Control Bones

1What a control bone is

A control bone is a driver relationship: you pick a bone and say take your angle, or scale, or position from this other bone. Once linked, the follower moves on its own whenever the master moves, so you animate one thing and get two (or ten) for free. This is different from parenting, where a child simply rides along with its parent, and different from a smart bone, which corrects a shape. A control bone is about one property feeding another, at a ratio you choose.

2The three driver fields

Open the Bones panel and select the bone you want to be the follower. You will find three driver fields waiting: Angle from, Scale from, and Position from. Each one lets you name a source bone whose movement will drive that aspect of the follower. You can use one, two, or all three at once on the same bone, so a follower could take its angle from one master and its scale from another. Every driver comes paired with a Ratio, which is where the real control lives.

3Angle from: the workhorse

Angle from is the one you will reach for most. Set a follower's Angle from to a master bone, and whenever the master rotates, the follower rotates too. This is how you make an ear swing when the head turns, or a second eyebrow copy the first. On its own it copies the rotation exactly, one to one, but paired with a Ratio you can make the follower turn more, less, or in the opposite direction. Most character rigs lean on this field heavily.

4Ratio, and the minus sign

The Ratio decides how much of the master's motion the follower takes. A ratio of 1 copies it exactly, 0.5 copies half (a soft, lagging drag), and 2 doubles it (an exaggerated, whippy follow). The useful move is a negative ratio, which mirrors the motion, so the follower turns the opposite way to the master. That minus sign is how you drive a left eyebrow and a right eyebrow from the same control, or mirror an arm across the body. One number gives you drag, exaggeration, or a mirror.

5Scale from: grow and shrink together

Scale from ties a follower's size to a master's size. As the master bone stretches or squashes, the follower scales in step, which is handy for squash-and-stretch chains or anything that should swell together. With a fractional Ratio the follower scales less than the master for a subtler effect, and with a larger ratio it exaggerates. Reach for this when a group of parts should breathe as one, like a chest and shoulders that puff up on a big inhale.

6Position from: follow the move

Position from links a follower's location to a master's, so as the master shifts, the follower slides along with it. Combined with a Ratio you can make the follower travel a fraction of the distance for a lagging, trailing feel, or more than the distance for an overshooting one. It is a subtler driver than the others but excellent for trailing elements, a bag swinging behind a walking figure, or a shadow shape that tracks its owner. Use it when what matters is where a bone sits, not how it turns.

7Set one up, step by step

This is the whole recipe. Select the follower bone in the Bones panel, choose the master in the relevant driver field (say Angle from), and type a Ratio. Now switch to a mode where you can move the master and rotate it: the follower should react instantly, with no key of its own. If the direction is wrong, flip the ratio's sign; if the amount is wrong, scale the number up or down. That is the entire loop, and it works the same for all three driver fields.

8Example: both eyebrows from one control

A classic setup: add a single control bone somewhere handy (off to the side is fine, since it need not sit on the art). Set the left eyebrow's Angle from to that control with a Ratio of 1, and the right eyebrow's Angle from to the same control with a Ratio of -1. Now rotating that one control raises both brows together, or the minus sign can make them do opposite things for a quizzical look. You animate one bone and get a full, symmetrical expression.

9Example: an ear that drags behind the head

For believable follow-through, give a floppy ear a lazy drag. Set the ear bone's Angle from to the head bone, but use a fractional Ratio like 0.6 so the ear only takes part of the head's turn. When the head snaps to look left, the ear swings a little less and a beat behind, exactly the overlapping action that makes motion feel weighty and alive. Tune the ratio to taste: lower for a heavier, laggier ear, higher for a stiffer one.

10Secondary motion for free

The value of control bones is that they animate without extra keyframes. You key the master, the big deliberate motion, and every follower reacts on its own for as long as the animation runs. That means no tedious hand-keying of ears, tails, dangly bits, or mirrored parts on every pose. Set the relationships up once in your rest skeleton and they hold across the entire piece. It is the closest thing to free animation the studio offers.

11How it composes with parenting

Control bones and parenting stack, and knowing the order keeps you sane. A bone still obeys its Parent (set in the Bones panel), riding along wherever the parent goes, and on top of that it takes any driver you assigned. So an ear parented to the head already moves with the head, and an Angle from the head adds an extra rotational drag beyond that ride. If you ever want a bone to ignore its parent's motion so the driver is the only influence, tick Isolate from parent.

12Stacking drivers, and the traps

You can drive several followers from one master, and even give a bone drivers on all three properties at once, which is where rigs get powerful. Two traps to avoid: do not make bone A drive bone B while bone B also drives bone A, because that circular reference has no sensible answer. And when you build mirror rigs, double-check your signs, since a stray positive where you wanted a negative will make both sides lurch the same way instead of mirroring. Keep names clear so you always know which bone is master and which is follower.

13Control bones versus smart bones and Actions

It helps to know when to reach for which tool. A control bone is best for a continuous, proportional relationship, like an ear that always drags at 60 percent of the head. A smart bone, built in the Actions panel with a control dial, is best for fixing a specific deformation as a dial turns. And an Action is a reusable block of keyframes you stamp onto the timeline. Control bones are the quiet, always-on option; the others are more deliberate and hand-authored. Often a good rig uses all three together.

14What good looks like

A well-rigged character feels responsive: turn the head and the ears, jaw, and hair all react in believable proportion without you touching them. The tells of good control-bone work are motion that has natural drag and overlap, mirrored parts that stay perfectly symmetric, and a timeline that stays clean because so much is happening automatically. Grab any master bone, waggle it, and watch the followers dance; if they react in sensible amounts and the right directions, your rig is doing its job. When it works, you will animate faster and the result will look richer.

Quick questions