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I'm currently at Animal Logic in Australia, back where I animated on Happy Feet. I'm now working on their next animated feature The Guardians of Ga'Hoole.
So Clym, that would be the main thing I'd fix along with the speed. But I also thought I'd go through the other drawings and suggest some subtle ways to exaggerate the poses and movement you have.
As I've shown below, the up and down motion you have on the character is quite even. I would be tempted to push this into more of a bouncing ball motion.
Let's start by looking at the first pose in this sequence; the contact position. One thing I noticed is that his body is in a very neutral pose, it would liven the action up if this was altered, and we had a stronger change of shape occurring.
We can see this by drawing a line following the spine, this is our 'line of action'. At the moment the line is straight.
By simply pushing the line of action, and therefore the body, into a slight curve we create a stronger more interesting pose.
So, this is how I would alter the contact position. By adding a more dynamic line of action and also raising the body up. I've also straightened the rear leg to better follow the flow of the spine.
In the next pose, your 'down' or 'squash', I have pushed the line of action the other way. This will give us a change of shape when we play the animation which will add extra life to the walk. I have taken it to quite an extreme here, you may want to be more subtle.
I have also lowered the pose and changed the rear leg. In your drawing it felt as if the leg had shrunk a bit.
In the next pose, the crossover, I have kept some of the curve of the previous pose in the body. I have also changed the lifted foot slightly as I felt it had slightly too much drag in your drawing.
I haven't shown it here, but it would also be a good idea to show part of the hand or the elbow protruding outside the figure's silhouette. At the moment the arm is contained in the shape of the body which means we lose it in motion.
The next pose is the one we mentioned earlier. I pushed his lifted leg further forward, and flattened the toes of his rear foot to look like they are still in contact with the ground. I also changed the angle of his body, so it looks less like he is tripping up.
We then arrive at the opposite contact pose, which I have altered in the same way as the first.
Here is a composite of all my drawings over your original ones. As you can see the heads now have more of a constant motion forward.
While the character's vertical motion forms a bouncing ball curve.