Wheeled Robots [omni.isaac.wheeled_robots]

The omni.isaac.wheeled_robots extension provides controllers, utilities, and omnigraph nodes for simulating wheeled robots in isaac sim.

Basic Usage

The classes and controllers provided by omni.isaac.wheeled_robots are designed to be run within the world simulation context provided by omni.isaac.core. Like many other classes provided by core, wheeled_robots are created by wrapping prims already present on the stage in an interface class. This API is expected by world to do things like initialize and reset data structures, apply drive commands, retrieve joint states, etc…

Creating this interface means specifying the articulation being managed, the name that world will know this object by, and the names of the drivable joints

# Assuming a stage context containing a Jetbot at /World/Jetbot
from omni.isaac.wheeled_robots.robots import WheeledRobot
jetbot_prim_path = "/World/Jetbot"

#wrap the articulation in the interface class
jetbot = WheeledRobot(prim_path=jetbot_prim_path,
                      name="Joan",
                      wheel_dof_names=["left_wheel_joint", "right_wheel_joint"]
                     )

Commanding the robot should be done prior to the physics step using an ArticulationAction, a type provided by omni.isaac.core to facilitate things like mixed command modes (effort, velocity, and position) and complex robots with multiple types of actions that could be taken.

from omni.isaac.core.utils.types import ArticulationAction

action = ArticulationAction(joint_velocities = np.array([1.14, 1.42]))
jetbot.apply_wheel_actions(action)

It is rarely the case however, that a user will want to command a robot by directly manipulating the joints, and so we also provide a suite of controllers to convert various types of general commands into specific joint actions. For example, you may want to control your differential base using throttle and steering commands…

from omni.isaac.wheeled_robots.controllers import DifferentialController

throttle = 1.0
steering = 0.5
controller = DifferentialController(name="simple_control", wheel_radius=0.035, wheel_base=0.1)
jetbot.apply_wheel_actions(controller.forward(throttle, steering))

Controllers

Differential Controller

class DifferentialController(name: str, wheel_radius: float, wheel_base: float, max_linear_speed: float = 1e+20, max_angular_speed: float = 1e+20, max_wheel_speed: float = 1e+20)

This controller uses a unicycle model of a differential drive. The Controller consumes a command in the form of a linear and angular velocity, and then computes the circular arc that satisfies this command given the distance between the wheels. This can then be used to compute the necessary angular velocities of the joints that will propell the midpoint between the wheels along the curve. The conversion is

\[ \begin{align}\begin{aligned}\omega_R = \frac{1}{2r}(2V + \omega b)\\\omega_L = \frac{1}{2r}(2V - \omega b)\end{aligned}\end{align} \]

where \(\omega\) is the desired angular velocity, \(V\) is the desired linear velocity, \(r\) is the radius of the wheels, and \(b\) is the distance between them.

Parameters

• name (str) – [description]

• wheel_radius (float) – Radius of left and right wheels in cms

• wheel_base (float) – Distance between left and right wheels in cms

• max_linear_speed (float) – OPTIONAL: limits the maximum linear speed that will be produced by the controller. Defaults to 1E20.

• max_angular_speed (float) – OPTIONAL: limits the maximum angular speed that will be produced by the controller. Defaults to 1E20.

• max_wheel_speed (float) – OPTIONAL: limits the maximum wheel speed that will be produced by the controller. Defaults to 1E20.

forward(command: numpy.ndarray) → omni.isaac.core.utils.types.ArticulationAction

convert from desired [signed linear speed, signed angular speed] to [Left Drive, Right Drive] joint targets.

Parameters

command (np.ndarray) – desired vehicle [forward, rotation] speed

Returns

the articulation action to be applied to the robot.

Return type

ArticulationAction

reset() → None

Resets state of the controller.

Holonomic Controller

class HolonomicController(name: str, wheel_radius: Optional[numpy.ndarray] = None, wheel_positions: Optional[numpy.ndarray] = None, wheel_orientations: Optional[numpy.ndarray] = None, mecanum_angles: Optional[numpy.ndarray] = None, wheel_axis: float = array([1, 0, 0]), up_axis: float = array([0, 0, 1]), max_linear_speed: float = 1e+20, max_angular_speed: float = 1e+20, max_wheel_speed: float = 1e+20, linear_gain: float = 1.0, angular_gain: float = 1.0)

This controller computes the joint drive commands required to produce the commanded forward, lateral, and yaw speeds of the robot. The problem is framed as a quadratic program to minimize the residual “net force” acting on the center of mass.

Hint

The wheel joints of the robot prim must have additional attributes to definine the roller angles and radii of the mecanum wheels.

stage = omni.usd.get_context().get_stage()
joint_prim = stage.GetPrimAtPath("/path/to/wheel_joint")
joint_prim.CreateAttribute("isaacmecanumwheel:radius",Sdf.ValueTypeNames.Float).Set(0.12)
joint_prim.CreateAttribute("isaacmecanumwheel:angle",Sdf.ValueTypeNames.Float).Set(10.3)

The HolonomicRobotUsdSetup class automates this process.

Parameters

• name (str) – [description]

• wheel_radius (np.ndarray) – radius of the wheels, array of 1 can be used if all wheels are the same size

• wheel_positions (np.ndarray) – position of the wheels relative to center of mass of the vehicle. number of wheels x [x,y,z]

• wheel_orientations (np.ndarray) – orientation of the wheels in quaternions relative to center of mass frame of the vehicle. number of wheels x [quaternions]

• mecanum_angles (np.ndarray) – mecanum wheel angles. Array of 1 can be used if all wheels have the same angle.

