Ball Joint - Makes 0 Sense

[AdamantiumFX]

Hello!

So I started what should have been a 30second job, and after 3 hours of googling, reading, moving axis, moving components and all sorts I'm still non the wiser. I found the "Mysteries of ball joints" which covered in depth the maths and goings on, but has in no way helped me to actually get it working.

So, the task is to get the ball of a rose joint/rod end bearing to rotate in its housing.

The joint snaps into place fine,  until I come to add limits of 15deg to pitch and yaw, whilst leaving the roll to free rotate. This is because Roll is mapping to the same axis as pitch, and overules the 15 degree limit. If I add limits to both axis  and find that it cant return to centre and it just gets messed up. 

I origonally was using World X as up, but changed this to Y becuase I hoped that would help, it didnt.

With the current layout, I want to roll around the Ball Components Y axis, but whatever I do, Roll always is the same as Pitch, even if I map custom pitch and yaw axis. Why isnt there a way just to specify Roll? This seems obvious and nessesary...

Link is here:

https://a360.co/2X0GIiB

(I read the bit that XYZ of the joint dont relate to XYZ of the components, they are just named the same to confuse you). 

If anyone can explain how to get this to work (prefeably without citing maths or coding) I'd really appreciate it. Fusion is driving me nuts at the moment.

[jhackney1972 · Accepted solution]

You have to specify a Roll joint limit also to control it.  If you do not then the others, Yaw and Pitch, lose their references.  i found 15 degrees to be a bit much if you want to keep the ball flanges from hitting the race.  Take a look at my Screencast.  My modification to your model is attached by a different name.

[AdamantiumFX]

Hi John

Thankyou for going to all the effort of putting together that video, I very much enjoyed your accent.

So I've done what you said and it works! Hurray!

But the concept still makes 0 sense. 

So what we have done is lock the 3rd axis off? Which means if I want my ball joint to be able to roll side to side, I would need to specify a revolute joint between the Ball, and the bolt that holds the ball down?

Is it just me or is it odd to have a 3 axis joint that only moves in two axis and that has to be set up in a very specific way in order to work? This seems very unintuative interface design to me no?

Anyway, thank you for your lovely video and the help!

[AdamantiumFX]

OK Update.

I just tried the whole process from scratch to see if it was repeatable. I reset to my prefered "Z is up" (Is this relevant?) and rebuilt the joint, but now Pitch is yaw, Yaw is roll and setting Roll limits to 0 locked off my actual Pitch movement, leaving me with a single axis movement. Please see the 4mb Video attached (sorry I have yet to get into screencast)

I then started again, drew a sketch in the middle of the ball to match the components X/Y/Z axis', and built the joint again, this time specifying my pitch and yaw axis. I set limits, and yay, it works.  Please see 24mb video

So is this seriously the right way to do this? I cant click on the Ball origin axis without drawing a sketch first?

[jeff_strater]

@AdamantiumFX - "Z" up vs "Y" up won't make any difference here.  I think "makes 0 sense" might be a bit of an exaggeration, but I understand the frustration.   Here is another good discussion about Fusion ball joints, and "gimbal" vs "Euler" formulation for that joint type:  scratching-the-ball   Ideally, Fusion should support both kinds of ball joint, IMO, and eventually I think we will get there.

[lure23]

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@AdamantiumFX wrote:

Is it just me or is it odd to have a 3 axis joint that only moves in two axis and that has to be set up in a very specific way in order to work? This seems very unintuative interface design to me no?

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Definitely you're not alone. 

I came here in order to finally file a bug report on the inability to control the three dimensions of a ball joint, individually. And here I read that it's due to some mathematical formulation working as intended, from the Makers point of view (programmers, product managers).

The problem is that Fusion 360 is intended for beginners. They get frustrated, and CAD seems hard - when it should not need to be.

I won't file my bug report (had captured a screencast and everything), since likely it makes no difference. I now know to set one dimension to 0 and think that there's not really ball joints, in the program. Fair.