Genesis World: Universal and Generative Physics Engine

This package provides a simplified MJCF (MuJoCo XML) description of the Universal Robots UR5e. It is derived from the official ROS-industrial URDF description.

Requirements:

• MuJoCo 2.3.3 or later.

Genesis World provides runnable demos organized into three functional layers that mirror its core architecture:

1. Physics: Demonstrates various solvers including Rigid body, FEM (Finite Element Method), MPM (Material Point Method), SPH (Smoothed Particle Hydrodynamics), PBD (Position Based Dynamics), and Stable Fluids. It also includes examples of multi-solver coupling (e.g., cloth on rigid bodies, rigid + MPM).
2. Rendering: Provides camera sensor setups including built-in paths (Nyx, Luisa, Pyrender) and advanced walkthroughs via the genesis-nyx repository (covering PBR materials, light types, and 3D Gaussian splatting).
3. Simulation Interface: Covers practical robotics and simulation tasks such as robot control, GUI tools (ImGui), heterogeneous environments, domain randomization, and a wide array of sensors (Depth, IMU, Lidar, Tactile, Contact Force, etc.).

This package provides a simplified MJCF (MuJoCo XML) description of the Franka Emika Panda robot. It is derived from the official Franka ROS URDF description and is optimized for use in MuJoCo simulations.

Requirements:

• MuJoCo 2.3.3 or later.

The franka_sim asset directory contains MuJoCo XML models for the Franka Panda robot. There are two primary configurations available:

1. Single Franka Panda: Defined in franka_panda.xml.
2. Dual Franka Panda (bi-franka): Defined in bi-franka_panda.xml, providing a setup with two Franka robots.

| Model Name | XML File |
| :--- | :--- |
| Franka Panda | `franka_panda.xml` |
| Bi-Franka Panda | `bi-franka_panda.xml` |

When parsing USD, there is a mapping between a USD Prim (denoted $i$) and a corresponding Genesis link (denoted $i'$).

There is no direct relationship between the local transform of a USD parent-child pair ($T^i_j$) and the Genesis parent-child pair ($Q^{i'}_{j'}$). Instead, the relationship is defined in world space:

$$T^w_i = Q^w_{i'} imes S^{i'}_i$$

Where:

• $T^w_i$ is the world-space transform of the USD Prim.
• $Q^w_{i'}$ is the world-space transform of the Genesis link.
• $S^{i'}_i$ is the scale matrix that transforms from the Genesis link to the USD prim (this scale is baked into the meshes on link $i'$).

Never attempt to detect changes in the simulation state by comparing two snapshots of data for equality (e.g., if current_state == previous_state:).

This approach is prohibited because:

1. It is computationally expensive (requires a gather and a compare).
2. It fails under zero-copy conditions (where both snapshots alias the same memory and will always appear equal).
3. It duplicates the source of truth.

Correct Approach: Use Genesis's dedicated change-detection facilities, such as solver StateChange subscriptions.

The drone simulations in this directory use the following technical configuration:

• Model: Crazyflie 2.X (urdf/drones/cf2x.urdf)
• Base Hover RPM: Approximately 14468
• Control Method: Differential RPM control. Movement is achieved by varying individual rotor RPMs to create directional thrust (e.g., adjusting front/back rotor pairs for forward/backward movement).
• Safety Limits: RPM changes are automatically clipped to a safe range of 0-25000 RPM.
• Physics: Includes realistic gravity and aerodynamics.

To maintain consistency in data structures, follow these naming patterns:

• Single Attribute Containers: Name them parent-type-first with the plural s on the first word only (e.g., links_dof_start, not dof_start_links). Alternatively, use a suffix like _pair, _set, _map, or _list.
• Nested Containers: Order words from highest to lowest in the hierarchy, applying plural markers at each level of nesting (e.g., geoms_vertices_idx).
• Avoid Generic Prefixes: Do not use all_ for containers; name the content specifically (e.g., joints_xanchor, links_inertia_i).