Welcome to ROS Robot Expansion Board repository

3. Robot keyboard control

The control in this section uses the Mecanum omni wheel as an example.

3.1、Key Description

3.1.1、direction control

3.1.2、speed control

3.2、run the program

3.2.1、Keyboard control code "yahboom_keyboard.py" path：

~/driver_ws/src/yahboom_ctrl/scripts

3.2.2、run

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cd ~/driver_ws/src/yahboom_bringup/launch
roslaunch bringup.launch        #start the driver
cd ~/driver_ws/src/yahboom_ctrl/launch
roslaunch yahboom_keyboard.launch   # keyboard control node

3.2.3、Analyze yahboom_keyboard.py

1）、Publish Topic: cmd_vel

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pub = rospy.Publisher('cmd_vel', Twist, queue_size=1)

So, just package the speed and publish it through pub.publish(twist), the speed subscriber of the chassis can receive the speed data, and then drive the car.

2）、Mainly used modules

• The select module is mainly used for socket communication, seeing changes in file descriptions, and completing non-blocking work
• The termios module provides an interface for IO-controlled POSIX calls to ttys
• The tty module is mainly used to change the mode of the file descriptor fd

3）、Mobility Dictionary and Speed Dictionary

• The mobile dictionary mainly stores the relevant characters of the direction control

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  moveBindings = {
      'i': (1, 0),
      'o': (1, -1),
      'j': (0, 1),
      'l': (0, -1),
      'u': (1, 1),
      ',': (-1, 0),
      '.': (-1, 1),
      'm': (-1, -1),
      'I': (1, 0),
      'O': (1, -1),
      'J': (0, 1),
      'L': (0, -1),
      'U': (1, 1),
      'M': (-1, -1),
  }
  

• The speed dictionary mainly stores the relevant characters of speed control

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  speedBindings = {
      'Q': (1.1, 1.1),
      'Z': (.9, .9),
      'W': (1.1, 1),
      'X': (.9, 1),
      'E': (1, 1.1),
      'C': (1, .9),
      'q': (1.1, 1.1),
      'z': (.9, .9),
      'w': (1.1, 1),
      'x': (.9, 1),
      'e': (1, 1.1),
      'c': (1, .9),
  }
  

  4）、Get current key information

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  def getKey():
      # tty.setraw(): change the file descriptor fd mode to raw; fileno(): return an integer file descriptor (fd)
      tty.setraw(sys.stdin.fileno())
      # select(): Directly call the IO interface of the operating system; monitor all file handles with the fileno() method
      rlist, _, _ = select.select([sys.stdin], [], [], 0.1)
      # Read a byte from the input stream
      if rlist: key = sys.stdin.read(1)
      else: key = ''
      # tcsetattr sets the tty attribute of the file descriptor fd from the attribute
      termios.tcsetattr(sys.stdin, termios.TCSADRAIN, settings)
      return key
  

  5）、Determine whether the t/Tor s/S is pressed

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   if key=="t" or key == "T": xspeed_switch = not xspeed_switch
              elif key == "s" or key == "S":
                  print ("stop keyboard control: {}".format(not stop))
                  stop = not stop
  

  6）、Check if a string is in a dictionary

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  #Whether the key string is in the mobile dictionary
  if key in moveBindings.keys():
                  x = moveBindings[key][0]
                  th = moveBindings[key][1]
                  count = 0
  #Whether the key character is in the speed dictionary
   elif key in speedBindings.keys():
                  speed = speed * speedBindings[key][0]
                  turn = turn * speedBindings[key][1]
                  count = 0
  

  6）、speed limit

  Both the angular velocity and the linear velocity have a limit value, which cannot be increased all the time. When starting, the program will first obtain the speed limit value, and when increasing the speed, it will judge and process the increased value.

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  linear_limit = rospy.get_param('~linear_speed_limit', 1.0)
  angular_limit = rospy.get_param('~angular_speed_limit', 5.0)