AckermannSteering Plugin limits the minimum angular velocity based on the minimum linear velocity, preventing steering to the right when set to 0

[Dyst-0]

Environment

• OS Version: Ubuntu 24.04
• Source build of gz-sim8
  Latest commit: 4c2797d

Description

When setting the minimum linear velocity to 0, then testing the steering commands, the following happens:

• Expected behavior: Front wheels turn anti-clockwise, then clockwise until the steering limit has been reached
• Actual behavior: Front wheels do not reach the steering limit in the clockwise direction. Instead, the wheels return to pointing straight.

In AckermannSteering.cc#L349, the minimum angular velocity is set to the same value as the minimum linear velocity. In the case when the value is 0, the wheel cannot turn right.

Steps to reproduce

1. Change the min_velocity value to 0 in ackermann_steering.sdf by replacing the line with the following:

<min_velocity>0</min_velocity>

2. Build and source the workspace
3. Run gz sim ackermann_steering.sdf -r
4. Publish the steering commands
   1 - gz topic -t "/model/vehicle_blue/cmd_vel" -m gz.msgs.Twist -p "angular: {z: 0.1}"
   then
   2 - gz topic -t "/model/vehicle_blue/cmd_vel" -m gz.msgs.Twist -p "angular: {z: -0.1}"

Output

Output after running the first steering command:

Output after running the second steering command:

Proposed Solution

1. Separate angular speed limiter parameters from linear ones in AckermannSteering.cc by replacing the code block with the following:

  // Parse speed limiter parameters.
  if (_sdf->HasElement("min_velocity"))
  {
    const double minVel = _sdf->Get<double>("min_velocity");
    this->dataPtr->limiterLin->SetMinVelocity(minVel);
  }
  if (_sdf->HasElement("min_angular_velocity"))
  {
    const double minAngVel = _sdf->Get<double>("min_angular_velocity");
    this->dataPtr->limiterAng->SetMinVelocity(minAngVel);
  }
  if (_sdf->HasElement("max_velocity"))
  {
    const double maxVel = _sdf->Get<double>("max_velocity");
    this->dataPtr->limiterLin->SetMaxVelocity(maxVel);
  }
  if (_sdf->HasElement("max_angular_velocity"))
  {
    const double maxAngVel = _sdf->Get<double>("max_angular_velocity");
    this->dataPtr->limiterAng->SetMaxVelocity(maxAngVel);
  }
  if (_sdf->HasElement("min_acceleration"))
  {
    const double minAccel = _sdf->Get<double>("min_acceleration");
    this->dataPtr->limiterLin->SetMinAcceleration(minAccel);
  }
  if (_sdf->HasElement("min_angular_acceleration"))
  {
    const double minAngAccel = _sdf->Get<double>("min_angular_acceleration");
    this->dataPtr->limiterAng->SetMinAcceleration(minAngAccel);
  }
  if (_sdf->HasElement("max_acceleration"))
  {
    const double maxAccel = _sdf->Get<double>("max_acceleration");
    this->dataPtr->limiterLin->SetMaxAcceleration(maxAccel);
  }
  if (_sdf->HasElement("max_angular_acceleration"))
  {
    const double maxAngAccel = _sdf->Get<double>("max_angular_acceleration");
    this->dataPtr->limiterAng->SetMaxAcceleration(maxAngAccel);
  }
  if (_sdf->HasElement("min_jerk"))
  {
    const double minJerk = _sdf->Get<double>("min_jerk");
    this->dataPtr->limiterLin->SetMinJerk(minJerk);
  }
  if (_sdf->HasElement("min__angular_jerk"))
  {
    const double minAngJerk = _sdf->Get<double>("min_angular_jerk");
    this->dataPtr->limiterAng->SetMinJerk(minAngJerk);
  }
  if (_sdf->HasElement("max_jerk"))
  {
    const double maxJerk = _sdf->Get<double>("max_jerk");
    this->dataPtr->limiterLin->SetMaxJerk(maxJerk);
  }
  if (_sdf->HasElement("max_angular_jerk"))
  {
    const double maxAngJerk = _sdf->Get<double>("max_angular_jerk");
    this->dataPtr->limiterAng->SetMaxJerk(maxAngJerk);
  }

2. Add the following tag to ackermann_steering.sdf anywhere inside the <plugin> tag

<min_angular_velocity>-1</min_angular_velocity>

3. Build and source the workspace
4. Run gz sim ackermann_steering.sdf -r
5. Publish the steering commands
   1 - gz topic -t "/model/vehicle_blue/cmd_vel" -m gz.msgs.Twist -p "angular: {z: 0.1}"
   then
   2 - gz topic -t "/model/vehicle_blue/cmd_vel" -m gz.msgs.Twist -p "angular: {z: -0.1}"

Output after running the first steering command:

Output after running the second steering command: