3. Adding A Controller¶
3.1. 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
3.2. Getting Started¶
Prerequisites
Review Hello Robot prior to beginning this tutorial.
Begin with the source code open from the previous tutorial, Hello Robot.
3.3. 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.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 from omni.isaac.examples.base_sample import BaseSample from omni.isaac.core.utils.nucleus import get_assets_root_path from omni.isaac.wheeled_robots.robots import WheeledRobot from omni.isaac.core.utils.types import ArticulationAction from omni.isaac.core.controllers import BaseController import numpy as np class CoolController(BaseController): def __init__(self): super().__init__(name="my_cool_controller") # An open loop controller that uses a unicycle model self._wheel_radius = 0.03 self._wheel_base = 0.1125 return def forward(self, command): # command will have two elements, first element is the forward velocity # second element is the angular velocity (yaw only). joint_velocities = [0.0, 0.0] joint_velocities[0] = ((2 * command[0]) - (command[1] * self._wheel_base)) / (2 * self._wheel_radius) joint_velocities[1] = ((2 * command[0]) + (command[1] * self._wheel_base)) / (2 * self._wheel_radius) # A controller has to return an ArticulationAction return ArticulationAction(joint_velocities=joint_velocities) class HelloWorld(BaseSample): def __init__(self) -> None: super().__init__() return def setup_scene(self): world = self.get_world() world.scene.add_default_ground_plane() assets_root_path = get_assets_root_path() jetbot_asset_path = assets_root_path + "/Isaac/Robots/Jetbot/jetbot.usd" world.scene.add( WheeledRobot( prim_path="/World/Fancy_Robot", name="fancy_robot", wheel_dof_names=["left_wheel_joint", "right_wheel_joint"], create_robot=True, usd_path=jetbot_asset_path, ) ) return async def setup_post_load(self): self._world = self.get_world() self._jetbot = self._world.scene.get_object("fancy_robot") self._world.add_physics_callback("sending_actions", callback_fn=self.send_robot_actions) # Initialize our controller after load and the first reset self._my_controller = CoolController() return def send_robot_actions(self, step_size): #apply the actions calculated by the controller self._jetbot.apply_action(self._my_controller.forward(command=[0.20, np.pi / 4])) return
3.4. 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
.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 from omni.isaac.examples.base_sample import BaseSample from omni.isaac.core.utils.nucleus import get_assets_root_path from omni.isaac.wheeled_robots.robots import WheeledRobot # This extension includes several generic controllers that could be used with multiple robots from omni.isaac.motion_generation import WheelBasePoseController # Robot specific controller from omni.isaac.wheeled_robots.controllers.differential_controller import DifferentialController import numpy as np class HelloWorld(BaseSample): def __init__(self) -> None: super().__init__() return def setup_scene(self): world = self.get_world() world.scene.add_default_ground_plane() assets_root_path = get_assets_root_path() jetbot_asset_path = assets_root_path + "/Isaac/Robots/Jetbot/jetbot.usd" world.scene.add( WheeledRobot( prim_path="/World/Fancy_Robot", name="fancy_robot", wheel_dof_names=["left_wheel_joint", "right_wheel_joint"], create_robot=True, usd_path=jetbot_asset_path, ) ) return async def setup_post_load(self): self._world = self.get_world() self._jetbot = self._world.scene.get_object("fancy_robot") self._world.add_physics_callback("sending_actions", callback_fn=self.send_robot_actions) # Initialize our controller after load and the first reset self._my_controller = WheelBasePoseController(name="cool_controller", open_loop_wheel_controller= DifferentialController(name="simple_control", wheel_radius=0.03, wheel_base=0.1125), is_holonomic=False) return def send_robot_actions(self, step_size): position, orientation = self._jetbot.get_world_pose() self._jetbot.apply_action(self._my_controller.forward(start_position=position, start_orientation=orientation, goal_position=np.array([0.8, 0.8]))) return
Press Ctrl+S
to save and hot reload the example. Then press the LOAD button to reload
the scene.
3.5. Summary¶
This tutorial covered the following topics:
Creating a custom controller to move a mobile robot
Using Controller classes from Omniverse Isaac Sim
3.5.1. 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.