Цей сайт найкраще переглядати в сучасному браузері з включеним JavaScript.

Fixed IK constrained bone tip...?

Abelius

Hi there,

The only things I'm animating so far are humans, so I usually want their feet to be horizontal to the ground and stable in height. In other words: completely fixed.

Right now I'm making a stand up (from a chair) animation, so for the rising movement I translate the hip bones, and that of course moves the legs and feet as well.

I have covered the lateral fixation with an IK constraint, like this...:

...but it still goes up with the rest of the skeleton, which is only to be expected.

What I need is that bone to be also constrained in translation, but not at its origin but at the tip.

I've experimented with a transform constraint, set to only translation and had high hopes in configuring its offset to point it to the tip... but it seems that I cannot touch that because all offset options are greyed out...:

So... I don't know how to achieve this. Is this supposed to be covered by a path or something? I've never used it and from what I've seen in the videos it seem to be designed for other purposes, but I could be wrong obviously.

Could you point me in the right direction with this, please?

Thank you for your time. 🙂

Nate

You can change offset in setup mode, though I'm not sure it does what you want.

Did you realize you can use 2 bone IK?

IK adjusts bone rotation so the child bone tip is nearest to the target. There isn't a way to prevent the target from being farther away than the child bone tip can reach?

Abelius

Nate написав
You can change offset in setup mode, though I'm not sure it does what you want.

Ok, that was pretty dumb by me. 😃

But you're right. It doesn't do what I thought. You can only offset by 50 pixels maximum.

Nate написав
Did you realize you can use 2 bone IK?

IK adjusts bone rotation so the child bone tip is nearest to the target. There isn't a way to prevent the target from being farther away than the child bone tip can reach?

Not sure what you mean by this. I've tried 2 bone IK's in the past, but they also translate if their parent bones are moved around. In this case the hip bones.

My main problem with feet is that they move up and down like crazy when I move the body, and even if I try to correct their height relative to the ground at key frames, the final result still looks horrible. I'm yet to make an animation that doesn't have this problem. Even my walk cycles have this jerkiness.

I've uploaded a video here so you can appreciate what I mean: Lousy stand up - YouTube Set it to 25% of play speed and you'll see how the foot moves up and down, and that's a "corrected" version! :p

I think my problems would disappear if I could fix the tip of that bone to a position, but also maintain its rotational IK capability. That is, that I could move the body around, the bone rotates to adjust itself to its target, but its tip doesn't move at all.

Of course I'd need to take care to not stretch the images too much (at the knee), but that would be infinitely less noticeable than the feet jumping around...

Nate

I think 2 bone IK is what you want. Parent your feet to the root, select the thigh and shin bones, New -> IK Constraint, click the foot to make it the target. Move the hip, the foot don't move at all, the leg bends.

Abelius

Thanks Nate.

Just a question... when you say "Parent your feet to the root", that it's literal? Do I need to reparent the foot to the skeleton root so I can select it when I make the 2-bone IK? Because if I try to make it being the foot a child bone of them both I cannot select it.

Moreover, I don't know if it's possible to reparent in Animation mode... If that is possible then I'd totally go for this approach because it seems to work reasonably well. But if I need to reparent the bone in Setup mode... well, you know, there are other animations that wouldn't take too well to have the feet so high in the skeleton hierarchy. 😃

Ok, I've just created the 2-bone IK pointing to a new bone (not the foot) under the root. Then I've put it at the foot bone origin, so this setup does the same thing.

It works very well, but I have some "rebounding" at the knee...

On the other hand, I also experimented a little more with the transform constraint, achieving a similar effect to what I need with a combination of translation and rotational transform constraint at the lower leg bone. I've had to set the target at it's origin of course, and then I've translated the target as needed and maintained the correct rotation at key frames.

You can see the result here: transform vs 2 bone IK - YouTube

The front leg is with transform constraint and the back leg is with 2-bone IK. Note the rebounding there...

Anyway, I think these two ways are enough to try and stabilize those crazy feet I have in all my animations so far. 😃

Thank you very much for your time Nate.

Nate

Abelius написав
Do I need to reparent the foot to the skeleton root so I can select it when I make the 2-bone IK? Because if I try to make it being the foot a child bone of them both I cannot select it.

The IK target cannot be a child of the constrained bones. It's unfortunate if changing the foot parent breaks animation, but it's likely the best setup.

I'm not sure what you mean by "rebounding". The animation looks good to me!

Abelius

Nate написав
Abelius написав
I'm not sure what you mean by "rebounding". The animation looks good to me!

The back knee goes left and right twice but yeah, it's not very noticeable... even at that size. :p