A brand new robot, designed
      to test out the concepts of using insect like antennas and small
      mammal whiskers to assist in internal home navigation. Only six
      inches in diameter, it is the perfect size for our robot arena
      test area and will be right for upstairs testing in the home
      environment. All programming is done using CCS-C.
 

      
The next phase
      in the development of this robot is to fix the corner escape
      problem. Once this is done, the robot can be free to roam the
      arena and do sensory experiments without getting stuck in the
      4 corners of the arena.

      
The general rules
      are:

      
1. Left whisker
      impact – Stop, backup and turn right, continue on.

      2. Right bumper impact – Stop, back up and turn left, continue
      on.

      

        

          
 
          
 This
            is a good formula to almost guarantee that your robot will be
            stuck or trapped in short order in your home environment, or
            even in a more controlled maze like arena like test area. First,
            as soon as the robot encounters a corner, it will be trapped
            in an endless bouncing back and forth movement until the batteries
            die. This is called "Corner Entrapment", or "Canyoning"
            and there are a number of solutions that can be implemented to
            correct this condition.
 
        
      

      

        

          
 
          
 This
            is the most common type of time correlated impact event robot
            experimenters encounter. In this case, the robot will become
            trapped in a corner of a room, or parts of furniture at the correct
            spacing by bouncing back and forth between adjacent walls. For
            example, when a robot hits the corner with its left whisker,
            it turns right evasively. But then a second later, it hits on
            the adjacent wall with its right whisker and then turns left
            evasively. This can go on indefinitely until the robots batteries
            run flat. Detecting and correcting this condition is of major
            importance if we expect the robot to function in a household
            environment. To correct this condition, we first have to detect
            it. This is done by recording the directions of the last four
            or five impact events in memory, and possibly the time between
            them. Then we examine the data to detect "canyoning".
 
        
      


      

        

          
 To
            implement this method, we will program the robot to remember.
            This is not difficult, and introduces the concept of learning
            matrixes. The basic idea is to set aside four or more variables
            that will be used to store direction or timing data. Then after
            every impact, we take a quick look at the list of for variables,
            which is really a 5 element array. If the pattern recorded over
            the last five impacts alternates right/left, than the corner
            entrapment condition has been detected. You can also time the
            period between impacts and if the sum is less than say 10 seconds,
            you have a series of rapid impacts that may requrie escape. For
            most cases this will suffice to escape the corner by rotating
            180 degrees.
 
          
 
        
      
Its probably
      99 percent effective at corner escape. A corner will record as:
      Right-Left-Right-Left or its inverse. If this occurs AND your
      time sum is short, then you are certain you are trapped in a
      corner.

      

        

          
 
          

            
 Left: Escaping
            a corner. Really, the only sure way to get out of a corner is
            to do a 180 degree turn away from it and drive off. While this
            may face the robot in the wrong direction to achieve its goal,
            it is better to do this than stay stuck indefinitely!

            
Below is a movie
            clip of the robot in the arena, in which it demonstrates the
            corner entrapment and escape after using only the directions
            to detect the condition.
          
        
      



      
Movie 3
Corner
      entrapment Escape

Some Example C code used to implement corner detection:
First we initialize the array at the top of the program:

int8 S[5] = {0,0,0,0,0};  //Right/Left storage array 0=Left, 1=Right

Each time we make contact with any whisker, we first assign the direction to the 4th and top element in the array:

For a Right hit:
 S[4] = 1;  //save direction
              
Next we test last 5 impacts to see if pattern emerges:
         
if ((S[4]==1) && (S[3]==0) && (S[2]==1) && (S[1]==0) && (S[0]==1)) {
            STATE=6;
            break;  }

State 6 is the corner escape state.

After taking normal evasive action on a whisker hit, such as turn left or right, we update the array and roll it down an element for next time:

 //Update direction array:
         S[0]=S[1];
         S[1]=S[2];
         S[2]=S[3];
         S[3]=S[4];

If this condition is not met - or its inverse - we continue on forward.  and just keep on saving the directions to the 5 array variables.
Now if we DO have to evade the corner, we then do a 180 degree, then clear the Array for the next set:

//Zero out direction array since you just escaped:
         S[4]=0;
         S[3]=0;
         S[2]=0;
         S[1]=0;
         S[0]=0;

Previous Uploads on this robot:

Intro page 1
First 4 whisker functioning!

 

HOME