Joystick RC with Spektrum DXe transmitter

Overview

This article shows how a Spectrum DXe remote control transmitter can be used with the help of a USB2PPM adapter and a notebook to fly a quadcopter with a joystick. This application is particularly interesting in that it allows you to check the almost delay-free command processing.

The project includes the following steps:

  • Preparation of the remote control transmitter
  • Building of the USB2PPM Adapter
  • Download the Joystick2PPM program
  • Settings and commissioning

In addition to the remote control transmitter, PC or notebook with Windows 10, USB2PPM adapter and joystick, a trainer cable is required to connect the remote control transmitter to the USB2PMM as well as a USB cable.

Preparation of the remote control transmitter

The spectrum DXe remote control transmitter is controlled by the teacher/student jack on the back of the transmitter. An external PPM signal can be fed into this jack – usually from a second transmitter, the student transmitter. The jack is a 3.5 mm standard jack and the cable connection is made via a corresponding mono-aux cable.

In order for the teacher to be able to take control quickly at any time, the student’s signal is only transmitted as long as the teacher pushes the bind / panic button. This practical implementation of the teacher-student operation naturally makes it difficult to take over the transmitter permanently, since you probably cannot or do not want to manually push the button down while flying.

Therefore, I have installed an additional switch in my Spectrum DXe in order to be able to permanently switch the remote control transmitter to student operation. Although the installation is simple, you should only consider it if you accept the likely loss of the warranty.

Installation of the additional switch for permanent student operation

The housing is opened as described in the manual. In the back half of the transmitter housing there is already a hole at the ideal position, which is covered from the outside by a sticker (see red arrow in the picture).

Expose the hole and insert the additional switch (see details).

The wiring is done in such a way that the Bind/Panik/Trainerbutton is shunted (see picture). For this purpose, a short piece of wire is soldered to the small printed circuit board.

I then attached a small arrow on the outside so that I always know in which mode the transmitter would be currently (see picture).

Building of the USB2PPM Adapter

The USB2PPM is built according to the construction instructions, but the last step (soldering the three-pole PIN header for the PPM signal) is omitted. Instead, a 3.5 mm jack is placed in the experimental field of the printed circuit board (see picture) to connect to the Spectrum DXe.

Adaption USB2PPM for Spektrum DXe

With this, all hardware bits and pieces for setting up the remote control are ready.

Download the Joystick2PPM program

The Joystick2PPM program takes over the evaluation of the joystick positions and the conversion into corresponding commands to the USB2PPM. This in turn generates the PPM pulse frame as an input signal for the remote control transmitter.

The Joystick2PPM program is open source and can be downloaded from the USB2PPM controller page. It is a Java program that only needs to be unzipped; an installation is not required. However, in some cases, the Java runtime may still need to be installed.

Settings and commissioning

Now connect the USB2PPM adapter and joystick to your PC. When connected for the first time, Windows 10 will automatically install drivers and associate the adapter with a COM port. After completing the driver installation, start the program Joystick2PPM by calling the Start-Windows Batch File (start x64.bat for a 64 bit system or start x86.bat at 32 bit).

Next, you would configure the joystick and assign channels of the remote control to the individual controls. To do this, switch to the tab labeled with the designator of your joystick.

First, you would assign “Throttle” to the “Slider”. To do this, click on the “+ button” in front of “Slider” and a selection window will pop up. Please confirm the assignment.

The assignment of the other channels is then analogous by selecting the + button. In my case, I placed the Y axis on channel 2, the X axis on channel 3, and the rotation on channel 4.

Select the COM port of the USB2PMM under “Port Settings” and click on the “Connect” button. If you still have the command window open, you will see the commands that are transmitted cyclically to the USB2PPM adapter.

Now turn on your transmitter and make sure that the transmitter is “paired” with the remote control model (trainer switch to “off”). Now, without turning off the remote control transmitter, connect the USB2PPM adapter using the training cable with the remote control transmitter. After turning on the trainer switch, you can remotely control your model with the joystick. If necessary, you can perform the trimming for the individual channels and a possible servo direction reversal on the PC.