· Game Dev · 1 min read
Procedural Spider Locomotion in Unreal Engine 5
How I built a fully procedural spider rig in UE5 using inverse kinematics, terrain raycasting, and a custom gait state machine — no animation clips required.
Overview
A fully procedural spider locomotion system built in Unreal Engine 5. No pre-baked animation clips — every footfall, body sway, and leg reach is computed at runtime from the geometry beneath the character.
System Design
Leg IK Solver
Each of the eight legs has an IK chain solved with UE5’s built-in FABRIK solver. A per-leg raycast probes the terrain ahead of the predicted foot position and anchors the IK target to the collision hit point.
Gait State Machine
A lightweight FSM governs stepping rhythm. When a leg’s current grounded position diverges more than a configurable threshold from its ideal position (relative to body velocity), a step is triggered. Steps are staggered across contralateral pairs to prevent simultaneous lift of adjacent legs.
Body Dynamics
The body height and roll are computed as a weighted average of all grounded foot heights, with a spring-damper smoothing pass to avoid jitter on uneven terrain.
Performance Notes
At 60 fps the full IK solve + raycasts for all 8 legs costs ~0.18 ms on a mid-range GPU. Batching the raycasts into a single async trace call was the biggest win.
Source
Blueprint + C++ hybrid — core math in C++, designer-tunable parameters exposed via Blueprint.
