Joint Stretches when Rotated

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  08 August 2017
Joint Stretches when Rotated

Good day!

I have a spine that rig in FK with three joints. However, I wanted the middle joint to only affect the top joint only by Rotation. So rather than a hierarchy (bottom>middle>top), I used a parent constraint tag. Here is the problem: When I start to rotate, the top joint stretches for some reason. Here is a video illustration. If you want to see the illustration file, you can check it here

Is there an option I am missing out? Thank you.

P.S. I still need the middle joint to adjust in Translate position (but again not affecting the top joint). This is a bit of a nonstandard as almost all FKs are constrained through rotation, but I kinda like it that way.
 
  08 August 2017
Originally Posted by ugrens:

Hi Ugren. Thanks for the reply. I tried that but that will rotate the top joint in place. I need the top joint to rotate as if it was included in a hierarchy.
 
  08 August 2017
You could start to check out the spine from the simple Rig in character object. It is what you want and uses the restriction tag and determine features there and also in the constrints
 
  08 August 2017
Originally Posted by ceen: You could start to check out the spine from the simple Rig in character object. It is what you want and uses the restriction tag and determine features there and also in the constrints
Hi. Thanks for the reply. I tried checking the pre-existing rig in the Character Object beforehand both the Simple Biped and the Advanced Biped. But they are either purely FK or purely IK.

As stated above, my approach is a bit nonstandard. As such I cannot find a readily available solution.
As a recap, there are three FK controls (bot, mid, and up). But the trick is that Mid only affects the Up by rotation. Mid can translate freely without moving the top.
 
  08 August 2017
Hi,
the advanced Biped has an IK/FK switch for spine is implemented so both is there. Are there any reasons why that unusal rig is needed when proven setups are just 3 clicks away?

In the Advanced Biped:
- Build Root and spine and make them editable for changes
- FK/IK switch is on Torso_con+
- Now delete restriction Tags on every FK_Spine_con+ you want to move
- Go to the FK_Spine_int joints and add Position in the constraint tags (is disabled by default setup)

You can now move the FK con+ with the joints in all axis. Is that what you want?
Problem is when switching to IK the joints go back to IK position and do not stay in FK pos. You would need custom xpresso setup with cycle value funtion to read and translate poisition of joints between IK and FK if even possible (I've never build sth. like that)

Cheers
 
  08 August 2017
Originally Posted by ceen: Hi,
the advanced Biped has an IK/FK switch for spine is implemented so both is there. Are there any reasons why that unusal rig is needed when proven setups are just 3 clicks away?

In the Advanced Biped:
- Build Root and spine and make them editable for changes
- FK/IK switch is on Torso_con+
- Now delete restriction Tags on every FK_Spine_con+ you want to move
- Go to the FK_Spine_int joints and add Position in the constraint tags (is disabled by default setup)

You can now move the FK con+ with the joints in all axis. Is that what you want?
Problem is when switching to IK the joints go back to IK position and do not stay in FK pos. You would need custom xpresso setup with cycle value funtion to read and translate poisition of joints between IK and FK if even possible (I've never build sth. like that)

Cheers

Sorry for the late response.

"Are there any reasons why that unusal rig is needed when proven setups are just 3 clicks away?" I was under the impression that the given illustration is easier to understand and thus easier to solve.

Thanks for your suggestion in tinkering the advance biped, but i still got the more or less the same problem.

You can see the video here based on your recommendation:https://www.dropbox.com/s/8uxsqeek4...tation.mp4?dl=0
The illustration file also based on your recommendation can be seen here:https://www.dropbox.com/s/avq0szqop...tation.c4d?dl=0
 
  08 August 2017
Hi there,
this isn't a very common way to go with it. But it seems the issue is without the Position, the Frozen rotation basically rotates around the parent's pivot point, which is at the base of the spine.
Making a parent null positioned at the midBack seems to produce the desired results. Feel free to test if it has any other side-effects:
https://www.dropbox.com/s/rw1a1mfos...y_root.c4d?dl=0
 
  08 August 2017
Originally Posted by 51M0N: Hi there,
this isn't a very common way to go with it. But it seems the issue is without the Position, the Frozen rotation basically rotates around the parent's pivot point, which is at the base of the spine.
Making a parent null positioned at the midBack seems to produce the desired results. Feel free to test if it has any other side-effects:
https://www.dropbox.com/s/rw1a1mfos...y_root.c4d?dl=0
Interesting! Thanks for sharing the file. I haven't tested out on a full rig yet as I am waiting for the mesh to come in but it worked out fine on my end. Never thought about having a dummy parent null would solve the problem. That's definitely a nugget for me. Thanks again!
 
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