![](../images/banner.png)

## Overview

*stretch_gazebo* is an implementation of simulating a Stretch robot with [Gazebo](http://gazebosim.org/) simulator.

## Details

The *urdf directory* contains [a xacro file](http://wiki.ros.org/xacro) that extends the capabilities of the original xacro files living in *stretch_description* package to include Gazebo functionality.

The *config* directory contains rviz files and [ros_control](http://wiki.ros.org/ros_control) controller configuration files for various parts of the robot including:

* Base: [diff_drive_controller/DiffDriveController](http://wiki.ros.org/diff_drive_controller)
* Arm: [position_controllers/JointTrajectoryController](http://wiki.ros.org/joint_trajectory_controller)
* Gripper: [position_controllers/JointTrajectoryController](http://wiki.ros.org/joint_trajectory_controller)
* Head: [position_controllers/JointTrajectoryController](http://wiki.ros.org/joint_trajectory_controller)
* Joints: [joint_state_controller/JointStateController](http://wiki.ros.org/joint_state_controller)

The *launch* directory includes:

* `gazebo.launch`: Opens up an empty Gazebo world and spawns the robot loading all the controllers, including all the sensors except Cliff sensors and respeaker.

The *script* directory contains a single python file that publishes ground truth odometry of the robot from Gazebo.

The *worlds* directory contains a sample [Gazebo world](http://gazebosim.org/tutorials?tut=ros_roslaunch#WorldFiles) file(s) that can be used to configure the environment in which Stretch is spawned.

## Setup

These set up instructions will not be required on newly shipped robots. Follow these instructions if *stretch_gazebo* is not present in your ROS workspace or you are simulating Stretch on external hardware. Clone stretch_ros and realsense_gazebo_plugin packages to your catkin workspace. Then install dependencies and build the packages, with the following set of commands:

```bash
mkdir -p ~/catkin_ws/src
cd ~/catkin_ws/src
git clone https://github.com/hello-robot/stretch_ros -b dev/noetic
git clone https://github.com/pal-robotics/realsense_gazebo_plugin
cd ~/catkin_ws
rosdep install --from-paths src --ignore-src -r -y
catkin_make
```

## Running Stretch Gazebo

![](../images/gazebo.png)

```bash
# Terminal 1:
roslaunch stretch_gazebo gazebo.launch rviz:=true
# Terminal 2:
roslaunch stretch_core teleop_twist.launch twist_topic:=/stretch_diff_drive_controller/cmd_vel linear:=1.0 angular:=2.0 teleop_type:=keyboard # or use teleop_type:=joystick if you have a controller
```

This will launch an Rviz instance that visualizes the sensors and an empty world in Gazebo with Stretch and load all the controllers. Although, the base will be able to move with the joystick commands, the joystick won't give joint commands to arm, head or gripper. To move these joints see the next section about *Running Gazebo with MoveIt! and Stretch*.

By default, Gazebo initializes Stretch in an empty environment. To initialize Gazebo with a different environment, use the "world" ROS argument to point to a [world file](http://gazebosim.org/tutorials?tut=ros_roslaunch#WorldFiles). The *worlds* directory within Stretch Gazebo, contains a sample world called "random_objects.world" and can be launched like this:

```bash
roslaunch stretch_gazebo gazebo.launch rviz:=true world:=`rospack find stretch_gazebo`/worlds/random_objects.world
```


### Running Stretch Gazebo with MoveIt! and Twist Teleop

```bash
# Terminal 1:
roslaunch stretch_gazebo gazebo.launch
# Terminal 2:
roslaunch stretch_core teleop_twist.launch twist_topic:=/stretch_diff_drive_controller/cmd_vel linear:=1.0 angular:=2.0 teleop_type:=keyboard # or use teleop_type:=joystick if you have a controller
# Terminal 3
roslaunch stretch_moveit_config demo_gazebo.launch
```

