How can I make joints in urdf file that have two parents and a single child?
Adding a virtual link is not working. urdf file is here
<robot name="excavator"> <link name="chain"> <inertial> <origin xyz="8.45755288817494 4.18565608014614 6.68537140356519" rpy="0 0 0"/> <mass value="13180.6164884539"/> <inertia ixx="29511.7945592359" ixy="-2776.03451562391" ixz="17.7388007765334" iyy="31532.589769304" iyz="-25.3267391725216" izz="55935.9315133107"/> </inertial> <visual> <origin xyz="0 0 0" rpy="0 0 0"/> <geometry> <mesh filename="package://excavator/meshes/chain.STL"/> </geometry> <material name=""> <color rgba="0.776470588235294 0.756862745098039 0.737254901960784 1"/> </material> </visual> <collision> <origin xyz="0 0 0" rpy="0 0 0"/> <geometry> <mesh filename="package://excavator/meshes/chain.STL"/> </geometry> </collision> </link> <link name="cabin"> <inertial> <origin xyz="0.00859305870677396 1.0103521325144 -2.02891355369916" rpy="0 0 0"/> <mass value="28884.5755827318"/> <inertia ixx="72463.9230836232" ixy="-75.4212523104064" ixz="-1395.02162162392" iyy="95358.0696804118" iyz="4987.30416309204" izz="38763.1860075468"/> </inertial> <visual> <origin xyz="0 0 0" rpy="0 0 0"/> <geometry> <mesh filename="package://excavator/meshes/cabin.STL"/> </geometry> <material name=""> <color rgba="0.792156862745098 0.819607843137255 0.933333333333333 1"/> </material> </visual> <collision> <origin xyz="0 0 0" rpy="0 0 0"/> <geometry> <mesh filename="package://excavator/meshes/cabin.STL"/> </geometry> </collision> </link> <joint name="cabin_cain" type="continuous"> <origin xyz="0 0 1.6" rpy="0 0 0"/> <parent link="chain"/> <child link="cabin"/> <axis xyz="0 0 1"/> </joint> <link name="boom_cylenders"> <inertial> <origin xyz="0 0 0" rpy="0 0 0"/> <mass value="103.364479304445"/> <inertia ixx="100.667128941694" ixy="-4.91017933874161E-07" ixz="2.86002958247966E-06" iyy="134.54435734305" iyz="0.00236275064146518" izz="36.0844141276187"/> </inertial> <visual> <origin xyz="0 0 0" rpy="0 0 0"/> <geometry> <mesh filename="package://excavator/meshes/boom_cylenders.STL"/> </geometry> <material name=""> <color rgba="0.647058823529412 0.619607843137255 0.584313725490196 1"/> </material> </visual> <collision> <origin xyz="0 0 0" rpy="0 0 0"/> <geometry> <mesh filename="package://excavator/meshes/boom_cylenders.STL"/> </geometry> </collision> </link> <joint name="boom_cylenders_cabin" type="revolute"> <limit effort="1000.0" lower="-.3" upper="2.2" velocity="0.5"/> <origin xyz="0 -1.3 0.42" rpy="0 0 0"/> <parent link="cabin"/> <child link="boom_cylenders"/> <axis xyz="1 0 0"/> </joint> <link name="rods"> <inertial> <origin xyz="0.574999999777758 1.08571374113353E-10 -1.09389975266783" rpy="0 0 0"/> <mass value="223.803963542738"/> <inertia ixx="116.930248975123" ixy="-1.36715940196171E-07" ixz="3.84160230701602E-08" iyy="190.848804032466" iyz="1.6628407095709E-08" izz="75.646374241794"/> </inertial> <visual> <origin xyz="0 0 0" rpy="0 0 0"/> <geometry> <mesh filename="package://excavator/meshes/rods.STL"/> </geometry> <material name=""> <color rgba="0.898039215686275 0.898039215686275 0.898039215686275 1"/> </material> </visual> <collision> <origin xyz="0 0 0" rpy="0 0 0"/> <geometry> <mesh filename="package://excavator/meshes/rods.STL"/> </geometry> </collision> </link> <joint name="rods_joint" type="prismatic"> <limit effort="1000.0" lower="0.2" upper="1.5" velocity="0.5"/> <origin xyz="0 0 2.7" rpy="0 0 0"/> <parent link="boom_cylenders"/> <child link="rods"/> <axis xyz="0 0 1"/> </joint> <link name="boom"> <inertial> <origin xyz="0 0 0" rpy ...
