Published October 9, 2024 © GPL3+

AI Autonomous Room Rover Robot (A2R3) - (Part 2)

AI Autonomous Room Rover Robot - wheel encoders & odometry. Part 2 Series.

AdvancedWork in progress6 hours270

AI Autonomous Room Rover Robot (A2R3) - (Part 2)

Things used in this project

Hardware components

AS5600 magnetic encoder

TCA9548A I2C Multiplexer

DFRobot 6 DOF Sensor - MPU6050

Pimoroni VL53L1X Time of Flight (ToF) Sensor Breakout

Software apps and online services

Arduino IDE

Hand tools and fabrication machines

3D Printer (generic)

Story

In the first part of this project series the rover had four wheels, looking good and was roving the room like a boss. It efficiently was avoiding obstacles, except with one problem: the back wheels drag while turning left and right. This causes the bot to drift on the side rather than turn in an angle freely. So, I decided to remove the back wheels and that big hideous box it was caring turning the rover in to a simple platform differential drive bot.

1 / 5 • Simple three wheel design improved version

I think it still looks good and also has now 360 degree freedom of rotation.I will keep improving the design but the first CAD design version is linked below.

PID control

The PID control solution comes to my mind as soon as I observe the bot drifts in a curve path. The motors on both wheels are the same! Infact they both are 6V, 1600 RPM. They draw the same current and have the same torque however; in reality the friction on both wheels is not the same and can not be the same. For this reason the robot drives in a curve path not in a perfect straight line. The bot has to respect physics.

The simple solution for this problem is to get a speed reading of both wheels and whenever a difference in speed is occurring in some time interval then control the speed of the wheels to be the same by adjusting it over time ( integral value ). In short PID ( proportional Integral derivative ) control.

This is the PID control snippet part from the code and I believe this is the easiest and simplest implementation.

PID control code snippet

First read angle values using the two wheel encoders of the motors. I used the AS5600 magnetic encoder and fitted them in the wheel stabilizers which I designed and 3D printed them from PCBWay for this purpose. PCBWay is the sponsor of 3D printing the wheel stabilizers and encoder cases for this project. Their service is awesome and I am definitely will be using their pcb service for my future projects.

The encoders are connected to the TCA9548A I2C multiplexer because the encoders have the same I2C bus address and they conflict if they are on the same I2C bus (pin 21 and 22). Then get the difference of the two readings as an "Error". An overall values of this error over time is the Integral. Which has to be between some -Max_INTEGRAL and + MAX_INTEGRAL to avoid clamping and I experimented with different values of MAX_INTEGRAL values as it is just a constant.I found MAX_INTEGRAL to be 50 as it is just optimal for my design. Then the derivative is the difference of errors overtime. Output = KP * error + KI * integral + KD * derivative; is the key variable to set the motor speed values over time. It can also be set two a constant MAX_OUTPUT = 50 also to avoid clamping. Finally the robot roves in a straight line as long as it doesn't encounter obstacles.

1. Set Up

Install the required libraries:

Wire.h for I2C communication. AS5600.h library for the AS5600 encoder (you may need to install it via the Arduino Library Manager or download it from a GitHub repository).

2. Wiring

Connect the TCA9548A to the ESP32:SDA → SDA

(ESP32, GPIO 21)SCL → SCL (ESP32, GPIO 22)VCC → 3.3V (ESP32)GND → GND (ESP32)

SDA → SDA (TCA9548A)SCL → SCL (TCA9548A)VCC → 3.3V (TCA9548A)GND → GND3

3. Code

You can check out my implementation of PID down in the attachment section.

Odometry

Left encoder is on channel 0, and right encoder is on channel 1 of the TCA9548A multiplexer.
The code reads the raw angle from the AS5600 encoders for both wheels and calculates the corresponding distance traveled based on the wheel's radius.
Odometry is calculated as the distance traveled by the wheel, using the formula Distance = (Angle / 360) * Wheel Circumference.
To get wheel circumference = 2*pi*r. r=20/2=10

circumference = 2*pi*r. r=20/2=10

1 / 3

Build and Demo

Build and straight drive Demonstration

Code

Wheel Odometry

#include <Wire.h>

#define AS5600_ADDR 0x36           // I2C address for AS5600
#define TCA9548A_ADDR 0x70         // I2C address for TCA9548A

// Function to select the channel on the TCA9548A
void tca9548aSelect(uint8_t channel) {
  if (channel > 7) return;
  Wire.beginTransmission(TCA9548A_ADDR);
  Wire.write(1 << channel);
  Wire.endTransmission();
}

// Function to read the angle from AS5600
uint16_t readAS5600Angle() {
  uint16_t angle = 0;
  
  // Start communication with AS5600
  Wire.beginTransmission(AS5600_ADDR);
  Wire.write(0x0C);  // High byte of angle register
  if (Wire.endTransmission() != 0) {
    Serial.println("Error: I2C communication failed!");
    return 0; // Return 0 if communication fails
  }
  
  // Request 2 bytes from AS5600 (high and low angle bytes)
  Wire.requestFrom(AS5600_ADDR, 2);
  if (Wire.available() == 2) {
    angle = Wire.read() << 8; // High byte
    angle |= Wire.read();     // Low byte
  } else {
    Serial.println("Error: Failed to read from AS5600!");
    return 0; // Return 0 if reading fails
  }
  
  return angle;
}

void setup() {
  Serial.begin(115200);
  Wire.begin(); // Initialize I2C communication
  
  // Optional: Check if AS5600 is connected properly
  Wire.beginTransmission(AS5600_ADDR);
  if (Wire.endTransmission() != 0) {
    Serial.println("AS5600 not detected. Check wiring!");
    while (1); // Stop the program if AS5600 is not found
  }

  // Select TCA9548A channel 0 where AS5600 is connected
  tca9548aSelect(0);
}

void loop() {
  // Ensure TCA9548A channel 0 is selected before reading
  tca9548aSelect(0);

  // Read the raw angle from AS5600
  uint16_t angleRaw = readAS5600Angle();
  
  // Convert the raw angle to degrees (12-bit resolution)
  float angle = angleRaw * (360.0 / 4096.0);
  
  // Print the angle in degrees to the Serial Monitor
  Serial.println(angle);

  // Optional: Add a small delay to avoid flooding the Serial Monitor
  delay(100);
}

Credits

Michael

3 projects • 5 followers

Nack for Tech and Science! Computer scientist!

AI Autonomous Room Rover Robot (A2R3) - (Part 2)

Things used in this project

Hardware components

Software apps and online services

Hand tools and fabrication machines

Story

PID control

Odometry

Build and Demo

Custom parts and enclosures

3D Model design parts

Code

Wheel Odometry

PID controller

Credits

Michael

Comments

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AI Autonomous Room Rover Robot (A2R3) - (Part 2)

AI Autonomous Room Rover Robot (A2R3) - (Part 2)

Things used in this project

Hardware components

Software apps and online services

Hand tools and fabrication machines

Story

PID control

Odometry

Build and Demo

Custom parts and enclosures

3D Model design parts

Code

Wheel Odometry

PID controller

Credits

Michael

Comments

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