Jan 15, 2013

Animating Dogs, Part 1: Anatomy and Some Gaits

It will come as a shock to anyone who knows me (or reads this blog) that I have a thing for drawing animals.  Once you've had a moment to calm yourself, I'd like to move into a discussion of animating a dog--their anatomy and their movement.  I've actually always been more of a cat person, but whatever.

Two places to begin when learning how dogs move:
  • real dogs
  • previously animated dogs

A third one I'll add to the list:

Dog Anatomy

I'll start with the anatomy, since that's required to understand any of this.  All dogs have the same basic skeletal structure, which is basically squashed and stretched to give you anything from a dachshund to a borzoi.


The most important bits to pay attention to are the legs, the shoulders, and the spine (and, to a lesser extent, the head).  The way these elements interact will determine whether your dog actually moves like a dog.  Here's a front view:


Let's start with the front legs/shoulders.  Dogs have, effectively, vertical legs and shoulders.  Shoulders angle very slightly inward and about 45 degrees to the back.  This is distinct from, say, a bear, which has massive inward-sloping shoulders.

A dog's front foot is similar in structure to a human hand.  If you were to hold your hand in such a way that the top of your palm were resting on a table, with your fingers slightly curled and your palm off the table, angled backwards, you would be recreating the dog's structure.  However, unlike you, a dog has a pad on which its 'palm' rests.



A dog's back leg is also similar in form to a human foot, with the bones arranged a bit differently.  Like many other quadrupeds, dogs walk on their toes, with their heels being high up compared to humans', giving the impression that their legs bend backward.  That's not at all the case; it's simply a different way of doing exactly what we do.



A dog's spine is very similar to a human's.  Unlike cats, who have incredibly bendable spines, dogs, while flexible, don't generally contort themselves in the same crazy fashion.  Walking and running will not involve too much bending of the spine, but some movements (especially playful ones) will.

The Walk

The basic walk cycle of dog is very simple, and very similar to other animals as well.  Cats, horses, deer, and most other quadrupeds walk in a similar pattern.  The walk, most basically, is defined as a gait in which at some point three feet are touching the ground.  In terms of steps, each sequence goes in this order:

  1. Left front (LF)
  2. Right hind (RH)
  3. Right front (RF)
  4. Left hind (LH)
Then repeat.  So, it forms a kind of hourglass pattern.

Where it gets difficult is figuring when the other legs pick up.  Here's the full order.

Feet off ground / Feet on ground

LF / RH,RF,LH
LF,RH / RF,LH
RH / RF,LH,LF
-- / RF,LH,LF,RH
RF / LH,LF,RH
RF,LH / LF,RH
LH / LF,RH,RF
-- / LF,RH,RF,LH
LF / RH,RF,LH

Confused?  Yeah, you should be.  A better way to think of it is probably this: two human walks happening simultaneously, with the same timings but at different points in the cycle.  A human walk goes like this:


This walk cycle has eight distinct points (the first and last in the picture above are the same).  If we label them 1 to 8, then we can figure out how it goes for a dog.  Let's assume the front legs are on 1.  Where are the back legs?  They are on 3.  When the front legs are on 3, the back legs are on 5.  That means the back legs are always two steps ahead of the front, which is a lot easier to remember.

That also gives you a clue to the hips and shoulders.  When the front legs are at their highest point, the back legs are at their lowest.




In the end, it will look like something like this (my first attempts):

video


video

Other Gaits

There are three (possibly more, depending on how you separate them) other regular gaits that dogs have:

  1. amble/pace
  2. trot
  3. run/gallop

Amble

In the amble, parallel legs on the dog move together, so both legs on the left side will move, then both on the right.  When the legs are picked up, the back leg goes first, followed quickly by the front leg, two(ish) frames behind.

When the dog ambles, the spine bounces up and down.  Each time one of the sides is at its highest point, the back arches, with the middle of the back at the highest point.  Each time a side lands, the back reverse arches, with the middle at the lowest point.


Ambles are used as a trot/run for very large animals, like elephants or hippos, because their body masses are too big for all legs to be off the ground at any moment.  See this website for more information about that.

Pace

A pace is a slightly faster amble, the difference being that in a pace there is almost no offset.  Front and hind legs pick up at the same time, and just as one side's legs touch the ground, the other side's are picking up.

Next time...

THE TROT!
THE RUN!
EXAMPLES OF ANIMATED DOGS!





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