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Docs Rigging

Bones & dynamics

Let a bone follow through and settle on its own instead of keyframing every last wobble by hand.

Dynamics adds spring physics to a bone's Angle, Position or Scale, each as its own channel with its own on/off switch in the bone's Properties. A dynamic bone still follows every key you set on its parent: dynamics only adds the lag and overshoot on top, the kind of motion a tail or a ponytail has that a rigid rotation does not.

The three channels

Angle, Position and Scale dynamics are independent: turn on only the ones a given bone needs. Angle dynamics is the one most rigs use, for the swing of a limb or a hanging chain; Position and Scale dynamics exist for bones whose translation or size should itself have spring and lag.

ChannelParameterDefaultRange
AngleStiffness10.00.1 to 100
AngleDamping0.800 to 1
AngleFlexibility100%0 to 100%
AngleGravity0-200 to 200
AngleWind Sensitivity100%0 to 200%
AngleTorque0.0-200 to 200
AngleWeight1.000.01 to 20
PositionSpring10.00.1 to 100
PositionDamping0.800 to 1
PositionTorque0-500 to 500
PositionWeight1.000.01 to 20
ScaleSpring10.00.1 to 100
ScaleDamping0.800 to 1
ScaleTorque0-100 to 100
ScaleWeight1.000.01 to 20
The Bone Dynamics section of the Properties panel with the Angle channel enabled and its Stiffness and Damping fields exposed.
On the Timeline these parameters sit in the bone's own group under the headers Angle Dynamics, Position Dynamics and Scale Dynamics. The longer names keep them apart from the bone's Angle, Stretch and Position channel rows just above them, which are the pose itself rather than the spring driving it.

What settles a bone, and what makes it overshoot

Stiffness (called Spring on the Position and Scale channels) is how hard the bone pulls back toward its keyed pose: raise it for a snappy, twitchy reaction, lower it for a slow, heavy sway. Damping, 0 to 1, is how quickly that pull loses energy: near 0 the bone swings past its target and oscillates for a while before settling, near 1 it eases in without any overshoot at all.

Weight stands in for mass: a heavier bone (a higher Weight) lags further behind the motion driving it before it catches up, a lighter one keeps up almost immediately. Torque adds a constant rotational (or positional, or scale) push regardless of what is moving the bone, useful for a steady lean rather than a reaction to motion. Gravity, on the Angle channel only, pulls the bone downward the same way at all times. Flexibility scales how much the whole channel is allowed to move at all. Lower it to pin a bone closer to its keyed pose while still letting a little dynamics through.

Wind

Wind Sensitivity decides how strongly this particular bone reacts to the shared wind field, 0 to 200% and defaulting to 100%. The wind itself (whether it is even on, and how strong) is set once for the whole scene in the Physics panel; see Physics & wind. A bone with Dynamics off never reacts to wind, however high its sensitivity is set.

A bone under IK takes no wind either, and neither does any bone in the chain the solve writes, from the effector up to the root. Both would otherwise be pulling the same joint at once: the solve holds the bone at the angle the target demands while the wind spring keeps pushing, and the artwork bound to it goes on swaying under a bone that is visibly standing still. Gravity, stiffness, damping and torque still apply to those bones, so a chain under IK still settles and still resists.

Determinism and why the playhead needs to move

Dynamics is a real simulation, not a random wobble: it steps forward one frame at a time from the bone's rest pose, and every frame's result depends on the frame before it. Celas Studio resolves that chain of frames however you get to a given frame (playing through it or scrubbing to it directly), so the same swing settles exactly the same way every time, and a paused frame never keeps drifting on its own.

Because each frame depends on the one before it, jumping straight to a distant frame does not skip the simulation. Celas Studio still resolves every frame along the way to get there before showing you the result.