Everything You Need to Know About 3D Animation Rigs in 5 Minutes
If you’re anything like us, you got into animation to spend your days flexing your creative muscles and creating cool stuff for video games and feature films. But animating in real life is a little more complicated than just making stuff look cool. You also need to know how to do more complex tasks, like rig and skin your 3D characters. Rigging introduces coding, complex anatomical structures, and mathematics into your work. It can feel a little overwhelming at first, but after you learn the ropes, you’ll appreciate how much easier high-quality rigging makes your life.
This article will teach you the basic terminology and concepts you need to know before starting with a rigging tutorial.
What is 3D rigging?
The 3D rigging process adds animation controls to a 3d model. Without a rig, your character can’t move. Even objects have simple rigs if they move position.
Specifically, a character rig is used to animate characters by keyframe or with motion capture. There are two main types of rigs; Forward Kinematics (FK) and Inverse Kinematics (IK).
- FK rigs allow for more mechanical movement as you have total control of each joint’s rotation and position.
- IK rigs are more advanced as they move an entire chain of joints. For example, if someone grabbed your wrist and pulled it to the left, your elbow joint would move and your shoulder joint might even rotate — that’s the basic premise of IK rigs.
3D rigging isn’t for everyone, but you will need to learn at least the basics of building and using a rig. Rigs are used in every aspect of 3D animation, and even 2D animation — so they’re a vital step in the animation pipeline. An animation studio will often have an entire department for rigging. It really is an essential skill.
What is skinning in 3D animation?
The skeletal system of any rig will mimic the bone structure of the subject (i.e. human bodies get a human skeletal bone structure). Once this bone structure (rig) is in place, a character mesh is attached to the digital skeleton in a process called skinning.
Skinning is complex to explain in writing, but pretty straightforward to actually do. Weight painting is part of the skinning process and pairs a weight scale percentage of manipulation on each vertex to a nearby bone. This can be clearcut (100% of the weight goes to a specific bone) or complex in the event of joint or muscle manipulation (eg. the upper arm bone might need to manipulate a bit of the mesh that’s close to the lower arm bone to produce a realistic effect. In the cases of bad skinning, you will notice defects and strange manipulations (e.g. When a character's arm moves, so do a few vertices on the feet). Without skinning, your rig would not produce physical movements in your mesh.
A control rig manipulates the joints and bones
Most pre-rigged characters have a control rig that allows animators to manipulate the skeletal system. While there’s a lot going on behind the scenes of a rig, all arrows, icons, and shapes (often displayed as brightly colored wires) are a part of the control rig. Animators set keyframes ONLY on the control curves, and NOT directly on bones. Control rigs exist for many reasons. At the most fundamental level, they’re there to help:
- Riggers create complex chain relationships between joints
- Animators have freedom to reset rigs back to their original state (e.g. T-pose)
Every modern rig built to the industry standard will have the following controls to allow animators the best movement possible.
The world control is typically located at the very top of the control rig hierarchy. Moving the world control will move the situation of the rig in 3D space. The world control is only used to position your character in 3D space — it’s never used to animate the character,
Root control is ground zero for all controls. The root control is most often used for translational movement. For example, many animators start with an in-place walk-cycle. If you want that walk to actually go somewhere in 3D space, you’ll need to move the root control at the correct speed.
Attribute sliders influence a wide array of elements, from blend shapes, to the translation of bones, to a cluster deformer. They are often reserved for a desired pose that would be unachievable via a typical bone rig setup. These sliders vary from rig to rig. A common slider is FK/IK blending. For example, during a ‘kick animation’ an animator may need to use FK for the action kick, but blend to IK when the character's foot touches the floor.
A blendshape (also known as morph target animation) morphs and deforms a 3D character model in a specific, controlled way. For example in facial animation which requires complex mesh manipulation, blendshapes are a requirement (working in conjunction with an FK rig to control jaw and tongue movement). You might also find “Corrective Blendshapes” within the rig controls of a character’s body. These help fix unavoidable mesh deformations that occurred during the skinning process. They don’t need to be manipulated by you directly.
Squash and Stretch
A derivative of blendshapes, squash and stretch is a control feature that is used to mimic the squash and stretch action often used in 2D animation. A rigging artist typically achieves this through a blendshape in conjunction with a complex bone setup that deforms the mesh by pulling it apart. Realistic rigs and stylized rigs can both benefit from this feature, though the latter is most common. Squash and stretch won’t have much influence over more realistic rigs.
