Remember, this will ONLY work on the Runners if you have updated your firmware with the MultiWii 2.4 firmware upgrade. This is NOT a Walkera supported capability or firmware image.
I have selected the Taranis X4RSB receiver for this project because of it’s small form factor and mostly because it has the SBUS capability.
The challenge with the Futaba SBUS protocol and our flight controllers is that they have inverted the signals. For the non-technical, that means that when the voltage should be high, the flight controller is being sent a low signal. When it should be low, the flight controller is being sent a high signal. So in order for us to get proper communications between the Taranis receiver and the Runner flight controller and this will be common with pretty much every receiver that support SBUS and even with other manufacturers of receivers that support SBUS. There are two ways to achieve this capability and that is making a slight modification to the X4R receiver or inserting a signal inverter between the receiver and the flight controller.
First option is to modify the X4RSB receiver. This is pretty straight forward. If remove the X4RSB out of the paper jacket, you will see empty pin holes on the edge of the board as shown in the diagram. Simply solder a jumper wire that you can connect a Servo connector to that will be your SBUS signal that you can connect direct to your Runner flight controller signal pin. You will still need to connect Power and Ground to the receiver to power up the X4RSB.
The second option is to insert a SBUS inverter between the flight controller and the Taranis X4R. This will be the easiest way for most to get proper communications going but these little devices seem to be hard to purchase.
I ordered one and it appears to be on the slowest boat from Singapore so I ended up testing with the modification above and making my own inverter with the schematic diagram. It is just a few simple parts and some soldering to make it work. I will be honest with you, I fought with this for a while until I found out that I had my transistor orientation backwards. I guess it had been a few years since I had played with this level of electronics. Basically, if it is not working for you then check that orientation because it worked like a charm once I had double checked my transistor orientation. For the transistor, pretty much any bipolar NPN transistor will work. I used the NTE 287 because that is what the local electronics store had but I am sure the trusty old 2n2222 would work perfectly.
All that is left to make this Tranis XD9 Plus and X4RSB work on the Walkera Runner is to go into our MultiWii 2.4 code Config.h file and enable the SBUS. Simply search for the SBUS section and copy and paste the dsm2 orangex so that you can create a Walkera line. You will want to add the “//” comment line after AUX4 as we don’t want the additional processing time for channels that you don’t need. If you want to run more than the 8 channels, since SBUS carries 16, then you will need to use WIN GUI to get access to those extra channels. Once you have your SBUS line entered, simply test compile, and then push the new firmware down on the controller.
I still need to do a flight test, but it definitely was working on the bench!