What I'm trying to achieve and what I think might be the issue

Hi,

I'm currently working on the simulation of my student club's tracked robot (Markhor) with Gazebo 9.16 and ROS Melodic. I want to be able to send cmdvel through the network to a ROS control diffdrive controller and make the robot move.

My issue is, when trying to control a robot using libSimpleTrackedVehiclePlugin, it seems like it doesn't communicate between the ROS controller and the track. This results in the robot not moving.

Also when I'm using the libKeysToCmdVelPlugin the robot moves but I don't want to control it through Gazebo.

I tried to isolate the issue and tested Clearpath's Husky repository which is using the same type of ROS control controller and it worked. Then I tried replacing the tracks on my robot with the wheels used on the husky and it worked.

So now I'm trying to figure out why our robot with the libSimpleTrackedVehiclePlugin is not moving. Since the same ROS control setup works with the husky wheel, I suspect that it might be something with the libSimpleTrackedVehiclePlugin.

How to replicate the issue

Download & packages installation

The repository needs to be inside a workspace. So you might want to create a repository and a src folder:

mkdir -p markhor_ws/src

cd markhor_ws/src

The repository of our robot can be found here: https://github.com/clubcapra/markhor/tree/diff_drive

You just need to download it and place it inside the src folder we just created. Also, the code for this feature is inside the branch diff_drive.

git clone https://github.com/clubcapra/markhor.git

cd markhor

git checkout diff_drive

Once this is done, you can download the dependencies with this command inside the markhor_ws folder:

cd ../..

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

Once all the downloads are done, we compile the project, by simply running the catkin_make command inside the markhor_ws folder.

Now we should be good to test for the issue.

Markhor robot with the husky wheels

First, inside a terminal we need to source the projet source devel/setup.bash Then we want to launch the simulation (make sure it is sourced with the project setup script):

roslaunch markhor_gazebo test_world_husky.launch

Then in a second terminal, we need to launch a cmd_vel node publisher:

rosrun teleop_twist_keyboard teleop_twist_keyboard.py cmd_vel:=/markhor/diff_drive_controller/cmd_vel Now if you try to use this terminal to move the robot with your keyboard it should move relatively slowly.

Also, everything inside the repository, that has the suffix "_husky" means that it was adapted to use the husky wheels for the simulation.

Markhor robot with the libSimpleTrackedVehiclePlugin tracks

Same thing as for the Markhor robot with the husky wheels, but we only change the launch file name. If you didn't try the simulation with the husky wheels you might need to source the workspace here.

roslaunch markhor_gazebo test_world.launch

Then in a second terminal, we need to launch a cmd_vel node publisher:

rosrun teleop_twist_keyboard teleop_twist_keyboard.py cmd_vel:=/markhor/diff_drive_controller/cmd_vel

Now if you try to use this terminal to move the robot with your keyboard it shouldn't move. But, if you select the robot by clicking on it inside the simulation and then using your arrow keys to move it, it should work.

How it is organized inside markhor_gazebo

You can find the related files in our repository inside the diffdrive branch: https://github.com/clubcapra/markhor/tree/diffdrive

launch files

test_world.launch

Inside the test_world.launch I'm simply launching Gazebo with the simple.world World.

spawn_markhor.launch

Inside the spawnmarkhor I set where the robot will be inside the simulation. Then I launch the controltrack.launch file and I set the spawnmodel to robotdescription argument, which is set inside the control_track.launch.

control_track.launch

In this file, I set the robotdescription with the xacro command and the markhor.urdf.xacro file, which is inside the markhordescription folder.

Then I load the config file for the controller and launch the controller manager, which creates the node for the diff_drive controller.

world file

simple.world

This world file is almost a copy of the trackedvehiculesimple.world file. We just remove the model definition so we could use our own.

Note: Also inside the trackedvehiclesimple.world there's a comment that says:

   <!--
      A demo world for tracked vehicles.
       Drive the vehicle by keyboard using arrows, or by publishing the
       desired velocity to ~/<vehicle name>/cmd_vel
       (x and yaw command the motion).
   -->

But I've tried it and it doesn't seem to work with the ~/<vehicle name>/cmd_vel option, only with the keyboard.

How should I solve the issue

So I'm kind of stuck with this issue and would like to know if I could have any pointers or insights on how to solve it. I've read the code for SimpleTrackedVehiclePlugin (and the files that it inherited), but couldn't find something suspicious relating to my issue.

I'm wondering what are my options, should I try and debug it by compiling and running Gazebo? Or is there something else I could try?