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.