Convert an old RC Transmitter to control an RC Simulator

I finally wanted to get into RC planes. Almost 20 years ago I built a glider (The Spirit from Great Planes) and never flew it because I had no experience in flying and I disliked the idea of blowing up several weeks of work in a couple of seconds. When I recently came across the Flite-Test site and saw their foam-built planes, I thought that I could try to build one of these. I downloaded the plans for the FT Simple Cub, grabbed some foam and started building it from scratch.

While building it, I thought it might be a good idea to check out how RC simulators evolved in the past 20 years. After some research, I decided to buy a basic version of the AeroFly RC Simulator. It appealed to me, because of its price and for one special feature: the permanent ground view which largely enhances the orientation of the pilot, especially during the landing approach.

After installing the program, I grabbed one of my kids' PS4 controllers and started to (sim-)fly around. Very soon I discovered though, that the feel wasn't right. The next step was to look for a way to connect my newly acquired FlySky FS-I6X transmitter to the simulator. Unfortunately, the FS-I6X has no USB connector to hook it up to the computer, but some more research revealed that the trainer port can be used together with some virtual joystick middleware: SmartPropoPlus. I than grabbed a SVGA (or PS/2) plug and a mono mini-jack and soldered the required cable.

The way this works is, that the PPM output of the transmitter is fed into the audio-input of the computer where it is sampled by SmartPropoPlus which sends movement data to a virtual joystick device. The RC simulator sees a regular joystick device mimicked by the vJoy device driver. So far so good! But, the resolution was poor and random glitches introduced some weird behavior during flight.

Wait! I still have an old Hitec Flash 5 transmitter lying around. As I did not plan to use it anymore, it was time to re-purpose it. It has 4 potentiometers on the two gimbals, 8 trim buttons and 4 switches, one of which is momentary. It quickly became clear, that an Arduino Nano could do the trick to handle all these Inputs.

The hardware conversion of the transmitter took about 2 hours and the result looks like this:

The software consists of a simple Arduino sketch to read the potentiometers' and switches' states and transmit them over the serial port in a compact text format. This text stream is read by a python script, decoded and fed into the vJoy device driver with this library.

Arduino Script:

 String line;  
   
 void setup() {  
  Serial.begin(19200);  
  pinMode(2, INPUT_PULLUP);  
  pinMode(3, INPUT_PULLUP);  
  pinMode(4, INPUT_PULLUP);  
  pinMode(5, INPUT_PULLUP);  
  pinMode(6, INPUT_PULLUP);  
  pinMode(7, INPUT_PULLUP);  
  pinMode(8, INPUT_PULLUP);  
  pinMode(9, INPUT_PULLUP);  
  pinMode(10, INPUT_PULLUP);  
  pinMode(11, INPUT_PULLUP);  
  pinMode(A4, INPUT_PULLUP);  
  pinMode(A5, INPUT_PULLUP);  
 }  
 void loop() {  
  line = analogRead(A0);  
  line += ",";  
  line += analogRead(A1);  
  line += ",";  
  line += analogRead(A2);  
  line += ",";  
  line += analogRead(A3);  
  line += ",";  
  line += digitalRead(2);  
  line += ",";  
  line += digitalRead(3);  
  line += ",";  
  line += digitalRead(4);  
  line += ",";  
  line += digitalRead(5);  
  line += ",";  
  line += digitalRead(6);  
  line += ",";  
  line += digitalRead(7);  
  line += ",";  
  line += digitalRead(8);  
  line += ",";  
  line += digitalRead(9);  
  line += ",";  
  line += digitalRead(10);  
  line += ",";  
  line += digitalRead(11);  
  line += ",";  
  line += digitalRead(A4);  
  line += ",";  
  line += digitalRead(A5);  
  Serial.println(line);  
  delay(10);  
 }  

Python Script:

 import pyvjoy, serial  
   
 controller = serial.Serial('COM4', 19200, timeout=5)  
 joystick = pyvjoy.VJoyDevice(1)  
 aileron, elevator, throttle, rudder = 512, 512, 512, 512  
 aileron_trim, elevator_trim, throttle_trim, rudder_trim = 0, 0, 0, 0  
 aileron_trim_left_clicked, elevator_trim_up_clicked, throttle_trim_up_clicked, rudder_trim_left_clicked = False, False, False, False  
 aileron_trim_right_clicked, elevator_trim_down_clicked, throttle_trim_down_clicked, rudder_trim_right_clicked = False, False, False, False  
   
 data = []  
 while len(data) != 16:  
   line = controller.readline().rstrip()  
   data = line.split(',')  
   
 while line:  
   vals = []  
   for text in data:  
     try:  
       val = int(text)  
     except:  
       val = 0  
     vals.append(val)  
   # - Throttle -  
   if vals[7] == 0:  
     if not throttle_trim_up_clicked:  
       throttle_trim += 10  
       throttle_trim_up_clicked = True  
   else:  
     throttle_trim_up_clicked = False  
   if vals[6] == 0:  
     if not throttle_trim_down_clicked:  
       throttle_trim -= 10  
       throttle_trim_down_clicked = True  
   else:  
     throttle_trim_down_clicked = False  
   # - Rudder -  
   if vals[4] == 0:  
     if not rudder_trim_left_clicked:  
       rudder_trim -= 10  
       rudder_trim_left_clicked = True  
   else:  
     rudder_trim_left_clicked = False  
   if vals[5] == 0:  
     if not rudder_trim_right_clicked:  
       rudder_trim += 10  
       rudder_trim_right_clicked = True  
   else:  
     rudder_trim_right_clicked = False  
   # - Aileron -  
   if vals[9] == 0:  
     if not aileron_trim_left_clicked:  
       aileron_trim -= 10  
       aileron_trim_left_clicked = True  
   else:  
     aileron_trim_left_clicked = False  
   if vals[8] == 0:  
     if not aileron_trim_right_clicked:  
       aileron_trim += 10  
       aileron_trim_right_clicked = True  
   else:  
     aileron_trim_right_clicked = False  
   # - Elevator -  
   if vals[11] == 0:  
     if not elevator_trim_up_clicked:  
       elevator_trim -= 10  
       elevator_trim_up_clicked = True  
   else:  
     elevator_trim_up_clicked = False  
   if vals[10] == 0:  
     if not elevator_trim_down_clicked:  
       elevator_trim += 10  
       elevator_trim_down_clicked = True  
   else:  
     elevator_trim_down_clicked = False  
   
   aileron = vals[0] + aileron_trim  
   elevator = vals[1] + elevator_trim  
   throttle = vals[3] + throttle_trim  
   rudder = vals[2] + rudder_trim  
   
   print('A=%s\tE=%s\tT=%s\tR=%s' % (aileron, elevator, throttle, rudder))  
   
   joystick.data.wAxisX = aileron * 32  
   joystick.data.wAxisY = elevator * 32  
   joystick.data.wAxisZ = throttle * 32  
   joystick.data.wAxisXRot = rudder * 32  
   buttons = (1 - vals[12]) + (1 - vals[13] << 1) + (1 - vals[14] << 2) + (1 - vals[15] << 3)  
   joystick.data.lButtons = buttons  
   joystick.update()  
   try:  
     line = controller.readline().rstrip()  
     data = line.split(',')  
   except:  
     line = ''  
   

Now, the transmitter, well the Arduino Nano, plugs via USB into the computer and the Python script can be run in a terminal window. The resolution and precision have greatly increased and flying became very precise. After several hours of "training", I went to a nearby field and gave my plane its maiden flight without crashing!