EV3 Track3r Line Follower

This is a post for EV3 Track3r line follower. Track3r has an attached color sensor which helps the track3r to follow the black line on the white surface. For the track3r to function, calibration of white and black color has to be done (which is not captured in this video.) The actual algorithm to follow the line is influenced by Jacek Fedorynski's Line Follower NXC program. The LeJOS (Java) program has one class EV3LF. This class initializes the color sensor and calibrates the sensor for Black and White values. This class has the algorithm to follow the line - given the calibrated black and white values and the light intensity at any given point in time.

The detail process of calibrating Black and White values is as follows. We can hear two beeps and the robot waits for press and release of ESCAPE button. While the robot is waiting, we have to manually adjust the color sensor such that the red light emitted by the color sensor will be focused over the white surface. Then press and release the ESCAPE button. This is the instant when the robot will fetch a sample from the color sensor. This sample will act as the threshold value for white color, which will be printed on the screen. 

Then, we can hear two beeps again and the robot waits for press and release of ESCAPE button. While the robot is waiting, we have to manually adjust the color sensor such that the red light emitted by the color sensor will be focused over the black line. Then press and release the ESCAPE button. This is the instant when the robot will fetch a sample from the color sensor. This sample will act as the threshold value for black color, which will be printed on the screen. 

We then initialize the motors B and C which will drive the robot forward. We power the large motors such that the power of each motor is a function of average light ((white + black)/2), instantaneous value of light (color[0]), white threshold and black threshold. We use this power to drive the motors forward. Let's analyze the formulae to calculate the power for the two large motors in detail. 

• The polarity of the second term is opposite for both the motors to calculate the speed requirements (as indicated by the RED circles). Due to the opposite polarity, the cSpeed and bSpeed function in opposite manner. That means, when cSpeed is positive, bSpeed is negative and vice-versa. Hence when the robot is on the black surface, it gets pushed on to white surface and when the robot is on white surface, it gets pushed on to black surface. Thus the robot moves in a zig-zag manner along the line. However, since the zig-zag movement is very subtle, it appears to be smooth. 
• The defaultPower is set to a constant value, which can be tuned based on the speed requirements.
• The multiplyingFactor is set to a constant value, which can be tuned such that cSpeed and bSpeed will function in opposite manner. 

Dinor3x

Dinor3x is a creation from Lego Mindstorms EV3 Fan robots which we attempted to program. This robot is a four legged robot. It starts walking as soon as it is powered on. When an object comes along its way (as detected by infrared sensor), it opens its mouth and acknowledges its presence. Please find the below code as well as a small video clip to see the performance of the robot.

This program consists of two classes. Dinor3x and OpenMouth. Let me explain the functionality of both the classes. Dinor3x is the class which has the main method. This method starts a thread OpenMouth. It also initializes both the large motors which control the legs of the Dinor3x. Based on the assembly of the Dinor3x, it looks like when I move the motors backwards, the Dinor3x moves forward. The Dinor3x moves forward, until ESCAPE button is un-pressed and the turnFlag is OFF (turnFlag represents the condition when there is an obstacle in front of the Dinor3x. I will explain it in detail while explaining the OpenMouth class). When the turnFlag is ON, that means when the Dinor3x mouth is open, both the large motors stop. As a result, the Dinor3x stops. 

Let's talk about the OpenMouth class now. Based on the assembly of the robot, we know that the medium motor controls the opening and closing action of the mouth. Also, the IR sensor in the front part of the Dinor3x activates the opening and closing action of the mouth. When we keep an obstacle (our hand) in the path of the robot, the IR sensor captures the presence of the obstacle. To capture this, the IR sensor has to be in Distance mode. The IR sensor then fetches a single sample of the distance (the distance of the obstacle in front of the robot). If this sample is of distance less than 20 cm, we make the Dinor3x open and close the mouth by moving the motor through 45 and -45 degrees respectively. If you carefully observe the movement of the mouth, the mouth quivers a little after closing. This phenomenon is achieved by rotating the medium motor through 2 and -2 degrees for 4 times. Once the object goes out of site, the medium motor is reinitialized to an angle of 45 degrees and the thread ends. 

 

Meanwhile, the turnFlag is turned on as soon as the object is sensed and it is turned off as soon as the object goes out of site (with more than 20cm distance). This is the same turnFlag which we use in the main method of Dinor3x class to stop the Dinor3x from walking when the object gets sensed.

 

      

We have also implemented the Dinor3x revolving around itself. The video of the revolving process is posted below. However, we have not posted the LeJOS code for the revolving Dinor3x. We suggest you to take this as an assignment. Believe us, it is going to be an interesting program!