I use following plugin for controlling joints. https://github.com/start-jsk/rtmros_gazebo/blob/master/hrpsys_gazebo_general/src/IOBPlugin.cpp
I'm sending velocity command to joint by SetVelocity function, and trying to get joint torque by GetForce function, but return value if GetForce is always zero.
When I send torque command by SetForce function, I can get correct joint torque by SetForce.