Autonomous Line-Following Robot

Autonomous Line-Folling Robot

Spring 2013

MIT

2.678 Electronics for Mechanical Systems Final Project

Instructors: Derek Rowell, Harrison Chin

THE CHALLENGE:

The task was to design and build an autonomous line-following robot, and compete against classmates in a speed/endurance competition with a project partner. The robot needed to follow a 1” wide blacktaped course on a white background.

MY EXPERIENCE:

I worked with Lauren Hernley. I made the electrical connections and assisted with the Arduino programing. We added three LEDs in a row to the front of the robot. If the sensor or robot was directly on top of the line, all three LEDs would be on. All LEDs would be off when the sensor detected high reflectance, or the white paper. For a sharp right turn, the left most LED would be on, a soft right turn, the center LED would also be on, and vice versa with left turns. Including the three LEDs allowed for easy debugging and added an aesthetic edge to our robot, #10. The competition recorded the fastest time as the final score. At the competition, our robot was very consistent. With a time of 43.1 secs, we recieved third place.

PART INFORMATION

We were provided with the following:

A tracked (tank-style) robot chassis with two motors, mounting plate, and battery.
A Pololu #713 dual motor driver.
An infrared reﬂectance sensor array.
Arduino Nano and carrier board as the controller.
LEDs and black tape
A test and competitive track.

The Robot:

The robot cart is a Dagu Robby RP5 caterpillar or tank style chassis with two geared motors, and a 9 volt (6 AA cells, 2600 mAh) battery holder. The basic chassis has been ﬁtted with a wide universal mounting plate (Pololu #1544), that is used to mount the Arduino Nano carrier board, and extra small breadboards for prototyping. A further breadboard has been
mounted to the front of the chassis to hold the infrared sensor array.

The Infrared Reflectance Sensor Array:

The infrared sensor array is used to monitor the relative position of the black “track” line on the white background. It consists of three Pololu #958 QTR-1A Reﬂectance Sensors. The QTR-1A sensor uses a single infrared LED and phototransistor pair (Fairchild QRE1113GR). The phototransistor is connected to a pull-up resistor to form a voltage divider that produces an analog voltage output between 0 V and VIN (which is typically 5 V) as a function of the reﬂected IR. Lower output voltage is an indication of greater reﬂection. The LED current-limiting resistor (220 Ω) is set to deliver approximately 20-25 mA to the LED when

VIN is 5 V. Some speciﬁcations are:

Dimensions: 0.3” x 0.5” x 0.1” (without header pins installed)
Operating voltage: 5.0 V
Output format: analog voltage
Output voltage range: 0 to supplied voltage
Optimal sensing distance: 0.125” (3 mm)
Maximum recommended sensing distance: 0.25” (6 mm)

The Pololu #713 Motor Controller:

This tiny board is an easy way to use Toshiba’s TB6612FNG dual motor driver, which can independently control two bidirectional DC motors or one bipolar stepper motor. A recommended motor voltage of 4.5 – 13.5 V and peak current output of 3 A per channel (1 A continuous) make this a great motor driver for low-power motors.

-http://www.pololu.com/catalog/product/713

The Track:
We were provided with two tracks, (a) a simple ﬁgure-of-eight track, and (b) a competitive track, which was revealed later. Both tracks were high contrast with a black line on a white background. On the ﬁrst track the line is 1” wide, which is wide enough that all three sensors can detect the tape at the same time. The ﬁrst track you will
use is approximately 3’ 6” 5’.

- Part information adapted from project lab manual