0
$\begingroup$

Rosanswers logo

I have created a URDF file that describes a vehicle with Ackermann steering (a Traxxas E-Maxx RC truck) and need to simulate the vehicle in Gazebo. To simulate Ackermann steering, I am considering writing a Gazebo controller plug-in like this:

ackermann_steering_controller:
    leftJointName (string)
    rightJointName (string)
    track (float)
    wheelbase (float)

The controller would subscribe to messages from joy_node, getting the steering angle from it, then would perform PID servo control on the left and right joints to keep them rotated to angles that satisfy the Ackermann equation. Is there a better way to do this? I've read the transmission tutorials, but haven't been able to figure out how to adapt the PR2 transmission system to a Gazebo simulation of Ackermann steering.

Originally posted by Jim Rothrock on ROS Answers with karma: 792 on 2011-03-19

Post score: 4

Original comments

Comment by joq on 2011-03-25:
I would like to use gazebo for an autonomous car with Ackermann steering. Please keep everyone posted on what you do.

Comment by mjcarroll on 2011-03-20:
I haven't done anything related to this, but you may be able to check out the Gazebo model for the ClodBuster. It's a 4-wheel Ackerman robot.

Improve this question
$\endgroup$

1 Answer 1

Reset to default
0
$\begingroup$

Rosanswers logo

One way is the implement the 4 bar linkage. Here's a simple model constructed with 4 bar linkage steering mechanism. I did not compute the exact linkage lengths for Ackermann steering, but the basic idea is there:

  <robot
        xmlns:gazebo="http://playerstage.sourceforge.net/gazebo/xmlschema/#gz"
        xmlns:model="http://playerstage.sourceforge.net/gazebo/xmlschema/#model"
        xmlns:sensor="http://playerstage.sourceforge.net/gazebo/xmlschema/#sensor"
        xmlns:body="http://playerstage.sourceforge.net/gazebo/xmlschema/#body"
        xmlns:geom="http://playerstage.sourceforge.net/gazebo/xmlschema/#geom"
        xmlns:joint="http://playerstage.sourceforge.net/gazebo/xmlschema/#joint"
        xmlns:controller="http://playerstage.sourceforge.net/gazebo/xmlschema/#controller"
        xmlns:interface="http://playerstage.sourceforge.net/gazebo/xmlschema/#interface"
        xmlns:rendering="http://playerstage.sourceforge.net/gazebo/xmlschema/#rendering"
        xmlns:physics="http://playerstage.sourceforge.net/gazebo/xmlschema/#physics"
        name="ackermann">

    <property name="M_PI" value="3.1415926535897931" />

    <link name="base">
      <inertial>
        <mass value="1.0" />
        <origin xyz="0 0 0" /> 
        <inertia  ixx="1.0" ixy="0.0"  ixz="0.0"  iyy="1.0"  iyz="0.0"  izz="1.0" />
      </inertial>
      <visual>
        <origin xyz="0 0 0" rpy="0 0 0" />
        <geometry>
          <box size="2.0 1.0 0.1" />
        </geometry>
      </visual>
      <collision>
        <origin xyz="0 0 0" rpy="0 0 0" />
        <geometry>
          <box size="2.0 1.0 0.1" />
        </geometry>
      </collision>
    </link>
    <gazebo reference="base">
      <material>Gazebo/Blue</material>
      <turnGravityOff>false</turnGravityOff>
    </gazebo>

    <link name="front_left_bar">
      <inertial>
        <mass value="1.0" />
        <origin xyz="0 0 0" /> 
        <inertia  ixx="1.0" ixy="0.0"  ixz="0.0"  iyy="1.0"  iyz="0.0"  izz="1.0" />
      </inertial>
      <visual>
        <origin xyz="-0.2 -0.2 0" rpy="0 0 0" />
        <geometry>
          <box size="0.4 0.5 0.01" />
        </geometry>
      </visual>
      <collision>
        <origin xyz="-0.2 -0.2 0" rpy="0 0 0" />
        <geometry>
          <box size="0.4 0.5 0.01" />
        </geometry>
      </collision>
    </link>
    <gazebo reference="front_left_bar">
      <material>Gazebo/Green</material>
      <turnGravityOff>false</turnGravityOff>
    </gazebo>
    <joint name="front_left_bar_joint" type="revolute" >
      <limit lower="-0.2" upper="0.2" effort="100" velocity="10" />
      <axis xyz="0 0 1" />
      <parent link="base" />
      <child link="front_left_bar" />
      <origin xyz="1.0 0.5 0.055" rpy="0 0 0" />
    </joint>

