The Robot

Specifications

ULTRON

Controller: Arduino Uno (Revision 0); 5-12 V
Motors: LEGO 43362 “Technic Mini-Motor” (2x); No Gear Reduction; INPUT: 9V, .9A
Motor Driver: Quadruple Half-Driver (Double H-Bridge); 16-pin DIP; TI SN754410-NE
Light Detectors: ??? (2x); (not implemented)
IR Detector: Demodulating, AGC3, 38 kHz, 45m range, PWM Output; INPUT: 2.5~5.5 V, 450 uA; Vishay TSOP32338
Power: Source: 12V (via wall adapter); H-Bridge VCC_2: 9V (via voltage regulator)

Circuit Components

Overview

Component Overview

This is a non-schematic representation of the entire robot.

The microcontroller provides 5 V to the H-Bridge and 3.5 V to each IR and Light Sensor via the onboard regulator. An additional 9 V is supplied to the H-Bridge via a Voltage Regulator (not pictured). Each motor is connected to the H-Bridge via two Voltage In and Ground Out pins. Neither motor is directly connected to the microcontroller. The microcontroller gives instructions to the H-Bridge through 3 pins per motor (see logic table below), which directs the H-Bridge to supply the correct amount and polarity of power to the individual motors. The IR Detector and both of the Light Sensors take a Voltage In from the microcontroller and return a Ground Out. The IR Detector and Light Sensors give to the microcontroller 1 Pulse Width Modulated signal each.

Schematics

voltage regulator and h-bridge schematic

Full Schematic of the Voltage Regulator and H-Bridge

These schematics represent the components of the solution. The power source is attached to the robot via 3.5mm barrel plug and provides 12V to the controller and external voltage regulator in parallel. The H-Bridge accepts 5V on VCC_1 (via the controller’s on-board regulator) and 9V on VCC_2 (via the external power regulator). The IR Detector is powered by the controller’s 3.5V on-board regulator.

Motor Logic

EN     SIGA   SIGB   Result
LOW    (X)    (X)    Full Stop
HIGH   LOW    HIGH   Turn Clockwise
HIGH   HIGH   LOW    Turn Counter-Clockwise

This truth table describes what a motor will do when logic is sent to the h-bridge from the microcontroller. Note that there are two motors which must spin in opposite directions (at the same rate) to make the robot move forwards. A total of 6 pins connect the microcontroller to the h-bridge. 2 pins connect each motor to the h-bridge. The motor has one 5 V supply (for logic) and one 9 V supply (to give to the motors).

The Physical Design

We decided to put the wheels at the center of the body (between front and back) to make a zero-degree turn possible. This would allow the robot to change direction without moving from the center of the square.
We also spread the wheels out horizontally. This way they have to travel more rotations in order to turn the robot, making turning more precise.
We spread the 2 light sensors out horizontally to allow for more accurate straightening when the robot reached a white line.
We wanted to make the robot relatively heavy. In combination with a low velocity this will create a greater friction with the board. Therefore there will be less sliding when the motors stop, providing more precision.