This exercise was harder than it looked.
I started by copying the key frames onto paper by eye. I started with Frame 4 because the body is fully stretched out at its highest point. I wanted to see the un-scrunched proportions. Then I compared it with the original in PhotoShop.
After making corrections:
In retrospect I can see that I didn't understand the actual head shape at the time. It's hard to make out from the original clip.
But I compared it again, and it looked okay:
Then I compared my outline of Frame 4 against Frame 1, so I could see how Flip moved from 1 to 4.
I did this so that when I copied Frame 1, it would be accurate in relation to Frame 4. Here's my Frame 1:
I drew the first four keys this way.
But they were crappy because I wasn't really seeing the underlying construction. When you study original animation frame by frame, you see a lot of wobblyness due to poor inbetweens and probably inking mistakes. Copying from that end result just makes it worse.
So I did this in Flash to analyze Flip's construction as he was walking. (This Flash will be out of sync. You need to refresh this page and it will be in sync!)
It's true I traced. But I wasn't so much tracing the final lines as trying to draw what the construction underneath should have been. I actually cleaned up a lot of places where the inbetweens weren't quite right.
If I were going to keep working on this, I would:
1. Try to make the volume of the body egg shape more consistent.
2. Study how the body squashes. Some of the frames in the original have a very obvious fold above the tummy, which makes sense as the leg raises to its high position while the head is moving to its low position in the middle of the step. But I didn't do it consistently with the movement.
3. Study the arcs.
4. Clean up all the wobbliness.
P.S. I worked on this for over week before I realized why he leans forward and backward on alternate steps: because he's compensating for the weight of the papers under his left arm! (I left out that action because it would have confused the body construction lines, and I didn't need any more confusion.)