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View Full Version : Gimbal Lock with Hands with IK



Ramen Sama
03-14-2008, 06:46 PM
Was curious how people setup IK for hands.

I use a null bone as a controller, a null object for a goal for the "hand" bone.
The Null object is parent to the controller bone, so far i seem to end up having really good results except ending up with gimbal lock in certain rotations. i've been messing around with pivot rotations and all sorts of other things, but i still can't seem to find the universal solution.

To complicate matters, i have a "forearm twist" bone that banks in regard to the controller bones bank, so i can't easily change the coord system.

Ramen Sama
03-14-2008, 07:02 PM
Forgot to mention the hand bone uses match goal orientation.

SplineGod
03-14-2008, 07:26 PM
You can use two goals instead of one. The 2nd one serves as an additional axis.
Parent one Null to the other.
LW 9 also has a tool called Quatro which uses quaternian based rotations so you dont get gimbal lock.

Ramen Sama
03-14-2008, 07:31 PM
Quatro? hmmm i haven't seen this tool. Maybe i saw it in IK Booster.

At the moment i am using a Goal object parented to a Null bone. This is sorta like you are describing. I noticed i can move the null object and still have the axis i need.

I'll look into this quatro tool more though, as i'd rather only move/rotate one null to controll the hands, but this might not be a possiblity.

SplineGod
03-14-2008, 07:40 PM
Its not part of IKBoost. It was a tool that was added back in LW9.0

Ramen Sama
03-14-2008, 07:42 PM
hmm found the tool, it seems iffy. I'd rotate the bone into a position where it has gimbal lock, activate the plugin. and it doesn't always want to respond. I can see the lines being drawn on the sphere. but it doesn't rotate.

Also, i'd probably be OK, if i could get the forearm bone to follow two objects bank at once. Maybe an expression could take care of this.

Ramen Sama
03-14-2008, 07:49 PM
Ok, figured it out. you must be in perspecive view for the rotations to occur like you'd imagine.

SplineGod
03-14-2008, 10:21 PM
you dont have to use it only in the perspective window.
Standard LW coords are Euler based which solves rotations around an axis. Quatro uses quaternians which solves around the outside of a sphere which is why the tool works the way it days. Quatro should work on the IKgoals or bones.

Ramen Sama
03-14-2008, 10:32 PM
Odd, for some reason i can only use it in perspective mode though. It seems. pretty handy, however, it doesn't work much different then if i switch the coord system to something else.

I think i will need to go with the double goal method. I've setup the Null to rotate only on the heading, while using the parent to rotate the other directions. seems like it will work fine. it's a little strange, perhaps i could create another null object to controll those two. that way i simply rotate/move one... to control the others. That sounds like a plan, maybe.

:)

Ramen Sama
03-14-2008, 10:56 PM
I think that the Local Coord work best to be honest... seems almost easist to use that and figure out some other method for controlling forearm deformation. no gimbal lock can occur using local coords.

Thanks for the help.