Walks and Runs are hard to teach in my opinion, because there is a great deal to consider all at once and a student is only capable of absorbing so much. Some estimate that a student only really remembers 10% of what you tell them.
It is with this in mind that I have been considering what is the best way to communicate what happens to the characters weight through a walk cycle, the thing is that you want to keep it as simple as possible while still communicating the essential bits. Most people star animating a walk using two kinds of main key frames, commonly referred to as the Extremes when the feet are furthest apart and the Passing Positions when one foot is in the air and is passing directly under the body on its way forward to start the next step. If these are news to you then you can find out more here.
So once you have these basic poses down you can start to think about what will happen on the frames between them, and in my opinion this where the water starts to get muddy. People start to talk about new keys that go between these ones things like a Push Of Key, a Taking The Weight Key and a Contact Point Key are common. These are all designed to ensure that the character passes through the points that are essential to communicate a walk that has weight to it, but I have found that when all of these keys are introduced to a student they can get very lost. Keeping track of all these keys and the criteria they meet distracts the student from the main game, building all of those individual key poses seems to water down the intent behind the animation, the character poses become stiff (especially in 3D), there is less emotion, and while getting thing right on one pose a student can negate or conflict with elements in other poses. This results in the students starting to move in circles, fixing one thing that messes up another, fixing that only to discover that it messes up something else and so on. All because the student (understandably) can't manage to implement all of that new information at once, it can become very frustrating for student and teacher alike.
So I thought I would expand on how I think of it, it may not be the right way for you in the end, the others who teach with the extra poses are animators I really respect so they know what they are talking about. I guess am trying to achieve the same thing as them, its mostly about how I set it up in my mind to make sure I don't throw the baby out with the bath water. So here we go...
- Get your extreme and passing point poses right first. Balance, Attitude, Everything. If your working in 3D key the whole character from top to bottom and check that you have the feet the exact same distance apart on each extreme. If it is a cycle then make the poses very close to exact opposites, in 3D I make them exact to start with and thin introduce some subtle differences, anything to different will read as a tick or limp or something.
- Now here is where I think I differ from the norm most. Instead of thinking of the extra key poses I start to think about individual elements and how they have to move between the main keys. I start with the pelvis. The highest point in a walk isn't at the Passing point, usually you continue pushing up and forward until you have pretty much reached the full extension of your foot and leg (or at least as far as you can go comfortably). Then you fall down, but luckily you have thrown your other foot out in front of you to catch the weight. See here in this clip.
- You can see here in the Graph Editor if we have a look at the up and down movement on the pelvis controller how I have kept it moving up for a few frames after the Passing Point, then it drops off quite quickly and there are a few frames where it continues down after the Extreme pose.The advantage here (I think) is that because I'm not think of entire new poses I can keep it simple in my mind I just have to get the pelvis right at this stage. Its good if you can get a rig like Max for Maya that allows you to turn off the visibility of the arms and legs so you can just watch the body moving up and down and get it feeling how you want. If you want to get technical I have added extra keys to the pelvis for the push off and taking the weight, but not key poses, I'm just keeping it as simple as I can in my mind.
- Next I would probably tackle the feet, in a 3D walk cycle I would end up with heaps of keys on the feet around where they come into contact with the ground and where they push off the ground, in 2D I would also manually position the feet during these parts so its pretty much the same. There are so many overlapping things going on here, the up and down movement in the pelvis affects the length of leg you have to play with (especially in 3D where its not so easy to cheat), the foot is moving through the air and rotating, it is pivoting at the ankle as it approaches and leaves the ground and it is bending at the ball and pivoting at the toe when it is on the ground. It has to move at a constant speed under the body, but is easing in and out as it moves through the air. YIKES!
- I'm sorry but there is only one solution, get up and do it, or watch someone else do it for you. Do you know that in 4 years of teaching I think I only ever saw 3 students act out a walk! That is SO frustrating. You have to know what you want it to look like, get in there and make it happen on a frame by frame basis. You want a nice smooth roll as the foot comes down onto the ground, you want a nice feeling of pushing off as the foot leaves the ground behind the body, you wand a nice arc on the heal and toe as the foot comes away from the ground and swing through to the contact point. If it is 3D you don't want any popping in the leg and 99% of the time you will want a nice smooth evolution in the angle behind the knee, a crucial part of this is getting poses in there that make it look like leg is stretching out to find the ground and stretching out to push off from the ground without actually pulling the IK limb 100% straight. The first and last point of contact won't necessarily coincide with the extremes by the time you are finished here, in my experience the foot is usually in touch with the ground a few frames more at each end (make it the same for both feet).
Its full on, but at least I'm only thinking about the feet and legs, even just one foot at a time.
- That's the hardest bit out of the way in my opinion, if you are working digitally save your scene because its time to play, now you can tweak some other bits if you want. You could for example choose to arch the back and twist the shoulders a little more at the highest point in the step. A few frames after the lowest point you could hunch the pose forward a little more so that the shoulders follow through after the low point. Adding drag to things, or choosing not to so that the character leads with its fists, its all creative fun stuff and experimentation from here. Don't do everything you can think of in one walk, its often about what you leave out as much as put in. Always compare with your original intention, determined, light-hearted, distracted, scared? Choose things that add to this meaning.
That's about it. I think the end result is much the same as other techniques. Its just that I think its easier to get your head around if you think about the way individual parts are going to have to move through into and out of the 2 main pose types rather than adding extra key poses. You have to consider them in the right order, and as with either approach you have to keep one eye on the big picture, how is your walk looking overall? Is this how you wanted it to be? Is the emotion clear? Do the poses, timing and spacing drive it home?
Hope this helps :)