# Using ROS demo

### Pre-launch Check

> **Tip** Please first acquire basic knowledge of `ROS`. You can refer to the [ROS1 Tutorial](https://wiki.ros.org/ROS/Tutorials) and [ROS2 Tutorial](https://docs.ros.org/en/iron/Tutorials.html) to understand the common conventions of the `ROS` system.

Please ensure the following are completed:

1. ROS-SDK installation is complete; if it is your first time installing the SDK, it is recommended to ***restart*** after the first installation.
2. Compilation has been completed without errors.
3. The workspace has been sourced.
4. If using the CAN-COM HUB, ensure the CAN bus is correctly connected and devices can be detected.

    * Use lsusb in the terminal to see the following devices.

5. Ensure the remote control is turned off; or if it is on, ensure it is set to CAN mode.
   > For information about the remote control and modes, please refer to the remote control section in the product user manual.

---
### Chassis Devices

> **Warning**
>    Be cautious, when attempting to control the robot with software for the first time, ensure there are no obstacles within the robot's range of motion, or elevate the robot.

**There are two test demos for the chassis:**

    * demo_basic_ctrl.launch
    * demo_key_ctrl.launch

`demo_basic_ctrl.launch` is a standard launch file that can be used directly with autonomous driving, controlling the robot's movement via the `/cmd_vel` topic.

`demo_key_ctrl.launch` supports keyboard control, using `turtle_teleop_key` to control the robot with the keyboard. If you have not yet seen the ROS `turtlesim` tutorial, please check it out first.

> **Tip**
>    Note that the movement is not controlled with the arrow keys, please check the usage tips printed in the terminal and press the forward button indicated.

**Successful launch will display the following terminal message**

[![startup.png](https://odocs.hexfellow.com/uploads/images/gallery/2024-07/scaled-1680-/VY6Ac9VV1j8sNoGA-startup.png)](https://odocs.hexfellow.com/uploads/images/gallery/2024-07/VY6Ac9VV1j8sNoGA-startup.png)

**For parameter settings and communication `msg` in the launch file, please refer to the `src/drivers/xpkg_vehicle/README.md` file, below are explanations of a few key parameters:**

* `calc_speed` sets the odometer calculation method, `true` for using speed, `false` for using motor encoder values, with the default setting recommended as false.
* `mode_can_lock` is the CAN mode lock setting, `true` forces CAN mode, switching to other modes with the remote control will trigger a warning and wait for recovery, setting `false` allows the user to choose the control mode.

!!!note
    If the chassis cannot be controlled, it may be because `mode_can_lock` is set to `false`, and it has been switched to another mode.

* `rate_x` controls the rate multiplier for input speed, 1 is full speed, it is recommended to set it below 0.2 during testing.

**After successfully launching the package, you can view ROS topics through `rostopic list`, below are a few key topics:**

* The chassis node sends messages of type `nav_msgs/Odometry` to the topic `/odom`. This message represents the chassis odometer information, including the current pose of the chassis as well as linear and angular velocity information.
* The chassis node sends messages of type `tf2_msgs/TFMessage` to the topic `/tf`, which include chassis tf transformation information, to be enabled in launch parameters.
* The chassis node subscribes to messages of type `geometry_msgs/Twist` from the topic `/cmd_vel`. Upon receiving this message, the chassis moves, where `linear.x`/`linear.y` represent linear velocity, and `angular.z` represents rotational speed.