I have to thank Shawn Kelly for this fantastic tip; he's the only animator I've ever heard talking about figure 8s as being really important in animation. How many of you animators out there are even aware of their existence?
Figure 8s are actually curves, loops, nothing more... so I guess you can get by with just a simple loop, sometimes, but using the figure 8 is so much better in many cases, such as wrists' movement in a walk cycle; pretty much any kind of loop can be a figure 8. But especially at the end/edge of a movement, when you need to return on a similar path: if you feel like animating an articulation on a path such as this (for a living creature that's not supposed to move like a robot):
don't. It's normally impossible. And it won't feel right. It would work though great as a:
Yeap, figure 8s can be very thin, almost like a simple line. In a walk cycle for instance, your hands should not use the same path as they go back and forward. Use a figure 8. Use figure 8s as much as you can, on all kinds of loopy, pendulum motion, and not only. Being aware of these 8s can improve your overall animation curves - you might have slow-ins or slow-outs that don't feel right at any given moment... Don't despair, don't spend countless hours fighting your timing, when the timing could have been correct in the first place... This is a good example complementing my previous essay, that spacing can be a more problematic issue. Use this knowledge to correct your curves/paths. Figure 8s feel very natural and should be used a lot :) Yaaaaaaaaahooooooooooooooo!!!!!!!!!
PS. There is something very powerful and appealing about figure 8s, I'm not sure what, maybe it's the twist... makes them my favourite kind of curves... :D