element_robotics_task

Task for element robotics, robotics engineer application

Install

To install clone this repo.

Requirements

Docker is the only requirement. Tested with the official Docker Engine install and Post Install instructions.

Usage

1. Build the image

   cd ~/element_robotics_task
   ./run.py build

2. Enter the docker environment. Do this in three terminals.

   ./run.py

3. Launch the simulation in the first docker terminal

   ros2 launch bringup simulation.launch.py

   This will launch gazebo, rviz, ros_gz_bridge, robot_localisation and the required navigation files.

4. Launch the waypoint_action_client in a second docker terminal

   ros2 launch run waypoint_action_node

   This will prompt you to enter points in x, y, z, yaw form. It will prompt you for more until you press enter without a point. This client submits an NavigateThroughPoses action request. This method was chosen as it utilises the Nav2 action that already exists and is the idiomatic ros2/nav2 way (the use of these action at least) to complete such a task.

   The node also subscribes to the /estop topic which takes an empty message and cancels the request. This was chosen as it allows easy integration into a GUI and allows other nodes to do things when the /estop is signalled. (This should be a service not a topic)

5. Launch the estop node in the third docker terminal

   ros2 run waypoint_action_client estop_node

   This will prompt you to to press enter and an empty message will be sent on the /estop topic (again this should really be a service)

6. The container can be deleted using:

   ./run.py rm

   And the image can be deleted using:

   ./run.py rmi

Design decisions

Many design decisions were driven by the amount of time before the deadline for the task.

Control of the X1 used gazebo's diff_drive_system. This was chosen over ros2_control as we were required to use the .sdf model provided and ros2_control integrate with .sdf is more difficult than when using urdf files.

Much of the Nav2 configuration was based on the nav2_bringup configurations. The significant notable exception was the costmap, where only the VoxelLayer and InflationLayer was used. This is because we are operating in 3d terrain and require a map that takes this into consideration. A mapping algorithm with a wider range and consideration of gradient would be better for this application however.

Bugs

• Behavoir when given a goal to close to an obstacle is not ideal. It should give up but it doesn't seem to. This likley requires some modifications to the behavior tree.
• NavigateThroughPoses action from waypoint_action_node ignored if a goal is already published in Rviz.

Limitations

Many of these limitations where choices made so I could complete as much of the task as possible

• Terrain: The terrain is flat with some obstacle as the provided world file did not work out of the box (physics stopped working). Attempts were made to fix this my own world file base on the same data but did not have time to complete this.
• Localisation: Currently the localisation only uses odometry. IMU and LiDAR/Visual Odometry should be integrated. The transform from map => odom is currently static and should be replaced with a slam package.
• LiDAR: LiDAR is used. Ideally a depth camera would be used instead as this is meant to be a space environment and LiDAR are not neccisarily suitible for such environments.
• ESTOP: The estop functionality only interupts the action started by the waypoint_action_client. This should be made safer and the /cmd_vel should be set to zeros to stop the rover.
• No Tests: Testing was not completed. This would have involved launching a headless simulation. Providing a set of goals and testing the true position when a goal is reached. The touch sensor also would have been used to check for collisions.
• RVIZ issues: When using NavigateThroughPoses the goals are not shown as poses in rviz. When the action is cancelled the path still displays.
• Range: There is a limited range. Resolution of the global map could be decreased and map size increased to help improve it.

TODO

• Make Tests
• Make Moon Terrain.
• Integrate IMU into robot_localization.
• Integrate rtab_map for slam and odometry.
• Improve ETOP functionality.
• Publish points from waypoint_action_client to a specific topic so rviz can display them.
• Clear the path after NavigateThroughPoses action is cancelled so it doesnt show in rviz.