• wheel_axis (np.ndarray) – the spinning axis of the wheels. Defaults to [1,0,0]

• up_axis (np.ndarray) – Defaults to z- axis

• max_linear_speed (float) – maximum “forward” speed (default: 1.0e20)

• max_angular_speed (float) – maximum “turning” speed (default: 1.0e20)

• max_wheel_speed (float) – maximum “twisting” speed (default: 1.0e20)

• linear_gain (float) – Multiplicative factor. How much the solver should “care” about the linear components of the solution. (default: 1.0)

• linear_gain – Multiplicative factor. How much the solver should “care” about the angular components of the solution. (default: 1.0)

build_base()

forward(command: numpy.ndarray) → omni.isaac.core.utils.types.ArticulationAction

Calculate wheel speeds given the desired signed vehicle speeds.

Parameters

command (np.ndarray) – [forward speed, lateral speed, yaw speed].

Returns

[description]

Return type

ArticulationAction

reset() → None

[summary]

Wheel Base Pose Controller

class WheelBasePoseController(name: str, open_loop_wheel_controller: omni.isaac.core.controllers.base_controller.BaseController, is_holonomic: bool = False)

This controller closes the control loop, returning the wheel commands that will drive the robot to a desired pose. It does this by exploiting an open loop controller for the robot passed at class initialization.

Hint

The logic for this controller is the following:

• calculate the difference between the current position and the target position, amd compare against the postion tolerance. If the result is inside the tolerance, stop forward motion (ie. stop if closer than position tolerance)

• calculate the difference between the current heading and the target heading, and compare against the heading tolerance. If the result is outside the tolerance, stop forward motion and turn to align with the target heading (ie. dont bother turning unless it’s by more than the heading tolerance)

• otherwise proceed forward

Parameters

• name (str) – [description]

• open_loop_wheel_controller (BaseController) – A controller that takes in a command of [longitudinal velocity, steering angle] and returns the ArticulationAction to be applied to the wheels if non holonomic. and [longitudinal velocity, latitude velocity, steering angle] if holonomic.

• is_holonomic (bool, optional) – [description]. Defaults to False.

forward(start_position: numpy.ndarray, start_orientation: numpy.ndarray, goal_position: numpy.ndarray, lateral_velocity: float = 0.2, yaw_velocity: float = 0.5, heading_tol: float = 0.05, position_tol: float = 0.04) → omni.isaac.core.utils.types.ArticulationAction

Use the specified open loop controller to compute speed commands to the wheel joints of the robot that will move it towards the specified goal position

Parameters

• start_position (np.ndarray) – The current position of the robot, (X, Y, Z)

• start_orientation (np.ndarray) – The current orientation quaternion of the robot, (W, X, Y, Z)

• goal_position (np.ndarray) – The desired target position, (X, Y, Z)

• lateral_velocity (float, optional) – How fast the robot will move forward. Defaults to 20.0.

• yaw_velocity (float, optional) – How fast the robot will turn. Defaults to 0.5.

• heading_tol (float, optional) – The heading tolerance. Defaults to 0.05.

• position_tol (float, optional) – The position tolerance. Defaults to 4.0.

Returns

[description]

Return type

ArticulationAction

reset() → None

[summary]

Robots

Wheeled Robot

class WheeledRobot(prim_path: str, name: str = 'wheeled_robot', robot_path: Optional[str] = None, wheel_dof_names: Optional[str] = None, wheel_dof_indices: Optional[int] = None, usd_path: Optional[str] = None, create_robot: Optional[bool] = False, position: Optional[numpy.ndarray] = None, orientation: Optional[numpy.ndarray] = None)

This class wraps and manages the articualtion for a two wheeled differential robot base. It is designed to be managed by the World simulation context and provides and API for applying actions, retrieving dof parameters, etc…

Creating a wheeled robot can be done in a number of different ways, depending on the use case.

• Most commonly, the robot and stage are preloaded, in which case only the prim path to the articualtion root and the joint labels are required. Joint labels can take the form of either the joint names or the joint indices in the articulation.

jetbot = WheeledRobot(prim_path="/path/to/jetbot",
                    name="Joan",
                    wheel_dof_names=["left_wheel_joint", "right_wheel_joint"]
                    )

armbot = WheeledRobot(prim_path="path/to/armbot"
                        name="Weird_Arm_On_Wheels_Bot",
                        wheel_dof_indices=[7, 8]
                    )

• Alternatively, this class can create and populate a new reference on the stage. This is done with the create_robot parameter set to True.

carter = WheeledRobot(prim_path="/desired/path/to/carter",
                        name = "Jimmy",
                        wheel_dof_names=["joint_wheel_left", "joint_wheel_right"],
                        create_robot = True,
                        usd_path = "/Isaac/Robots/Carter/nova_carter.usd",
                        position = np.array([0,1,0])
                    )

Hint

In all cases, either wheel_dof_names or wheel_dof_indices must be specified!

Parameters

• prim_path (str) – The stage path to the root prim of the articulation.

• name ([str]) – The name used by World to identify the robot. Defaults to “wheeled_robot”

• robot_path (optional[str]) – relative path from prim path to the robot.

• wheel_dof_names (semi-optional[str]) – names of the wheel joints. Either this or the wheel_dof_indicies must be specified.

• wheel_dof_indices – (semi-optional[int]): indices of the wheel joints in the articulation. Either this or the wheel_dof_names must be specified.

• usd_path (optional[str]) – nucleus path to the robot asset. Used if create_robot is True

• create_robot (bool) – create robot at prim_path using asset from usd_path. Defaults to False

• position (Optional[np.ndarray], optional) – The location to create the robot when create_robot is True. Defaults to None.

• orientation (Optional[np.ndarray], optional) – The orientation of the robot when crate_robot is True. Defaults to None.

apply_action(control_actions: omni.isaac.core.utils.types.ArticulationAction) → None

Apply joint positions, velocities and/or efforts to control an articulation

Parameters

• control_actions (ArticulationAction) – actions to be applied for next physics step.

