<xacro:macro name="transmission_block" params="joint_name">
<transmission name = "train1">
<type>transmission_interface/SimpleTransmission</type>
<joint name="${joint_name}">
<hardwareInterface>hardware_interface/PositionJointInterface</hardwareInterface>
</joint>
<actuator name = "motor1">
<hardwareInterface>hardware_interface/PositionJointInterface</hardwareInterface>
</actuator>
</xacro:macro>
the transmission part can not hint plz!!!!!!!!!