ByteRider documentation

INTRODUCTION

HOW DOES IT WORK?

The BitByteRider RC car is powered by ESP32-C3 Breadboard & Power adapter developmemt board.

Reserved Pins & GPIOs

The following table summarizes GPIOs and pins reserved for operations purposes.

The GPIO numbers correspond to those on the ESP32-C3 WROOM microcontroller. The Pin number corresponds to the pin on the Breadboard and Power adapter development board.

x- and y- axis

The GPIO0 and GPIO1 assigned to measuring the voltage of x- and y- axis of the Joystick. Lastly, there is a group of GPIO pairs responsible for PWM for DC motors.

Direction and Speed

The pairs of DC motors on the left side are wired to the dedicated PWM channels. This means that ESP32-C3 Breadboard DevBoard can control rotation speed and direction of DC motors in pairs only (i.e. left and right side). Consequently, only four PWM channels are sufficient for controlling the direction of the RC car. Based on this constraint, the RC car can only move front, back, and turn/rotate left and right. Any other movements are not possible (i.e. diagonal or sideways).

A pair of PWM channels are required for defining rotation speed and direction of the DC motors on each side. In particular, GPIO6 and GPIO5 provide PWM to the left- and right- side DC motors to rotate in a clockwise direction. Similarly, GPIO4 and GPIO7 provide PWM to the left- and right- side DC motors to rotate in a counter-clockwise direction. Changing PWM on each channel determines the speed and direction of the RC car.

The following images illustrate various PWM duty cycles registered by oscilloscope (duty cycles 0%, 48% and 91%, resp.).

DC Motor PWM duty cycle 0%

DC Motor PWM duty cycle 47.6%

DC Motor PWM duty cycle 90.8%

GPIO	Pin	Function	Notes
0	16	Joystick x-axis	ADC1_CH0
1	15	Joystick y-axis	ADC1_CH1
8	5	Joystick push button
6	4	PWM for clockwise rotation of left-side motors	LEDC_CHANNEL_1
5	3	PWM for clockwise rotation of right-side motors	LEDC_CHANNEL_0
4	2	PWM for counter-clockwise rotation of right-side motors	LEDC_CHANNEL_2
7	6	PWM for counter-clockwise rotation of left-side motors	LEDC_CHANNEL_3

Fusion of Software with Hardware

The struct for storing motors PWM values.

struct motors_rpm {
    int motor1_rpm_pwm;
    int motor2_rpm_pwm;
    int motor3_rpm_pwm;
    int motor4_rpm_pwm;
};

The function for updating motors’ PWM values.

// Function to send data to the receiver
void sendData (void) {
    sensors_data_t buffer;              // Declare data struct

    buffer.crc = 0;
    buffer.x_axis = 0;
    buffer.y_axis = 0;
    buffer.nav_bttn = 0;
    buffer.motor1_rpm_pwm = 0;
    buffer.motor2_rpm_pwm = 0;
    buffer.motor3_rpm_pwm = 0;
    buffer.motor4_rpm_pwm = 0;

    // Display brief summary of data being sent.
    ESP_LOGI(TAG, "Joystick (x,y) position ( 0x%04X, 0x%04X )", (uint8_t)buffer.x_axis, (uint8_t)buffer.y_axis);
    ESP_LOGI(TAG, "pwm 1, pwm 2 [ 0x%04X, 0x%04X ]", (uint8_t)buffer.pwm, (uint8_t)buffer.pwm);
    ESP_LOGI(TAG, "pwm 3, pwm 4 [ 0x%04X, 0x%04X ]", (uint8_t)buffer.pwm, (uint8_t)buffer.pwm);

    // Call ESP-NOW function to send data (MAC address of receiver, pointer to the memory holding data & data length)
    uint8_t result = esp_now_send(receiver_mac, &buffer, sizeof(buffer));

    // If status is NOT OK, display error message and error code (in hexadecimal).
    if (result != 0) {
        ESP_LOGE("ESP-NOW", "Error sending data! Error code: 0x%04X", result);
        deletePeer();
    }
    else
        ESP_LOGW("ESP-NOW", "Data was sent.");
}

The onDataReceived() and onDataSent() are two call-bacl functions that get evoked on each corresponding event.

// Call-back for the event when data is being received
void onDataReceived (uint8_t *mac_addr, uint8_t *data, uint8_t data_len) {

    buf = (sensors_data_t*)data;                            // Allocate memory for buffer to store data being received
    ESP_LOGW(TAG, "Data was received");
    ESP_LOGI(TAG, "x-axis: 0x%04x", buf->x_axis);
    ESP_LOGI(TAG, "x-axis: 0x%04x", buf->y_axis);
    ESP_LOGI(TAG, "PWM 1: 0x%04x", buf->motor1_rpm_pwm);
}

// Call-back for the event when data is being sent
void onDataSent (uint8_t *mac_addr, esp_now_send_status_t status) {
    ESP_LOGW(TAG, "Packet send status: 0x%04X", status);
}

The rc_send_data_task() function runs every 0.1 second to transmit the data to the receiver.

// Continous, periodic task that sends data.
static void rc_send_data_task (void *arg) {

    while (true) {
        if (esp_now_is_peer_exist(receiver_mac))
            sendData();
        vTaskDelay (100 / portTICK_PERIOD_MS);
    }
}

Schematic

DATA STRUCT

The struct serves as the data payload for sending control signals from transmitting device to the receiver using ESP-NOW. In addition, it may contain additional data such as telemetry, battery status, etc.

The sensors_data_t struct is designed as a data payload that encapsulates all control commands and sensor states relevant to the vehicle’s operation. It’s intended to be sent from a transmitting device (like a remote control or master controller) to a receiver (such as a microcontroller onboard the vehicle).

typedef struct {
    int         x_axis;             // Joystick x-position
    int         y_axis;             // Joystick y-position
    bool        nav_bttn;           // Joystick push button
    bool        led;                // LED ON/OFF state
    uint8_t     motor1_rpm_pwm;     // PWMs for 4 DC motors
    uint8_t     motor2_rpm_pwm;
    uint8_t     motor3_rpm_pwm;
    uint8_t     motor4_rpm_pwm;
} __attribute__((packed)) sensors_data_t;

When used with communication protocols like ESP-NOW, this struct is encoded into a byte stream, then transmitted at regular intervals or in response to user input, and finally decoded on the receiving end to control hardware.

Data Payload

x_axis and y_axis fields capture analog input from a joystick, determining direction and speed. nav_bttn represents a joystick push-button.

led allows the transmitter to toggle an onboard LED and is used for status indication (e.g. pairing, battery warning, etc).

motor1_rpm_pwm to motor4_rpm_pwm provide individual PWM signals to four DC motors. This enables fine-grained speed control, supports differential drive configurations, and even allows for maneuvering in multi-directional platforms like omni-wheel robots.

Why use __attribute((packed))?

ESP-NOW uses fixed-size data packets (up to 250 bytes). The __attribute__((packed)) removes compiler-added padding for precise byte alignment.

As packed attribute tells the compiler not to add any padding between fields in memory, this makes the struct:

• Compact

• Predictable for serialization over protocols like UART or ESP-NOW

• Ideal for low-latency transmission in embedded systems

This ensures the receiver interprets the exact byte layout you expect, minimizing bandwidth and maximizing compatibility across platforms.

TRANSMITTER

Data Encapsulation

RECEIVER

WORK-IN-PROGRESS WALK THROUGH

Finished Work

Chassis

Completed chassis with only DC motor controllers installed.

Wiring

Completed wiring.

Motor Wires Harness

DC Motors wires secured inside harnes.