• indices (Optional[Union[list, np.ndarray]], optional) – degree of freedom indices to apply actions to. Defaults to all degrees of freedom.

Hint

High stiffness makes the joints snap faster and harder to the desired target, and higher damping smoothes but also slows down the joint’s movement to target

• For position control, set relatively high stiffness and low damping (to reduce vibrations)

• For velocity control, stiffness must be set to zero with a non-zero damping

• For effort control, stiffness and damping must be set to zero

Example:

>>> from omni.isaac.core.utils.types import ArticulationAction
>>>
>>> # move all the robot joints to the indicated position
>>> action = ArticulationAction(joint_positions=np.array([0.0, -1.0, 0.0, -2.2, 0.0, 2.4, 0.8, 0.04, 0.04]))
>>> prim.apply_action(action)
>>>
>>> # close the robot fingers: panda_finger_joint1 (7) and panda_finger_joint2 (8) to 0.0
>>> action = ArticulationAction(joint_positions=np.array([0.0, 0.0]), joint_indices=np.array([7, 8]))
>>> prim.apply_action(action)

apply_visual_material(visual_material: omni.isaac.core.materials.visual_material.VisualMaterial, weaker_than_descendants: bool = False) → None

Apply visual material to the held prim and optionally its descendants.

Parameters

• visual_material (VisualMaterial) – visual material to be applied to the held prim. Currently supports PreviewSurface, OmniPBR and OmniGlass.

• weaker_than_descendants (bool, optional) – True if the material shouldn’t override the descendants materials, otherwise False. Defaults to False.

Example:

>>> from omni.isaac.core.materials import OmniGlass
>>>
>>> # create a dark-red glass visual material
>>> material = OmniGlass(
...     prim_path="/World/material/glass",  # path to the material prim to create
...     ior=1.25,
...     depth=0.001,
...     thin_walled=False,
...     color=np.array([0.5, 0.0, 0.0])
... )
>>> prim.apply_visual_material(material)

apply_wheel_actions(actions: omni.isaac.core.utils.types.ArticulationAction) → None

applying action to the wheels to move the robot

Parameters

actions (ArticulationAction) – [description]

disable_gravity() → None

Keep gravity from affecting the robot

Example:

>>> prim.disable_gravity()

property dof_names: List[str]

List of prim names for each DOF.

Returns

prim names

Return type

list(string)

Example:

>>> prim.dof_names
['panda_joint1', 'panda_joint2', 'panda_joint3', 'panda_joint4', 'panda_joint5',
 'panda_joint6', 'panda_joint7', 'panda_finger_joint1', 'panda_finger_joint2']

property dof_properties: numpy.ndarray

Articulation DOF properties

DOF properties

Index	Property name	Description
0	type	DOF type: invalid/unknown/uninitialized (0), rotation (1), translation (2)
1	hasLimits	Whether the DOF has limits
2	lower	Lower DOF limit (in radians or meters)
3	upper	Upper DOF limit (in radians or meters)
4	driveMode	Drive mode for the DOF: force (1), acceleration (2)
5	maxVelocity	Maximum DOF velocity. In radians/s, or stage_units/s
6	maxEffort	Maximum DOF effort. In N or N*stage_units
7	stiffness	DOF stiffness
8	damping	DOF damping

Returns

named NumPy array of shape (num_dof, 9)

Return type

np.ndarray

Example:

>>> # get properties for all DOFs
>>> prim.dof_properties
[(1,  True, -2.8973,  2.8973, 1, 1.0000000e+01, 5220., 60000., 3000.)
 (1,  True, -1.7628,  1.7628, 1, 1.0000000e+01, 5220., 60000., 3000.)
 (1,  True, -2.8973,  2.8973, 1, 5.9390470e+36, 5220., 60000., 3000.)
 (1,  True, -3.0718, -0.0698, 1, 5.9390470e+36, 5220., 60000., 3000.)
 (1,  True, -2.8973,  2.8973, 1, 5.9390470e+36,  720., 25000., 3000.)
 (1,  True, -0.0175,  3.7525, 1, 5.9390470e+36,  720., 15000., 3000.)
 (1,  True, -2.8973,  2.8973, 1, 1.0000000e+01,  720.,  5000., 3000.)
 (2,  True,  0.    ,  0.04  , 1, 3.4028235e+38,  720.,  6000., 1000.)
 (2,  True,  0.    ,  0.04  , 1, 3.4028235e+38,  720.,  6000., 1000.)]
>>>
>>> # property names
>>> prim.dof_properties.dtype.names
('type', 'hasLimits', 'lower', 'upper', 'driveMode', 'maxVelocity', 'maxEffort', 'stiffness', 'damping')
>>>
>>> # get DOF upper limits
>>> prim.dof_properties["upper"]
[ 2.8973  1.7628  2.8973 -0.0698  2.8973  3.7525  2.8973  0.04    0.04  ]
>>>
>>> # get the last DOF (panda_finger_joint2) upper limit
>>> prim.dof_properties["upper"][8]  # or prim.dof_properties[8][3]
0.04

enable_gravity() → None

Gravity will affect the robot

Example:

>>> prim.enable_gravity()

get_angular_velocity() → numpy.ndarray

Get the angular velocity of the root articulation prim

Returns

3D angular velocity vector. Shape (3,)

Return type

np.ndarray

Example:

>>> prim.get_angular_velocity()
[0. 0. 0.]

get_applied_action() → omni.isaac.core.utils.types.ArticulationAction

Get the last applied action

Returns

last applied action. Note: a dictionary is used as the object’s string representation

Return type

ArticulationAction

Example:

