Howto:Build and run FlightGear on Raspberry Pi 4

From FlightGear wiki
Revision as of 20:15, 20 February 2020 by Puffergas (talk | contribs) (→‎Joysticks)
Jump to navigation Jump to 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’.

Compiling

Performance settings

Interfacing