Widunder

I just thought I would share some general tips for Motion Builder work flow. There isn’t a lot of documentation on Motion Builder out there, since the software is still fairly new within the game industry. And when I learned it I had to figure a lot of stuff out for myself. Things that would have saved me a lot of trouble of someone had been there and told me how to do certain things.

Anyways, so first up is just a small walk through on how to remove foot sliding or other weird movement that can occur in motion capture data.
Let’s say the original file looks like this (don’t mind the quality for the skinning or the rest of the animation, it has nothing to do with this little tutorial):

And a start is to make the left foot standing still, it shouldn’t move and rotate up and down like that at all.
The first time I tried to solve this problem I instantly tried to set a new key frame on the foot on a new layer. And the copy it to the end of the part where I wanted the foot to stand still. This doesn’t work at all since a keyframe without any new information doesn’t do anything at all, except maintaining the information from the Base Layer. This is kind of obvious if you know Motion Builder well, but I didn’t know this right away when I started out. Another way that I tried is to create a pose of the character on the first frame, and then applying the  pose again at the last frame and then only key the foot. This doesn’t work at all either since it still moves in between. It still gets the information from the base layer that it should move.
So just edit the base layer! It could sound scary if you want to keep your motion capture data in case anything goes wrong, but just save backups so you have everything unedited in case you need it later on.

If we take a look in the FCurves we can see that this part of the animation has curves like this:

Curves

The curves go all over place. So what we do is just delete the part of the animation where we want the foot to stay still. Except the first frame of that part of course. Now the curves should be flat, but the animation will probably look like this:

Which is not good at all obviously. The problem can be found in the curves:

Curves

There is only one frame between have a planted foot and having it lifted from the ground.
The solution is just to delete a couple of the key frames right after the last keyframe of the standing still-part. So there will be a bit of blend time in between the “standing still” and rest of the animation. The curves should now look like this:

Curves

And the result is that we have a foot that does not move weirdly while the character should have them standing still, and there is a nice blend to the rest of the animation for that foot.
Hope this was helpful. This stuff is very obvious way of solving this, but it could still take some trial and error before you figure it out for yourself if you’re new to this stuff. Like me, I was too focused with solving it with the layers and not touch the original motion capture data at all.