How can I run multiple turtlebots in gazebo?

Q1. Can I run multiple robots in gazebo at once? (In my case, it was turtlebot, but it can be PR2 or something else.) Q2. If it works, how can I send messages to each robot? -------------- Hi, I'm trying to run multiple turtlebots in gazebo. I'm making new package and writing .launch file based on turtlebot_gazebo. These are some of following launch files that I wrote. launch/robots.launch : : -------- launch/single_robot.launch From this trial, I can see 2 different (hexagon stack & circle stack) turtlebots in gazebo. But, I tried to run 3 turtlebots. In terminal, I can see error log like this. [ERROR] [14......, 3.19.....]: SpawnModel: Failure - model name turtlebot already exists. Is there no any way to run same turtlebots in gazebo? ------------- After grouping each nodes, I can see same nodes in different group. But, I cannot use existing turtlebot packages to interact each robot. Do I need to write all existing turtlebot packages in each group?