>>> # last applied action: joint_positions -> [0.0, -1.0, 0.0, -2.2, 0.0, 2.4, 0.8, 0.04, 0.04]
>>> prim.get_applied_action()
{'joint_positions': [0.0, -1.0, 0.0, -2.200000047683716, 0.0, 2.4000000953674316,
                     0.800000011920929, 0.03999999910593033, 0.03999999910593033],
 'joint_velocities': [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0],
 'joint_efforts': [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]}

get_applied_joint_efforts(joint_indices: Optional[Union[List, numpy.ndarray]] = None) → numpy.ndarray

Get the efforts applied to the joints set by the set_joint_efforts method

Parameters

joint_indices (Optional[Union[List, np.ndarray]], optional) – indices to specify which joints to read. Defaults to None (all joints)

Raises

Exception – If the handlers are not initialized

Returns

all or selected articulation joint applied efforts

Return type

np.ndarray

Example:

>>> # get all applied joint efforts
>>> prim.get_applied_joint_efforts()
[ 0.  0.  0.  0.  0.  0.  0.  0.  0.]
>>>
>>> # get finger applied efforts: panda_finger_joint1 (7) and panda_finger_joint2 (8)
>>> prim.get_applied_joint_efforts(joint_indices=np.array([7, 8]))
[0.  0.]

get_applied_visual_material() → omni.isaac.core.materials.visual_material.VisualMaterial

Return the current applied visual material in case it was applied using apply_visual_material or it’s one of the following materials that was already applied before: PreviewSurface, OmniPBR and OmniGlass.

Returns

the current applied visual material if its type is currently supported.

Return type

VisualMaterial

Example:

>>> # given a visual material applied
>>> prim.get_applied_visual_material()
<omni.isaac.core.materials.omni_glass.OmniGlass object at 0x7f36263106a0>

get_articulation_body_count() → int

Get the number of bodies (links) that make up the articulation

Returns

amount of bodies

Return type

int

Example:

>>> prim.get_articulation_body_count()
12

get_articulation_controller() → omni.isaac.core.controllers.articulation_controller.ArticulationController

Get the articulation controller

Note

If no articulation_controller was passed during class instantiation, a default controller of type ArticulationController (a Proportional-Derivative controller that can apply position targets, velocity targets and efforts) will be used

Returns

articulation controller

Return type

ArticulationController

Example:

>>> prim.get_articulation_controller()
<omni.isaac.core.controllers.articulation_controller.ArticulationController object at 0x7f04a0060190>

get_articulation_controller_properties()

get_default_state() → omni.isaac.core.utils.types.XFormPrimState

Get the default prim states (spatial position and orientation).

Returns

an object that contains the default state of the prim (position and orientation)

Return type

XFormPrimState

Example:

>>> state = prim.get_default_state()
>>> state
<omni.isaac.core.utils.types.XFormPrimState object at 0x7f33addda650>
>>>
>>> state.position
[-4.5299529e-08 -1.8347054e-09 -2.8610229e-08]
>>> state.orientation
[1. 0. 0. 0.]

get_dof_index(dof_name: str) → int

Get a DOF index given its name

Parameters

dof_name (str) – name of the DOF

Returns

DOF index

Return type

int

Example:

>>> prim.get_dof_index("panda_finger_joint2")
8

get_enabled_self_collisions() → int

Get the enable self collisions flag (physxArticulation:enabledSelfCollisions)

Returns

self collisions flag (boolean interpreted as int)

Return type

int

Example:

>>> prim.get_enabled_self_collisions()
0

get_joint_positions(joint_indices: Optional[Union[List, numpy.ndarray]] = None) → numpy.ndarray

Get the articulation joint positions

Parameters

joint_indices (Optional[Union[List, np.ndarray]], optional) – indices to specify which joints to read. Defaults to None (all joints)

Returns

all or selected articulation joint positions

Return type

np.ndarray

Example:

>>> # get all joint positions
>>> prim.get_joint_positions()
[ 1.1999920e-02 -5.6962633e-01  1.3480479e-08 -2.8105433e+00  6.8284894e-06
  3.0301569e+00  7.3234749e-01  3.9912373e-02  3.9999999e-02]
>>>
>>> # get finger positions: panda_finger_joint1 (7) and panda_finger_joint2 (8)
>>> prim.get_joint_positions(joint_indices=np.array([7, 8]))
[0.03991237  3.9999999e-02]

get_joint_velocities(joint_indices: Optional[Union[List, numpy.ndarray]] = None) → numpy.ndarray

Get the articulation joint velocities

Parameters

joint_indices (Optional[Union[List, np.ndarray]], optional) – indices to specify which joints to read. Defaults to None (all joints)

Returns

all or selected articulation joint velocities

Return type

np.ndarray

Example:

>>> # get all joint velocities
>>> prim.get_joint_velocities()
[ 1.91603772e-06 -7.67638255e-03 -2.19138826e-07  1.10636465e-02 -4.63412944e-05
  3.48245539e-02  8.84692147e-02  5.40335372e-04 1.02849208e-05]
>>>
>>> # get finger velocities: panda_finger_joint1 (7) and panda_finger_joint2 (8)
>>> prim.get_joint_velocities(joint_indices=np.array([7, 8]))
[5.4033537e-04 1.0284921e-05]

get_joints_default_state() → omni.isaac.core.utils.types.JointsState

Get the default joint states (positions and velocities).

