Howto:Build and run FlightGear on Raspberry Pi 4

From FlightGear wiki
Revision as of 20:46, 24 February 2020 by Puffergas (Talk | contribs) (Avare)

Jump to: navigation, search

Joysticks

You will find that controlling your aircraft, with the official Raspberry Pi keyboard and mouse, too be rather difficult. A joystick will solve this problem. The Logitech Extreme 3D PRO is plug and play, for the most part, with FlightGear. Most modern joysticks should also work. There is a dialog box to assign common joystick controls, in FlightGear. Controls are also properties, however that is for later. This joystick dialog box is found in the top menu bar under 'Files'. Next you will find 'Joystick Configuration' to click on and that will bring up the desired dialog box.

If the joystick’s travel is not being used efficiently or the neutral dead band is not right, the joystick can be calibrated. Install jstest-gtk through the Raspbian software installer or use the terminal and apt-get install command.

sudo apt-get install jstest-gtk

After running jstest-gtk click on your joystick within the jstest-gtk window. Next click on the 'Calibration' button. The calibration can be performed within this dialog box. Consider making note of these values before performing the calibration. Do not forget to cycle the hat switch that is on top of the stick. This is because this switch is considered as a proportional input just like the stick axis. In order to save these new settings, after a reboot or new power up, do not close jstest-gtk at this moment. First open a terminal and enter the below command in order to save the new calibration values. The 'device_name' of the joystick is in the first dialog box of jstest-gtk. It will be something like js0, js1 etc.

sudo jscal-store /dev/input/js0


Some or most Linux distributions will need more work to store these new calibration values, in the way of RULES. However, it seems that Raspbian doesn’t require anymore work.

The above calibration may not adjust for any center dead band. Notice that the calibration values are representing binary numbers in that the maximums are in power of two’s. Except where the maximum value is 1 or -1. It is common to see these values close to 512 or 1024. Consider the values below. To find the maximum value add the RangeMin to the RangeMax. For example; 0 + 1024 = 1024. Since this scheme starts with 0, not 1, 1022 or 510 might be the maximum value. The first pair of numbers, not considering the axis number, should add up to the maximum value.

Axis CenterMin CenterMax RangeMin RangeMax
0 511 511 0 1022
1 511 511 0 1022
2 127 127 0 254
3 127 127 0 254
4 0 0 -1 1
5 0 0 -1 1

In order to introduce a dead band consider the values below:

Axis CenterMin CenterMax RangeMin RangeMax
0 491 531 20 1002
1 491 531 20 1002
2 117 137 10 254
3 117 137 10 254
4 0 0 -1 1
5 0 0 -1 1

Or the values in the calibration dialog box screenshot, entitled "Joystick calibration using jstest-gtk dialog box".

Axis 4 and 5 are examples of the hat switch.

Joystick calibration using jstest-gtk dialog box.

Saitek Saitek Pro Flight Quadrant

This throttle quadrant is now produced by Logitech and works with FG and the Raspberry Pi4. If used with a single engine aircraft or a multi engine aircraft where the engines are controlled with one stick on the quadrant, this will be a plug and play setup. However, there will be a noticeable dead band in the middle of the travel. Furthermore, it is possible that all the usable stick travel is not utilized. Both of these issues can be addressed by calibrating the quadrant as in the joystick example above. Below is the calibration data before calibration and below that is the data after calibration. Notice that the center dead band is removed.

Axis CenterMin CenterMax RangeMin RangeMax
0 112 124 15 239
1 112 124 15 239
2 112 124 15 239

After calibration below:

Axis CenterMin CenterMax RangeMin RangeMax
0 127 127 0 255
1 127 127 0 255
2 127 127 0 255

If this quadrant is used with a multi engine aircraft and each engine throttle is controlled by a separate quadrant lever, the levers will only use half of its travel. In order to resolve this, the joystick configuration file will need a small edit. This file is located in homepi/.fgfs/Input, assuming your user name is ‘pi’. Notice that ‘.fgfs’ is a hidden folder in your Home folder. Only edit the joystick configuration files that are in your Home folder. Do not edit the files that are native to FlightGear. In this example we will be editing ‘Saitek-Saitek-Pro-Flight-Quadrant.xml’.

Let us assume that this configuration is for the twin engine DC-3 Dakota and axis-0 will be assigned to ALL engine mixture levers, axis-1 will be assigned to ‘Throttle Engine 0’ and axis-2 is assigned to ‘Throttle Engine 1’. Note that within this .XML configuration file that <axis> is another way to express <axis n=’0’>. The axis-0 doesn’t need the n=’0’. Find <axis n=’1’> and change the ‘offset’ from 0 to -1 also change ‘factor’ from 1 to -0.5. Do the same for <axis n='2'>.

