# Difference Between robot_walk.xml and robot_allcollisions.xml in Microduck RL > Understand the core difference between robot_walk.xml and robot_allcollisions.xml in Microduck RL. Optimize simulations by choosing the right collision geometry for your RL tasks. - Repository: [Pollen Robotics/microduck_rl](https://github.com/pollen-robotics/microduck_rl) - Tags: comparison - Published: 2026-09-01 --- **robot_walk.xml strips out collision geometries to maximize simulation throughput for locomotion tasks, while robot_allcollisions.xml retains exhaustive collision meshes for full self-collision detection at the cost of computational overhead.** The Microduck RL repository by Pollen Robotics maintains two parallel MuJoCo model definitions that share identical kinematic trees, actuator configurations, and visual meshes, but diverge critically in their collision geometry architecture. Selecting the correct XML file determines whether your reinforcement learning pipeline prioritizes raw simulation speed or physical contact fidelity. ## Collision Geometry Architecture Both files define the same 3D robot structure using identical visual meshes and joint hierarchies. The divergence lies entirely in how collision detection primitives are assigned to body parts. ### Minimal Coverage in robot_walk.xml In [`src/mjlab_microduck/robot/microduck/robot_walk.xml`](https://github.com/pollen-robotics/microduck_rl/blob/main/src/mjlab_microduck/robot/microduck/robot_walk.xml) (429 lines), most body parts declare only a single `` with **no** corresponding collision geometry. Only select components—such as the `power_support` and specific leg segments—retain `` tags. This selective approach limits self-collision checks to a handful of explicitly tagged geoms. ### Exhaustive Coverage in robot_allcollisions.xml Conversely, [`src/mjlab_microduck/robot/microduck/robot_allcollisions.xml`](https://github.com/pollen-robotics/microduck_rl/blob/main/src/mjlab_microduck/robot/microduck/robot_allcollisions.xml) (435 lines) attaches a dedicated `` to every major body part. Examples include: - `` (line 102) - `` - `` This expansion ensures every movable link possesses explicit collision geometry, enabling comprehensive self-collision detection across the entire robot surface. ## Performance and Computational Impact The geometric differences directly translate to measurable runtime characteristics in MuJoCo simulations. ### Simulation Speed Trade-offs **robot_walk.xml** executes significantly faster because the narrow-phase collision checker evaluates fewer primitive pairs. This optimization proves critical when running thousands of parallel environments for walking policy training. **robot_allcollisions.xml** incurs higher CPU load per timestep due to the additional collision manifold calculations, making it suitable for lower-throughput tasks requiring contact precision. ### CPU Load Characteristics When training velocity-tracking policies, the minimal collision set in [`robot_walk.xml`](https://github.com/pollen-robotics/microduck_rl/blob/main/robot_walk.xml) reduces the computational bottleneck, allowing vectorized environments to scale efficiently. The full collision fidelity in [`robot_allcollisions.xml`](https://github.com/pollen-robotics/microduck_rl/blob/main/robot_allcollisions.xml) becomes necessary only when the reward function or safety constraints depend on accurate self-contact sensing (e.g., obstacle avoidance, manipulation, or robustness testing). ## Environment Configuration Mapping The repository maps specific training tasks to the appropriate XML file through environment configuration classes. ### Velocity and Walking Tasks Locomotion-focused environments defined in [`src/mjlab_microduck/tasks/microduck_velocity_env_cfg.py`](https://github.com/pollen-robotics/microduck_rl/blob/main/src/mjlab_microduck/tasks/microduck_velocity_env_cfg.py) default to [`robot_walk.xml`](https://github.com/pollen-robotics/microduck_rl/blob/main/robot_walk.xml). These configurations assume the policy controls gait patterns where inter-body collisions are rare or irrelevant to task success, rendering the extra collision fidelity unnecessary. ### All-Collisions and Manipulation Tasks Complex interaction scenarios—implemented in [`src/mjlab_microduck/tasks/microduck_allcollisions_env_cfg.py`](https://github.com/pollen-robotics/microduck_rl/blob/main/src/mjlab_microduck/tasks/microduck_allcollisions_env_cfg.py)—explicitly