Content
RC-Link and Telemetry
People say RFD900x is good so we are going with that. The RFD900x will handle both telemetry and RC-link.
We can use a USB to FDTI cable to connect and power the RFD900x from the PC, however to avoid brownouts, we might want to consider using an external power source. (To power off USB, a jumper is needed to connect pins 4 and 6)
(see the RFD900x hardware docs on how to wire up the USB to FDTI cable)
The default serial port settings are as follow:
57600 baud, no parity, 8 data bits, 1 stop bit
We can then communicate with the RFD900x via a COM port? via UART
Configuration
To configure the RFD900x, either use the RFD900 Tools GUI, or more likely, AT Commands.
The sequence “+++” without quotes can be used in a serial terminal connected to the radio to enter AT command mode, and the “ATO” command will exit the mode.
For more information on AT commands see section 4.2 of RFD900x software docs
For an example of using the RFD900x using python see this repo
Connection
Assuming P2P connection between the ground station and the drone RFD900x
Assuming default baud rate of 57600 (not sure if this is good)
2 nodes who have compatible parameters and are within range should sync automatically, a solid green LED indicates success. This should be good enough for testing for now.
For better stability, set network ID to the same number on both nodes using the ATS3=X command to set the network ID to X [0,255]. Make sure to save configs using AT&W and then reboot modem ATZ
To communicate, exit AT Command mode and send information through serial.
In python, simply open a serial communication on the appropriate COM port.
Relevant Resources
Tracking Antenna
A directional antenna would be combined with 2 servos, controlling its pan(yaw) and tilt(pitch).
The antenna would have a GPS chip on board in a fixed location relative to the antenna. The distance and offset would be measured and inputted on the ground staiton, and sent to the Nucleo.
During operation, ground station would stream the GPS position of the drone to the tracking antenna system. From there, simple trigonometry can be applied to find the correct pan and tilt.
Note for self: earth is round
Questions to be answered/Discussion needed
The tracking system is currently open-loop, as there is currently no way of knowing how much and which direction the antenna is off by.
Plans of adding a camera to the tracking antenna have been proposed for monitoring its performance visually in ground station. Would it be possible for the ground station to also perform some simple CV on it and track and drone visually, then send this information back to the Nucleo?
GPS tracking can be used as a fallback in this case.
How effective is tracking antenna signal wise when there is no light of sight?
How to avoid gimble lock when the tilt angle of the antenna approaches 90. Would this even be of concern (will drone fly over the ground station, or will it stay in a fixed direction) and would it be worth the extra mechanical design considerations.
References
A Portable UAV Tracking System for Communications and Video Transmission (researchgate.net)
Other
RC-Links:
dragonlink, either 433 or 915 http://www.fpvpro.com/dragon-link-complete-systems
crossfire, 915, either the full version or a nano or micro version https://www.team-blacksheep.com/products/prod:xf_nanotx_startset
Telemetry:
dragonlink, crossfire, rfd900x
Xbees
Video:
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