This is a re-post of another thread - I put it in the wrong place…
If you’ve ever used a package that doesn’t have Quaternion rotation interpolation (like Lightwave or older Messiah), you’ve gotten used to having to deal with “gimble lock” and all that that implies. You usually have to set things up very carefully, or risk having your joints “lock up” at some inconvenient time.
Recently, I was trying to get a particular setup to work on a character - the test rigs I was building were working flawlessly - but when I put the same rig on a character, they didn’t work at all - then it hit me: AM is hiding certain things about how their bones work, and by adapting a little trick I learned in Lightwave, my setup became rock solid on my character.
Basically, the jist is this: Child bones get their “knowledge” about their relationship to the world from their parent bone. So, the parent determines which direction is X,Y, or Z rotation. With Quaternions, you add that demonic “W” element into things, and if you’re too close to a particular rotational relationship in the world, you get flipping and wiggy behavior so that the bone can maintain it’s IK committment.
What I did was add a small bone at the root of my chain that is created with the same orientation as the model bone - so that the chain has the same local orientation as if it were just sitting there by itself (which leads to more stable behavior). Here’s an image that I hope will explain it better:
If you’ve ever built a model with the intent on adding hair guide splines later, or added hair splines THEN tried to drag the material down that looooooooooong list of splines (only to slip your mouse cursor outside the window and have AM puke) - well, there’s a little trick that will save you some time and pain. Go ahead and create your model and your guide splines. Now, pick your guide splines and Copy them to the clipboard and paste them back in. This will put the splines at the TOP of the spline list and save you from having to look all over for them (delete your original splines).