RC-N3 Android Bluetooth Gamepad

简体中文

Turn a DJI RC-N3 remote controller into a standard Bluetooth HID gamepad by using an Android phone as a small, read-only USB-to-Bluetooth bridge. A native macOS monitor is included for checking the connection, buttons, sticks and gimbal wheel in real time.

Experimental community project. It is not affiliated with or endorsed by DJI. Hardware support is currently limited to the verified setup below.

Android application that receives DJI RC-N2/RC-N3 controls through the upper USB-C port and exposes them to a paired computer as a standard Bluetooth HID gamepad. There is no Wi-Fi or network relay in the control path.

Highlights

• Standard Bluetooth HID Gamepad; no Wi-Fi relay or companion server.
• Automatically opens when the matching RC-N3 Type-C accessory is attached.
• USB accessory is opened read-only and no DJI/DUML command is transmitted.
• Five signed 16-bit axes and eight HID button slots.
• Neutral report is sent immediately when the USB input source disappears.
• Native macOS visual monitor for connection and live input testing.
• Dependency-free Android build based on SDK command-line tools.

Verified platform

• Remote controller: DJI RC-N3
• Phone: Honor Play COR-AL10
• OS: HarmonyOS 2.0.0 / Android API 28
• USB role: RC-N3 is host and power source; phone is Android Open Accessory
• Accessory model: com.dji.logiclink

Project layout

• AndroidManifest.xml: minimal Android application manifest
• src/com/rcn3relay/probe/MainActivity.java: automatic USB accessory entry, read-only LogicLink reader and live status UI
• src/com/rcn3relay/probe/Rcn3Decoder.java: verified 26-byte input decoder
• src/com/rcn3relay/probe/BluetoothGamepad.java: Android Bluetooth HID Device registration, pairing target and automatic reconnection
• src/com/rcn3relay/probe/HidGamepadReport.java: standard five-axis/eight-button HID gamepad descriptor and report encoder
• build.sh: dependency-free APK build using Android SDK command-line tools

Build requirements

• JDK 17
• Android SDK platform 28
• Android build-tools 35.0.0

The build script uses the Homebrew locations installed during hardware bring-up by default. Override ANDROID_SDK_ROOT, JAVA_HOME, or RCN3_PROBE_KEYSTORE when using different locations.

Safety boundary:

• Opens the Android Open Accessory file descriptor read-only.
• Creates only a FileInputStream; it has no USB FileOutputStream.
• Does not send DUML, simulator, pairing, flight, or firmware commands.
• Sends a neutral Bluetooth HID report as soon as the RC-N3 USB source stops.
• Does not synthesize input when no fresh RC-N3 frame is available.

Automatic startup:

• The manifest matches DJI / com.dji.logiclink with Android's USB_ACCESSORY_ATTACHED intent.
• Connecting the upper RC-N3 Type-C port opens the app and starts reading.
• After the one-time Bluetooth pairing and target selection, the app registers RC-N3 Gamepad and reconnects to the saved computer automatically.
• For unattended setup, enter the Mac Bluetooth controller address shown by macOS System Information and tap 首次配对/连接此 Mac; the address is saved.

Build:

./build.sh

Run the decoder and HID encoder tests:

./test.sh

Install and launch over wireless ADB:

adb -s PHONE_IP:5555 install -r build/rc-n3-relay-probe.apk
adb -s PHONE_IP:5555 shell am start -n \
  com.rcn3relay.probe/.MainActivity

Capture logs:

adb -s PHONE_IP:5555 logcat -s RCN3Gamepad:I '*:S'

macOS visual monitor

Build the small native connection and input monitor:

./build-monitor.sh
open "build/RC-N3 Monitor.app"

The monitor reads the standard HID Gamepad locally. A green status indicator means the phone relay is connected; pressed buttons turn green and the five axis rows move in real time. It never writes to the controller.

Bluetooth HID mapping

RC-N3 input	HID control
Left stick horizontal / vertical	X / Y
Right stick horizontal / vertical	Rx / Ry
Left shoulder gimbal wheel	Rz
RTH, Fn, shutter, photo/video	Buttons 1-4
C, N, S switch positions	Buttons 5-7, one-hot

The measured raw center 1024 and endpoints 364 / 1684 are normalized to signed 16-bit HID axes. Values within 20 raw counts of center are zeroed.

Measured RC-N3 input frame

Tested on an Honor Play COR-AL10 running HarmonyOS 2.0.0 / Android API 28. The upper RC-N3 USB-C port presents a DJI Android Open Accessory named com.dji.logiclink. Its LogicLink records contain a 26-byte input frame.

The five little-endian 16-bit analog values start at inner-frame offsets 11, 13, 15, 17 and 19:

Offset	Input	Center	Observed ends
11	Right stick horizontal	1024	364 / 1684
13	Right stick vertical	1024	364 / 1684
15	Left stick vertical	1024	364 / 1684
17	Left stick horizontal	1024	364 / 1684
19	Left shoulder gimbal wheel	1024	364 / about 1672

Inner-frame byte 22 contains the mode switch and RTH button:

Mask/value	Input
byte22 & 0x30 == 0x20	Cine (C) mode
byte22 & 0x30 == 0x10	Normal (N) mode
byte22 & 0x30 == 0x00	Sport (S) mode
byte22 & 0x08 != 0	Flight Pause/RTH button held

Inner-frame byte 23 contains the remaining reported buttons:

Mask	Input	Behavior
0x01	Photo/Video toggle	Set for the full physical press
0x10	Customizable/Fn	Short pulse; no continuous long-hold state
0x40	Shutter/Record	Set for the full physical press

Holding Fn suppresses the normal gimbal-wheel analog value. No replacement zoom value was observed in any passively received frame; releasing Fn produces the 0x10 pulse. A single power-button press is local to the controller and is not reported over USB. Powering off terminates the USB read with EIO; after powering on, the saved Android accessory permission allows reading to resume.

The input frame was observed at about 9 Hz while idle.

Limitations

• Verified only with the hardware and OS versions listed above.
• The Android app uses a debug-style local signing key by default. Use your own release key before distributing production APKs.
• The RC-N3 power button is local to the controller and is not exposed as a HID button.
• The app does not control an aircraft and does not implement DJI pairing, firmware or flight commands.

Contributing

Bug reports and hardware compatibility results are welcome. Please include the phone model, Android version, controller model and a sanitized log. See CONTRIBUTING.md.

License

Released under the MIT License.