reference [`robot_allcollisions.xml`](https://github.com/pollen-robotics/microduck_rl/blob/main/robot_allcollisions.xml). These tasks require precise contact detection between limbs and external objects or between the robot's own body parts, necessitating the full collision mesh set. ## Implementation: Loading and Switching Models You can instantiate either model directly in Python or configure training scripts to toggle between them. ### Direct MuJoCo Loading For fast locomotion simulations: ```python import mujoco model = mujoco.MjModel.from_xml_path( "src/mjlab_microduck/robot/microduck/robot_walk.xml" ) sim = mujoco.MjSim(model) ``` For full collision fidelity: ```python import mujoco model = mujoco.MjModel.from_xml_path( "src/mjlab_microduck/robot/microduck/robot_allcollisions.xml" ) sim = mujoco.MjSim(model) ``` ### Environment Configuration Override When constructing training environments programmatically: ```python from src.mjlab_microduck.tasks.microduck_velocity_env_cfg import make_microduck_velocity_env_cfg # High-throughput walking (robot_walk.xml) walk_cfg = make_microduck_velocity_env_cfg() walk_cfg.robot_xml = "robot/microduck/robot_walk.xml" # Precision collision mode (robot_allcollisions.xml) collision_cfg = make_microduck_velocity_env_cfg() collision_cfg.robot_xml = "robot/microduck/robot_allcollisions.xml" ``` ## Summary - **robot_walk.xml** prioritizes simulation throughput by omitting most collision geometries, using only `self_collision_only` tags for critical parts like `power_support`. - **robot_allcollisions.xml** provides complete physical fidelity with explicit `` entries for every major body part (e.g., `hip_l`, `jaw`, `np_f970`). - **Performance gap**: The walk configuration runs faster in parallelized vectorized environments, while the all-collisions configuration incurs higher computational cost per timestep. - **File paths**: Both reside in `src/mjlab_microduck/robot/microduck/`, differing by only six lines (429 vs. 435) of collision geom definitions. - **Task mapping**: Velocity environments use [`robot_walk.xml`](https://github.com/pollen-robotics/microduck_rl/blob/main/robot_walk.xml); manipulation and obstacle-heavy tasks require [`robot_allcollisions.xml`](https://github.com/pollen-robotics/microduck_rl/blob/main/robot_allcollisions.xml). ## Frequently Asked Questions ### Can I use robot_walk.xml for manipulation tasks requiring object interaction? No, you should use [`robot_allcollisions.xml`](https://github.com/pollen-robotics/microduck_rl/blob/main/robot_allcollisions.xml) for manipulation. The walk configuration lacks collision geometries on most body parts, meaning the arm links will pass through objects or the robot's own torso without registering contacts. Accurate grasping and obstacle avoidance require the explicit collision meshes defined in the all-collisions variant. ### Which file should I use for high-throughput walking policy training? Use [`robot_walk.xml`](https://github.com/pollen-robotics/microduck_rl/blob/main/robot_walk.xml) for high-throughput locomotion training. According to the Microduck RL source code, velocity environment configurations ([`microduck_velocity_env_cfg.py`](https://github.com/pollen-robotics/microduck_rl/blob/main/microduck_velocity_env_cfg.py)) default to this file specifically because the reduced collision checks minimize CPU overhead when running thousands of parallel environments. ### Are the visual meshes different between the two XML files? No, the visual meshes are identical. Both [`robot_walk.xml`](https://github.com/pollen-robotics/microduck_rl/blob/main/robot_walk.xml) and [`robot_allcollisions.xml`](https://github.com/pollen-robotics/microduck_rl/blob/main/robot_allcollisions.xml) reference the same STL and OBJ files for rendering. The divergence is strictly limited to the collision geometry layer—one uses `class="visual"` only for most parts, while the other supplements with `class="collision"` geoms. ### How do I switch between the two models in my training script? Override the `robot_xml` attribute in your environment configuration object. Instantiate your configuration from `make_microduck_velocity_env_cfg()`, then assign either `"robot/microduck/robot_walk.xml"` or `"robot/microduck/robot_allcollisions.xml"` to the `robot_xml` field before passing the config to the environment constructor.