    <link name="front_right_bar">
      <inertial>
        <mass value="1.0" />
        <origin xyz="0 0 0" /> 
        <inertia  ixx="1.0" ixy="0.0"  ixz="0.0"  iyy="1.0"  iyz="0.0"  izz="1.0" />
      </inertial>
      <visual>
        <origin xyz="-0.2 0.2 0" rpy="0 0 0" />
        <geometry>
          <box size="0.4 0.5 0.01" />
        </geometry>
      </visual>
      <collision>
        <origin xyz="-0.2 0.2 0" rpy="0 0 0" />
        <geometry>
          <box size="0.4 0.5 0.01" />
        </geometry>
      </collision>
    </link>
    <gazebo reference="front_right_bar">
      <material>Gazebo/Green</material>
      <turnGravityOff>false</turnGravityOff>
    </gazebo>
    <joint name="front_right_bar_joint" type="revolute" >
      <limit lower="-0.2" upper="0.2" effort="100" velocity="10" />
      <axis xyz="0 0 1" />
      <parent link="base" />
      <child link="front_right_bar" />
      <origin xyz="1.0 -0.5 0.055" rpy="0 0 0" />
    </joint>

    <link name="front_left_wheel">
      <inertial>
        <mass value="1.0" />
        <origin xyz="0 0 0" /> 
        <inertia  ixx="1.0" ixy="0.0"  ixz="0.0"  iyy="1.0"  iyz="0.0"  izz="1.0" />
      </inertial>
      <visual>
        <origin xyz="0 0 0" rpy="${M_PI/2} 0 0" />
        <geometry>
          <cylinder radius="0.2" length="0.01" />
        </geometry>
      </visual>
      <collision>
        <origin xyz="0 0 0" rpy="${M_PI/2} 0 0" />
        <geometry>
          <cylinder radius="0.2" length="0.01" />
        </geometry>
      </collision>
    </link>
    <gazebo reference="front_left_wheel">
      <material>Gazebo/Red</material>
      <turnGravityOff>false</turnGravityOff>
    </gazebo>
    <joint name="front_left_wheel_joint" type="continuous" >
      <axis xyz="0 1 0" />
      <parent link="front_left_bar" />
      <child link="front_left_wheel" />
      <origin xyz="0 0.1 0" rpy="0 0 0" />
    </joint>

    <link name="front_right_wheel">
      <inertial>
        <mass value="1.0" />
        <origin xyz="0 0 0" /> 
        <inertia  ixx="1.0" ixy="0.0"  ixz="0.0"  iyy="1.0"  iyz="0.0"  izz="1.0" />
      </inertial>
      <visual>
        <origin xyz="0 0 0" rpy="${M_PI/2} 0 0" />
        <geometry>
          <cylinder radius="0.2" length="0.01" />
        </geometry>
      </visual>
      <collision>
        <origin xyz="0 0 0" rpy="${M_PI/2} 0 0" />
        <geometry>
          <cylinder radius="0.2" length="0.01" />
        </geometry>
      </collision>
    </link>
    <gazebo reference="front_right_wheel">
      <material>Gazebo/Red</material>
      <turnGravityOff>false</turnGravityOff>
    </gazebo>
    <joint name="front_right_wheel_joint" type="continuous" >
      <axis xyz="0 1 0" />
      <parent link="front_right_bar" />
      <child link="front_right_wheel" />
      <origin xyz="0 -0.1 0" rpy="0 0 0" />
    </joint>

