Servo - April 2013

more, there are some books to check out in the sidebar. Okay, I’ve introduced you to new terms and concepts perhaps. Now, you need to know how to design and implement them, so read on.

Designing a Subsumption Architecture

Figure 1

implementing behaviors in your robots. (This way, the next time you hear someone say “Braitenberg Type 2” robot, you’ll know exactly what they are talking about!)

This is going to be a very simple introduction to behavioral programming, involving only a few behaviors. The beauty of the system, however, is that you can layer on more behaviors as you get them to work without modifying existing ones. This means that your behaviors are modular and can be modified without worrying about other behaviors that are currently working fine. Your emergent behaviors might change, however ...

Our new Roomba code will have three defined behaviors to start with: I am going to discuss basic subsumption architecture in this article. There are variants on this theme. A behavioral module may have inputs that are suppressed and replaced with other inputs. Or, it may have outputs which can be inhibited to allow outputs from other modules to be used. We will keep this discussion focused on suppressors and timers.

1. Wander
2. Escape
3. “I see a wall”

Listing 1: DoWanders behavior code.

void DoWander(void)
// Define a wander algorithm, or just go straight.
{
  if (priority < wander)
  {
 Serial.println("Wander");
 priority = wander;
 GoForward();
  }
}

Listing 2: RoombaBehave1 main Arduino loop.

/*
*  The nice thing about state machines is that they allow your
*  main loop to be really simple.
*/
void loop(void)
{
  UpdateSensors();
  DoWall();
  DoWander();
  DoAvoid();
  DoEscape();
  DoPanic();
}

The first two behaviors control the drive motors that move the Roomba around. The third one just lights up LEDs and turns on the sweeper motor to tell us that it saw a wall with the wall sensor.

Figure 1 shows what the subsumption network looks like using these three behaviors.

In Figure 1, each of the square boxes are behaviors. The Do Wall behavior stands by itself and has a sensor input and output actuators that are LEDs and the sweeper brush. That behavior isn’t all that interesting, but this is how it is represented.

The next two behaviors have subsumption characteristics. The Do Wander behavior has no sensor input, but it does run the motors. As you can see in Listing 1, Do Wander just makes the robot go forward — not interesting, but it does something.