ROS Tutorial - Turtlesim

# Exercises

Below you can find some recap exercises.

But first try to add a new turtle. You don't have to stop the rosnode turtlesim.

An additional turtle can be spawn with a service parameter /spawn

The info of the ros parameter can be looked up with:

rosservice call /spawn info
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Output

Node: /turtlesim
URI: rosrpc://127.0.0.1:49803
Type: turtlesim/Spawn
Args: x y theta name
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With example command a second turtle will be spawn.

rosservice call /spawn 3 3 0 turtle2
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To delete a turtle the command below can be used:

rosservice call /kill "name: 'turtle2'"
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WARNING

It isn't possible to move the second turtle with the turtle_teleop_key.

# Exercise 1

Try to move the second turtle to position -2 -2 1 (x y theta) by terminal

Solution Exercise 1 
rosservice call /turtle1/teleport_absolute 2 2 0
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# Exercise 2

Try to read out the current position of the second turtle by terminal

Solution Exercise 2 
rostopic echo /turtle2/pose
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# Exercise 3

Try to control the turtle by command (cmd_vel) to used updaterate should be 10ms by terminal

Solution Exercise 3 
rostopic pub /turtle2/cmd_vel geometry_msgs/Twist -r 1 -- '[1.0, 0.0, 0.0]' '[0.0, 0.0, 1.8]' 

rostopic pub /turtle2/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" -r 10
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# Exercise 4

Try to visualise the current position in rqt_plot by terminal

Solution Exercise 4 
rqt_plot  -e /turtle2/pose/x:y:z
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# Exercise 5

Try to find the update rate of cmd_vel of the second turtle by terminal

Solution Exercise 5 
rostopic hz /turtle2/cmd_vel
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# Exercise 6

Try to change the color of the pen set by the turtle on the screen.

TIP

check the rosservice list

Solution Exercise 6 
rosservice list
rosservice info /turtle2/set_pen 
rosservice call /turtle2/set_pen 125 125 125 2  0
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