Unrealistic rotation behavior in Gazebo

[jukindle]

Please provide the following information:

• OS: Ubuntu 20.04
• ROS Distro: Noetic
• Built from source or installed: apt-package
• Package version: jackal_simulator 0.4.0, gazebo version 11.10.2

Expected behaviour
By commanding a constant rotational velocity of 0.2rad/s, we would expect the robot to roughly rotate at 0.2rad/s about z-axis.

Actual behaviour
Even though the robot rotates at the desired velocity, whenever the x-axis is axis-aligned with the diagonals in the x-y-plane, the robot seems to get stuck and the rotational velocity drops.

To Reproduce
Provide the steps to reproduce:

1. Install the simulator by running sudo apt install ros-noetic-jackal-simulator

2. Launch the simulation running roslaunch jackal_gazebo jackal_world.launch

3. Command the robot to rotate on spot by running

    rostopic pub -r 50 /jackal_velocity_controller/cmd_vel geometry_msgs/Twist "linear:
      x: 0.0
      y: 0.0
      z: 0.0
    angular:
      x: 0.0
      y: 0.0
      z: 0.2" 
   

Other notes
Video of the bug

According to this issue on the gazebo repository, this error seems to a bug in the friction pyramid implementation in gazebo. Two solutions were proposed: either change the friction model to cone, or increase the ERP to 0.6. Unfortunately, both solutions did not work for me and the only thing which helped is to drastically decrease the friction of the wheels. This results in unrealistic behavior as the robot would slip down slopes.

Do you see any possibility to solve this issue? I would love to use gazebo to test my software before deploying it to the real system, but with such unrealistically simulated skid-steer behavior, I am unable to do so.

[peci1]

Yeah, it would be nice if somebody found the culprit for this. I definitely don't have time for that now, but feel free to ping me for a review if you find something ;)

[peci1]

Could you maybe test it with other dynamics engines?

[AlexGisi]

The dart engine seems to be slightly better about this, but it is still a serious problem (Gazebo 11.11.0).