IGVC Self-Drive Gazebo Simulator

This repository provides a Gazebo model of a Polaris GEM, as well as worlds and models to simulate the tasks of the competition.

After cloning into a ROS workspace, run the following the command from the root of the workspace to install the necessary ROS package dependencies to make everything work correctly:

rosdep install --from-paths src --ignore-src -r

Starting the Simulator

roslaunch gazebo_ros empty_world.launch

To load a custom Gazebo world file, pass its file path to the world_name argument:

roslaunch gazebo_ros empty_world.launch world_name:=<complete path to world file here\>

Spawn the GEM model in Gazebo with spawn_gem.launch in the igvc_self_drive_gazebo package:

roslaunch igvc_self_drive_gazebo spawn_gem.launch

The spawn_gem.launch file has arguments that allow the user to control some aspects of the spawned GEM:

• start_x, start_y, start_z: The x, y, z position of the vehicle in Gazebo

• start_yaw: The direction the vehicle faces relative to the Gazebo world frame

• twist_mode: If true, the GEM subscribes to a geometry_msgs/Twist topic to move around the world. If false, it subscribes to individual actuator command topics. See the discussion of these modes below.

• pub_tf: If true, a ground truth TF transform from world frame to base_footprint frame is published

Simulating IGVC Tasks

The self_drive_tasks.world file in the igvc_self_drive_gazebo package simulates the specific tasks as described in the official rules document, which can be found [here].

To load the world and spawn the vehicle at the starting point for a particular task, run the corresponding launch file in the igvc_self_drive_gazebo package. For example, to run task F3, the right turn test where the vehicle has to stop at the intersection:

roslaunch igvc_self_drive_gazebo f3_gazebo.launch

At the moment, the F9 task is not implemented in the self_drive_tasks.world Gazebo world, even though the launch file for it exists.

Sensor Data Topics

The following topics are published by Gazebo:

• /fix: GPS position given in latitude and longitude in the form of a sensor_msgs/NavSatFix message

• /camera_front/image_raw/*: Standard group of image topics from image_proc

• /scan: LIDAR scan data in the form of a sensor_msgs/LaserScan message

• /twist: The current measurement of the vehicle’s speed and yaw rate in a geometry_msgs/TwistStamped message. The linear.x field contains the speed in m/s and angular.z contains the yaw rate in rad/s

• /gear_state: The current gear of the vehicle in a std_msgs/UInt8 message:
  • 0 = Forward
  • 1 = Reverse
• /sonar/*: Group of 10 sonar sensor range measurement topics in separate sensor_msgs/Range messages. There are three sensors on the front of the vehicle, three on the rear, and two on either side.

Controlling the Simulated Vehicle

The Gazebo GEM model can be controlled in two different modes:

• Twist Mode: Send a geometry_msgs/Twist message on the /cmd_vel topic with desired speed and yaw rate, and let the simulation generate the appropriate actuator commands.

• Actuator Mode: Send throttle, brake, steering, and gear actuator commands directly to the simulator.

Twist Mode (default)

The control mode is specified by setting the twist_mode argument to the spawn_gem.launch file to true or false. This argument defaults to true, so if you don’t have to change anything to use Twist Mode.

The linear.x field of the user’s geometry_msgs/Twist message should contain the desired speed in m/s, and the angular.z field should contain the desired yaw rate in rad/s.

Actuator Mode

By setting the twist_mode argument to false, the Gazebo plugin instead subscribes to four separate actuator command topics so the user can control them directly:

• /throttle_cmd: std_msgs/Float64 topic containing commanded throttle percentage (0 to 1)

• /brake_cmd: std_msgs/Float64 topic containing commanded brake torque in Newton-meters (0 to 1000)

• /steering_cmd: std_msgs/Float64 topic containing commanded steering wheel angle in radians (-9.5 to +9.5)

• /gear_cmd: std_msgs/UInt8 topic containing commanded gear, as controlled by the switch on the dashboard of the real vehicle:

  • 0 = Forward
  • 1 = Reverse

Some Useful Kinematics Parameters

• Gear ratio between steering wheel and equivalent bicycle steer angle = 17 : 1

• Wheelbase = 2.4 meters

• Track width = 1.2 meters

• Wheel radius = 0.36 meters