Returns

an object that contains the default joint positions and velocities

Return type

JointsState

Example:

>>> state = prim.get_joints_default_state()
>>> state
<omni.isaac.core.utils.types.JointsState object at 0x7f04a0061240>
>>>
>>> state.positions
[ 0.012  -0.57000005  0.  -2.81  0.  3.037  0.785398  0.04  0.04 ]
>>> state.velocities
[0. 0. 0. 0. 0. 0. 0. 0. 0.]

get_joints_state() → omni.isaac.core.utils.types.JointsState

Get the current joint states (positions and velocities)

Returns

an object that contains the current joint positions and velocities

Return type

JointsState

Example:

>>> state = prim.get_joints_state()
>>> state
<omni.isaac.core.utils.types.JointsState object at 0x7f02f6df57b0>
>>>
>>> state.positions
[ 1.1999920e-02 -5.6962633e-01  1.3480479e-08 -2.8105433e+00 6.8284894e-06
  3.0301569e+00  7.3234749e-01  3.9912373e-02  3.9999999e-02]
>>> state.velocities
[ 1.91603772e-06 -7.67638255e-03 -2.19138826e-07  1.10636465e-02 -4.63412944e-05
  245539e-02  8.84692147e-02  5.40335372e-04  1.02849208e-05]

get_linear_velocity() → numpy.ndarray

Get the linear velocity of the root articulation prim

Returns

3D linear velocity vector. Shape (3,)

Return type

np.ndarray

Example:

>>> prim.get_linear_velocity()
[0. 0. 0.]

get_local_pose() → Tuple[numpy.ndarray, numpy.ndarray]

Get prim’s pose with respect to the local frame (the prim’s parent frame)

Returns

first index is the position in the local frame (with shape (3, )). Second index is quaternion orientation (with shape (4, )) in the local frame

Return type

Tuple[np.ndarray, np.ndarray]

Example:

>>> # if the prim is in position (1.0, 0.5, 0.0) with respect to the world frame
>>> position, orientation = prim.get_local_pose()
>>> position
[0. 0. 0.]
>>> orientation
[0. 0. 0.]

get_local_scale() → numpy.ndarray

Get prim’s scale with respect to the local frame (the parent’s frame)

Returns

scale applied to the prim’s dimensions in the local frame. shape is (3, ).

Return type

np.ndarray

Example:

>>> prim.get_local_scale()
[1. 1. 1.]

get_measured_joint_efforts(joint_indices: Optional[Union[List, numpy.ndarray]] = None) → numpy.ndarray

Returns the efforts computed/measured by the physics solver of the joint forces in the DOF motion direction

Parameters

joint_indices (Optional[Union[List, np.ndarray]], optional) – indices to specify which joints to read. Defaults to None (all joints)

Raises

Exception – If the handlers are not initialized

Returns

all or selected articulation joint measured efforts

Return type

np.ndarray

Example:

>>> # get all joint efforts
>>> prim.get_measured_joint_efforts()
[ 2.7897308e-06 -6.9083519e+00 -3.6398471e-06  1.9158335e+01 -4.3552645e-06
  1.1866090e+00 -4.7079347e-06  3.2339853e-04 -3.2044132e-04]
>>>
>>> # get finger efforts: panda_finger_joint1 (7) and panda_finger_joint2 (8)
>>> prim.get_measured_joint_efforts(joint_indices=np.array([7, 8]))
[ 0.0003234  -0.00032044]

get_measured_joint_forces(joint_indices: Optional[Union[List, numpy.ndarray]] = None) → numpy.ndarray

Get the measured joint reaction forces and torques (link incoming joint forces and torques) to external loads

Note

Since the name->index map for joints has not been exposed yet, it is possible to access the joint names and their indices through the articulation metadata.

prim._articulation_view._metadata.joint_names  # list of names
prim._articulation_view._metadata.joint_indices  # dict of name: index

To retrieve a specific row for the link incoming joint force/torque use joint_index + 1

Parameters

joint_indices (Optional[Union[List, np.ndarray]], optional) – indices to specify which joints to read. Defaults to None (all joints)

Raises

Exception – If the handlers are not initialized

Returns

measured joint forces and torques. Shape is (num_joint + 1, 6). Row index 0 is the incoming joint of the base link. For the last dimension the first 3 values are for forces and the last 3 for torques

Return type

np.ndarray

Example:

>>> # get all measured joint forces and torques
>>> prim.get_measured_joint_forces()
[[ 0.0000000e+00  0.0000000e+00  0.0000000e+00  0.0000000e+00  0.0000000e+00  0.0000000e+00]
 [ 1.4995076e+02  4.2574748e-06  5.6364370e-04  4.8701895e-05 -6.9072924e+00  3.1881387e-05]
 [-2.8971717e-05 -1.0677823e+02 -6.8384506e+01 -6.9072924e+00 -5.4927128e-05  6.1222494e-07]
 [ 8.7120995e+01 -4.3871860e-05 -5.5795174e+01  5.3687054e-05 -2.4538563e+01  1.3333466e-05]
 [ 5.3519474e-05 -4.8109909e+01  6.0709282e+01  1.9157074e+01 -5.9258469e-05  8.2744418e-07]
 [-3.1691040e+01  2.3313689e-04  3.9990173e+01 -5.8968733e-05 -1.1863431e+00  2.2335558e-05]
 [-1.0809851e-04  1.5340537e+01 -1.5458489e+01  1.1863426e+00  6.1094368e-05 -1.5940281e-05]
 [-7.5418940e+00 -5.0814648e+00 -5.6512990e+00 -5.6385466e-05  3.8859999e-01 -3.4943256e-01]
 [ 4.7421460e+00 -3.1945827e+00  3.5528181e+00  5.5852943e-05  8.4794536e-03  7.6405057e-03]
 [ 4.0760727e+00  2.1640673e-01 -4.0513167e+00 -5.9565349e-04  1.1407082e-02  2.1432268e-06]
 [ 5.1680198e-03 -9.7754575e-02 -9.7093947e-02 -8.4155556e-12 -1.2910691e-12 -1.9347857e-11]
 [-5.1910793e-03  9.7588278e-02 -9.7106412e-02  8.4155573e-12  1.2910637e-12 -1.9347855e-11]]
>>>
>>> # get measured joint force and torque for the fingers
>>> metadata = prim._articulation_view._metadata
>>> joint_indices = 1 + np.array([
...     metadata.joint_indices["panda_finger_joint1"],
...     metadata.joint_indices["panda_finger_joint2"],
... ])
>>> joint_indices
[10 11]
>>> prim.get_measured_joint_forces(joint_indices)
[[ 5.1680198e-03 -9.7754575e-02 -9.7093947e-02 -8.4155556e-12 -1.2910691e-12 -1.9347857e-11]
 [-5.1910793e-03  9.7588278e-02 -9.7106412e-02  8.4155573e-12  1.2910637e-12 -1.9347855e-11]]

get_sleep_threshold() → float

Get the threshold for articulations to enter a sleep state

Search for Articulations and Sleeping in PhysX docs for more details

Returns

sleep threshold

Return type

float

Example:

