RT assignment 2nd

by Zhouyang Hong 
sid: 5197402

how to use

Here, compiles those nodes

1. enter the directory of your ROS-workspace
2. run: cd src
3. run: git clone git@github.com:qq765490023/research-track-ass2.git
#### pull all the files inside /research-track-ass2 to current /src directory
4. run: cd ..
5. run catkin_make on  ROS-workspace to build those nodes
*************************************************************

Now we are going to run those generated ros-nodes, put cmmoands below on your terminal

1. roscore
2. rosrun stage_ros stageros $(rospack find second_assignment)/world/my_world.world &
3. rosrun ass_2 controller
#### open another window
4. rosrun ass_2 user_interact

Now you can control the robot on "user_interface" window by inputting the following commands:

    1. w
    2. s
    3. r
1. When you press 'w'+"return",the robot will increase its speed by 10%. 
2. In the meanwhile 's'+"return" will decrease the speed by 10%. 
3. you can press 'r'+"return" to put the robot to its initial position.

Structure of controller.cpp

devide the base_scan data into 180 pieces and choose 3 ranges and take the minimum

Here, I divided the data into 180 pieces to simulate a 180 degree angle. Then it will be ease to choose the specific angle range that I desired. Finally I chose a range set of 36->72, 85->95 and 108->144.

The pseudo code for choosing them is:

 while: index<720
   if 36*4<=index<72*4
        if ranges[index] < minimum_fleft
                minimum_fleft = ranges[index]
   if 85*4<=index<95*4
        if ranges[index] < minimum_front
                minimum_front = ranges[index]
   if 36*4<=index<72*4
        if ranges[index] < minimum_fright
                minimum_fright = ranges[index]

Now, minimum_fleft,minimum_front,minimum_fright stores the nearest object in those three directions.

Driving decision making

By comparing the above minimum distances from three directions with a threshold, and the connections of comparison results. the robot is able to decide turn left, turn right or keep moving. The table below shows the connections.

speed control

In order to control the speed of robot, there is a global variable which works as a coefficient of both linear and rotational speed. When this service-node received the changing-speed-command request, inside the service callback-function just change the value of the global variable so as to change the speed.

Structure of user_interface.cpp

introduction

This node consists of two service clients. One is for telling controller to change the speed and another is for resetting the position of robot. In the code structure, It constantly waiting for a key input and decide what do to. 'w' is for increasing the speed by 10 percent 's' is for decreasing the speed by 10 percent 'r' is for placing the robot at the initial point

pseudo code

while true:
  cmmd = get_a_key()
  if cmmd == 'w'
        send 'w' to speed_control service
  if cmmd == 's'
        send 's' to speed_control service
  if cmmd == 'r'
        call reset_positions service