Electrical

Overview

Purple Tape features a robust system of electrical components to allow it to navigate and interact with the game field. Coordinated by two PIC32 microcontrollers communicating through SPI, Purple Tape features a leader PIC that manages the core game functionality such as intake and processing of coal/balls, depositing the coal into the buckets, and other game logistics. A follower PIC is dedicated to Purple Tape's navigation, allowing for RPM control of drivetrain motors and line-following drive.

System Diagram

Featured Components

PIC32 Microcontrollers

Two Microchip PIC32MX170F256B microcontrollers communicating by SPI were used.
The leader PIC managed the subsystems necessary for processing balls/coal and other game logistical features.
The follower PIC managed the navigation of the bot, including beacon and line detection, as well as the wheel motors.

DC Motors & Magnetic Encoders

Follower

Two Igarashi 12V DC Gear motors, each with their own motor driver, were used to drive the wheels of the bot.
These were paired with Polulu magnetic encoders to received RPM data for closed-loop control. The encoders were mounted to the back of the motor shafts, provided 150 ticks per revolution.

Leader

Two Igarashi 12V DC Gear motors and a single motor driver were also used to rotate the conveyor belt and fly wheel for ball/coal transportation from dispenser to bucket.

Servo Motors

Three Hitec HS-322HD Servo motors and one SG90 Micro Servo motors were used
HS-322HD Servo was used to actuate the arm of the bot of bring the bucket down
HS-322HD was also used to actuate ball intake arm to remove coal from the dispenser
HS-322HD was used to open the door of the container to drop coal into the bucket
The SG90 Micro Servo indicated the side the bot was placed on.

IR Beacon Detection

A phototransistor was used to detect IR pulses from the different beacons on the field.
The beacon signal was processed with an MCP6294 op-amp, then coupled with a LM339N comparator to create digital pulses detected by the PIC input capture.

Line Detection

Polulu QTR-HD-01A line sensors were used for line following on the field.
Five total sensors were used for detecting different parts of the tape on the field.
Three line following sensors were placed in the middle of the chassis to align with the tape.
Two other sensors were placed to each side off the center axis to detect intersctions in the tape.

Button & Limit Switch

Two switches were used
One was used for the start button to start gameplay mode
One was used for detection of the ball dispensing when retrieving coal.

Featured Circuit Schematics

Leader PIC32

Subsystems managed by the leader include servo motors for gameplay, DC motors for coal processing, start button, limit switch for coal intake, and LED for gameplay indication.
The leader PIC32 sends commands to the follower PIC32 based on higher-level gameplay, and receives information based on the navigation controlled by the follower.

Follower PIC32

Subsystems managed by the follower include drivetrain DC motors for navigation, IR line sensors for line following, and the beacon detection circuit (featured below).
The follower PIC32 receives commands and queries from the leader PIC32, then updates the leader when commands are done or new information is processed.

Beacon Detection Signal Conditioning

Our beacon detection is a simple circuit that utilizes a phototransistor to detect IR pulses from field beacons.
Phototransistor output current is amplified and converted into voltage using a transimpedance amplifier.
Amplified signals are then digitized using a comparator with hysteresis to allow for interrupt capture of signals.

Drivetrain DC Motors and Encoders

Our DC motors used in the drivetrain were controlled using TLE-5206 H-bridges for output-capture PWM control.
Encoders signals were received using input capture to detect RPM of the DC motors.

Full Circuit Schematic

Purple Tape Schematic.pdf

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