Exploring joint rotation order

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As you rotate a joint in Maya, you will see that each axis, red, green and blue

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all follow as it moves,

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they all stay locked equally distance from each other,

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which makes animation so much easier.

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The problem is this is all a lie.

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We aren't actually looking at the correct axes.

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If I hold down, control and shift

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and then right click,

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we get this marking menu

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in here, we can change how the manipulator looks and how it works.

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Let's change this from object to gimbal.

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You will see that the blue circle has now disappeared.

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What you will also notice is that you can't manipulate the joint now,

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not without selecting an axis.

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Now, if I rotate the Y axis, the red X axis follows but the blue Z axis doesn't.

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But if I select the Z axis and rotate that the other two follow it,

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what's even more confusing is if I switch to the X axis, neither of the others move.

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So what's going on?

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What we are seeing are the true rotational axes.

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So instead of them all moving as one,

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what you can see is that they are in a hierarchy of their own

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much like our joint chain.

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In this setup, Z is a parent axis,

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Y is then parent to this

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and then X sits at the end of the chain. So it has no Children beneath it.

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So this is why Z moves everything Y only affects X

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and X doesn't alter the other axes.

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It's because of this set up, we can do something like this.

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If I rotate Y to this point,

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you will see that the X and Z axis are overlapping.

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And this is gimbal lock

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when two axes occupy the same plane.

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So essentially both rotate the same way

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locking this joint until the Y axis moves again.

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So how do we get around this issue?

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Unfortunately, there is no easy fix which will work in all situations.

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Not without creating a complicated system of nodes. Anyway,

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what we can do though is change the hierarchy.

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So we can dictate which axis will affect which

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and we can do this with the rotate order attribute

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by default, it is set to XYZ

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and this is almost the reverse of what the hierarchy is representing.

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So X is actually at the bottom of the chain.

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Why is in the middle

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and Z is at the top?

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There are lots of other options for you to experiment with.

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Let's try the next one down YZX.

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So this should mean that Y is now at the bottom of the chain. Then Z

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and then X should be at the top and affect everything else.

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OK. So why doesn't move anything else?

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Z moves Y

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and X moves the others.

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OK. Let's try another

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Zyx.

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So this time Z has the least control,

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why is in the middle

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and X is the dominant axis?

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So you can now see how that changes how the joint rotates.

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The idea is that you would set this up to minimize the chances of gimbal lock.

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So you work out which axis will be used most often

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and then set the rotate order to reflect this.

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So if this were an arm,

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we would use Z to lower the limb

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and then we can use Y to move it forwards and backwards,

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leaving X to be used as the twist.

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You see we still do hit that lock here.

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And it's important to say that you will never completely avoid it.

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What you can do is set the rotate order to reduce the chances of it happening.

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Don't spend too much time worrying about each

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and every joint though in your character,

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in most cases,

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the default XYZ will be fine because most joints

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will only need to rotate one particular way.

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The elbow, for example, should only need to move like this.

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But even then we hit a lock at this point.

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So in this instance,

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we know that Y is the primary axis so we can change the rotate order to ZXY

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that fixes it.

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This is just something to keep in mind as you're building your skeleton

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work out,

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which axis is the most important and update that rotate order accordingly.

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Don't worry too much though

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you can change this later. So long as no animation has been done using the rig,

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changing the rotation order after it's been animated

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will break the animation.

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Another important thing to mention is that

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all your controls and offset groups if you

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use them should also have the same rotation order as the joints they are moving.