code: def _left_hand_total_velocity(self):
          
  
          # Use jacobian to translate joint velocities to end effector velocities.
          Jp = self.sim.data.get_body_jacp("left_hand").reshape((3, -1))
          Jp_joint = Jp[:, self._ref_joint_vel_indexes[7:]]
  
          Jr = self.sim.data.get_body_jacr("left_hand").reshape((3, -1))
          Jr_joint = Jr[:, self._ref_joint_vel_indexes[7:]]
  
          eef_lin_vel = Jp_joint.dot(self._joint_velocities)
          eef_rot_vel = Jr_joint.dot(self._joint_velocities)
          return np.concatenate([eef_lin_vel, eef_rot_vel])
docs: Returns the total eef velocity (linear + angular) in the base frame as a numpy
          array of shape (6,)