>>> prim.get_sleep_threshold()
0.005

get_solver_position_iteration_count() → int

Get the solver (position) iteration count for the articulation

The solver iteration count determines how accurately contacts, drives, and limits are resolved. Search for Solver Iteration Count in PhysX docs for more details.

Returns

position iteration count

Return type

int

Example:

>>> prim.get_solver_position_iteration_count()
32

get_solver_velocity_iteration_count() → int

Get the solver (velocity) iteration count for the articulation

The solver iteration count determines how accurately contacts, drives, and limits are resolved. Search for Solver Iteration Count in PhysX docs for more details.

Returns

velocity iteration count

Return type

int

Example:

>>> prim.get_solver_velocity_iteration_count()
32

get_stabilization_threshold() → float

Get the mass-normalized kinetic energy below which the articulation may participate in stabilization

Search for Stabilization Threshold in PhysX docs for more details

Returns

stabilization threshold

Return type

float

Example:

>>> prim.get_stabilization_threshold()
0.0009999999

get_visibility() → bool

Returns

true if the prim is visible in stage. false otherwise.

Return type

bool

Example:

>>> # get the visible state of an visible prim on the stage
>>> prim.get_visibility()
True

get_wheel_positions()

[summary]

Returns

[description]

Return type

List[float]

get_wheel_velocities()

[summary]

Returns

[description]

Return type

Tuple[np.ndarray, np.ndarray]

get_world_pose() → Tuple[numpy.ndarray, numpy.ndarray]

Get prim’s pose with respect to the world’s frame

Returns

first index is the position in the world frame (with shape (3, )). Second index is quaternion orientation (with shape (4, )) in the world frame

Return type

Tuple[np.ndarray, np.ndarray]

Example:

>>> # if the prim is in position (1.0, 0.5, 0.0) with respect to the world frame
>>> position, orientation = prim.get_world_pose()
>>> position
[1.  0.5 0. ]
>>> orientation
[1. 0. 0. 0.]

get_world_scale() → numpy.ndarray

Get prim’s scale with respect to the world’s frame

Returns

scale applied to the prim’s dimensions in the world frame. shape is (3, ).

Return type

np.ndarray

Example:

>>> prim.get_world_scale()
[1. 1. 1.]

get_world_velocity() → numpy.ndarray

Get the articulation root velocity

Returns

current velocity of the the root prim. Shape (3,).

Return type

np.ndarray

property handles_initialized: bool

Check if articulation handler is initialized

Returns

whether the handler was initialized

Return type

bool

Example:

>>> prim.handles_initialized
True

initialize(physics_sim_view=None) → None

[summary]

is_valid() → bool

Check if the prim path has a valid USD Prim at it

Returns

True is the current prim path corresponds to a valid prim in stage. False otherwise.

Return type

bool

Example:

>>> # given an existing and valid prim
>>> prims.is_valid()
True

is_visual_material_applied() → bool

Check if there is a visual material applied

Returns

True if there is a visual material applied. False otherwise.

Return type

bool

Example:

>>> # given a visual material applied
>>> prim.is_visual_material_applied()
True

property name: Optional[str]

Returns: str: name given to the prim when instantiating it. Otherwise None.

property non_root_articulation_link: bool

Used to query if the prim is a non root articulation link

Returns

True if the prim itself is a non root link

Return type

bool

Example:

>>> # for a wrapped articulation (where the root prim has the Physics Articulation Root property applied)
>>> prim.non_root_articulation_link
False

property num_bodies: int

Number of articulation links

Returns

number of links

Return type

int

Example:

>>> prim.num_bodies
9

property num_dof: int

Number of DOF of the articulation

Returns

amount of DOFs

Return type

int

Example:

>>> prim.num_dof
9

post_reset() → None

[summary]

property prim: pxr.Usd.Prim

Returns: Usd.Prim: USD Prim object that this object holds.

property prim_path: str

Returns: str: prim path in the stage

set_angular_velocity(velocity: numpy.ndarray) → None

Set the angular velocity of the root articulation prim

Warning

This method will immediately set the articulation state

Parameters

velocity (np.ndarray) – 3D angular velocity vector. Shape (3,)

Hint

This method belongs to the methods used to set the articulation kinematic state:

set_linear_velocity, set_angular_velocity, set_joint_positions, set_joint_velocities, set_joint_efforts

Example:

>>> prim.set_angular_velocity(np.array([0.1, 0.0, 0.0]))

set_default_state(position: Optional[Sequence[float]] = None, orientation: Optional[Sequence[float]] = None) → None

Set the default state of the prim (position and orientation), that will be used after each reset.

Parameters

• position (Optional[Sequence[float]], optional) – position in the world frame of the prim. shape is (3, ). Defaults to None, which means left unchanged.

• orientation (Optional[Sequence[float]], optional) – quaternion orientation in the world frame of the prim. quaternion is scalar-first (w, x, y, z). shape is (4, ). Defaults to None, which means left unchanged.

