Bidirectional setup for the joint chain

[stass3d]

Hi All!

I`ve a question.

Is there some way in Houdini to setup a bidirectional setup for the joint chain. Like in Motion Builder.

For example, I want to move a arm controller, and if it goes farther as a staight arm, the spine joints go with it.

If i move a spine, the arm become moving with the arm controller.

Any ideas?

[jrgauthier]

I really wish you get a positive answer for that question!!

[stass3d]

Lets try to find the answer!

I think - this could be a very cool solution!

[ofer]

Hi,

Try something like that, for moving the arms IK controller with after the body, when the arms are stretched (I hope I understood you correctly):

The IK end affector shoulder be parented to a blend object, which blends between the control NULL, and another NULL which is parented to the spine's tip. The blend weight will be some expression

involving the distance between the arm's root, and the chain's end. Like when doing stretchy IK. If it equals or bigger then the sum of both bones lengths, the arm is straight and you should blend over to the 'spine tip NULL',

other wise, you should blend over to the arm controller. I think this solution will create a 'jump' when the arm switches parents, but I also think this is a good base for the exact solution. So with some tweaks to this setup, it might work.

The same for the other way around, except then you might want the spine to bend, and for this you'll need to setup some expressions or another IK chain maybe.

I hope Im sending you in the right direction...

Good luck.