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arm.legacy

Full IK/FK arm rig template module

Overview​

arm.legacy provides a complete arm rig with IK/FK blending. It shares a common module base with leg.legacy and quad.legacy, meaning their construction and logic are nearly identical.

Template Structure​

  • The root of the template marks the shoulder position.
  • The rest of the chain defines the elbow, wrist, carpal, and fingertip.
  • You do not need to orient joints manually; orientation is handled automatically during rig build.
  • An optional clavicle joint can be placed above the shoulder joint. This acts as the pivot for the clavicle rig, which the arm will then be parented to.

Options​

  • clavicle (bool, default: on): Enables the clavicle rig.
  • reverse_lock (bool, default: off): Enables a reverse foot-style locking system.
  • effector_plane (enum, default: z): Orientation vector used to auto-orient the wrist joint chain.
    • x, y, z: World-space up vectors.
    • auto: Based on the plane formed by the joint positions (useful for wings).
    • ground: Forces wrist orientation perpendicular to the ground plane (used for feet).
  • pv_space (node, default: *::space.cog): Global parent space for the pole vector.
  • pv_space_default (float, 0-1, default: 0): Default weight for the pole vector space switch.

IK Stretching​

  • default_stretch (bool, default: on): Enables IK stretching by default.
  • soft_distance (float, 0-1, default: 0.05): Soft IK activation threshold relative to stretch distance.
  • stomp_power (float, -1 to 0, default: -0.5): Volume compensation power factor. -0.5 corresponds to inverse square root falloff.

Interpolation​

  • smooth_type (enum, default: length): Mode for distributing intermediate joints along the limb.
    • length: Interpolated along the deformation.
    • parametric: Interpolated at fixed parameter points.
  • blend_joints (bool, default: on): Enables skinning roll joints at key articulations.

Twist System​

  • twist_joints_up (int, min: 2, default: 3): Number of twist joints between shoulder and elbow.
  • twist_joints_dn (int, min: 2, default: 3): Number of twist joints between elbow and wrist.
  • add_chains (list[str], optional): Adds multiple twist/shear chains for advanced deformation control.
  • advanced_twist (bool, default: off): Adds a correction rig for twist artifacts using extra attributes.
  • space_switch (bool, default: on): Enables default space switches on key controllers.

Not Yet Implemented​

  • aim_axis (enum, default: -y): Not yet supported.
  • up_axis (enum, default: -x): Not yet supported.
  • up_axis2 (enum, default: z): Not yet supported.