Single actuator for two moving linkages in a gripper

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Hi, I have a custom robotic gripper, that has two moving finger links actuated via single servo, similar to this one. So the first link joint is actuated directly from a servo and passes the torque to the second via 1:1 gear. My question is, what is the proper way to model such gripper in urdf/gazebo/ros_control? Is it possible to use a single interface like JointPositionController to move both finger links in simulation? I would appreciate any advice.