Ball Joint Mysteries

[Anonymous]

I think I understand ball joint motions but I don't understand how to set them up, install them correctly, orient them or change them.

My goal is to animate the mannequin's arms (see below) to imitate the corresponding motions of the mechanical wings (second image) but I'm not making much headway.

I don't understand the dialog boxes, the animations or the joint-flags. For instance, in the "edit joint limits" dialog box, both the Pitch and Roll animations seem to show exactly the same motions, i.e., rotation about the long axis of the arm. I can't get  simple sweeps of an arm without some twisting action being thrown in and sometimes some bending at the elbow and/or wrist. There are strange jumps when joint limits are exceeded and sometimes an arm snaps back to its starting position (or some new position) and sometimes not.

I've had some success by creating a rigid group between the mannequin's left hand and the haptic interface handgrip (third image) but the motion is severely limited and temporarily crashes the program when limits are exceeded.

Clearly, I need some help. Are there any Screencasts or other instructions out there that might explain how all of this works?

I've attached the mannequin's .f3d file.

 

 

[MichaelT_123]

Hi Mrs Kgrunawalt,

It is the helpful verbose and graphical explanation of tricky and not always too intuitive movement as represented by the class of Euler's joints.

I have encountered quite a difficulty dealing with them (still do). 

https://forums.autodesk.com/t5/fusion-360-design-validate/scratching-the-ball/m-p/7567779  

Perhaps, to ease mine (and others) anxieties could you please answer the following:

- Is there an API method or the external procedure to convert standard rotation matrix3d into Euler angles?

  Addressing only one  - 'ZXZ' axes configuration (amongst 24) would suffice. 

- Is there any prospect of having the additional joint type ( I would call it a spherical joint ) matching rotation schema already implemented in matrix3d objects?

Regards

MichaelT

[trevor.jack]

Perhaps this has been covered elsewhere and it is too late to reignite this topic. But this is the closest I've found to anything useful. Not being able to resolve it has cost me several hours so far.

I can't get more than 2 degrees of freedom into a ball joint.  I've created joint origins on each component then made the ball joint.  When editing the joint motions, pitch and roll show rotation about the same axis. Given the ZX'Z'' implementation, it's not clear what pitch, roll and yaw mean in this context. Is there a definition/specification? Do they refer to the fixed joint origin or sequentially to the origin as rotated by earlier rotations?

My screen capture doesn't capture the dialog box (a different window) so a recording showing the above behaviour is not much use. How best to illustrate the problem?

I effectively have a tie rod end (it's actually a quite complicated traction kite arrangement with the ball joint modelling the tow point connection of the kite lines to a vehicle). With the two degrees of freedom that are available, I can position the tie rod end at any angle - so it can point to any point on the sphere. But as the tie rod (in my case a kite) is not symmetric about the radius, I need to show how that rotates. Is this possible?"

[TheCADWhisperer]

---

@trevor.jack wrote:

Perhaps this has been covered elsewhere and it is too late to reignite this topic.

---

@trevor.jack 

It would probably have been best to start a new discussion thread with a link back to this thread for reference.

In any case,

Can you File>Export your *.f3d or *.f3z file to your local drive and then Attach it here to a Reply?

[trevor.jack]

Thanks CADWhisperer.  
KOASv9.f3d attached.  Note that there are 2 versions of the ball joint.  The first (in the timeline) is suppressed.  The 2nd was created from two explicit joint origins - that didn't help. Neither allows the 3 degrees of freedom I seek.  I suspect there will be a very simple solution...but I've not found it.

[jhackney1972]

In the attached video you will see that I drive all three axis independently by locking two of the axis and then driving the third.  I repeat this until all axis prove they are working.

[trevor.jack]

Thanks John.

I'm afraid I can't reproduce what you do. I also can't capture a video that includes dialog boxes. (I see from another discussion that you use Techsmith Snagit. I'll see what I can sort out for future use. For now, attached are a few images.) If, having locked all 3 axes, I select "drive joints ", there are 3 "handles" that can be used to drive orientation. But 2 of them produce motion about the same axis. This is in fact the same as your video shows. The axis of rotation in your video for both pitch and roll is the same. Can you do an example where you sequentially move about the 3 axes? As my application is for a boat, I'll use the conventional meaning of roll, pitch and yaw (they seem to have arbitrary meaning in Fusion 360). I'd like to be able to position my kite (ball joint) by specifying roll, then pitch about the new pitch axis (ie after the specified roll) then yaw about the new yaw axis (ie after the specified roll and pitch motions). Is there not some way to do that? (BJ_AllLocked.png)

If I unlock one degree of freedom (roll in my example) I can change the other two degrees of freedom from the drive menu. (BJRollNotLocked.png)

Edit (20231109):  That 2 axes are aligned (ie rotation about each of 2 of the canonical axes gives the same motion) may have something to do with kgrunawalt's discussion of the ZX'Z" implementation. That is, if Z and X' are at 0, then Z'' maybe aligned with Z. Having reoriented one of the joint origins, so that z axes are not aligned, rotational behaviour is slightly better - I'm still working with it to see if I can do what I need.  But I've run into another problem.  While trying to set up one of the joint origins, I get the ReOrient.png (attached) dialog box.  I'd like to reorient x.  But there seems to be no way to select it. 

[MichaelT_123]

Hi Fellows,

The selection of compounded joints and, in particular, a ball (gimbal) joint is still, after years of F360 development, a subject of contention.
I have had my say about the issue already; however, as evidence shows, it is without visible effect.
Nevertheless, why not try again as the situation becomes so critical that people... can’t rock a boat?!
Hence, I will scribe something about the subject within a couple of days. It will be a separate post with the title starting with capital S.

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

Regards
MichaelT

[DavidFawkes]

It would be good if there was a tutorial video on this subject please. It seems to be the one problem I have had with Fusion, everything else so far has been intuitive.  

[MichaelT_123]

Hi Mr DavidFawkes

Consider ... looking at:

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

You might find some useful info there.

Regards

MichaelT