ESP-NOW Transmitter for MultiWii Drone

ESP32-based RC transmitter for the MultiWii ESP32 drone flight controller using ESP-NOW wireless protocol.

Features

• 4-channel control (Throttle, Yaw, Pitch, Roll)
• 2 AUX switches for flight modes
• Bi-directional telemetry from drone
• 16x2 I2C LCD display
• 50Hz update rate
• 500ms failsafe timeout
• Signal strength (RSSI) monitoring

Hardware Requirements

Components

Component	Quantity	Notes
ESP32 Dev Board	1	Any ESP32 with ADC1 pins
Analog Joysticks	2	2-axis with button (optional)
Toggle Switches	2	For AUX1/AUX2
16x2 I2C LCD	1	Address 0x27 (optional)
Battery	1	1S-2S LiPo recommended

Wiring (MH-ET LIVE MiniKit)

Function	GPIO	MiniKit Pin	Notes
Throttle	36	Pin 3	Left stick Y-axis (ADC, input-only)
Yaw	39	Pin 4	Left stick X-axis (ADC, input-only)
Pitch	34	Pin 5	Right stick Y-axis (ADC, input-only)
Roll	35	Pin 6	Right stick X-axis (ADC, input-only)
AUX1	26	Pin 10	Flight mode switch
AUX2	27	Pin 11	Secondary function
Left JS Btn	4	Pin 26	Left joystick button (optional)
Right JS Btn	16	Pin 27	Right joystick button (optional)
Battery	32	Pin 7	Voltage divider (optional)
LCD SDA	21	Pin 9 (right)	I2C data
LCD SCL	22	Pin 12 (right)	I2C clock

Notes:

• GPIO 34-39 are input-only (no internal pullups) - perfect for joystick ADC
• GPIO 26, 27 have internal pullups for switches
• Avoid GPIO 0, 2, 5, 12, 15 (strapping pins)
• Avoid GPIO 6-11 (connected to internal flash)

Software Setup

1. Install ESP32 Board Support

In Arduino IDE:

1. File > Preferences
2. Add to Additional Board URLs:

   https://raw.githubusercontent.com/espressif/arduino-esp32/gh-pages/package_esp32_index.json
   

3. Tools > Board > Boards Manager > Install "ESP32 by Espressif" (version 3.0.7+)

2. Install Libraries

• LiquidCrystal_I2C - For LCD display (install via Library Manager)

3. Configure the Transmitter

Edit ESP_NOW_Transmitter.ino:

Set Drone MAC Address (Required)

// Line 27 - Replace with your drone's MAC address
uint8_t RECEIVER_MAC[] = {0xAA, 0xBB, 0xCC, 0xDD, 0xEE, 0xFF};

Get the drone's MAC address from its Serial Monitor output at boot:

ESP32 Receiver MAC Address: AA:BB:CC:DD:EE:FF

Calibrate Joysticks

1. Upload code with Serial Monitor open (115200 baud)
2. Move each joystick to min, center, and max positions
3. Note the raw ADC values (divided by 4 for 10-bit scale)
4. Update calibration arrays:

// Lines 52-55
int throttleCal[] = {13, 524, 1015};   // {min, center, max}
int yawCal[]      = {50, 505, 1020};
int pitchCal[]    = {12, 544, 1021};
int rollCal[]     = {34, 522, 1020};

Reverse Stick Directions (if needed)

// Lines 58-61
bool throttleReverse = true;   // Set false to invert
bool yawReverse      = true;
bool pitchReverse    = true;
bool rollReverse     = true;

4. Upload

1. Select Tools > Board > ESP32 Dev Module
2. Select correct COM port
3. Click Upload

Usage

Pairing

1. Power on the drone first
2. Power on the transmitter
3. Transmitter auto-pairs when it receives first packet from drone
4. LCD shows "TX OK" then telemetry data when linked

LCD Display

With telemetry:

3.7V 85% ARM
T:127 ANGLE

• Line 1: Drone battery, signal strength, armed status
• Line 2: Throttle value, flight mode

Without telemetry:

TX OK  NO LINK
T:127 AUX1:0

Serial Debug Output

Open Serial Monitor at 115200 baud:

TX: T=0 Y=128 P=128 R=128 AUX=0/0 | OK | Drone: 3.7V 85% ARM ANG

Arming the Drone

1. Ensure throttle is at minimum (stick down)
2. Move yaw stick fully right and hold for ~1 second
3. LCD shows "ARM" when armed
4. To disarm: throttle minimum + yaw left

Data Structures

Control Data (TX → Drone)

struct struct_message {
  uint8_t throttle;  // 0-255
  uint8_t yaw;       // 0-255
  uint8_t pitch;     // 0-255
  uint8_t roll;      // 0-255
  uint8_t AUX1;      // 0 or 1
  uint8_t AUX2;      // 0 or 1
  uint8_t switches;  // Reserved
};

Telemetry Data (Drone → TX)

struct struct_ack {
  uint8_t vbat;     // Battery (0.1V units, 37 = 3.7V)
  uint8_t rssi;     // Signal strength (0-100%)
  int16_t heading;  // Compass heading (degrees)
  int16_t pitch;    // Pitch angle (0.1 degrees)
  int16_t roll;     // Roll angle (0.1 degrees)
  int16_t alt;      // Altitude (cm)
  uint8_t flags;    // Status flags
};

Flag bits:

Bit	Meaning
0	Armed
1	Angle mode
2	Horizon mode
3	Baro mode

Troubleshooting

"TX --" on LCD / No Connection

• Verify drone is powered and ESP-NOW initialized
• Check MAC address matches exactly
• Ensure both devices on same WiFi channel (default: auto)

Joysticks Not Responding Correctly

• Re-calibrate joystick values
• Check wiring to correct GPIO pins
• Verify using ADC1 pins (32-39)

LCD Not Working

• Check I2C address (try 0x3F if 0x27 doesn't work)
• Verify SDA/SCL wiring (21/22)
• Run I2C scanner sketch to find address

Controls Inverted

• Toggle the *Reverse boolean for that axis
• Or swap the wiring on the joystick potentiometer

Customization

Change Update Rate

#define TX_INTERVAL_MS  20  // 50Hz (default)
// Use 10 for 100Hz, 50 for 20Hz

Add More AUX Channels

The switches byte is reserved for additional channels. Modify both transmitter and ESP_NOW_RX.cpp to use individual bits.

Remove LCD

Comment out LCD code and remove the library include if not using a display.

License

GPL (inherited from MultiWii project)

Credits

• Original nRF24 transmitter: ELECTRONOOBS
• ESP-NOW conversion: Claude Code
• MultiWii flight controller: Alexandre Dubus