More Joint Confusion

[Anonymous]

Every time I think I've figured out joints, they prove me wrong...  In the attached assembly, I have an air cylinder that drives a ratchet mechanism.  The position of the air cylinder body is adjustable by a pin-slot joint, which is attached to the nose of the air cylinder.  A clevis attaches the air cylinder shaft to the ratchet wheel.  I can get all but one of the joints to work as I want, but whenever I try to enable all of them, I get conflicts, but I don't understand how to set the joint properties to make it work correctly.

In the attached design, the ratchet wheel is locked, and the pin-slot joint refuses to resolve, apparently, at least in part, because the position of the "swivel" piece relative to the air cylinder is wrong, and that position seems adjustable only by entering a hard distance into one of the offset settings of the joint.  Shouldn't it be willing to set that offset to whatever is required to resolve the revolute constraint already in place between the air cylinder and the swivel?

Regards,

Ray L.

[TrippyLighting]

The joint between the cylinder and piston should be a slider joint, not a cylindrical joint. While a cylindrical joint would be how this works in reality, it just requires Fusion 360 to evaluate one more degree of freedom and for cases such as this it is not required and just wastes computing resources.

In the main assembly it is the pin-slot that causes the over constraint. The pin-slot joint has only 2 degrees of freedom and no vertical float. When you create the joint between the cylinder and the swivel the assembly will complain. I created a cylindrical joint between the Ratchet and the Ratchet pawl to provide that additional vertical degree of freedom.

That prevents the assembly form locking up.

Then I apply a vertical offset to the pun-slot joint so the Ratchet Pawl is in the correct vertical location.

[Anonymous]

OK, so if I'm following correctly....  You used a cylindrical joint (rather than the revolute joint I had) to attach the pawl to the wheel.  You then measured how far out of line the pawl was from the wheel, and applied that offset to the pin-slot joint to get things lined up correctly?

Regards,

Ray L.

[TrippyLighting]

Yep. That's it.

[Anonymous]

Well,  I thought that was what I did, but it doesn't quite work, and I can't figure out why.  See attached model.

Regards,

Ray L.

[Anonymous]

Anyone???

This issue still has me confused.  I have worked around the issue by re-designing but I'd still like to understand what's happening with the above model.  It seems like there are positions mid-travel where the constraints conflict, but I don't see why, and I'm certain the physical mechanism would work perfectly.

Regards,

Ray L.