Class 3 - Week 7 - Anatomy of the Feet

So feet. How exactly do they work? We use them every day in our walking, running, skipping, dancing, jumping, and stomping, but have we ever really taken a look at the mechanics of it all?

The human foot and ankle is an amazingly strong and complicated appendage made up of 26 bones, 33 joints (20 of which are articulated), and more than 100 muscles, tendons, and ligaments. All of which is able to support and move the weight of the human body while we run, jump, twist, and turn. It can also communicate emotions, attitude, and personality almost as well as the hands and face.



Getting a good sense of movement in the feet is easier that most limbs, since most of the time they're planted firmly on the ground, but there are times when you have to move the feet in complicated arcs, or try and give them an appealing pose. The best way I've found to do that naturally is to first learn about the anatomy of the foot, and the controls offered to you on the rigs.

Anatomy of the feet and legs

The first thing we should talk about is how exactly the foot is connected to the body, and how it moves. This will give us a stronger understanding of what limitations we have going in, and also allow us to bend the rules of anatomy in the right ways once we know how things work.

All legs and feet, including those of most animals, are made up of 3 sections: The thigh (upper leg), the calf (lower leg), and the foot. And connecting those together are 3 joints: the hip, the knee, and the ankle.

Since Ballie, Stu, Stewie, and Bishop all have very simple legs, we won't be going over musculature much in this article, but we will look at each joint and see what kind of rotations each one allows, and how far they can be pushed.

Let's start from the root and work our way down. The hips are made of ball and socket joints for optimal rotation, which means the leg can pivot and rotate in either the x, y, or z axes, kind of like our shoulders. There are some limitations of course. Because of the muscles and tendons, we can't spin our legs round all we want, (Though it would be pretty awesome if we could!), and despite trying to find a chart to depict the range of movement, a person's flexibility all really depends on who they are and how well trained their bodies are, from a arthritic old man to a nimble gymnast.

Next we have the knees. At their simplest, knees are made of hinge joints which are far more restrictive and only allow for rotation in the x axis, just like the elbow.

Finally, the ankles are made of a complex combination of a hinge joint combined with a ball in socket joint. This means that the major rotation of the ankle will happen in the x axis, but also allows for some slight rotation in the y and z axes, similar to the wrist.



Using Rotations VS Footroll, & Ballrock/twist

One of the biggest hurdles people seem to have is figuring out which foot controls to use and when. Do you use the footroll, ballrock, and balltwist attributes? Or do you use the Rx, Ry & Rz instead? Maybe it's a mix and match. But if it is, how do you avoid having to counter animate the similar attributes like Rx and footroll?



There are many ways you can do this, but here is the method we find works well for a wide range of uses. Whenever the foot is planted on the ground, try to use the footroll, ballrock, and ball twist exclusively, since those attributes give much better control over moving the foot while keeping it firmly planted to the ground. Sometimes though you need to use a bit of rotation to get the foot positioned just how you want it, usually with the Ry so that you can get the foot angled properly. But apart from that, try to keep the use of Rx and Rz down to a minimum. The reason for this is because the pivot points on the ballrock, footroll. and ball twist controls are designed to be used on the ground, giving you a strong and accurate control over where the foot goes in comparison to having to counter translate any rotations you do using the Rotations.

That was for the ground controls. Now as the foot peels off the ground, the moment it fully comes off the floor, zero out all the footroll, ballrock, and balltwist attributes and reposition the foot using the rotation controls. All this should happen over a span of 1 frame to avoid having counter animation issues when you go into splines. Zeroing out the roll, rock, and twist controls and using the rotations will allow you to have a full range of motion with the foot, without having to try and counter animate the foot angles you had on the ground. This also makes the curves in the graph editor much, much easier to read as you animate.

The moment the foot contacts the ground again, zero out the rotation apart from the Ry and go back to using the footroll, ballrock, and ball twist attributes like before!

Using this method is "the best of both worlds". You have the ease of use of the twist, rock, and roll controls for the ground, as well as the simplicity of positioning a foot in the air using the rotations. And by zeroing out each set of attributes between ground and air, you guarantee that you won't need to counter animate your feet at all throughout the shot.

Let's take a moment to also go over something mentioned above: foot peels. This is something that can be a bit tricky if you haven't discovered the incredibly helpful ToeBreak control attribute. As you can see in the image below, starting with planted foot, as it peels off the ground the heel lifts first, using the footroll attribute.



Once the foot is up on the toes, the next thing you would do is start lowering the toebreak attribute until only the tip of the toes are on the ground. Finally the foot pulls off the ground completely, which is where you would reset the footroll, balltwist, ballrock, and toebreak attributes and reposition the foot with rotations, using the ballroll attribute to give the toes a bit of drag for a nice overlap.

Expression and Emotion in Feet

With the anatomy and workflow out of the way, it's time to talk a bit about adding emotion to the feet. Feet aren't just simple paddles that we humans walk on to get from point A to point B. While not quite as emotive as a person's hands or face, feet can tell you a fair amount about a person. You already know that a walk can add personality to a character, be it male/female, happy/sad, heavy/light, and many other emotions/varieties. But even a standing character's feet can tell you a lot about them, from gender, to personality, to emotion. A great example of this is Disney's Hercules. As a kid, Hercules had a very awkward stance, showing just how unsure he was of himself and emphasizing his clumsiness. After he grew up and trained to be a hero, his stance widened and his feet had a much more confident stance, showing the personal growth from head to toe.

 
 


The best way to figure out how to pose and animate emotion and character into your feet is to simply try it out yourself, and maybe shoot some video reference. There are a myriad of ways to express yourself, and only by studying the actual actions will you be able to really sell the performance.

Bonus Foot Planting Tip

Another thing I want to cover in this article is a simple foot tip that I've found really helps to add an organic "fleshiness" to foot contacts.

Whenever a foot contacts the ground, add an ever so slight amount of upward Ty to the foot on the contact frame so that it isn't quite touching the ground. Then on the frame after, plant it solidly on the floor. This will help to give a "softness" to the step that is felt but not seen, making it feel like the feet are fleshy and not made of something hard like wood.

And lastly, here are some great references for feet, both for drawing and posing. It's also where I found the drawings for this article, so feel free to check them out!

Character Design Notes Foot Reference - Part I
Character Design Notes Foot Reference - Part II

Thank you for taking the time to read my post. I hope it's been helpful,
and as always, if you have any comments, questions or suggestions,
you're more than welcome to leave a comment or send either Beau or
me a message on AM.

2 comments:

  1. Really nice article dude, well written and I learned a couple new tricks from it! Thanks a lot!

    ReplyDelete
  2. Very helpful, and great foot planting tip! I'll definitely use it. Thanks!

    ReplyDelete