Reverse Kinematics

# 1 21-03-2005 , 08:23 PM

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Join Date: Aug 2004

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Hey, I'm an animator (mostly of solid objects using keyframes and path animations) and I was wondering if there was a function to switch the direction of the joint forward kinematics tool? Sure, its just as easy to create a series of small forward kinematic rotations which all add up to the movement you wished -- but is it possible to flip the direction of control so instead of controlling from the joint DOWN the chain, to control from the joint UP the chain? Sounds like an easy toggle enough to have been implemented.

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# 2 24-03-2005 , 08:59 AM

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You can blend from Inverse Kinematics ("UP the chain") to Forward Kinematics ("DOWN the chain") to do your FK animations and back from FK to IK to do IK animations.
Follow this link and check my post in the thread in where I describe a few steps how to go about it.

Hope it's what u're looking for.

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# 3 24-03-2005 , 06:31 PM

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Actually, what I was trying to describe was if you have, for instance, a guy standing on one leg. When the guy wobbles, it will be around his ankle... however, if I try and move the ankle joint via rotating the joint-- the foot will move but his leg and up will not -- so instead of having a guy wobble, you'll just be clipping his foot through the ground.

Is there any way that you can toggle that moving the ankle joint will move the leg and up, but leave his foot unrotated (with relation to the ground).

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# 4 25-03-2005 , 01:03 AM

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It's a hierarchy matter.
Just imagine it were you. When you rotate your ankle, .... you'd be moving the bones from the ankle down. Your foot only, right?
When you wobble on one leg, it's not the ankle that is wobbling, but you wobble on your feet. Your entire body is moving right, left and forward while your foot is positioned stationary. Thus the body moves around the ankle. So you move your root node in your joint skeleton instead (usually the pelvis).

The IK-handle for the leg should be set to sticky if you don't have it keyframed yet (keyframing an IK-handle will automatically make it sticky). This should keep the ankle positioned while the body moves around.
However,.. when standing on one leg, the other leg should dangle with the body. But of course you have IK-handles there too. They will keep the ankle stationary like the foot on the ground but only in the air, what you don't want. You have to blend IK/FK for this dangling leg (see previous post).

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