Corrective controls are often present in rigs in order to fix issues in certain poses. Unlike corrective blendshapes, they can be manipulated at the animator's discretion. However, depending on the rig they can also exist as driven controls. They are usually bound to small sections of the model in order to make fine, minute adjustments to the overall shape of the mesh (e.g. forearm deformations).
Cloth and Hair Controls
Generally, cloth and hair are rigged in FK for easy incorporation of overlapping lines and curves. Being rigged in FK also means that the animator can run fake-dynamic scripts or basic dynamic simulations.
Animators set these controls using driven keys, so that when they move a limb in a certain direction the cloth control follows corroding, essentially doing all the “cloth animation” for them.
External Controls are an essential element to a facial rig in particular. As the name implies, they exist “outside” the rig. These range from standard eye drivers or as vessels for driven controls and/or blendshapes. They are typically universal in usage and it is up to the rigger to decide what they want to achieve with external nodes.
While not strictly a control, you can use a rig picker to select controls via a separate 2D menu (instead of via the viewport controls or side panel). Use of this menu depends completely on the animator’s preferred method.
3D rigging software
There are many 3D animation packages and each has its own pros and cons. We suggest you choose the software most suitable for your project or workflow.
The Animation and rigging workflow in Maya, 3DS Max, Blender and Cinema 4D:
The majority of rigs in these programs have the same functions and operations. They tend to look similar and all use a control rig system to actually animate a character. After creating the initial skeletal system, riggers will “bind” the character mesh to the bones of the rig via the skinning process. After adding the control rig, a 3D artist will begin to tweak areas of the rig to avoid “breaking” or unusual deformations in the character mesh. Rigs are not compatible cross-program due to differing implementations of IK solvers.
Keyframe animation: Keyframe animation software requires manually setting key positions for each of the character's bones. It is the most common type of animation.
Motion capture animation: Motion capture animation is achieved through retargeting mocap data onto a rig. This re-targeting process is usually achieved via a plugin (here’s a free one). There are plenty of tutorials for the motion capture animation process online.
The Animation and rigging workflow in Unity and Unreal Engine:
Unity and Unreal Engine are first and foremost game engines; they’re built to create games. These programs optimize your computer’s resources to keep frame rates high and render in real-time. In recent years, Unreal Engine has become exceedingly popular with virtual live streamers (known as “VTubers” who use a virtual avatar). Others have used Unreal and motion capture to build highly accurate pre-vis sets for productions (known as virtual productions). Finally, the entertainment industry uses Unreal for virtual event productions like music concerts. In most cases, you will want to bring a pre-rigged and pre-animated character into a game engine. You can rig in Unity, but the majority of animators prefer using software like Blender or Maya.
Keyframe animation: Keyframe animation in game engines is rudimentary. Most keyframe animation is done via more animation-friendly software, and is baked into the character’s digital bones.
Motion capture animation: Motion capture can either be pre-recorded or recorded live in game engines via a plugin (here’s a free one). All you need to do is re-target the animation and you have realistic motion in real time. Here’s a quick tutorial.
Is there a difference between the rig you need for motion capture, and the one you need for keyframe animation?
Nope, a good rig is a good rig! Any fully rigged character can be used for both motion capture and animation. Most modern rigs are built with motion capture in mind and already contain the specific blendshapes and connections needed. However, it is possible your rig doesn’t meet up to the specific needs of your motion capture hardware and software. In cases like these, refer to your mocap animation software’s recommendation.
Can I “skip to the good part” and avoid creating a complex rig?
Surprisingly — you can avoid complex rigging! You can create simple character rigs for your character using tools like Mixamo and MotionBuilder. These tools create extremely simple biped rigs that you can use for fast character animation on your custom meshes. The process is pretty simple — you just click on the joints, and that’s it. As you likely suspect, this simplicity comes at a cost — quality. These click-on rigs are only useful for large body movements on characters with a standard shape and are pretty impossible to use for fine finger movement. They also won’t help you breeze past facial expressions — you still need to make blendshapes. It’s only a good option for background characters or low-budget short film projects.
Many animators use Mixamo rigs to get started with motion capture animation if their character design is simple. In most cases, we advise against short-changing yourself with a basic rig. Instead, you can download a rig asset and character mesh online! Check out some great free and paid rigs in this guide.
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