Some time ago someone mentioned on a blog that he believes an OpenTX radio combined with a weatronic module would be the best RC radio. I really like OpenTX – because its features – and I created a redundant RC transmitter module which I believe can be even better than weatronic modules. Here we go. In this project I add my redundant RC transmitter module to my Radiomaster TX16S to create a superior communication link.
Hardware mods
To add my redundant RC transmitter module to TX16S was straightforward. I just attached the module in a piece of breadboard which was sized to fit into the external module bay (“project box” as they call it). I also attached a connector to connect my module to the TX16S pins in the module bay. My module communicates to TX16S via crossfire protocol. Note the SWD cables: the firmware is still under development.
I removed the standard antenna and created a new mount for my module antennas (two 2.4GHz ceramic patch antenna). I created this from a 7cm long carbon tube (D=10) and moulded a fiberglass stand which can hold the antennas. Note that I also mounted an SMA connector into the tube which is connected to the internal module of the TX16S. In this way I can still use the internal module if I attach an antenna there.
Firmware mods
I added crossfire communication protocol support into my module’s firmware. In order to use my module for a model I needed to change the Model Setup: switch Internal RF off and enable External RF with CRSF mode:
Note: the receiver number is not handled yet but will be used, so the module can be used for multiple models. To be honest I don’t really understand the RSSI value displayed by OpenTX I rather send the RSSI value calculated by the SX1280 which is a negative value. I also planned to repurpose the SNR (Signal To Noise) value of the Crossfire telemetry to send a calculated RSSI value similar to OpenTX RSSI. I just need to figure out the math. At the moment only the LinkStatistics is implemented, but it does not seem that difficult to implement the other telemetry values (vario, RX battery voltage, orientation, etc): it’s a perfect winter project, so stay tuned…
Conclusion
The concept works very well. I tested with the first 8 channels what the receiver handles currently. During the winter I will work on the following improvements in the firmware:
- Implement all telemetry data
- Use receiver number
- Experiment with Lora connection (implement something similar to Ghost)
- Implement/experiment faster frame rate (150Hz or 200Hz)
