Controller which ignores parts of IK Chain (R13)


#1

Hello all,

I’ve got a simple IK humanoid rig. The thigh, knee, and ankle joints are under the IK influence, and the leg is a child of the lowest spine joint (where the pelvis is).

Everything works grand - moving the ankle goal does as expected, moving the pelvis moves both IK legs accordingly.

What I’d like is another controller on the pelvis so that, if the character is on its knees, the new pelvis controller can be moved so the knees stay in position (as they are on the floor) and only the thigh joints move with the hips.

Any advice on how to set up the constraints would be appreciated. Or, if I should have set the rig up differently with that goal in mind…I’ll be grateful to hear that too.

I can’t upload attachment yet, so here’s a picture. If I move the Hip joint the knees adjust, which I’d like to prevent without abandoning IK, thus trying to figure out a constrained Hip controller.


#2

RE: if the character is on its knees, the new pelvis controller can be moved so the knees stay in position (as they are on the floor) and only the thigh joints move with the hips.

I think what you are after is a lock feature. See illustration below:
https://www.dropbox.com/s/3wbkdsvuq84rji7/c4d_lock_feature.mp4?dl=0

The rig above is from an auto rigging I’m working. It’s a bit tedious to explain since I’m using it alongside with a bendy/twist/stretch set-up but basically, you’ll have a separate joint chain dedicated to the lock and just swap them with the regular joint chain.

Fortunately, the character object has a lock feature. You can make it editable and analyze the set-up.


#3

I THINK I might have actually found the beginnings of a solution.
I created a null and positioned it exactly between the knees. Then, I made the entire rig (which starts at the hip) a child of that null.

If I rotate this new parent null, this ensures that the hip’s new position is always equidistant from the anchored knee location, and thus, the IK isn’t affected. Then it’s a simple FK to rotate the torso back up.
It’s not 100% perfect, the knees still twitch a tiny bit during the torso FK move, but maybe there’s a way to counter that?

No word yet on if this breaks anything down the road, but the immediate result is fairly close!

EDIT: Further refined - pulled the null controller out of the hierarchy and put a parent constraint tag on the hip targeting the null. Depending on the settings I get results with different types of refinement needed, but it seems a lot cleaner than before.