Inverse Kinematics

[gitarrenvogel]

Hey, I have an IK-related question. When I draw a 2D-chain for an upper and lower arm (2 bones), then it should be automatically in IK-mode and it really is - for the hand control. But when I move the shoulder, the whole arm moves. How to build an arm, where I can move the shoulder and the hand stays where it is and still be able to blend to FK?
Cheers, Lukas

[EricTRocks]

constrain the effector to a control object using a position constrain

[gitarrenvogel]

Oh, that was simple - I don't understand why that works, but it works fine!
Thank you very much!

[gitarrenvogel]

So, one other question... Do you know a way, that there is no transition from FK to IK and back? So that the FK gets its kinematics from IK, while in IK mode and vice versa and I can conrol FK/IK with a boolean instead of a scalar? I guess, that's pretty difficult, especially with an up vector?
I followed this https://vimeo.com/22081337 tutorial and it does what I mean (from 2:58), but just in one direction and the blending in the other direction isn't really smooth - it's already full IK when at 0.5 or so.
So, after that I built an ICE-tree to control the FK/IK-blend value by a nulls y-position and rounded and clamped that value to 0 and 1. (not the greatest way, I guess) Out of that I made a second value, so that 0=1 and 1=0 and with that I control the blend-amount for a pose-constraint with which the hand-IK-control follows the chain, when in FK. I hope I can explain, what I mean. I know, I use some not very elegant solutions, but I'm a real beginner to rigging. So far I'm happy, that it works a little bit but not with the up-vector and when I try to constrain this to the three points of the bones, while in FK-mode I get a cycle. So here's my scene https://dl.dropboxusercontent.com/u/178 ... ik_arm.scn Hope you can help me again. The blue pyramid's y-position controls FK/IK-switching and it has the ICE-tree. And there's a second null called FK_IK-tmpValue for the 0=1 and 1=0 values, which control the constraints blend. I hope I could explain everything, so you can understand it.

Cheers, Lukas

[EricTRocks]

Welcome to rigging where nothing comes easy and solutions for matching FK to IK and vice versa isn't just a matter of constraining things and flipping switches but will have to be scripted.

I created a tool in Species for this but it is very dependent on the rig setup and isn't easily transferable, and again, it is a scripted solution.

[gitarrenvogel]

Ok, thanks! Good to know, that it's pointless to try to constrain everything together

[EricTRocks]

Just to be clear there are ways to setup arm / leg rigs where you can blend from one to the other smoothly. It's just matching one to the other that is tricky.

[gitarrenvogel]

Yeah, I understood that part and I already knew, because I saw some rigs, where this was made. But I had hoped, that it would be possible by constraining or something like that, not scripting. So I have to go with the blending version. I also tried the ICE-IK version from the examples, but it seems, that this IK has some other orientation results, than the normal IK-chain, so for me, that wasn't really usable.

[dwigfor]

I made a ice 2 bone ik solver with up vector support compound a while back. Maybe it's useful for you. I haven't tested it in production, but it should be stable, no weird flips.

http://www.si-community.com/community/viewtopic.php?f=15&t=2515&hilit=bone+upvector

[gitarrenvogel]

Thank you - unluckily it's a bit too late for my graduation project. Don't have time to change the rig, now. But thank you anyway - I will try this out the next time