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answered 2011-03-25 20:40:29 -0600

hsu gravatar image

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="ackerman">

    <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="ackerman_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="ackerman_bar">
      <material>Gazebo/Green</material>
      <turnGravityOff>false</turnGravityOff>
    </gazebo>
    <joint name="ackerman_bar_joint" type="continuous" >
      <axis xyz="0 0 1" />
      <parent link="front_left_bar" />
      <child link="ackerman_bar" />
      <origin xyz="-0.4 -0.2 0.05" rpy="0 0 0" />
    </joint>

    <gazebo>
      <joint:hinge name="ackerman_bar_loop_joint">
        <body1>front_right_bar</body1>
        <body2>ackerman_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>

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="ackerman">
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="ackerman_bar">
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="ackerman_bar">
reference="ackermann_bar">
      <material>Gazebo/Green</material>
      <turnGravityOff>false</turnGravityOff>
    </gazebo>
    <joint name="ackerman_bar_joint" name="ackermann_bar_joint" type="continuous" >
      <axis xyz="0 0 1" />
      <parent link="front_left_bar" />
      <child link="ackerman_bar" link="ackermann_bar" />
      <origin xyz="-0.4 -0.2 0.05" rpy="0 0 0" />
    </joint>

    <gazebo>
      <joint:hinge name="ackerman_bar_loop_joint">
name="ackermann_bar_loop_joint">
        <body1>front_right_bar</body1>
        <body2>ackerman_bar</body2>
<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>
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