Example:

>>> # configure default state
>>> prim.set_default_state(position=np.array([1.0, 0.5, 0.0]), orientation=np.array([1, 0, 0, 0]))
>>>
>>> # set default states during post-reset
>>> prim.post_reset()

set_enabled_self_collisions(flag: bool) → None

Set the enable self collisions flag (physxArticulation:enabledSelfCollisions)

Parameters

flag (bool) – whether to enable self collisions

Example:

>>> prim.set_enabled_self_collisions(True)

set_joint_efforts(efforts: numpy.ndarray, joint_indices: Optional[Union[List, numpy.ndarray]] = None) → None

Set the articulation joint efforts

Note

This method can be used for effort control. For this purpose, there must be no joint drive or the stiffness and damping must be set to zero.

Parameters

• efforts (np.ndarray) – articulation joint efforts

• joint_indices (Optional[Union[list, np.ndarray]], optional) – indices to specify which joints to manipulate. Defaults to None (all joints)

Hint

This method belongs to the methods used to set the articulation kinematic state:

set_linear_velocity, set_angular_velocity, set_joint_positions, set_joint_velocities, set_joint_efforts

Example:

>>> # set all the robot joint efforts to 0.0
>>> prim.set_joint_efforts(np.array([0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]))
>>>
>>> # set only the fingers efforts: panda_finger_joint1 (7) and panda_finger_joint2 (8) to 10
>>> prim.set_joint_efforts(np.array([10, 10]), joint_indices=np.array([7, 8]))

set_joint_positions(positions: numpy.ndarray, joint_indices: Optional[Union[List, numpy.ndarray]] = None) → None

Set the articulation joint positions

Warning

This method will immediately set (teleport) the affected joints to the indicated value. Use the apply_action method to control robot joints.

Parameters

• positions (np.ndarray) – articulation joint positions

• joint_indices (Optional[Union[list, np.ndarray]], optional) – indices to specify which joints to manipulate. Defaults to None (all joints)

Hint

This method belongs to the methods used to set the articulation kinematic state:

set_linear_velocity, set_angular_velocity, set_joint_positions, set_joint_velocities, set_joint_efforts

Example:

>>> # set all the robot joints
>>> prim.set_joint_positions(np.array([0.0, -1.0, 0.0, -2.2, 0.0, 2.4, 0.8, 0.04, 0.04]))
>>>
>>> # set only the fingers in closed position: panda_finger_joint1 (7) and panda_finger_joint2 (8) to 0.0
>>> prim.set_joint_positions(np.array([0.04, 0.04]), joint_indices=np.array([7, 8]))

set_joint_velocities(velocities: numpy.ndarray, joint_indices: Optional[Union[List, numpy.ndarray]] = None) → None

Set the articulation joint velocities

Warning

This method will immediately set the affected joints to the indicated value. Use the apply_action method to control robot joints.

Parameters

• velocities (np.ndarray) – articulation joint velocities

• joint_indices (Optional[Union[list, np.ndarray]], optional) – indices to specify which joints to manipulate. Defaults to None (all joints)

Hint

This method belongs to the methods used to set the articulation kinematic state:

set_linear_velocity, set_angular_velocity, set_joint_positions, set_joint_velocities, set_joint_efforts

Example:

>>> # set all the robot joint velocities to 0.0
>>> prim.set_joint_velocities(np.array([0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]))
>>>
>>> # set only the fingers velocities: panda_finger_joint1 (7) and panda_finger_joint2 (8) to -0.01
>>> prim.set_joint_velocities(np.array([-0.01, -0.01]), joint_indices=np.array([7, 8]))

set_joints_default_state(positions: Optional[numpy.ndarray] = None, velocities: Optional[numpy.ndarray] = None, efforts: Optional[numpy.ndarray] = None) → None

Set the joint default states (positions, velocities and/or efforts) to be applied after each reset.

Note

The default states will be set during post-reset (e.g., calling .post_reset() or world.reset() methods)

Parameters

• positions (Optional[np.ndarray], optional) – joint positions. Defaults to None.

• velocities (Optional[np.ndarray], optional) – joint velocities. Defaults to None.

• efforts (Optional[np.ndarray], optional) – joint efforts. Defaults to None.

Example:

>>> # configure default joint states
>>> prim.set_joints_default_state(
...     positions=np.array([0.0, -1.0, 0.0, -2.2, 0.0, 2.4, 0.8, 0.04, 0.04]),
...     velocities=np.zeros(shape=(prim.num_dof,)),
...     efforts=np.zeros(shape=(prim.num_dof,))
... )
>>>
>>> # set default states during post-reset
>>> prim.post_reset()

set_linear_velocity(velocity: numpy.ndarray) → None

Set the linear velocity of the root articulation prim

Warning

This method will immediately set the articulation state

Parameters

velocity (np.ndarray) – 3D linear velocity vector. Shape (3,).

Hint

This method belongs to the methods used to set the articulation kinematic state:

set_linear_velocity, set_angular_velocity, set_joint_positions, set_joint_velocities, set_joint_efforts

Example:

>>> prim.set_linear_velocity(np.array([0.1, 0.0, 0.0]))

set_local_pose(translation: Optional[Sequence[float]] = None, orientation: Optional[Sequence[float]] = None) → None

Set prim’s pose with respect to the local frame (the prim’s parent frame).

Warning

This method will change (teleport) the prim pose immediately to the indicated value

Parameters

• translation (Optional[Sequence[float]], optional) – translation in the local frame of the prim (with respect to its parent prim). shape is (3, ). Defaults to None, which means left unchanged.

• orientation (Optional[Sequence[float]], optional) – quaternion orientation in the local frame of the prim. quaternion is scalar-first (w, x, y, z). shape is (4, ). Defaults to None, which means left unchanged.

Hint

This method belongs to the methods used to set the prim state

Example:

>>> prim.set_local_pose(translation=np.array([1.0, 0.5, 0.0]), orientation=np.array([1., 0., 0., 0.]))

set_local_scale(scale: Optional[Sequence[float]]) → None

Set prim’s scale with respect to the local frame (the prim’s parent frame).

