IK Problem At Animating (shaking)

  • Hi,
    I am using final poser and when i try to use IK at my animations, it goes mad with ultra shaking.
    For example if you want to make push ups with V4, the arms go so shaky, it kills the smooth animation feel. It goes same to try to make walking with humans or animals. It was not so bad before, maybe at old poser versions.
    I tried many thing but when i need to have hands stable (like holding something or stand same place when the body moves), i can't find a good solution for it.
    If you got any tricks, please help! thx!

  • That's a common problem, specially with hands in forward positions (as in the front of the chest). The problem is that you're exceeding joint limits, so the IK solutions change suddenly when one limit is exceeded. Possible solutions (with their associated limitations & problems):

    (a) Uncheck Use Limits for the figure; that will allow the joints to go to whatever angle they want as their first solution, instead of judging the first solution as unacceptable and then looking for other solutions. Problem is that you may end up with extreme angles.

    (b) Add some rotation at the base (or up) the hierarchy chain; for hands, that would be the shoulder, forearm and arm. So, frequently, by moving the shoulder forward or up or rotate the arms that will get the IK hands under control. Problem is that I've learned that's a kind of hit of miss kind of thingie, so sometimes no matter what you do up the hierarchy the twitching persists.

    (c) Increase the joint limits, and apply (b) for the cases where these limits are exceeded. That will allow a greater range of movement in the joints. Problem is that many times it's not clear which joint limit is getting exceeded and should require the increase, so it's a kinda slow, case by case analysis.

    (d) Use IK to set your movement end locations, make sure these are under control, key those end positions, then remove IK. Now the angles will be smooth. Problem is that the hands will move in between keys, so you may need multiple keys for precise movements (say 1 key every 4 frames or so).

  • Oh, and I was forgetting; this is a very, very, very non-intuitive thing:

    (e) Change the default position for the figure (that is, Figure / Set Default Pose). The default position (that is, standing up with some small angles in most joints) is used by Poser as the starting point for looking for IK solutions in any other position (like doing push ups). This is one of those arcane things in Poser; if you have a default position with angles say Xrot = 1degree, Zrot=2degrees, Yrot=3degrees, then I believe it will prefer to do Y rotations to resolve the IK chains; meanwhile default positions of Xrot=3degrees, Zrot=2degrees, Yrot=1degree it will prefer to do X rotations.

    So, these tiny angles in the default positions are really really important for resolving IK. I once thought this: "ah! I want the default position to have all zero angles!!!" and did that - next thing, that character would walk in a very odd way, because Poser had no hints of which rotations it should prefer, to just got random ones.

    Problem with this is that the relationship between the tiny angles in the default pose and the actual effect of what happens when you do an IK pose is terribly unintuitive, complicated and arcane; you can very easily ruin your character if you do the wrong thing. But if someone knows (more than me) what's happening and what he's doing, it should help on getting those IK chains resolved the way you expect them to be.

  • Open the twist channel of the upper joint in the IK chain(s) in the graph editor.
    Upper arm, thigh, etc
    It probably looks really erratic more often than not, and this is usually where the oddities come from.
    Delete some (or all) of the keys out of the twist channel, and adjust (add new keys) the twist accordingly.

    IK works best in combination with FK.
    And Poser doesn't really have an easy way to do that.