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Assembly- Ball Joint- Degrees of Freedom
warren_pegley
Member Posts: 14 ✭
https://cad.onshape.com/documents/3fd38eba6a0f8034f45c6045/w/ef56e87ef6df24d331817d22/e/a0b5fd9b95974e5ebdf3e38c
Hello Onshape
If you were able to limit the degrees of freedom in the Ball joint assembly function there would be beneficial added realistic design functionality, such as shown in the attached document.
In this example chain is modelled, Restrained with Ball Joint & Pin slot (limits only 2d). There really needs to be a ball joint limit with 3d rotational restraints.
Hello Onshape
If you were able to limit the degrees of freedom in the Ball joint assembly function there would be beneficial added realistic design functionality, such as shown in the attached document.
In this example chain is modelled, Restrained with Ball Joint & Pin slot (limits only 2d). There really needs to be a ball joint limit with 3d rotational restraints.
0
Comments
It's been 20 years since I've studied linkages so I'm a little rusty. I remember something about 3 angular degrees of freedom not being solvable implicitly and you have to iterate for a solution. I never realized you don't have limits with a ball joint. One of the rules of Onshape is that its state is always solvable implicitly, since this can't be solved, then it ain't there. I'm probably wrong.
An assembly on the other hand does solve inverse kinematics and I enjoy trying to break it. Currently it's beating me solving things more often than not. I really like Onshape's assemblies.
This is my link. I'm going to stack 3 rotates to mimic your ball joint. This will force the assembly to solve the 3 angles vs. the mate trying to solve 3 angles:
This is an assembly of a moving link. There's a lot to it, there's 2 revolves with the 3rd coming when assembling in the higher level assembly:
Here's my top assembly which takes in moving links. The cool thing about Onshape is that lower level assembly mates are inherited forming the the chain:
If you look at my public version of your document, you'll see that I got the limits working. I'm not sure that's actually a chain's motion and feel that it's a contact problem (or in older terminology, physical dynamics).
I can't edit your public document, so I had to copy yours and then make it public. We now have 2 public documents:
https://cad.onshape.com/documents/ba73f8d2b388740e6a8cbec9/w/bef7c1074dba7d862b8318bd/e/a0f9f075c22a76a42a445d5b