2.2. Architecture of a 3pi robot

Overview of the 3pi

Top and bottom side of the robot are visible in the images below.

Figure 1. General features of the Pololu 3pi robot, top view.
Figure 2. Labeled bottom view of the Pololu 3pi robot.

Simplified diagram


To be powered up, the robot needs 4 AAA batteries.

CPU - microcontroller

The microcontroller used is a AVR Atmega328p which has the following characteristics:

  • Flash : 32 KB
  • SRAM : 2KB
  • EEPROM : 1KB
  • Operating frequency: 20MHz ( it is able to execute 20.000.000 instructions per second)
  • Operating voltage : 1.8 - 5.5 V


The robot uses an array of five sensors. Each sensor is an infrared reflectance sensor.

How does it work?

  1. it emits an infrared wave
  2. the wave hits the object's surface and it reflects back
  3. the reflected wave is detected and converted into a signal

A black material will have a lower reflectance index compared to a white one, in other words, a black material will reflect less than a white one.

Motor driver

The motor driver is a dedicated integrated circuit (IC) which drives the motors. The IC is controlled by the microcontroller.

The robot has two direct current (DC) motors. Each motor has a gearbox with the gear ratio of 30:1, which means that for every 30 turns of the motor shaft the wheel will spin once. The maximum speed of both motors is about 100cm/s.

User LEDs

On the bottom side the robot has two LED (a red one and a green one). Each LED can be turned on/off or it can be toggled.


The LCD on the robot is a 8×2 LCD. That means it has eight columns and two lines. In other words, you can display eight characters on each line.


roboticsisfun/chapter2/ch2_2_3pi_architecture.txt · Last modified: 2012/11/18 17:25 by liviu.radoi