gazebo7 hardware_interface/PositionJointInterface EffortJointInterfacerobot being hung up

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I simulate my robot with ros-indigo&&gazebo2 every thing is ok,but when I update gazebo2 to gazebo7 or update ros-indigo to ros-kinetic(default gazebo7) I meet some weird thing.

<xacro:macro name="transmission_block" params="joint_name"> <transmission name="tran1"> <type>transmission_interface/SimpleTransmission</type> <joint name="${joint_name}"> <hardwareinterface>hardware_interface/>EffortJointInterface</hardwareinterface> </joint> <actuator name="motor1"> <hardwareinterface>hardware_interface/>EffortJointInterface</hardwareinterface> <mechanicalreduction>1</mechanicalreduction> </actuator> </transmission> </xacro:macro>

when I set EffortJointInterface gazebo7 is ok

but when I set PositionJointInterface， my robot looks like being hung up, it cannot leave the Z axis ,and even can leave the ground

<xacro:macro name="transmission_block" params="joint_name"> <transmission name="tran1"> <type>transmission_interface/SimpleTransmission</type> <joint name="${joint_name}"> <hardwareinterface>hardware_interface/PositionJointInterface</hardwareinterface> </joint> <actuator name="motor1"> <hardwareinterface>hardware_interface/PositionJointInterface</hardwareinterface> <mechanicalreduction>1</mechanicalreduction> </actuator> </transmission> </xacro:macro>

I cannot handle this problem