Moving a robot in Gazebo

asked 2011-04-03 04:20:55 -0500

ncw000
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updated 2014-01-28 17:09:28 -0500

ngrennan
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I'm trying to use the gazebo package to simulate a simple car-like robot moving around a field. Currently, I've been able to load a model of my robot into a simulation. However, I haven't had any luck understanding how to go about making the robot move via external commands (keyboard presses, etc.).

The documentation seems to gloss over this, or at least I can't find where it's described. How would I go about making a robot move in the a Gazebo simulation?

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answered 2011-05-23 11:50:27 -0500

hsu
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updated 2011-05-23 11:55:08 -0500

You can write a gazebo plugin to send torque or velocity commands to each wheel and the steering joint. Possibly wrapping a simple PID controller around each controlled joint. An empty gazebo_plugin template has been provided for your convenience. Also, please take a look at the diffdrive example for reference on how to construct a plugin that sends velocity commands to individual joints.

Alternatively, if you are familiar with pr2_mechanism control stacks, you can use some predefined robot mechanism controllers to control your joints. A simple controlled joint example can be found in the single link example as shown here.

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The Link for empty gazebo plugin template doesn't work.

cybodroid ( 2015-12-27 02:41:53 -0500 )edit

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answered 2011-04-03 06:09:28 -0500

Bart
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In Gazebo, Stage and real-world navigation initiating movement usually involves some variant of the "cmd_vel" topic, which is based on the "Twist" message format. For simple testing there are a number of nodes in different stacks (turtlebot, pr2) that provide this function using keyboard commands, usually named something like "keyboard_teleop".

I suggest that you examine the turtlesim tutorial (http://www.ros.org/wiki/ROS/Tutorials/UnderstandingTopics) for a good start. It uses "rosrun turtlesim turtle_teleop_key". Use rxgraph to inspect the topics/messages in your simulation and be prepared to remap topic names as required.

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This is true and helpful, but keep in mind that Twist is not really a very useful or natural interface for car-like robots.

joq ( 2011-04-03 13:52:42 -0500 )edit

If an appropriate message type doesn't already exist, it is straighforward to create a new message type and topic name (eg - front_wheel_angle, drive_wheel_velocity as "cmd_car"). Appropriate tutorial is ROS/Tutorials/CreatingMsgAndSrv. You still have to write some code at the receiving end to interpret this command.

Bart ( 2011-04-03 14:36:54 -0500 )edit

I would support adding a standardized car command interface to `common_msgs` somewhere. We should be able to get that into E-turtle if we did an API review some time soon.

joq ( 2011-04-03 15:51:15 -0500 )edit

More about /cmd_vel and Twist Messages in car-like robots here -> http://answers.ros.org/question/585/cmd_vel-and-move_base

Pablo Iñigo Blasco ( 2011-04-05 19:54:36 -0500 )edit

I understand that movement commands take that format and how turtlesim uses keyboard_teleop, but I'm still not sure how to actually interact with the Gazebo robot simulation. Is there a specific topic to publish to, or some other method that causes the robot to move? Where do I send move data to?

ncw000 ( 2011-04-09 16:53:30 -0500 )edit

There is a ros package called teleop_twist_keyboard (http://wiki.ros.org/teleop_twist_keyb...). This can be used to read from the keyboard and publish to /cmd_vel

k2108 ( 2021-08-09 13:12:14 -0500 )edit

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answered 2011-07-08 07:20:42 -0500

Aidan1488
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If you're still interested this two tutorials helped me a lot in a very similar problem. I use the pr2 controllers 'cause I don't have the time to make my own so I just build my own stats over the pr2. Hope it helps you:

http://www.ros.org/wiki/pr2_controllers/Tutorials/Using%20the%20robot%20base%20controllers%20to%20drive%20the%20robot

http://www.ros.org/wiki/pr2_controllers/Tutorials/Using%20the%20base%20controller%20with%20odometry%20and%20transform%20information