Lab session 5

02102009

Attendees: Jesper Jakobsen, Mads Hansen Lund og Michael Nygaard Pedersen

Goal

In this lesson we will modify the LEGO 9797 car and make it follow a black line and stop at the end of the line when the car drives into a goal zone - a green rectangular piece of paper at the end of the black line. The idea is that we will try to use the light sensor to detect three different colors.

Sub goals

To build a simple robot inspired by the LEGO 9797 building instructions.

To evaluate a black and white distinguisher java class and expand the functionality to also detect the color green.

Plan

· Build a robot with a light sensor

· Code the robot and evaluate the result based on default code

· Experiments involving different environments to evaluate color distinguishing performance

· Test the expanded class and implement line follower functionality

Results

Description of experiment

Beneath the main sequence of the line follower combined with a stop sequence is presented. A “time1” variable is declared once with starts. The total operation time (totalTime) is calculated in the stop sequence.

// Line follower

if (sensor1.light() <>

// On white, turn right

Car.forward(0, power);

}

else{

Car.forward(power, 0);

}

// Stop at green

if( sensor1.light() <> sensor1.getGreenValue()-Hysteresis){

time2 = System.currentTimeMillis();

totalTime = time2 – time1;

Car.forward(0, 0);

}

Programming attempts

The original code was expanded and will now calibrate for three different colors. The main functionality is shown beneath.

public boolean black() {

return (ls.readValue()< blackWhiteThreshold && ls.readValue()< blackGreenThreshold);

}

public boolean white() {

return (ls.readValue()> blackWhiteThreshold && ls.readValue()> greenWhiteThreshold);

}

public boolean green() {

return (ls.readValue()< greenWhiteThreshold && ls.readValue()> blackWhiteThreshold);

}

Measurements

The light sensors have been evaluated in Lab session 1 . The experiment in this Lab session has been done in the same way as Lab session 1.

Light reflection measurements

	Sensor 1	Sensor 2	Sensor 3
Lightgreen	29	25	30
Green	23	16	23
White	33	28	33
Black	22	15	22

Table 1 – Measurement made to distinguish between white, green and black

Pictures of Lego model

Figure 1 - Picture of robot

Problems encountered

The battery is a common issue when building a NXT robot. The robot performs very bad, if the battery is not fully charged.

Conclusion

The color disguising class can easily be expanded and a stop sequence has been added to the line follower code with success.

References

Ref 1 http://legocarsten.blogspot.com/2009/09/lab-session-1.html