[ROS play with turtle turtle]

Turtlesim It's a place for learning ROS Lightweight simulator for , Because it has a turtle , So it is often called Little Turtle ．

I am a ROS beginner , Just touched , Let me share with you ROS My learning experience , Want to learn ROS My friends can refer to . Use to ： ubuntu ,ros

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One _ Keyboard control turtle movement

1. The first thing to do is to open it ROS Master , Open a new terminal （Ctrl+alt+T）, Input ：

~$ roscore

2. Open another terminal , Start the little turtle simulator ：

~$ rosrun turtlesim turtlesim_node

A window appears after successful startup ：

3. Open a new terminal , Start the little turtle control node , Input ：

~$ rosrun turtlesim turtle_teleop_key

After success

[email protected]:~$ rosrun turtlesim turtle_teleop_key
Reading from keyboard
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Use arrow keys to move the turtle. 'q' to quit.

Place the cursor in the current window , Use the keyboard up, down, left and right to control the movement of the little turtle ：

< ctrl > + < C > You can exit keyboard control

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Two _ Command line control turtle movement

Open a new terminal , Input ：

[email protected]:~$ rostopic pub  /turtle1/cmd_vel geometry_msgs/Twist "linear:
  x: 1.0
  y: 0.0
  z: 0.0
angular:
  x: 0.0
  y: 0.0
  z: 0.0" 

among linear It's linear velocity ,angular It's angular velocity
take linear Under the x Set to 1.0, The little turtle will walk along x Move a little bit in the direction , To keep the little turtle moving , stay pub Add... After the order -r 10 ： That is, a transmission frequency is set 10hz, So the little turtle will keep moving in one direction , Also press < ctrl > + < C > Control can be exited , The little turtle stopped moving .

[email protected]:~$ rostopic pub -r 10  /turtle1/cmd_vel geometry_msgs/Twist "linear:
  x: 1.0
  y: 0.0
  z: 0.0
angular:
  x: 0.0
  y: 0.0
  z: 0.0" 

So we can find a way to make the little turtle draw a circle , Input ：

[email protected]:~$ rostopic pub -r 10  /turtle1/cmd_vel geometry_msgs/Twist "linear:
  x: 1.0
  y: 0.0
  z: 0.0
angular:
  x: 0.0
  y: 0.0
  z: 1.0" 

Let the little turtle have x Linear displacement of shaft and z Angular displacement in the axial direction , A complete circle appears ：

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3、 ... and _ Control the turtle's movement according to the memory route

1. Memory path generation
   Keep the previous terminal window , Create a new window , Input ：~$ rosbag record -a -O cmd_record Start recording the turtle's path , appear ：

[email protected]:~$ rosbag record -a -O cmd_record
[ INFO] [1655641849.095812339]: Recording to 'cmd_record.bag'.
[ INFO] [1655641849.096922059]: Subscribing to /turtle1/color_sensor
[ INFO] [1655641849.098730076]: Subscribing to /turtle1/cmd_vel
[ INFO] [1655641849.100702759]: Subscribing to /rosout
[ INFO] [1655641849.102427902]: Subscribing to /rosout_agg
[ INFO] [1655641849.105294212]: Subscribing to /turtle1/pose

Place the cursor on the terminal that starts the keyboard control , Control the movement of the little turtle , At this time, the path information of the little turtle has been recorded , After recording, place the cursor on the terminal that opens the recording path Press down < ctrl > + < C > Stop recording , The home folder will generate a .bag The file is our record file ：

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2. Follow the memory path
   Turn off all previous terminals , Open the turtle control window again according to the steps , Open a new terminal input ：

~$ rosbag play cmd_record.bag

The little turtle began to move according to the previously recorded path ～～～