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"Left Hand-IK"?

I've got player models with varying arm lenghts, so an animation for holding a rifle, for example, will cause the left hand to be where it doesn't belong. The rifle is attached to the right index finger, so naturally it always fits.

I thought the best way to deal with this is by using IK with a marker/offset that is local to the rifle itself, but it seems that UE4 simply doesn't have an IK function that gives you control over both tip-rotation and joint-orientation.

If I use a 2-bone-IK node, I have (at least some) control over where the elbow is to point, but I can't set a target rotation for the hand. If I use FABRIK, I can set a target rotation, but UE will bend the arm in "unnatural ways" and there's nothing I can do about it.

Isn't this pretty pathetic for a so-called IK-system? Or do I miss something?

Product Version: UE 4.10
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asked Mar 13 '16 at 07:04 AM in Using UE4

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FABRIK is the right one. You want the tip to be hand_l and the joint to be upperarm_l. Effector transform space should be "World Space" and Effector rotation source should be "Maintain Local...". Then feed the Effector transform with GetSocketTransform in the event graph. Doing it like that works for me.

The problem with this method is that the socket transform you get is from one frame earlier so the left hand always trails behind a bit. To fix that, do what Jonas does in this tutorial. https://www.youtube.com/watch?v=tCgZxeFN5_8

The key is that when you use another bone as an effector, the transform parameter becomes an offset from that bone. So you can tie the left arm to the right hand and then eyeball the offset like the video shows.

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answered Dec 19 '16 at 06:42 AM

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avatar image MaxPower42 Dec 22 '16 at 05:25 AM

Ok, but the problem I described still remains. You can't set any rotation limits and you can't define where the "middle bone" should face. So this works with small adjustments, but anything larger will often arbitrarily twist the character's limbs and produce useless results.

Before coming to UE I experimented with Unity for some time. There was this plugin called "Full Body IK" (iirc). UE4 IK is basically a joke when you compare the two. I often thought about writing my own IK anim nodes, because I have read that the math is relatively simple. But then again, implementing custom anim-nodes is already tricky enough by itself and I can't really afford spending so much time on this.

So, I'm still hoping for Epic to patch in an IK system worthy of the name or some powerful and affordable plugin.

avatar image Jin_VE Dec 22 '16 at 09:36 PM

Ah. Just getting rid of that frame-lag is a miracle. I ended up using a virtual bone. Have you tried IKinema? That's way beyond what UE4 does. Really impressive stuff.

avatar image MaxPower42 Dec 23 '16 at 04:53 PM

I even wrote an email to the IKinema support telling them that, if I make 100.000 € with my project, I will end up paying twice as much to them for an IK-solver as I will have to pay to Epic for an entire game engine.

They told me to make more profit then...


But there are one or two plugin projects in development. I will check on them again every few months.

avatar image Jin_VE Dec 24 '16 at 01:15 AM

Yeah so they're targeting larger studios. That just means there's room for competition. If you know what it takes, maybe you should help the other projects or even start your own. I know I'd love something like IKinema that was also reasonably priced.

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