diff drive robot cannot rotate in bullet-feathestone

[jsupratman13]

Environment

• OS Version: Ubuntu 24.04
• Binary, gz-physics7 installed along with ros2 jazzy

Description

I apologize if this was address somewhere before. I'm working on a robot with differential drive using bullet-featherstone physics engine. The robot can move forward and backward without any issues but struggles to rotate in place. Instead of rotating, the robot slips, with no significant rotation. Even with the sample diff_drive.sdf, the vehicle is unable to turn or rotate in place. I also tried setting the caster friction to 0 but to no avail.

• Expected behavior: Diff drive robot can rotate in place
• Actual behavior: Diff drive robot does not rotate in place

Steps to reproduce

1. gz sim diff_drive.sdf --physics-engine gz-physics-bullet-featherstone-plugin
2. gz topic -t /model/vehicle_green/cmd_vel -m gz.msgs.Twist -p "linear: {x: 0.0}, angular: {z: 5.0}"

Output

issue-2024-10-25_11.51.19.mp4

[iche033]

I think the default torsional friction value in bullet is causing this issue. As a workaround, try setting it to 0 to all the wheels and the ground plane, i.e. add this to the <collision> element in sdf:

          <surface>
            <friction>
              <torsional>
                <coefficient>0.0</coefficient>
              </torsional>
            </friction>
          </surface>

[jsupratman13]

I see, thank you for your help!
Setting the wheel and the ground plane torsional friction to 0 works.