Implementation:Facebookresearch Habitat lab ArticulatedAgentBase

Knowledge Sources	Facebookresearch_Habitat_lab
Domains	Embodied_AI, Robot_Control
Last Updated	2026-02-15 00:00 GMT

Overview

ArticulatedAgentBase provides a generic base implementation for robots with a controllable base, handling URDF loading, joint motor management, base position/rotation control, and leg joint control.

Description

ArticulatedAgentBase extends ArticulatedAgentInterface to provide a concrete implementation for articulated robots in Habitat-Sim. It manages the full lifecycle of a simulated robot with a controllable base, including:

• URDF Loading -- The reconfigure() method loads the robot from a URDF file via the simulator's articulated object manager, setting up the fixed/free base configuration and link order preservation for PyBullet compatibility.

• Motor Management -- Configures joint motor settings for wheels and legs with specific position gains, velocity gains, and maximum impulse values. The motor settings cache is updated after reconfiguration for efficient future lookups.

• Base Position/Rotation -- Properties base_pos and base_rot provide get/set access to the robot's ground position and Y-axis rotation angle. The position is computed using a configurable local offset from the origin, and rotation is represented as a scalar angle in the range (-pi, pi).

• Leg Joint Control -- For leg-type robots, provides leg_motor_pos and leg_joint_pos properties for reading and writing leg motor targets and joint positions, with both kinematic and dynamic motor control support.

• Input Validation -- The _validate_ctrl_input method ensures control inputs match joint dimensions and are not NaN.

The class supports two base types: "mobile" and "leg", with assertions enforcing valid type selection.

Usage

Use ArticulatedAgentBase as a parent class for specific robot implementations. It is inherited by MobileManipulator (combined with Manipulator) to create robots with both controllable bases and arms. It should not typically be instantiated directly.

Code Reference

Source Location

• Repository: Facebookresearch_Habitat_lab
• File: habitat-lab/habitat/articulated_agents/articulated_agent_base.py
• Lines: 1-299

Signature

class ArticulatedAgentBase(ArticulatedAgentInterface):
    def __init__(
        self,
        params,
        urdf_path: str,
        sim: Simulator,
        limit_robo_joints: bool = True,
        fixed_based: bool = True,
        maintain_link_order=False,
        base_type="mobile",
        sim_obj=None,
        **kwargs,
    ):

Import

from habitat.articulated_agents.articulated_agent_base import (
    ArticulatedAgentBase,
)

I/O Contract

Inputs

Name	Type	Required	Description
params	object	Yes	Parameter object for the articulated agent (e.g., MobileManipulatorParams)
urdf_path	str	Yes	Path to the articulated agent's URDF file
sim	Simulator	Yes	The Habitat-Sim simulator instance
limit_robo_joints	bool	No (default=True)	Whether to enforce joint limits
fixed_based	bool	No (default=True)	Whether the robot's base is fixed
maintain_link_order	bool	No (default=False)	Whether to preserve URDF link order for PyBullet compatibility
base_type	str	No (default="mobile")	Base type, must be "mobile" or "leg"
sim_obj	object	No (default=None)	Pointer to an existing simulated articulated object

Outputs

Name	Type	Description
base_pos	mn.Vector3	The robot base ground position (property)
base_rot	float	Scalar rotation angle around Y axis in radians (property)
base_transformation	mn.Matrix4	The full 4x4 transformation matrix of the sim object (property)
leg_joint_pos	List[float]	Current leg joint positions (property, leg-type only)
leg_motor_pos	np.ndarray	Current leg motor target positions (property, leg-type only)

Usage Examples

Basic Usage

import magnum as mn
from habitat.articulated_agents.articulated_agent_base import ArticulatedAgentBase

# ArticulatedAgentBase is typically used as a parent class.
# In MobileManipulator, it is initialized as:
ArticulatedAgentBase.__init__(
    self,
    urdf_path=agent_cfg.articulated_agent_urdf,
    params=params,
    sim=sim,
    limit_robo_joints=True,
    fixed_based=True,
    sim_obj=self.sim_obj,
    base_type="mobile",
)

# After reconfigure(), access base properties:
# position = agent.base_pos
# agent.base_pos = mn.Vector3(1.0, 0.0, 2.0)
# rotation = agent.base_rot
# agent.base_rot = 1.57  # radians

Related Pages

• Facebookresearch_Habitat_lab_ArticulatedAgentInterface
• Facebookresearch_Habitat_lab_MobileManipulator