Hi Ian, Thank you for the confirmation.  For the convenience of  other people, if you are using a Robotiq 3-finger gripper with correct coupling elements, attached file is our calculation of Inertia, COM etc. it works well in our case   <?xml version="1.0"?> <robot xmlns:xacro="http://www.ros.org/wiki/xacro" name="basic_robotiq_gripper"> <xacro:macro name="basic_robotiq_gripper" params="side"> <joint name="${side}_gripper_base" type="fixed"> <origin rpy="0 0 0" xyz="0.0 0.0 0.0"/> <!-- Enter the 3D pose of your end effector frame here w.r.t. end of arm --> <parent link="${side}_hand"/> <child link="${side}_robotiq_gripper"/> </joint> <link name="${side}_robotiq_gripper"> <inertial> <origin rpy="0 0 0" xyz="-8.0e-3 0.0 60.0e-3"/> <!-- only modify this if there is an C.O.M. offset w.r.t your gripper_base joint above --> <mass value="2.6"/> <!-- Enter your mass and inertial properties here --> <inertia ixx="7424e-6" ixy="0" ixz="-650e-6" iyy="8924e-6" iyz="0" izz="7243e-6"/> </inertial> </link> </xacro:macro> <xacro:basic_robotiq_gripper side="right"/> </robot>     Jianlan
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