I recently purchased a new RC plane from Ready Made RC, the Strix StratoSurfer model. It's what happens when I am sitting around the homestead during the winter months and need an RC project to work on. Since I wanted to set this up for FPV flying, I looked around for a suitable flight controller (FC). I wanted a FC that wasn't near its end of life and had good support from the open source community for the flight control software. Matek Systems recently released their new F765-Wing and I decided it warranted some further research. It was supported by both the iNAV and ArduPilot software platforms. From a hobbyist standpoint, it was higher-end FC and had plenty of processor power, memory, and more I/O ports than I could think about using. It had a reasonable footprint as far as a fixed wing controller was concerned and the majority of the I/O ports were on accessible from servo pin style connectors. And lastly, it had an onboard voltage management system with 4 different BECs and also voltage and current sensing. It could handle an 8S battery and it supported two cameras with a built-in video switcher.
I decided to try the iNAV software on the FC. As I began the task of learning iNAV and configuring the FC, I realized I wanted a wireless connection between my PC and the flight controller. It's well known that USB connectors are the weak-link component on a FC board and that was the motivation for the wireless connection. I also didn't wish to mess around with a USB cable when I was at the field and needed to make configuration changes to the FC. The first handful of flights will require adjustments and tweaks before getting everything dialed in....and I tripping over a cable seemed like the perfect way to rip that USB connector right off the board.
A Bluetooth wireless connection seemed like an inexpensive and logical wireless option. However, the necessary interface pins needed for Bluetooth connectivity were solder pads and NOT the convent servo pins I mentioned earlier. Why? I don't know, maybe the engineers ran out of space. I almost gave up the wireless idea because I really didn't want to solder on the FC board....not after soldering 72 pins along with the battery, ESC, and BEC wiring. Let's be honest here.....I'd not mucked up anything yet and I didn't want to push my luck any further than I already had.
Wait a second.....I have a brand new 915 Mhz telemetry radio sitting in a spare parts box. It was a backup radio for a quadcopter that finally met its final flight. Time to do some research on the net and see if this could be adapted for use on my particular FC and if so, what would I have to do for configuration support.
This clone of the very common 3DR telemetry radio came from RC Timer. As I write this article, they are selling them for $9 for the 2 radio kit. One of the radios plug directly into a regular USB port while the other is intended for the aircraft, using the supplied cable. This 915 Mhz radio, which when configured for maximum output, provides 100 mW of power running from a 5 volt supply. It is spread spectrum and seems to do a good job. As I mentioned, I had it on a quad and never lost telemetry flying it LOS.
With a power level significantly higher than any Bluetooth signal, I can keep an active link with the plane in the air beyond LOS distance. Given that I'll be starting my FPV adventures with 2.4 Ghz control, I'll loose control and failsafe back to the launch point before I run out of signal from this radio.
This photo and the previous one were screen clips from the iNAV Configurator software, which is used to setup and program the Matek F765 flight controller. These were taken with the FC and telemetry radio sitting outside and linked to my PC which was in the basement....hence the low RSSI and HDOP indications.
Here is a closeup of the radio plugged into my PC. The included antenna can swivel and bend 90 degrees which makes it very easy to plug into a laptop or desktop PC. With an OTG connection on your tablet or cell phone, you could manage the FC very easily out in the field.
Here is the aircraft radio module. The pins are labled on the back of the board. From top to bottom Red=Power, Yellow=TX, Green=RX, and Black=Ground. As you can see, there is no case for these radios. A piece of heat shrink insulates the module from shorting against something and I use either a ziptie or hook & loop material to keep it in place.
More Telemetry Radio
4x4 Off-Road Homestead Firearms RC Flying