    <link name="ackermann_bar">
      <inertial>
        <mass value="1.0" />
        <origin xyz="0 0 0" /> 
        <inertia  ixx="1.0" ixy="0.0"  ixz="0.0"  iyy="1.0"  iyz="0.0"  izz="1.0" />
      </inertial>
      <visual>
        <origin xyz="-0.05 -0.3 0" rpy="0 0 0" />
        <geometry>
          <box size="0.1 0.6 0.01" />
        </geometry>
      </visual>
      <collision>
        <origin xyz="-0.05 -0.3 0" rpy="0 0 0" />
        <geometry>
          <box size="0.1 0.6 0.01" />
        </geometry>
      </collision>
    </link>
    <gazebo reference="ackermann_bar">
      <material>Gazebo/Green</material>
      <turnGravityOff>false</turnGravityOff>
    </gazebo>
    <joint name="ackermann_bar_joint" type="continuous" >
      <axis xyz="0 0 1" />
      <parent link="front_left_bar" />
      <child link="ackermann_bar" />
      <origin xyz="-0.4 -0.2 0.05" rpy="0 0 0" />
    </joint>

    <gazebo>
      <joint:hinge name="ackermann_bar_loop_joint">
        <body1>front_right_bar</body1>
        <body2>ackermann_bar</body2>
        <anchor>front_right_bar</anchor>
        <axis>0 0 1</axis>
        <anchorOffset>-0.4 0.2 0</anchorOffset>
      </joint:hinge>
    </gazebo>

    <link name="rear_left_wheel">
      <inertial>
        <mass value="1.0" />
        <origin xyz="0 0 0" /> 
        <inertia  ixx="1.0" ixy="0.0"  ixz="0.0"  iyy="1.0"  iyz="0.0"  izz="1.0" />
      </inertial>
      <visual>
        <origin xyz="0 0 0" rpy="${M_PI/2} 0 0" />
        <geometry>
          <cylinder radius="0.2" length="0.01" />
        </geometry>
      </visual>
      <collision>
        <origin xyz="0 0 0" rpy="${M_PI/2} 0 0" />
        <geometry>
          <cylinder radius="0.2" length="0.01" />
        </geometry>
      </collision>
    </link>
    <gazebo reference="rear_left_wheel">
      <material>Gazebo/Red</material>
      <turnGravityOff>false</turnGravityOff>
    </gazebo>
    <joint name="rear_left_wheel_joint" type="continuous" >
      <axis xyz="0 1 0" />
      <parent link="base" />
      <child link="rear_left_wheel" />
      <origin xyz="-1.0 0.6 0" rpy="0 0 0" />
    </joint>

    <link name="rear_right_wheel">
      <inertial>
        <mass value="1.0" />
        <origin xyz="0 0 0" /> 
        <inertia  ixx="1.0" ixy="0.0"  ixz="0.0"  iyy="1.0"  iyz="0.0"  izz="1.0" />
      </inertial>
      <visual>
        <origin xyz="0 0 0" rpy="${M_PI/2} 0 0" />
        <geometry>
          <cylinder radius="0.2" length="0.01" />
        </geometry>
      </visual>
      <collision>
        <origin xyz="0 0 0" rpy="${M_PI/2} 0 0" />
        <geometry>
          <cylinder radius="0.2" length="0.01" />
        </geometry>
      </collision>
    </link>
    <gazebo reference="rear_right_wheel">
      <material>Gazebo/Red</material>
      <turnGravityOff>false</turnGravityOff>
    </gazebo>
    <joint name="rear_right_wheel_joint" type="continuous" >
      <axis xyz="0 1 0" />
      <parent link="base" />
      <child link="rear_right_wheel" />
      <origin xyz="-1.0 -0.6 0" rpy="0 0 0" />
    </joint>
  </robot>

Originally posted by hsu with karma: 5780 on 2011-03-25

This answer was ACCEPTED on the original site

Post score: 5

Original comments

Comment by hsu on 2011-03-25:
adjusting the 4 bar linkage lengths so the 4 bar linkage enforces Ackermann steering. After that you still need a transmission to control one of the linkage joints using a pr2_controllers if you wish.

Improve this answer
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.