably need to put rotational limits on the lever.  Where the big piece on the end pivots, I replaced the revolve joint with a cylindrical joint.  A cylindrical joint gives you rotation but also will allow movement along the pivot centerline just in case it is needed and I thought it was here.  My model is attached with a different name.

[davebYYPCU]

I have checked for misalignment, sometimes the Inspect tool can see it, but double checking, or moving the view window, and remeasuring the same faces it is not there.

@jeff_strater can you check this out, I can find misalignment readings between the pin and the outside of the block face, at random - not always there.

Order of selection does it, and Joints use selection order.

Might help....

[Anonymous]

Thanks, @jhackney1972!  The intent for this thing is to make it easier to lock in a piece of acrylic on the front of my 3D printer enclosure, so pushing that lever towards the catch/hook moves it forward and then up to release the top edge of the acrylic (bottom edge is pivoting on some mounts at the bottom of the enclosure opening.  I've been able to replicate your solution in my design by changing the joint between the catch and catch-hook to a cylindrical joint.  I wonder if the sometimes misalignment @davebYYPCU observed is what drives the need for the additional degree of freedom in that joint (over the original revolve joint)?

@davebYYPCU I'd be curious to know if there's some way to fix that alignment, thanks for poking at that!

[davebYYPCU]

No, I think the problem is well known that if the design has a number of Revolves, changing to Cylindrical, is the fix, unless there is construction misalignment.  Your model is not in misalignment., but does benefit from the Cylindrical fix.

however the Inspect Tool, behaviour has come under notice as well, this file as it was may be helpful to the team looking at it.  Depending on which way I examined the alignments, I was getting these inconsistencies, it took a while to find the repeatable part of the bug.