// How to Orientate the LRA of a Joint //

Software Used:

Maya

If you’re new to what a local rotation axis is, let’s start with a scenario you may have already seen and didn’t know how to fix.

Let’s say I’m creating a new rig for a character and working on the arm specifically. I click out a series of joints for the arm, but they aren’t quite in the right place for my mesh so I have to move them to get them in the position of the arm. (Unless you built your arms straight out along the grid, you usually have to move them some. Like if you built them in the front view, you’ll likely have to move them to line them up with the arm in the side view. And for the sake of this tutorial, let’s assume I’m really bad at placing joints so it’s easier to see the point I’m trying to demonstrate.) (Fig.01).

Fig.01

After clicking out the joints I’m going to move them into the place I want them. Don’t ever rotate your joints into place if you can avoid it. You always want to have clean rotations on your joints so your animators can zero out the rotations later if needed to get the rig back into its bind pose. If you do need to rotate them to get them into position, you should use Modify > Freeze Transformations to reset your rotations (Fig.02).

Fig.02

TIP: If you want to move a joint at the top of a chain without moving its children, you can just move its pivot point. Because that’s all joints are: pivot points. You can hit the Insert key to toggle Pivot Mode on and off. You can also hold down the D key to move it as long as you are holding down the key (Fig.03).

The problem we have now is if I want to rotate the elbow. From an animator’s stand point, since the elbow only bends on one axis, it’d be easiest to animate the elbow if it also used on animation axis to bend. But if we look at it right now, it’s going to bend on multiple axes in the channel controls, to appear to be bending in on the axis (e.g: rather than being able to just rotate Rotate X, you have this crazy combination of Rotate X, Y and Z, which is impossible to get a real handle on in your graph editor later) (Fig.03).

Fig.03

But this is an easy fix. We can orient what is called the Local Rotation Axis. You may have noticed that if you just click out a series of joints and don’t move them after creating them, there is one axis that is lined up with the joints and it probably makes more sense when rotating it. There’s a good chance that if I had built the chain in this position to start with, it’d be oriented correctly and we wouldn’t have that issue. But that’s rarely the case when placing joints.

To edit the LRA of the joint we want to start off with having the joint we want to edit, or its chain’s parent selected. We’re going to go into Component mode and then turn on the filter for Miscellaneous Components (The ? button.) (Fig.04 – Fig.05).

Fig.04

Fig.05

In this mode we can now see our LRAs. We can edit them by simply rotating them. But first, I want to get a bit more technical about how they’re aligned. I want to be able to set up the joints where at least one axis can spin the bone like a top. That means one of those axes has to be aligned right up with the joint. How do we do that? We have it aim at its child joint. But easier than that, there is actually an Orient Joint command that does it. For a selection, we either need to select each LRA we want to orient, or I can just go back to Object Mode and select the base of the chain I want to orient. In this case I will select the chain on the arm. Then I will go to Skeleton > Orient Joint (Fig.06).

Fig.06

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'Maya'

'How to Orient the Local Rotation Axis (LRA) of a Joint'

Software Used: