3DSMax - Limb snapping issue when using IK

PolyHertz

When using a solver, like IK/HI, limb movement is difficult to get right because whenever they are extended to fa they 'pop' into a strait line, which look extremely unnatural and is a pita to avoid. Is there some way to avoid this issue when making a rig?

monster

No easy fix really. I usually just try not over extend them. If you create the rig with stretchy limbs, usually you don't notice the snapping as much, but it still happens.

Zhalktis

It is possible to make "Soft-IK" rigs (if googling doesn't help, I could probably write down a simple tutorial) that slow down when approaching the full extension, but they have a different problem: the final position of a Soft-IK joint is no longer precise, so you can't put a hand on a table and expect it to stay there - it'll move a bit depending on the extension of the elbow/knee.

Animators usually learn to not extend IKs fully. We used to use soft-IK rigs, but reverted to regular IKs quite soon: it is easier not to extend a limb, rather than counter-animate the "sliding" of the final joint. Now we only make those rigs when the animation quality is no longer a priority and we know the animation would be outsourced... as often they don't bother with fixing IK pops.

PolyHertz

Thanks for the info! I'm reading up on Soft IK now. That does seem like quite the drawback though. Do most animators just us an IK/FK toggle for times when they want more precise extended limb movements?

Zhalktis

No, I wouldn't say switching to FK helps in such cases; when you want a hand to stay on a table while the body moves about, FK would be a really bad idea. Usually FK is used for movements requiring precise arcs (like arm swings in a walkcycle), while IK is used for precise end positioning, either on objects (hand on a table, hand "linked"to another object, etc), or just in space (hand gestures while talking).

I guess if the animation was about waving an extended limb, FK would make sense. In other cases generally an animator would simply adjust the movement so that the IK would come close to fully extending, but not quite extend to the point of a visible snap.

antweiler

What also helps against the "ik popping" is to have more bend in the knee joint than in the skinned geometry, when doing the rig. This way animators will less likely get into the critical zone of almost straight joints.
During animation, a good way to manually adress ik popping for feet is to use a foot roll setup. Using this, animators can slightly lift the feet to bend the knee joint, without having to touch the hip or footcontroller themselves, the lifting is often so subtle that its invisible

PolyHertz

I suppose the limbs could bend slightly backwards using that method, but that's actually a really nice a simple solution. Surprised I hadn't considered it before.

Anyhow, thread has been really enlightening. I think with this I'm set with solutions to solving this issue. Thanks everyone for the help!