Gimbal Joint aka. Fusion's Ball Joint

[MichaelT_123]

Hi TF360,

The topic of the Ball Joint and its implementation in Fusion has been a frequent source of frustration, as evidenced on The Forum, and I suspect it is even more so, although it has not been directly pronounced here.

Without draining my liver bile further, and reiterating the issue, please refer to the following posts.

https://forums.autodesk.com/t5/fusion-design-validate-document/scratching-the-ball/td-p/7567779

https://forums.autodesk.com/t5/fusion-design-validate-document/spherical-joint-and-golden-hind/m-p/1...

I am sure that the search on The Forum will supply ample thoughts to digest.

I am bringing the issue once again ... because I stumbled upon it once again ... where the Gimbal (Ball) Joint causes significant implementation obstacles, while the Spherical Joint (XYZ rotation) would offer a TRIVIAL solution.

So, here is the question for TF360...

Are there any plans to bring the Fusion kinematics toolset to the modern CAD standards?

Regards

MichaelT

[TrippyLighting]

I've reposted the question  with a link to this thread on the Fusion EE Slack Channel. 

We'll see what response we'll get.

[kgrunawalt]

You can use the new point-point constraint if you don't need a solution that controls motion via parameter values.

If you need to drive motion using 3 angles, you are stuck with possible gimbal lock. There are a number of Euler angle combinations and we could allow the user to choose. They have different pros and cons. The one we choose has some nice pros with respect to adding limits, but it has cons too. It is not old fashioned. There is no magic 3 angle solution that avoids gimbal lock. As far as cad standard goes, systems often provide a euler angle choice which we could do not currently. Maybe one of the choices, like xyz vs zxz, would answer your needs. For some it would not so the solution is to provide a choice I think. These choices always include rotations that provide gimbal lock.

The alternatives like quarternions or rotation matrix values have angle-related values that will be meaningless to designers without a calculator.

[kgrunawalt]

See this maya related video for a great discussion.
Fusion uses a gimbal for the ball joint so you can be precise with 3 angle values.

We chose ZXZ because it has great limit and rotation behaviors for joy-stick like rotations -- fairly common.

But there is no perfect choice. We could use XYZ (Tait Bryan euler angle choice). It is not in gimbal lock from the start but it has less useful limit and rotation behavior for many applications.

https://www.youtube.com/watch?v=XCh-yEkHPMo

[kgrunawalt]

In this old fusion video, you can see the standard ZXZ fusion ball joint on the left has nice rotations for the joy stick. Fusion joints align coordinate systems where Z axes are aligned, so ZXZ works nicely, but it is in gimbal lock right away! This is not so nice, but it is easy to resolve with a rotation if needed. The other ball joint on the right is a ZXY Tait Bryan euler ordering which is not in gimbal lock initially but it has less attractive behavior in this particular case.

But for some ball joint applications, you may not want the ZXZ behavior. That is where a rotation order choice would help.

[MichaelT_123]

Hi Mr KGrunawalt,

Thank you for the input into the discussion about my liver indigestion. Your suggestions are solid, have some soothing effect ... but do not address the causes of the symptoms.

Just as ... shoot in the arm ... we all remember. 

I can cope with the mathematics of juggling between Euler and Cartesian coordinate spaces ... but such necessity (being in Fusion environment) is the GREAT, GREAT, GREAT inconvenience. It is also beyond the capacity of many.

Thus, I HAVE A DREAM ... that one day TF360 announce a new Fusion release with a Spherical Joint implemented on both UI and API levels.

Regards

MichaelT

PS.

... on the unconnected subject. Typing your name (nickname), I was struck by its similarity to the event that happened in 1410 AD - the Battle of Grunwald.

On which side have you been fighting?