BrickAgx 0.4.0

Brick.AGX python interface development

BRICK AGX

The brickagx package implements all Brick bundles such as Physics, Robotics, DriveTrain and Simulation using AGX Dynamics Real-time multi-body simulation. The package contains python bindings and native libraries needed to load and run .brick files.

See BRICK documentation for more info on BRICK.

Prerequisites

• Python 3.9 on Windows or OSX
• Python 3.8 on Ubuntu 20.04
• Python 3.10 on Ubuntu 22.04
• AGX Dynamics 2.37.2.0 and an AGX Dynamics License

At BRICK documentation you can find out which older version of BRICK matches which version of AGX.

Install

To get the version corresponding to your AGX on Windows do:

setup_env.bat
pip install %AGX_DATA_DIR%/agx-pypi
pip install -U brickagx

To get the version corresponding to your AGX on OSX and Linux do:

source setup_env.sh
pip3 install $AGX_DATA_DIR/agx-pypi
pip3 install -U brickagx

License

Apache License 2.0

Usage Examples

Given the python file and brick file below, run with:

python3 inverted_pendulum.py

To just simulate the brick file without controllers, do:

brickview inverted_pendulum.brick

or python3 -m rebrick.brickview inverted_pendulum.brick

Store contents below in a new file named inverted_pendulum.brick:

Rod is Physics3D.Bodies.RigidBody:
    inertia.mass: 10
    geometry is Physics3D.Charges.Box:
        size: Math.Vec3.fromXYZ(0.1, 0.1, 1)
    arrow is Physics3D.Charges.Box:
        local_transform:
            position.z: 0.5
            rotation: Math.Quat.angleAxis(Math.PI / 4, Math.Vec3.Y_AXIS())
        size: Math.Vec3.fromXYZ(0.071, 0.1, 0.071)
    mate_connector is Physics3D.Charges.MateConnector:
        position.z: -geometry.size.z * 0.7
        main_axis: Math.Vec3.Y_AXIS()
        normal: Math.Vec3.Z_AXIS()

Cart is Physics3D.Bodies.RigidBody:
    inertia.mass: 10
    geometry is Physics3D.Charges.Box:
        size: Math.Vec3.fromXYZ(0.1, 0.1, 0.1)
    connector is Physics3D.Charges.MateConnector:
        main_axis: Math.Vec3.X_AXIS()
        normal: Math.Vec3.Z_AXIS()
    rotated_connector is Physics3D.Charges.MateConnector:
        main_axis: Math.Vec3.Y_AXIS()
        normal: Math.Vec3.Z_AXIS()

PendulumScene is Physics3D.System:
    world_connector is Physics3D.Charges.MateConnector:
        main_axis: Math.Vec3.X_AXIS()
        normal: Math.Vec3.Z_AXIS()

    cart is Cart
    rod is Rod

    prismatic is Physics3D.Interactions.Prismatic:
        charges: [world_connector, cart.connector]

    cart_motor is Physics3D.Interactions.LinearVelocityMotor:
        desired_speed: 0
        charges: prismatic.charges

    hinge is Physics3D.Interactions.Hinge:
        initial_angle: 0
        charges: [cart.rotated_connector, rod.mate_connector]

    motor_input is Physics3D.Signals.LinearVelocityMotorVelocityInput:
        motor: cart_motor
    
    hinge_angle_output is Physics3D.Signals.HingeAngleOutput:
        hinge: hinge
    hinge_angular_velocity_output is Physics3D.Signals.HingeAngularVelocityOutput:
        hinge: hinge
    
    cart_position_output is Physics3D.Signals.RigidBodyPositionOutput:
        rigid_body: cart
    cart_velocity_output is Physics3D.Signals.RigidBodyVelocityOutput:
        rigid_body: cart

Store contents below in a new file named inverted_pendulum.py:

import os
import signal
import agxOSG
import agxSDK
from brickbundles import bundle_path

# Import useful utilities to access the current simulation, graphics root and application
from agxPythonModules.utils.environment import init_app, simulation, root

from rebrick import Math, Physics, Physics3D, Signals
from rebrick import InputSignalListener, OutputSignalListener, load_brick_file

def file_dir():
    return os.path.dirname(os.path.abspath(__file__))

def pendulum():
    return f"{file_dir()}/inverted_pendulum.brick"

# pylint: disable=C0103

class PDController:
    def __init__(self, kp, kd, goal):
        self.kp = kp
        self.kd = kd
        self.goal = goal

    def observe(self, x, xdot):
        error = self.goal - x
        return self.kp * error - self.kd * xdot


class CartController(agxSDK.StepEventListener):
    motor_input: Physics3D.Signals_LinearVelocityMotorVelocityInput
    cart: PDController
    pole: PDController

    def __init__(self, motor_input: Physics3D.Signals_LinearVelocityMotorVelocityInput):
        super().__init__()
        self.motor_input = motor_input
        self.cart = PDController(kp=10, kd=5, goal=0)
        self.pole = PDController(kp=20, kd=5, goal=0)

    def pre(self, time):
        if time == 0.0:
            hinge_angle = 0
            hinge_angular_velocity = 0
            cart_position = Math.Vec3.fromXYZ(0,0,0)
            cart_velocity = Math.Vec3.fromXYZ(0,0,0)
        else:
            signal_values = {signal.source().getName():signal.value().value() for signal in Signals.getOutputSignals()}
            hinge_angle = signal_values["PendulumScene.hinge_angle_output"]
            hinge_angular_velocity = signal_values["PendulumScene.hinge_angular_velocity_output"]
            cart_position = signal_values["PendulumScene.cart_position_output"]
            cart_velocity = signal_values["PendulumScene.cart_velocity_output"]

        u_cart = self.cart.observe(cart_position.x(), cart_velocity.x())
        u_pole = self.pole.observe(hinge_angle, hinge_angular_velocity)

        Signals.sendInputSignal(Physics.Signals_RealInputSignal.create(-u_cart - u_pole, self.motor_input))


def buildScene():

    result = load_brick_file(simulation(), pendulum(), bundle_path(), "")
    assembly = result.assembly()
    brick_scene = result.brick_object()
    # Add a signal listener so that signals are picked up from inputs
    input_signal_listener = InputSignalListener(assembly)
    output_signal_listener = OutputSignalListener(assembly, brick_scene)
    simulation().add(input_signal_listener, InputSignalListener.RECOMMENDED_PRIO)
    simulation().add(output_signal_listener, OutputSignalListener.RECOMMENDED_PRIO)
    simulation().add(assembly.get())
    agxOSG.createVisual(assembly.get(), root())

    motor_input: Physics3D.Signals_LinearVelocityMotorVelocityInput = brick_scene.getDynamic("motor_input").asObject()
    controller = CartController(motor_input)
    simulation().add(controller)


def handler(_, __):
    os._exit(0)

signal.signal(signal.SIGINT, handler)

init = init_app(name=__name__,
                scenes=[(buildScene, '1')],
                autoStepping=True,  # Default: False
                onInitialized=lambda app: print('App successfully initialized.'),
                onShutdown=lambda app: print('App successfully shut down.'))