Adding a Controller#

Learning Objectives#

This tutorial describes how to create and use a custom controller to move a mobile robot. It then describes how to use the controllers available in Omniverse Isaac Sim. After this tutorial, you should be more comfortable with adding and controlling robots in Omniverse Isaac Sim.

10 Minute Tutorial

Getting Started#

Prerequisites

Begin with the source code open from the previous tutorial, Hello Robot.

Creating a Custom Controller#

First, code an open-loop controller that uses the unicycle model for differential drive. Controllers in Omniverse Isaac Sim inherit from the BaseController interface. You will need to implement a forward method, and it has to return an ArticulationAction type.

 1from omni.isaac.examples.base_sample import BaseSample
 2from omni.isaac.core.utils.nucleus import get_assets_root_path
 3from omni.isaac.wheeled_robots.robots import WheeledRobot
 4from omni.isaac.core.utils.types import ArticulationAction
 5from omni.isaac.core.controllers import BaseController
 6import numpy as np
 7
 8
 9class CoolController(BaseController):
10    def __init__(self):
11        super().__init__(name="my_cool_controller")
12        # An open loop controller that uses a unicycle model
13        self._wheel_radius = 0.03
14        self._wheel_base = 0.1125
15        return
16
17    def forward(self, command):
18        # command will have two elements, first element is the forward velocity
19        # second element is the angular velocity (yaw only).
20        joint_velocities = [0.0, 0.0]
21        joint_velocities[0] = ((2 * command[0]) - (command[1] * self._wheel_base)) / (2 * self._wheel_radius)
22        joint_velocities[1] = ((2 * command[0]) + (command[1] * self._wheel_base)) / (2 * self._wheel_radius)
23        # A controller has to return an ArticulationAction
24        return ArticulationAction(joint_velocities=joint_velocities)
25
26
27class HelloWorld(BaseSample):
28    def __init__(self) -> None:
29        super().__init__()
30        return
31
32    def setup_scene(self):
33        world = self.get_world()
34        world.scene.add_default_ground_plane()
35        assets_root_path = get_assets_root_path()
36        jetbot_asset_path = assets_root_path + "/Isaac/Robots/Jetbot/jetbot.usd"
37        world.scene.add(
38            WheeledRobot(
39                prim_path="/World/Fancy_Robot",
40                name="fancy_robot",
41                wheel_dof_names=["left_wheel_joint", "right_wheel_joint"],
42                create_robot=True,
43                usd_path=jetbot_asset_path,
44            )
45        )
46        return
47
48    async def setup_post_load(self):
49        self._world = self.get_world()
50        self._jetbot = self._world.scene.get_object("fancy_robot")
51        self._world.add_physics_callback("sending_actions", callback_fn=self.send_robot_actions)
52        # Initialize our controller after load and the first reset
53        self._my_controller = CoolController()
54        return
55
56    def send_robot_actions(self, step_size):
57        #apply the actions calculated by the controller
58        self._jetbot.apply_action(self._my_controller.forward(command=[0.20, np.pi / 4]))
59        return

Using the Available Controllers#

Omniverse Isaac Sim also provides different controllers under many robot extensions. Re-write the previous code using the DifferentialController class and add a WheelBasePoseController.

 1from omni.isaac.examples.base_sample import BaseSample
 2from omni.isaac.core.utils.nucleus import get_assets_root_path
 3from omni.isaac.wheeled_robots.robots import WheeledRobot
 4# This extension includes several generic controllers that could be used with multiple robots
 5from omni.isaac.wheeled_robots.controllers.wheel_base_pose_controller import WheelBasePoseController
 6# Robot specific controller
 7from omni.isaac.wheeled_robots.controllers.differential_controller import DifferentialController
 8import numpy as np
 9
10
11class HelloWorld(BaseSample):
12    def __init__(self) -> None:
13        super().__init__()
14        return
15
16    def setup_scene(self):
17        world = self.get_world()
18        world.scene.add_default_ground_plane()
19        assets_root_path = get_assets_root_path()
20        jetbot_asset_path = assets_root_path + "/Isaac/Robots/Jetbot/jetbot.usd"
21        world.scene.add(
22            WheeledRobot(
23                prim_path="/World/Fancy_Robot",
24                name="fancy_robot",
25                wheel_dof_names=["left_wheel_joint", "right_wheel_joint"],
26                create_robot=True,
27                usd_path=jetbot_asset_path,
28            )
29        )
30        return
31
32    async def setup_post_load(self):
33        self._world = self.get_world()
34        self._jetbot = self._world.scene.get_object("fancy_robot")
35        self._world.add_physics_callback("sending_actions", callback_fn=self.send_robot_actions)
36        # Initialize our controller after load and the first reset
37        self._my_controller = WheelBasePoseController(name="cool_controller",
38                                                        open_loop_wheel_controller=
39                                                            DifferentialController(name="simple_control",
40                                                                                    wheel_radius=0.03, wheel_base=0.1125),
41                                                    is_holonomic=False)
42        return
43
44    def send_robot_actions(self, step_size):
45        position, orientation = self._jetbot.get_world_pose()
46        self._jetbot.apply_action(self._my_controller.forward(start_position=position,
47                                                            start_orientation=orientation,
48                                                            goal_position=np.array([0.8, 0.8])))
49        return

Press Ctrl+S to save and hot reload the example. Then press the LOAD button to reload the scene.

Summary#

This tutorial covered the following topics:

  1. Creating a custom controller to move a mobile robot

  2. Using Controller classes from Omniverse Isaac Sim

Next Steps#

Continue to the next tutorial in the Essential Tutorials series, Adding a Manipulator Robot, to learn how to add a manipulator robot to the simulation.

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