Quick Trick: Push Off !

Well, seeing as this is an animation blog - its about time I posted something up that actually moves. Well here goes. The video link below is a walk I did recently, mosty as a test for a new rig my super talented colleague Goosh is currently working on, but also something that I can use as a good medium to discuss a certain aspect of walk cycles that commonly gets overlooked.


This was really fun to animate. It`s not "true" quadruped locomotion, as it was difficult to accomodate the large stretch of the back legs with the front legs that are shorter and still retain a nice feeling of timing and contact.

First off - this isn`t by a long shot the worlds greatest walk cycle - in fact its pretty run of the mill, but something that I see time and time again in 3D walk cycles is the lack of a good "push off" in the feet, and believe it or not I see it over and over in most CG features.
What I mean is this - as the foot travels backwards in contact with the floor, and begins to get ready to lift up and travel back towards the front, there is a subtle but very important rotation that travels from the ball of the foot and through to the toes. The mechanism for this movement, and the logic behind it, is that the foot tries to retain contact with the ground as long as possible, essentially rolling the foot as far onto the toes as it can go without looking stupid. The body uses more energy to lift the leg through the passing position that it does keeping it planted on the floor.
Many animators overlook this push off, and start to bring the foot back towards the front with hardly any rotation from the toes. It still works, but the feeling of weight and locomotion gets diminished.
We often hear as animators how important it is to show "contacts". This is so true, and good contact poses will be integral to selling a feeling of weight and interactivity with the world. But "push offs" are also contacts - they just happen as the contact is getting broken rather than created.


I've isolated the back legs in this video to clarify this idea ( ignore the repeat frame ). You can see as the foot travels back, there is a pretty large rotation, that travels through the foot, and the toes are still contacted for alost a full 7 frames after the other foot has made its opposite contact plant. OK, this is a pretty stylized ( cartoony ) walk, but the concept still holds very true in more realistic animation.

As a general rule through all my animstion, cycles or not, I try to keep weight bearing contacts planted for as long as possible without looking stupid. It's also generally good to use as least amount of footplant possible to carry out an action, unless the creature's character would dictate otherwise.