BrickAgx 0.0.18

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.

Prerequisites

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

BRICK version	Required installed AGX version
0.0.14 - 0.0.15	2.36.1.4
0.0.16 - 0.0.17	2.36.1.5

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.view inverted_pendulum.brick

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

Rod is Physics3D.RigidBody:
    inertia.mass: 10
    geometry is Physics3D.Box:
        size: Math.Vec3.fromXYZ(0.1, 0.1, 1)
    arrow is Physics3D.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.MateConnector:
        position.z: -geometry.size.z * 0.7
        main_axis: Math.Vec3.Y_AXIS()
        normal: Math.Vec3.Z_AXIS()

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

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

    cart is Cart
    rod is Rod

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

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

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

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

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

import agxOSG
import agxSDK
import os
import signal
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, Simulation, Signals
from rebrick import InputSignalListener, OutputSignalListener, load_brickfile

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

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


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: Simulation.LinearVelocityMotorVelocityInput
    cart: PDController
    pole: PDController

    def __init__(self, motor_input: Simulation.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, t):
        if t == 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() 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(Simulation.RealInputSignal.create(-u_cart - u_pole, self.motor_input))


def buildScene():

    brick_scene, assembly = load_brickfile(simulation(), pendulum(), bundle_path(), "")
    # 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: Simulation.LinearVelocityMotorVelocityInput = brick_scene.getDynamic("motor_input").asObject()
    controller = CartController(motor_input)
    simulation().add(controller)


def handler(signum, frame):
    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.'))