Brachiosaurus Model
A sauropod-inspired quadrupedal simulation model designed for four-legged locomotion and head-positioning tasks.
Generated specifications
These values are generated from the environment and compiled MJCF model. “Dynamic mass” is a simulator property, not an anatomical weight estimate.
| Gait | Quadrupedal |
|---|---|
| Observation dimension | 83 |
| Action dimension / actuators | 30 |
| Generalized coordinates (nq) | 38 |
| Generalized velocities (nv) | 37 |
| Compiled dynamic model mass | 175.3 kg |
| Plant contract revisions | Policy r6 · physics r4 · visual r2 |
| Model | environments/brachiosaurus/assets/brachiosaurus.xml |
Current curriculum configuration
The Stable-Baselines3 budgets and early-advancement gates below come from the current TOML files and can differ from older published runs. A stage also ends when its configured budget is exhausted. JAX/MJX uses the same task sequence, but its CLI and notebook gate behavior is not yet equivalent.
| Stage | Objective | SB3 configured budget | SB3 early-advancement gate |
|---|---|---|---|
| 1 — Balance | Learn to stand on four legs without falling | 6M | reward ≥ 1,040; episode length ≥ 950; ≥ 10 episodes/evaluation; 3 consecutive passes |
| 2 — Locomotion | Learn coordinated quadrupedal walking | 16M | reward ≥ 100; episode length ≥ 750; avg. velocity ≥ 0.75 m/s; ≥ 10 episodes/evaluation; 3 consecutive passes |
| 3 — Food Reach | Move the head tip within the configured distance threshold of food | 12M | reward ≥ 100; task success ≥ 50.0%; ≥ 10 episodes/evaluation; 3 consecutive passes |
Backend-specific task-success semantics
- Stable-Baselines3 / JAX/MJX — Head-tip distance-threshold success: The head-tip site comes within the configured food-reach threshold of the food target while the food-reach bonus is enabled.
Published run summaries
These are historical experiment records. A result is not evidence for the current model revision unless its provenance is explicitly marked current and verified.
PPO · Stable-Baselines3 · 2026-07-18
Provenance: Historical model · unverified · 30 evaluation episodes · Stable-Baselines3 (version not recorded)
| Stage | Trained steps | Best eval reward | Avg. forward velocity | Task success (Stable-Baselines3) | Passed |
|---|---|---|---|---|---|
| 1 — balance | 6M | 1740.53 | 0.01 m/s | — | Yes |
| 2 — locomotion | 16M | 6634.60 | 1.42 m/s | 3.3% | Yes |
| 3 — food reach | 12M | 1368.13 | 0.71 m/s | 100.0% | Yes |
Current Stable-Baselines3 definition for this task label: The head-tip site comes within the configured food-reach threshold of the food target while the food-reach bonus is enabled.
Features
- First quadrupedal species in the project
- Articulated 4-segment neck with head control (6 actuators)
- Front legs longer than rear, producing the model's raised-front posture
- Simplified column-like legs for support
- Head-positioning behavior using neck articulation
- 3-stage curriculum learning (balance, locomotion, food reach)
Unique Characteristics
Brachiosaurus differs from the bipedal species in the project:
- Quadrupedal gait instead of bipedal
- Target-proximity task using the head tip instead of a predatory contact task
Diagnostic Metrics (Stage 3)
After each training stage the eval command reports:
| Metric | Description |
|---|---|
mean_forward_velocity | Average forward speed (m/s) |
gait_symmetry | Left/right stride symmetry ∈ [0, 1] |
stride_frequency | Step frequency (Hz) |
cost_of_transport | Energy efficiency (lower is better) |
mean_pelvis_height | Torso height stability (m) |
success_rate | Fraction of episodes where the head tip enters the configured distance threshold around the food target |
min_prey_distance | Closest approach to food (m, head_food_distance) |
Training Videos
Published videos for Brachiosaurus, where available. Artifact provenance is shown on each stage.
Balance
Learn to stand on four legs without falling
PPO · Stable-Baselines3 artifact · historical model · unverified · backend version not recorded. It is not evidence for the current model or stage config.
Locomotion
Learn coordinated quadrupedal walking
PPO · Stable-Baselines3 artifact · historical model · unverified · backend version not recorded. It is not evidence for the current model or stage config.
Food Reach
Move the head tip within the configured distance threshold of food
No published video is available for this stage.
Usage
cd environments/brachiosaurus
# View the model
python scripts/view_model.py
# Train stage 1 using its current TOML-configured budget
python scripts/train_sb3.py train --stage 1