This will launch an Rviz instance that visualizes the joints with markers and an empty world in Gazebo with Stretch and load all the controllers. There are pre-defined positions for each joint group for demonstration purposes. There are three joint groups, namely *stretch_arm*, *stretch_gripper* and *stretch_head* that can be controlled individually via Motion Planning Rviz plugin. Start and goal positions for joints can be selected similar to [this moveit tutorial](https://ros-planning.github.io/moveit_tutorials/doc/quickstart_in_rviz/quickstart_in_rviz_tutorial.html#choosing-specific-start-goal-states). A few notes to be kept in mind:

* Planning group can be changed via *Planning Group* drop down in Planning tab of Motion Planning Rviz plugin.
* Pre-defined start and goal states can be specified in *Start State* and *Goal State* drop downs in Planning tab of Motion Planning Rviz plugin.
* *stretch_gripper* group does not show markers, and is intended to be controlled via the joints tab that is located in the very right of Motion Planning Rviz plugin.
* When planning with *stretch_head* group make sure you select *Approx IK Solutions* in Planning tab of Motion Planning Rviz plugin.

![](../images/gazebo_moveit.gif)

### Running Stretch Gazebo with Stretch Navigation

See the Stretch Navigation [README](../stretch_navigation/README.md#running-in-simulation) for an explanation of the `mapping_gazebo.launch` and `navigation_gazebo.launch` launch files, which allow for mapping and navigation within the Gazebo simulated world.

## Differences in Gazebo vs Stretch

The simulated Stretch RE1 differs from the robot in the following ways.

### Gazebo Sensors vs Stretch Sensors

|         Sensor        |       Gazebo       |       Stretch      |       Notes       |
|:---------------------:|:------------------:|:------------------:|:-----------------:|
|         LIDAR         | :heavy_check_mark: | :heavy_check_mark: |                   |
|        Base IMU       | :heavy_check_mark: | :heavy_check_mark: |                   |
|  Wrist Accelerometer  | :heavy_check_mark: | :heavy_check_mark: | Modeled as an IMU |
|    Realsense D435i    | :heavy_check_mark: | :heavy_check_mark: |                   |
| Respeaker (Mic Array) |         :x:        | :heavy_check_mark: |                   |
|     Cliff Sensors     |         :x:        | :heavy_check_mark: |                   |

*Notes:* Although there is no microphone in Gazebo, Respeaker can be represented with a ROS node that accesses compputer's microphone. Cliff sensors are not modeled but they can also be represented as 1D LIDAR sensors. See LIDAR definition in *stretch_gazebo.urdf.xacro* file.

### MoveIt Controllers vs stretch_core

Actuators are defined as *ros_control* transmission objects in Gazebo using [PositionJointInterfaces](http://docs.ros.org/en/melodic/api/hardware_interface/html/c++/classhardware__interface_1_1PositionJointInterface.html). MoveIt is configured to use three different action servers to control the body parts of stretch in Gazebo through the srdf file in *stretch_moveit_config* package. See the section above about MoveIt for details. Please note that this behavior is different than *stretch_core* as it works with a single Python interface to control all the joints.

### Uncalibrated XACRO vs Calibrated URDF

We provide [stretch_calibration](../stretch_calibration/README.md) to generate a calibrated URDF that is unique to each robot. The calibrated URDF is generated from the nominal description of Stretch RE1, the xacro files that live in [stretch_description](../stretch_description/README.md). The simulated Stretch RE1 is generated from the gazebo xacro description in the *urdf directory* and is not calibrated.

### Topic Names

|        Stretch        |                 Gazebo                 |
|:---------------------:|:--------------------------------------:|
|   /stretch/cmd_vel    | /stretch_diff_drive_controller/cmd_vel |
|         /odom         |  /stretch_diff_drive_controller/odom   |
| /stretch/joint_states |             /joint_states              |

## License

For license information, please see the LICENSE files.