lab session 10

Attendances: Carsten, Dan
Duration: 11:30 - 13:30

Goal

The goal this week is to experiment with the LejOS behavior-based
architecture. we also look at sensor listeners.

Plan

We experiment with a robot called Bumper Car. This robot runs around
until it bumps into a wall (detected using a touch sensor). After
being bumped it backs up and turns to before continuing to drive
around.

We follow the exercise plan.

• Investigate bumper car and its source code.
• Implement a new behavior.
• Implement a sensor listener
• Improve detect wall
• Put detection of wall into the detection of wall sequence.

Robot

Our robot this week is the same as from lab 9 with a touch sensor.

PICTURE

Code

Our modified BumperCar.java.

Investigate bumper car and its source code.

When the touch sensor is pressed it backs up and turns left. When hold
down the robot continuously backs up and turns left. This shows that
the avoid behavior has higher priority than drive forward.

Arbitrator loops through it's behaviors checking if takeControl()returns true. If a behavior returns true the arbitrator breaks() from
the loop, meaning it stops checking for other behaviors. So when
DetectWall is active, DriveForward's takeControl() is not checked.

It seems the highest priority is the last in the behaviors array. The
[ 2] link from the exercise text suggested it was opposite.

Implement a new behavior.

• Implement a new behavior that checks for Escape presses and stops
  the program if detected.

We implemented this by checking if the escape button is pressed intakeControl(). We sat it as the highest priority by setting it as
the last entry in the array of behaviors.

When the robot is going forwards, escape is registered
immediately. When the touch sensor is pressed down and the robot is
continuously avoiding the escape is not always registered. This is
because takeControl() is only run on or escape behavior between each
avoidance pattern.

The Sound.pause(x) command pauses the robot for x number of
ms. Setting it to 2000 sets a delay of 2 seconds between each
avoidance pattern (when touch sensor is kept pressed). This pause is
required to allow the sound waves sent from the sonic sensor to get
back to the robot and be registered.

Implement a sensor listener

We make a thread to check the sonic sensor if a wall is detected. This
thread running in the background means we don't have to pause in
detectwalls takeControl() to check sensor.

We implemented this by making a sampler thread. This thread is started
from detectWalls. In detectWalls takeControl() function the sampler
thread is the last sonic value is close enough to indicate a wall is
detected.

With a separate thread, a sound.pause(2000) doesn't cause pauses
between avoidance patterns as it did before.

Improve detect wall

We add a 1 second backing up before turning in the avoidance
pattern. We initially did this by going backwards and waiting a second
by using Sound.pause(1000) then doing the turning. This caused the
robot to make a weird jump in the transition from backing up to
turning. This is probably just because the backward and rotate motor
functions operate at different motor speeds.

We improved the behavior by checking if the touch sensor is pressed
after the robot has backed up. If it is pressed, we move backwards
another 2 seconds. We implemented this in the detect wall action()method by checking if the touch sensor is pressed after having gone
backwards. If it is we stop the function. The function will be started
again by the arbitrator as the touch sensor is pressed.

Put detection of wall into the detection of wall sequence.

Motivation functions have each behaviors takeControl() function
return integer signifying how much they want control.

To implement that in our DetectWall and have it be able to run again
if touch is pressed again afterwards. We could do this by these settings:

• previous_motivation = 0 and touch.isPressed(): return 10;
• previous_motivation > 0 and touch.isPressed(): return previous_motivation / 2;
• !touch.isPressed(): return 0;

This sets a high motivation value if the touch sensor is pressed, if
it is continuously pressed the motivating value will decrease. But if
the touch is released ad pressed again we will have a high motivation
again.