RC Multi Joystick PPM Trainer Port

Description

A multi-joystick PPM generator for RC trainer ports, featuring hotplug support, trim, expo, inversion, and an inspector utility.

If you’ve ever wanted to fly your RC craft with real plane-style controllers or even an Xbox controller connected via USB

Now the sky is not the limit!

Example Video (MP4)

Features

• 8-Channel PPM Generation
  Generate a PPM signal on GPIO 18 using the pigpio library.

• Multi-Joystick & Hotplug Support
  Dynamically detects multiple joysticks. If no joystick is present, no PPM signal is generated, so the RC transmitter reverts to its own controls.

• Per-Channel Customization
  Configure channel mapping, trim, expo, and inversion (using a ! prefix).

• Status LEDs

  • RED LED (GPIO 22): Solid ON once the system is initialized.
  • GREEN LED (GPIO 23): Blinks continuously while the main loop is running.

• Inspector Utility
  A separate script (joystick_inspector.py) monitors all joystick events (axes, buttons, hats) and prints a live table of computed PPM pulse widths.

Hardware Requirements

• Raspberry Pi (tested on Pi Zero 2)
• RC Transmitter with a trainer port that accepts a PPM signal
• USB Joystick(s)
• LEDs (Optional)
  • RED LED (with resistor) on GPIO 22
  • GREEN LED (with resistor) on GPIO 23
• Wiring
  • GPIO 18 → Transmitter trainer port signal
  • GND → Transmitter ground

Software Requirements

• Raspberry Pi OS (or similar Linux distro)
• Python 3
• pigpio library & daemon (pigpiod)
• pygame

Installation

1. Clone the Repository

   git clone https://github.com/Itay-Sharoni/RC-Multi-Joystick-PPM-Trainer-Port.git
   cd RC-Multi-Joystick-PPM-Trainer-Port

2. Install Dependencies

   python3 -m venv venv
   source venv/bin/activate
   pip install pigpio pygame

3. Enable and Start pigpio Daemon

   sudo systemctl enable pigpiod --now

   If step 3 failed, please install using apt-get and try again

   sudo apt-get install python3-pigpi
   sudo systemctl enable pigpiod --now

Wiring Diagram

## Wiring Diagram

- **PPM Output**  
- **GPIO 18** → Transmitter trainer port signal
- **GND** → Transmitter ground

- **Status LEDs (Optional)**  
- **RED LED** → GPIO 22 (with resistor)
- **GREEN LED** → GPIO 23 (with resistor)

    Raspberry Pi              3‑Pole (TRS) Connector (Headphones Cable)
  ------------------          -------------------------
  |                |          |         |           |
  |   GPIO 18      | -------->|   TIP   |  (PPM signal)
  |   (PPM out)    |          |         |           
  |                |          |         |           
  |   GND ---------| -------->| SLEEVE  |  (Ground)
  |                |          |         |
  ------------------          |  RING   |  (Not used)
                             -------------------------

Configuration

Open joystick_ppm_multi.py and edit the top section:

• CHANNEL_MAP
  Maps each channel (0–7) to a joystick control.
  Example:

  CHANNEL_MAP = {
      0: "joy0:axis:0",   # normal axis
      1: "!joy0:axis:1",  # inverted axis
      2: "joy0:axis:2",
      3: "joy1:axis:0",
      4: "none",
      5: "none",
      6: "none",
      7: "none",
  }

  A leading ! inverts the final value. If VERBOSE = True, a live table of channel pulse widths will be displayed.

• TRIM & EXPO Set per-channel trim (µs offset) and expo (0 = linear, 1 = full expo) in:

  TRIM = [0, 0, 0, 0, 0, 0, 0, 0]
  EXPO = [0, 0, 0, 0, 0, 0, 0, 0]

• PPM Parameters Adjust MIN_PULSE_US, MID_PULSE_US, MAX_PULSE_US, and FRAME_LENGTH_MS as needed.

Running the Scripts

PPM Generator

python3 joystick_ppm_multi.py

Joystick Inspector

python3 joystick_inspector.py

This script prints all joystick events and a table of computed channel outputs, useful for verifying your mapping before flight.

Running as a Systemd Service

To have the PPM generator start automatically at boot:

1. Create the Service File
   For example, /etc/systemd/system/joystick_ppm.service:

   [Unit]
   Description=Multi-Joystick PPM Generator Service
   After=pigpiod.service
   Requires=pigpiod.service
   
   [Service]
   Environment="TERM=linux" "XDG_RUNTIME_DIR=/run/user/1000"
   ExecStart=/home/pi/ppm/venv/bin/python3 /home/pi/ppm/joystick_ppm_multi.py
   WorkingDirectory=/home/pi/ppm/
   StandardOutput=journal
   StandardError=journal
   Restart=always
   KillSignal=SIGKILL
   SendSIGKILL=yes
   TimeoutStopSec=5
   User=pi
   Group=pi
   
   [Install]
   WantedBy=multi-user.target

2. Create the Service File

   sudo systemctl daemon-reload
   sudo systemctl enable joystick_ppm.service
   sudo systemctl start joystick_ppm.service

Calibrating Your Joystick

OS-Level Calibration:

sudo apt-get install joystick
jscal -c /dev/input/js0

Follow the prompts to calibrate the axes so that the center position is zero and the extremes are properly mapped.

Author & Acknowledgements

• Author: Itay Sharoni
• Contact: [GitHub]

Acknowledgements

• pigpio library & daemon
• pygame library
• jsa/flystick for the original concept & inspiration.

License

This project is licensed under the GPL-3.0 License.