How to Stop Key Drift
by Matt Estela

Note: Since writing this Armando Afre (who originally explained this whole concept on the mailing list) has pointed out that it really should be called 'spline drift' or 'channel drift'. You'll understand why by the time you finish this tut.

Once you move beyond flying logos and spaceship fly-by's, you'll come up against an ugly artifact of 3d keyframing: key drift. Say you're trying to make your character do a jump. This could be broken down into the following poses:

Working straight from these key poses, I created these in an action. Here's what it looked like:

(double click to start playing, single click to pause, use left and right arrow keys to move frame by frame)

See how the feet are sliding everywhere? To fix this, I added two keys so that AM knew exactly when the feet leave the ground, and when they hit the ground, ie the start and end points for the actual jump:

So now it should be correct. Shouldn't it?

(double click to start playing, single click to pause, use left and right arrow keys to move frame by frame)

Now what's going on here? I'm telling the software don't move the feet between the initial pose and the start of the jump, but they're still sliding!

Why? 1