View Full Version : jerky head

02 February 2002, 10:28 AM
I'm animating a little character and I have a problem with the head jerking slightly when it is moved slow. It is set up with ik. Any body know how I can fix this?


02 February 2002, 06:16 PM
mmm... I don't know too much about IK but have you checked that it might not be something to do with the graphs?
I know that TCB splines on the graph editor cause unwanted movement between keyframes. Linear splines are often a good way to fix it.
But as I said, I'm really not clued up about IK.

02 February 2002, 07:38 PM
Explain a bit more about your rig. Is the head rigged with IK?

02 February 2002, 12:02 AM
I did try modifying the graph to make it so there was no movement, but i would like a slight motion. It's when it moves very slow in the opposite direction of the next motion that it become jerky.

The head is using ik. There is a kneck bone and then a head bone. I think they are both set to ik on heading and pitch. I've tried changing the stiffness a little and it doesn't seem to make all the much difference. I have null parented to the head bone which has a goal of another null. I've also tried changing the goal strength but it still seems to jitter a little. I think i've also set one of the bones to follow the rotation of the goal null. But there isn't really and major rotation when the head jitters.


02 February 2002, 12:33 AM
I've never come across a head rigged with ik. What's the reason you can't just use fk for the head instead?

One thing to look out for is the scale of your model. It turns out that the strength factor works odd (meaning numbers less than 1 create more strength) if your model's scale is large. Make sure your model is in a reasonable size range ( 1 to 2 meters or so). I created a rather large robot (50 meters tall) and the IK rig I created had big problems with jerky behaviour. I ran across this in 7 so I'm not sure it's still a problem in 7b.

02 February 2002, 12:45 AM
IK can do some unpredictable things even when its set up properly. i NEVER use IK on anything unless its absolutley necessary. You pretty much always need it on the legs but i'll only use it on the arms if the character has to do something that requires its use . . . like lean on a wall etc.

why do you need IK on the neck and head?

02 February 2002, 03:17 AM
Sounds like a slight case of gimble lock to me..... I'd just use FK.

02 February 2002, 05:16 AM
Okay I'll try that. I've never done this before so i just figured ik would make it easier to animate, but I guess not.

Thank you

02 February 2002, 07:07 AM
IK definitely has it's place and is wonderfully useful... but the most successful character setups usually include hybrid IK and FK setups.

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