# How to Use Controller

> This tutorial guides you on how to use a controller to control a robot.

## Pre-defined Controllers

The directory [`internutopia_extension/controllers/`](https://github.com/InternRobotics/InternUtopia/tree/main/internutopia_extension/controllers) contains a list of all pre-defined controllers:

```
internutopia_extension/
└── controllers
    ├── aliengo_move_by_speed_controller.py
    ├── dd_controller.py
    ├── franka_mocap_teleop_controller.py
    ├── g1_move_by_speed_controller.py
    ├── gr1_move_by_speed_controller.py
    ├── gr1_teleop_controller.py
    ├── gripper_controller.py
    ├── h1_move_by_speed_controller.py
    ├── ik_controller.py
    ├── joint_controller.py
    ├── move_along_path_points_controller.py
    ├── move_to_point_by_speed_controller.py
    ├── move_to_point_oracle_controller.py
    ├── recover_controller.py
    ├── rmpflow_controller.py
    └── rotate_controller.py
    ...
```

For each robot, we provide some ready-to-use controller configurations for each robot in `internutopia_extension/configs/robots/{robot_name}.py`.

## How to Use a Controller

A controller must be used with a robot, and the corresponding action must be specified in each step to control the robot with that controller.

```{code-block} python
:emphasize-lines: 8,25,39-40

from internutopia.core.config import Config, SimConfig
from internutopia.core.gym_env import Env
from internutopia.core.util import has_display
from internutopia.macros import gm
from internutopia_extension import import_extensions
from internutopia_extension.configs.robots.jetbot import (
    JetbotRobotCfg,
    move_by_speed_cfg,
)
from internutopia_extension.configs.tasks import SingleInferenceTaskCfg

import_extensions()

headless = not has_display()

config = Config(
    simulator=SimConfig(physics_dt=1 / 240, rendering_dt=1 / 240, use_fabric=False, headless=headless, webrtc=headless),
    task_configs=[
        SingleInferenceTaskCfg(
            scene_asset_path=gm.ASSET_PATH + '/scenes/empty.usd',
            robots=[
                JetbotRobotCfg(
                    position=(0.0, 0.0, 0.0),
                    scale=(5.0, 5.0, 5.0),
                    controllers=[move_by_speed_cfg],
                )
            ],
        ),
    ],
)

env = Env(config)
obs, _ = env.reset()

i = 0

while env.simulation_app.is_running():
    i += 1
    action = {move_by_speed_cfg.name: [0.5, 0.5]}
    obs, _, terminated, _, _ = env.step(action=action)

    if i % 1000 == 0:
        print(i)
        print(obs)

env.close()
```

<video width="720" height="405" controls>
    <source src="../../../_static/video/tutorial_use_controller.webm" type="video/webm">
</video>

In the above example, first we import the `move_by_speed_cfg` for jetbot. It'a a ready-to-use controller config for jetbot to use the `DifferentialDriveController` to move around:

[`internutopia_extension/configs/robots/jetbot.py`](https://github.com/InternRobotics/InternUtopia/blob/main/internutopia_extension/configs/robots/jetbot.py)

```python
move_by_speed_cfg = DifferentialDriveControllerCfg(name='move_by_speed', wheel_base=0.1125, wheel_radius=0.03)
```

The controller config is then added to the robot config to declare it as an available controller for the robot in that episode. In each step, we define the action to be applied to the robot, that is, a dict with the controller name as the key and desired action as the value. The format of action is defined by the `action_to_control` method of the specific controller. For the above example, we can check it in the `DifferentialDriveController` class:

[`internutopia_extension/controllers/dd_controller.py`](https://github.com/InternRobotics/InternUtopia/blob/main/internutopia_extension/controllers/dd_controller.py)

```python
class DifferentialDriveController(BaseController):
    def action_to_control(self, action: List | np.ndarray) -> ArticulationAction:
        """
        Args:
            action (List | np.ndarray): n-element 1d array containing:
              0. forward_speed (float)
              1. rotation_speed (float)
        """
        assert len(action) == 2, 'action must contain 2 elements'
        return self.forward(
            forward_speed=action[0],
            rotation_speed=action[1],
        )
```

So with the action `[0.5, 0.5]` the jetbot will move forward at 0.5 m/s and rotate at 0.5 rad/s.

You can try more controllers with the controller configurations defined in [`internutopia_extension/configs/robots/jetbot.py`](https://github.com/InternRobotics/InternUtopia/blob/main/internutopia_extension/configs/robots/jetbot.py).