  <axis>
    <desc type="string">Mixture All Engines</desc>
    <binding>
      <command type="string">property-scale</command>
      <property type="string">/controls/engines/mixture-all</property>
      <factor type="double">1</factor>
      <offset type="double">0</offset>
    </binding>
  </axis>
  <axis n="1">
    <desc type="string">Throttle Engine 0</desc>
    <binding>
      <command type="string">property-scale</command>
      <property type="string">/controls/engines/engine[0]/throttle</property>
      <offset type="double">-1.0</offset>
      <factor type="double">-0.5</factor>
    </binding>
  </axis>
  <axis n="2">
    <desc type="string">Throttle Engine 1</desc>
    <binding>
      <command type="string">property-scale</command>
      <property type="string">/controls/engines/engine[1]/throttle</property>
      <offset type="double">-1.0</offset>
      <factor type="double">-0.5</factor>
    </binding>
  </axis>

Thrustmaster Flight Rudder Pedals

There could be two adjustments needed for these rudder pedals. The toe brakes are reversed and delete the toe brake center dead band. Use the same method to delete the dead band as in the above throttle quadrant. Do not delete the dead band for the rudder unless that is what you want to do. Below is a calibration data example:

Axis CenterMin CenterMax RangeMin RangeMax
0 511 511 0 1022
1 511 511 0 1022
2 448 574 63 959

Reversing the toe brake direction in FlightGear, using it's joystick dialog box, does't work. The easiest method is to reverse them using jstest-gtk and check the invert box for axes 0 and axes 1.

Depending on the version of FlightGear, there could be a bug where one of the toe brakes do not show up in the FlightGear joystick dialog box. If so this is easy to edit in the configuration file. It might also be beneficial to delete controls that are not part of this rudder pedal so not to produce any conflicts. See below:

  <name type="string">Thrustmaster T-Rudder</name>
  <axis>
    <desc type="string">Brake Right</desc>
    <binding>
      <command type="string">property-scale</command>
      <property type="string">/controls/gear/brake-right</property>
      <factor type="double">0.5</factor>
      <offset type="double">1</offset>
    </binding>
  </axis>
  <axis n="1">
    <desc type="string">Brake Left</desc>
    <binding>
      <command type="string">property-scale</command>
      <property type="string">/controls/gear/brake-left</property>
      <factor type="double">0.5</factor>
      <offset type="double">1</offset>
    </binding>
  </axis>
  <axis n="2">
    <desc type="string">Rudder</desc>
    <binding>
      <command type="string">property-scale</command>
      <property type="string">/controls/flight/rudder</property>
      <factor type="double">1</factor>
      <offset type="double">0</offset>
    </binding>
  </axis>

Compiling

Performance settings

Interfacing

Expanding the flight simulator system beyond the primary Raspberry Pi4, that is running FlightGear, is one way to increase the computing power of such a small computer.

Avare

Avare is a free aviation app, with no ads, that works well with FlightGear. It is an app that is used by many pilots. It will provide a moving map of the FlightGear aircraft, using all FAA charts and a lot more. These charts are for the USA, however some of these FAA Charts cover Puerto Rico, plus parts of Canada, Mexico and the Caribbean. For other parts of the world, there are other apps that might work. Avare can be downloaded from Google Play Store. A tablet is a good choice for running this app.

FlightGear and Avare are easy to bind together. Along with the main Avare app, the I/O app will also need to be installed on the tablet. This app is ‘Avare External I/O Plugin’. The scheme is that the Raspberry Pi4 and FlightGear will become the GPS signal used by the Avare app, this position is transferred via WiFi. So, the tablets internal GPS needs to be OFF. Avare will always prompt you to turn ON the internal GPS, so when asked to ‘Turn On GPS’, choose ‘No’. In ‘Preferances’ the GPS position source can and should be set to ‘Avare IO Module Only’, however the prompt to turn ON the internal GPS will still pop up when starting the app.

The below command tells FlightGear what to connect to and it's protocol. This can be placed in the GFly type programs or if in Terminal, place the command after fgfs. The address, 192.168.??.?, needs to be the address of the tablet running Avare. Some home networks will randomly choose an address, hence this could change. It will be displayed in the IO app. The number 49002 needs to be the same number that is in the Avare IO app. Use the Xplane option.

--generic=socket,out,2,192.168.??.??,49002,udp,avare

After FlightGear has started with the above command, open the Avare External I/O Plugin app. Choose the Xplane option and then tap on ‘Listen’. There should be lines of communication being displayed after ‘Listen’ is enabled. Leave this running and now open the main Avare app. Do not choose to use the internal GPS. Now your FlightGear aircraft placement should be displayed on the FAA map of choice.

Phi & 7" Touch Screen

Avare connected to the Raspberry Pi4 and FlightGear. Avare is a moving aviation chart app.

Cooling

The video core GPU temperature can be read with the use of the terminal and the below command:

vcgencmd measure_temp

The Raspberry Pi4 starts to throttle, reduce frequency, with temperatures over 85c. When flying the DC-3 Dakota at a steady cruse altitude, in a low scenery dense area, the core temperature was reported to be ~75c. This was with ambient temperature of ~24c. The temperature rapidly dropped to ~45c when the cooling fan was energized. There was no heat sink installed for this test. FlightGear was running in fullscreen mode on monitor 1 and terminal was running on monitor 2. Screen resolution was possibly 1024 x 768.

The fan in the photo is a Noctua NF-A4x10 5V. It is installed with two rubber bands forming an X. Then the fan is simply sandwiched in the middle of the X. The ends of the rubber bands are looped over the ends of the four standoffs. The rubber bands, in addition to holding the fan, help to isolate vibrational noise. In this setup the fan was powered by an orphaned cell phone charger.

Noctua cooling fan used to cool the Raspberry Pi4 while running FlightGear.