1. Overview

The 3pi+ 32U4 is a versatile, high-performance, user-programmable robot that measures just 9.7 cm (3.8″) in diameter. At its heart is an ATmega32U4 AVR microcontroller from Microchip (formerly Atmel), and like our A-Star 32U4 programmable controllers, the 3pi+ 32U4 features a USB interface and ships preloaded with an Arduino-compatible bootloader, so all you need to program it is a USB A to Micro-B cable (not included). A software add-on is available that makes it easy to program the robot from the Arduino environment, and we have Arduino libraries and example sketches to help get you started. For advanced users who want to customize or enhance their robots with additional peripherals, the robot’s power rails, power system controls, and microcontroller’s I/O lines can be accessed via several 0.1″-pitch expansion ports.

3pi+ 32U4 OLED Robot, front view.

3pi+ 32U4 OLED Robot, side view.

3pi+ 32U4 OLED Robot, rear view.

The 3pi+ (or 3𝜋+) features two H-bridge motor drivers and a variety of integrated sensors, including a pair of quadrature encoders for closed-loop motor control, a complete inertial measurement unit (3-axis accelerometer, gyro, and magnetometer), five downward-facing reflectance sensors for line-following or edge-detection, and left and right bump sensors along the front face of the robot. Three on-board pushbuttons offer a convenient interface for user input, and a 128×64 graphical OLED display (LCD on original version), buzzer, and indicator LEDs allow the robot to provide feedback.

The robot also features a unique power system that runs the motors at a constant 8 V independent of the battery charge level, so the speed of the motors does not vary with the battery voltage.

3pi+ 32U4 versions

The original version of the 3pi+ 32U4 includes an 8×2 character LCD, while the newer 3pi+ 32U4 OLED incorporates a graphical OLED display instead. The information in this user’s guide generally applies to both versions, and the name “3pi+ 32U4” covers both the original (LCD) and OLED versions except where specific differences are noted.

Our Pololu3piPlus32U4 Arduino library generally allows code written for the LCD version to work on the OLED version with minimal changes (and the reverse is also true as long as your code does not make use of the OLED’s graphical capabilities).

3pi+ 32U4 Robot, top view.

3pi+ 32U4 OLED Robot, top view.

Comparison with the original 3pi

The 3pi+ 32U4 offers many major improvements over the original 3pi, including:

• ATmega32U4 microcontroller with Arduino-compatible bootloader can be programmed directly through a USB connection
• Quadrature encoders on both motors for closed-loop position and speed control
• Graphical OLED display (OLED version only)
• Full 9-axis IMU (three-axis gyro, accelerometer, and compass)
• Bottom-loading battery holders keep batteries accessible even if additional levels are added
• Full wrap-around bumper to protect electronics from collisions
• Two bump sensors on the front

The 3pi+ 32U4 uses a different microcontroller with different pin mappings compared to the older 3pi, and some of the software library interfaces are different, so programs written for the original 3pi will not work on the 3pi+ 32U4 without modification.