Bone Dynamics and Secondary Motion
The best animation has motion the animator never keyed: a ponytail that swings a beat after the head turns, a cloak that settles after a stop, ears that flop on a landing. That is secondary motion, and in FoundryInk it comes from marking a bone Dynamic. Set that one checkbox and tune Stif, Damp, and Inert, and the studio springs those parts for you. This page teaches the whole feel of it.
1What secondary motion is
Primary motion is what you key: the character turns, jumps, stops. Secondary motion is what those actions cause: the hair keeps moving after the head stops, the tail swings wide and settles, the coat flares and drops. It follows the laws of lag and momentum, and animating it by hand on every strand is a nightmare. Bone dynamics let the studio compute that follow-through automatically, so your rig gets a layer of life for almost free.
2Turn on Dynamic for a bone
Pick the bone that runs through the floppy part, a strand of hair, a tail, an ear, and open the Bones panel. Tick the Dynamic checkbox. That bone is now physics-driven: instead of you keying its every wiggle, it swings and settles in response to how its parent moves. Ticking Dynamic reveals its three tuning fields, Stif, Damp, and Inert, which shape exactly how it behaves.
3Stif: how eager it is to hold its shape
Stif is stiffness, the springiness that pulls a dynamic bone back toward its rest pose. High stiffness makes a part behave like a stiff wire that barely bends and snaps back fast, good for a firm quiff or a starched collar. Low stiffness makes it floppy and loose, like limp hair or soft rope that swings far and lazily. It is the single biggest dial for the character of the motion.
4Damp: how quickly it calms down
Damp is damping, how fast the motion bleeds off and comes to rest. High damping makes a part settle almost immediately, with barely a wobble, like hair moving underwater. Low damping lets it swing back and forth several times before stopping, like a pendulum or a bouncy spring. Damping controls the number of after-swings, so it is your tool for choosing between a quick settle and a long, playful jiggle.
5Inert: how much it resists a change
Inert is inertia, the sense of weight and reluctance to start or stop moving. High inertia makes a part feel heavy: it lags noticeably when the body starts, then overshoots when the body stops, like a weighty braid or a heavy tail. Low inertia makes it feel light and responsive, following the body almost at once, like fine hair or a light ribbon. Inertia is where you dial in how much a part seems to weigh.
6How the three dials work together
The three fields are a team. Stif sets how hard the part springs back, Damp sets how fast that springing calms, and Inert sets how heavy it feels doing it. A bouncy ponytail is moderate stiffness, low-to-mid damping, and light inertia. A heavy cloak is low stiffness, higher damping, and high inertia. There is no single correct set of numbers, only the feel you are chasing, so adjust one dial at a time and watch.
7Build a chain for a tail or a strand
A single dynamic bone bends at one point, which is fine for a stubby ear but stiff for a long tail. For flowing motion, build a chain of several bones down the length of the tail or hair, each a child of the one before, and mark them all Dynamic. The motion then ripples down the chain like a wave, with each bone lagging its parent, which is what gives hair and cloth that smooth whip and settle.
8Best candidates for dynamics
Reach for dynamics on the parts that trail and dangle: hair and ponytails, tails, floppy ears, antennae, scarves and cloak hems, earrings, and loose cloth. Anything that hangs off the body and would keep moving after the body stops is a candidate. Avoid it on structural parts like the backbone, the upper arm, or a firmly held prop, which you want to control precisely by hand. Dynamics are for the fringe, not the frame.
9Tune it lightly so it does not whip
The most common mistake is overdoing it. Cranked-up dynamics make hair whip wildly and cloth flail like it is in a storm, which reads as cartoonish and distracting. Start subtle and add only as much motion as the shot needs. A little lag and a soft settle is almost always more convincing than a big dramatic swing. If your eye goes straight to the flailing hair instead of the character's face, you have gone too far.
10Ignore wind when a part should stay calm
A dynamic part can also respond to sway, but sometimes you want one particular strand to sit still while the rest move. Each bone has an Ignore wind checkbox for exactly that: tick it and that bone opts out of the ambient sway, holding steady while its neighbours drift. It is a handy way to keep, say, a character's front lock calm and readable while the back of the hair flows.
11There is no scene-wide wind panel
Now the real limit. FoundryInk has no global wind or whole-scene physics panel where you set a breeze for the entire shot. The only wind control is the per-bone Ignore wind toggle you just met. If you want a windswept look, you get it from Dynamic bones: their natural lag and sway, tuned loose, reads as a breeze once the character moves through the scene. Sway comes from the springs, not from a wind slider.
12Test, watch, and adjust
Dynamics only show their true behaviour in motion, so test them properly. Switch to Test mode and swing the parent around, or hit Play on an actual bit of animation and watch the trailing parts respond. Look for the lag on the start, the overshoot on the stop, and how many wobbles it takes to settle. Then go back and nudge Stif, Damp, or Inert until the feel matches what is in your head.
13What good secondary motion feels like
Good secondary motion is felt more than seen. The hair follows the head a beat late and settles without a fuss, the tail swings with a weight that matches the body, and nothing flails for attention. It makes the character feel like it has mass and belongs in a world with gravity. When a viewer believes the character is real without being able to say why, the quiet lag of well-tuned dynamics is usually a big part of the reason.
14Dynamics on top of everything else
Dynamics stack neatly with the tools from earlier pages. Your keyed poses drive the body, your IK targets plant the feet, and dynamics ride along on the hair and cloak on top of all of it. You do not choose between them; a finished rig uses posing, IK, and dynamics together. Turn dynamics on last, once the acting reads, and they become the polish that makes solid animation feel genuinely alive.
Dynamics questions
Select the bone running through it, open the Bones panel, and tick Dynamic. That bone becomes physics-driven, swinging and settling based on how its parent moves, and it reveals the Stif, Damp, and Inert fields to tune the feel.
Stif is stiffness, how hard it springs back to rest. Damp is damping, how fast the swinging calms down. Inert is inertia, how heavy it feels and how much it lags and overshoots. Together they shape the whole character of the motion.
You have overdone it. Lower the overall motion, raise Damp so it settles faster, and consider more Stif so it does not swing as far. Gentle lag reads better than a big flail, so dial it back until it stops stealing the shot.
Build a chain of several bones down the tail, each a child of the one before, and mark them all Dynamic. For a drawn tail, Flexi Bind the shape to the chain so its points carry smoothly. The motion then ripples down the length.
No. There is no scene-wide wind or whole-scene physics panel. The only wind control is the per-bone Ignore wind checkbox. To get a windswept look, use loose Dynamic bones and let their natural sway do the work as the character moves.
Yes. Tick Ignore wind on that strand's bone and it opts out of the ambient sway while its neighbours drift. It is per bone, so you can mix calm and moving strands within a single head of hair.
After. Get the primary poses and acting working first, then add dynamics as a finishing pass. Springy hair on a stiff body just looks like a stiff body with wobbly hair, so let the good animation come first.
Your rig moves with follow-through
You taught hair to lag, tails to swing, and cloth to settle, all from one Dynamic checkbox and three honest dials. That layer of automatic follow-through is what makes a rig feel like it belongs in a real world. Next, learn to squash and stretch whole pieces of art with the Warp tool, for the impact and weight that bones alone cannot give.