Parameters

scale (Optional[Sequence[float]]) – scale to be applied to the prim’s dimensions. shape is (3, ). Defaults to None, which means left unchanged.

Example:

>>> # scale prim 10 times smaller
>>> prim.set_local_scale(np.array([0.1, 0.1, 0.1]))

set_sleep_threshold(threshold: float) → None

Set the threshold for articulations to enter a sleep state

Search for Articulations and Sleeping in PhysX docs for more details

Parameters

threshold (float) – sleep threshold

Example:

>>> prim.set_sleep_threshold(0.01)

set_solver_position_iteration_count(count: int) → None

Set the solver (position) iteration count for the articulation

The solver iteration count determines how accurately contacts, drives, and limits are resolved. Search for Solver Iteration Count in PhysX docs for more details.

Warning

Setting a higher number of iterations may improve the fidelity of the simulation, although it may affect its performance.

Parameters

count (int) – position iteration count

Example:

>>> prim.set_solver_position_iteration_count(64)

set_solver_velocity_iteration_count(count: int)

Set the solver (velocity) iteration count for the articulation

The solver iteration count determines how accurately contacts, drives, and limits are resolved. Search for Solver Iteration Count in PhysX docs for more details.

Warning

Setting a higher number of iterations may improve the fidelity of the simulation, although it may affect its performance.

Parameters

count (int) – velocity iteration count

Example:

>>> prim.set_solver_velocity_iteration_count(64)

set_stabilization_threshold(threshold: float) → None

Set the mass-normalized kinetic energy below which the articulation may participate in stabilization

Search for Stabilization Threshold in PhysX docs for more details

Parameters

threshold (float) – stabilization threshold

Example:

>>> prim.set_stabilization_threshold(0.005)

set_visibility(visible: bool) → None

Set the visibility of the prim in stage

Parameters

visible (bool) – flag to set the visibility of the usd prim in stage.

Example:

>>> # make prim not visible in the stage
>>> prim.set_visibility(visible=False)

set_wheel_positions(positions) → None

[summary]

Parameters

positions (Tuple[float, float]) – [description]

set_wheel_velocities(velocities) → None

[summary]

Parameters

velocities (Tuple[float, float]) – [description]

set_world_pose(position: Optional[Sequence[float]] = None, orientation: Optional[Sequence[float]] = None) → None

Ses prim’s pose with respect to the world’s frame

Warning

This method will change (teleport) the prim pose immediately to the indicated value

Parameters

• position (Optional[Sequence[float]], optional) – position in the world frame of the prim. shape is (3, ). Defaults to None, which means left unchanged.

• orientation (Optional[Sequence[float]], optional) – quaternion orientation in the world frame of the prim. quaternion is scalar-first (w, x, y, z). shape is (4, ). Defaults to None, which means left unchanged.

Hint

This method belongs to the methods used to set the prim state

Example:

>>> prim.set_world_pose(position=np.array([1.0, 0.5, 0.0]), orientation=np.array([1., 0., 0., 0.]))

set_world_velocity(velocity: numpy.ndarray)

Set the articulation root velocity

Parameters

velocity (np.ndarray) – linear and angular velocity to set the root prim to. Shape (6,).

property wheel_dof_indices

[summary]

Returns

[description]

Return type

int

Holonomic Robot USD Setup

class HolonomicRobotUsdSetup(robot_prim_path: str, com_prim_path: str)

Sets up the attributes on the prims of a holonomic robot. Specifically adds the isaacmecanumwheel:radius and isaacmecanumwheel:angle attributes to the wheel joints of the robot prim

Parameters

• prim_path (str) – path of the robot articulation

• com_prim_path (str) – path of the xform representing the center of mass of the vehicle

from_usd(robot_prim_path, com_prim_path)

if the USD contains all the necessary information, automatically extract them and compile

get_articulation_controller_params()

get_holonomic_controller_params()

property mecanum_angles

property up_axis

property wheel_axis

property wheel_dof_names

property wheel_orientations

property wheel_positions

property wheel_radius

Utilities

Quintic Polynomial

class QuinticPolynomial(xs, vxs, axs, xe, vxe, axe, time)

calc_first_derivative(t)

calc_point(t)

calc_second_derivative(t)

calc_third_derivative(t)

Quintic Polynomials Planner

class quintic_polynomials_planner(sx, sy, syaw, sv, sa, gx, gy, gyaw, gv, ga, max_accel, max_jerk, dt)

quintic polynomials planner

Parameters

• sx (_type_) – start x position [m]

• sy (_type_) – start y position [m]

• syaw (_type_) – start yaw angle [rad]

• sv (_type_) – start velocity [m/s]

• sa (_type_) – start accel [m/ss]

• gx (_type_) – goal x position [m]

• gy (_type_) – goal y position [m]

• gyaw (_type_) – goal yaw angle [rad]

• gv (_type_) – goal velocity [m/s]

• ga (_type_) – goal accel [m/ss]

• max_accel (_type_) – maximum accel [m/ss]

• max_jerk (_type_) – maximum jerk [m/sss]

• dt (_type_) – time tick [s]

Returns

time result rx: x position result list ry: y position result list ryaw: yaw angle result list rv: velocity result list ra: accel result list

Return type

time

Stanly Control

class stanley_control(state, cx, cy, cyaw, last_target_idx, p=0.5, i=0.01, d=10, k=0.5)

Stanley steering control. :param state: (State object) :param cx: ([float]) :param cy: ([float]) :param cyaw: ([float]) :param last_target_idx: (int) :return: (float, int)

PID Control

class pid_control(target, current, Kp=0.1)

Proportional control for the speed. :param target: (float) :param current: (float) :return: (float)

Omnigraph Nodes