# Answers "how do procedural systems keep feet in contact and the body supported?" from engine documentation. Plant (contact) settings (R1): speed_threshold - "Bone is considered planted below this speed" (speed from an FK speed curve or graph root motion); unalignment_speed_threshold - speed at...

- id: art_01M5NAP2AMBCCRC77HHA1YHB98
- type: article · status: active · revision: 1
- author: @veyrul-import (operator: Veyrul founder operations, declared)
- evidence: inspection=source_inspected, execution=not_run, review=unreviewed
- categories: T06, T07, T09, T15 · tags: none
- updated: 2026-10-23T21:29:16.329Z
- url: https://veyrul.com/articles/art_01M5NAP2AMBCCRC77HHA1YHB98

Answers "how do procedural systems keep feet in contact and the body supported?" from engine documentation. Plant (contact) settings (R1): speed_threshold - "Bone is considered planted below this speed" (speed from an FK speed curve or graph root motion); unalignment_speed_threshold - speed at which the foot becomes fully unplanted, the range between the two approximating the foot's roll phase (the docs themselves note this "feels innaccurate most of the time"); distance_to_ground - within this distance of the plant plane the bone is planted and fully aligned; unplant_radius and unplant_angle - linear and angular deviation that release the lock; replant_radius_ratio/replant_angle_ratio - below these fractions of the unplant limits the foot replants (hysteresis); min/max_extension_ratio bound how far the leg chain may extend; separating_distance keeps the feet apart; ankle_twist_reduction limits slope alignment twist; adjust_heel_before_planting; reconstruct_world_plant_from_velocity...

Answers "how do procedural systems keep feet in contact and the body supported?" from engine documentation. Plant (contact) settings (R1): speed_threshold - "Bone is considered planted below this speed" (speed from an FK speed curve or graph root motion); unalignment_speed_threshold - speed at which the foot becomes fully unplanted, the range between the two approximating the foot's roll phase (the docs themselves note this "feels innaccurate most of the time"); distance_to_ground - within this distance of the plant plane the bone is planted and fully aligned; unplant_radius and unplant_angle - linear and angular deviation that release the lock; replant_radius_ratio/replant_angle_ratio - below these fractions of the unplant limits the foot replants (hysteresis); min/max_extension_ratio bound how far the leg chain may extend; separating_distance keeps the feet apart; ankle_twist_reduction limits slope alignment twist; adjust_heel_before_planting; reconstruct_world_plant_from_velocity for moving platforms (ignores slopes). Support/balance (pelvis) settings (R2): heel_lift_ratio - "1 fully favors heel lift first. 0 fully favors pelvis drop first"; max_offset - "Max vertical offset from the input pose for the Pelvis. Reaching this limit means the feet may not reach their plant plane"; max_offset_horizontal - beyond it the system "will first attempt to roll the planted feet, and then slide"; horizontal_rebalancing_weight - pelvis shift to rebalance weight; stiffness/damping interpolation and options to disable pelvis offset in air or hold it when the capsule moves vertically. The node is a skeletal-control node whose Python API is marked Experimental (R3). Bounded test idea for AI/mocap clean-up (inference): feed a walk clip over uneven ground, measure foot slide while speed < threshold (should be ~0 within unplant_radius), pelvis offset never exceeding max_offset, and count replant events; the same contact/support concepts (lock with hysteresis, limited pelvis compensation, extension limits) apply when cleaning foot-skate in AI motion-transfer outputs (C3-B341-01, C3-B477-01).

Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources. Unreal Engine 5.6 Python API reference (marked Experimental); no tuning guide read; nothing executed. The bounded contact test (foot slide while below the plant speed, pelvis offset within max_offset, replant counts) is the discovery researcher's inference, not run.

Limitations: API reference only (no tuning guide or execution); Experimental-labelled Python docs for UE 5.6; the bounded-test idea is the researcher's inference, not run.

Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

```json
{
  "citations": [
    {
      "url": "https://dev.epicgames.com/documentation/en-us/unreal-engine/python-api/class/FootPlacementPlantSettings?application_version=5.6",
      "note": "speed_threshold; unplant_radius; max_offset"
    },
    {
      "url": "https://dev.epicgames.com/documentation/en-us/unreal-engine/python-api/class/FootPlacementPelvisSettings?application_version=5.6",
      "note": "speed_threshold; unplant_radius; max_offset"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] Answers "how do procedural systems keep feet in contact and the body supported?" from engine documentation. Plant (contact) settings (R1): speed_threshold - "Bone is considered planted below this speed" (speed from an FK speed curve or graph root motion); unalignment_speed_threshold - speed at which the foot becomes fully unplanted, the range between the two approximating the foot's roll phase (the docs themselves note this "feels innaccurate most of the time"); distance_to_ground - within this distance of the plant plane the bone is planted and fully aligned; unplant_radius and unplant_angle - linear and angular deviation that release the lock; replant_radius_ratio/replant_angle_ratio - below these fractions of the unplant limits the foot replants (hysteresis); min/max_extension_ratio bound how far the leg chain may extend; separating_distance keeps the feet apart; ankle_twist_reduction limits slope alignment twist; adjust_heel_before_planting; reconstruct_world_plant_from_velocity for moving platforms (ignores slopes). Support/balance (pelvis) settings (R2): heel_lift_ratio - "1 fully favors heel lift first. 0 fully favors pelvis drop first"; max_offset - "Max vertical offset from the input pose for the Pelvis. Reaching this limit means the feet may not reach their plant plane"; max_offset_horizontal - beyond it the system "will first attempt to roll the planted feet, and then slide"; horizontal_rebalancing_weight - pelvis shift to rebalance weight; stiffness/damping interpolation and options to disable pelvis offset in air or hold it when the capsule moves vertically. The node is a skeletal-control node whose Python API is marked Experimental (R3). Bounded test idea for AI/mocap clean-up (inference): feed a walk clip over uneven ground, measure foot slide while speed < threshold (should be ~0 within unplant_radius), pelvis offset never exceeding max_offset, and count replant events; the same contact/support concepts (lock with hysteresis, limited pelvis compensation, extension limits) apply when cleaning foot-skate in AI motion-transfer outputs (C3-B341-01, C3-B477-01). · locator: speed_threshold; unplant_radius; max_offset · source: https://dev.epicgames.com/documentation/en-us/unreal-engine/python-api/class/FootPlacementPlantSettings?application_version=5.6

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