Original subtitles

- [Instructor] This video,

we are going to finish the polish stage of our run cycle

animation by polishing the arms.

Whenever you are walking with forward kinematic chains

like our arms,

we need to start from the root of the chain

and then go down to the tip of the chin.

So in this case,

we will start with the shoulders, then work on the arms,

Then forearms, and finally hands.

To polish the shoulder animation.

I will work first on the rotation,

but this time I won't be isolating each rotation channel

one by one, but I will work on the free channel

at the same time.

The idea is to smooth out the shoulder rotation,

make sure that we don't have any weird movement

into the shoulder or glitches.

And the second thing is to make sure that the extreme will

reads well and that we pushed the pose.

So that we get a nice and contrasted animation.

The thing to remember is that the shoulder

lead the motion of the torso,

the shoulder pulled the whole chest up.

So rotation wise,

we should avoid making the shoulder drag too much.

So Kev, why is it so a little more complex

to explain that what we did with the spine?

But my method is to move the keys channel by channel

and see all of the character behaves per channel

and then work on the pose.

So in this case, this is the moment where are the shoulder

should be hitting it's extreme pose

a little before the chest,

so I'm trying to push the shoulder up

and then polish the curve,

make it a little smoother

so that I don't have weird left to right motion

during the transition.

If we have a look to the final curve here,

we can see that it has a pretty classic shape in the end.

We get a plateau on the X rotation and the Z rotation

whenever we are reaching the extreme.

So it means that the shoulder is not rotating that much

once it hit its highest pose

whether it's forward or backward.

And then we have the fast transition during

the passing pose.

The work on the wire rotation curve is less sensitive.

We do have to work on it because it could cause

a gimbal lock, but the twisting motion is

that is driven by the Y eular rotation

is not quite natural, but once combined with the X and Z

rotation curves, it blends pretty smoothly.

So the idea is just to kind of fix the orientation

of the shoulder on those specific poses.

I know it can sound a bit abstract here,

but what I'm trying to avoid is any distortions

in the shoulder shape

while the X and Z curves are here to drive the motion.

Don forget to use the motion path

to double-check your arcs and spacing.

And that you can use to tail off the bone

or tip of the bone to calculate this motion path.

In this case,

it result in showing you the tip of the shoulder,

not the root of the clavicles.

At this stage, you can call the shoulder polishing done,

or you can push it a little further using location.

Using the Y and Z location curve,

I will make the shoulder drag a bit just before it hits

it's extreme, but I don't want to delay the shoulder.

So I reset the pose by moving the keys that has a zero value

on frame six.

And then I will slightly push the shoulder down

during the passing pose so that when you put weight

into the shoulder,

as if just after the impact,

it was getting pulled down by its own weight,

then I will do the same in the pose just after

it reaches it's highest point.

I will push it a little higher

as if there was momentum into the shoulder

that make it go a little further up.

So I keep it very subtle.

The idea is just to emphasize what we did before.

Whenever the shoulder is in it's down pose,

I make it drag a little bit just to touch

and I push it down a little more.

And when it has reach its highest point,

one or two frame later,

I will just raise it a little more

to bring a bit of momentum into the shoulder motion.

The heavy lifting was done with the rotation,

and this is what will brings you nice arcs.

And then you can bring some texture to your animation

using location.

Again, it must be subtle because if you push too far,

you will break the shape of the shoulder and it will look

pointy or out of place.

Unleashing the arm is pretty straightforward.

One of the first thing you may do is track the position

of the elbow tweak controller

so that you can easily track your arcs from the elbow.

I also often use the end position using the wrist

tweaker controller,

but at this stage it will be better

to focus on the elbow position.

While on the reference,

we have seen that there was a slight slowing down

during the passing pose,

and then reaccelerating whether forward or backward,

this is really noticeable when using extreme slow motion.

And when I've tried, it felt a bit weird.

So in my case,

I prefer to have a fast motion during the passing

and ease into the extreme and old pose,

which clearly shows when we look

at the spacing on those arcs,

we have a large spacing during the passing

and it gets tighter on up pose.

Shape wise from a side view, the arc is very smooth.

From the front view,

my main concern was not to make the elbow

going too far on the outside

because the faster you run,

the closer to the body your elbow will be.

And then I make sure it goes slightly on the inside

on both extremes.

Third wise, we have a smooth sensory dull shape

regarding the X rotation,

which mainly influence the distance between the chest

and the elbow from the front view.

And then the Z and Y rotation curve mainly drive

the swing of the arm.

So we can spot on them our usual plateaus shape

when we reach the extreme,

weave the fast transition during the passing.

I've also slightly worked the W curve

just to remove any glitches.

The W curve is generally involved

whenever you are trying to reach an extreme

with the other curve and the quaternions can't solve it.

So unless you are doing a full revolution,

the W curve is generally not that much involved.

But it does need some attention on such a moving part,

since it's a long forward kinematic chain,

it's in everything, the movement of the torso,

then the movement of the shoulder, et cetera.

So we do need to double check the motion path of the elbow

and eye my Y, Z and X rotation curve are kind of smooth

in the graph editor.

I'm just double checking that the W curve

is not bringing any glitches.

In the end, as for every cycle we've been working on,

make sure that your first and last keys are the same

and they are aligned.