Practical info on transmit and receive signals - controller to drone and drone to controller

garthkh

garthkh

Member
Please explain to me (or point me to a practical link) the transmit/receive sequence between a controller in ones hand and a drone. Hopefully with good explanatory pictures.
My budget drone is a $300 5G FPV with a 2.4GHz controller frequency for the basic hand controller. There is no display on the controller - only some lights. The Phone App, I presume, controls the drone via the 5G link (or not?). My drone is a Kai One Max and has 3 antennas - I stripped it right down to see what's inside and done a few mods.
I am an ex Radio Ham and I'm trying to figure out the TX/RX links in the controls. When I connect the hand controller to the drone there is a delay before flight until the drone tells the controller that it has found 8 satellites. A light comes on on the controller. So some telemetry has been received by the controller via the 2.4GHz link. Also, if I flyout of range, the controller is notified that the drone is now in RTH mode. Therefore there is a receiver in the controller. Does this receiver share the same single antenna?
The Phone App can also control the drone without the use of the basic hand controller and the phone App controls the drone, receives video and images from the onboard camera , AND it receives telemetry regarding the satellites, distance, height, etc . The drone's wifi board for the 5.8GHz signals use two antennas. Is one TX and the other RX?
So my question is actually twofold -
1. How the TX/RX signals share a single antenna on the hand controller.
2. Is it possible to enhance my hand controller with some form of telemetry board and display to show the same as I'm getting on the phone App display? IE. the battery status, compass, satellites, height, distance. I have already modified the controller and the drone to improve the antennas, and have doubled the flight and video range. I'd like to try and add this extension if possible.

These images are of the telemetry display on the top of the phone App display and the antenna tests I've been trying out. The cloverleaf is definitely the best and two 5.8GHz cloverleaf addon's on the drone for improved video.
 

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So I don't know what specific tx and Rx you're using but can search for the source code and hardware specs for elrs since is all open source transmitter and receiver and includes telemetry. Tbh I don't know the details but just imagined it is using the same antenna for some sort of bidirectional communication, believe elrs is in some ways derivative from LoRa long range radio protocol but again details of that beyond be except that it exists :D (is low bandwidth and long range, elrs let's you trade off refresh rate for range broadly).

On my transmitter (a tx16s) I am running opentx software also open source and used their configuration tool to flash it and then transfer lua script over for configuring the elrs module speed and power from the tx itself so can adjust on the fly. Elrs and opentx both take a while to understand but do offer the telemetry and a lot of other features and customization.
 
Hi Wafflejock. We chatted a while back re backing up drone software.
This drone and controller are proprietry so there's no info or software available. Chinese budget drone. Best I can do is to show the chip codes on the circuit boards.
 
Hiya yup so unfortunately there's like a hundred different wireless protocols used and which a given manufacturer decided to go with or "clone" or if they just made up their own protocol for the wireless transmission is basically up in the air (pun unintended :D). A few of the more popular wireless protocols for quads are DSMX (Spektrum radios) which is a derivative of a Navy developed wireless protocol or there is FrSky I believe "invented"/defined by Taranis, CrossFire protocol from Team Black Sheep TBS is also a popular one. That said again it could be "Traxxas protocol" or "Futaba Protocol" or any number of other TX/RX wireless protocols being used so there isn't really a standard there. Between the receiver board itself and the "main board" of a TX or FC on a quad they are typically using SBUS for the line/wire level protocol so it's a bit more "standardized" there but again could be basically any kind of protocols used between boards.

Most of the GPS modules I've encountered use UART for communication of the GPS data so it's possible could tap into that UART data and log the info coming out of the GPS module directly but would need some decoding (I want to say the GPS data on UART lines is one of two popular protocols NMEA or UBLOX.

Oscar Liang's site is always helpful for these kinds of edge casey things he covers ELRS pretty in depth as well:
oscarliang.com

How to Setup GPS Rescue in Betaflight (FPV Drone Return to Home) - Oscar Liang

Learn how to setup Betaflight GPS Rescue mode, help your FPV drone return to home in failsafe. Sharing tips on optimizing reliability and accuracy.
oscarliang.com oscarliang.com
 
wafflejock said:
Hiya yup so unfortunately there's like a hundred different wireless protocols used and which a given manufacturer decided to go with or "clone" or if they just made up their own protocol for the wireless transmission is basically up in the air (pun unintended :D). A few of the more popular wireless protocols for quads are DSMX (Spektrum radios) which is a derivative of a Navy developed wireless protocol or there is FrSky I believe "invented"/defined by Taranis, CrossFire protocol from Team Black Sheep TBS is also a popular one. That said again it could be "Traxxas protocol" or "Futaba Protocol" or any number of other TX/RX wireless protocols being used so there isn't really a standard there. Between the receiver board itself and the "main board" of a TX or FC on a quad they are typically using SBUS for the line/wire level protocol so it's a bit more "standardized" there but again could be basically any kind of protocols used between boards.

Most of the GPS modules I've encountered use UART for communication of the GPS data so it's possible could tap into that UART data and log the info coming out of the GPS module directly but would need some decoding (I want to say the GPS data on UART lines is one of two popular protocols NMEA or UBLOX.

Oscar Liang's site is always helpful for these kinds of edge casey things he covers ELRS pretty in depth as well:
oscarliang.com

How to Setup GPS Rescue in Betaflight (FPV Drone Return to Home) - Oscar Liang

Learn how to setup Betaflight GPS Rescue mode, help your FPV drone return to home in failsafe. Sharing tips on optimizing reliability and accuracy.
oscarliang.com oscarliang.com
Click to expand...
Ok thanks. I'm not wanting to dig into the protocol so much as to know how they are using a single antenna for TX and RX. I wonder if the data streams are more like packet radio and TCP/IP which I used to experiment with in my HAM days, where there is a send and receive of packets of data on the single channel.- switching from one to the other,
I think these machines are based on what DJI are doing it seems. They feature quite a lot of their AI functionality. So I guess they do use UARTs. There is certainly no detail given by these manufacturers of component boards, the codes and protocols they use.
 
Gotcha yah I've wondered on and off what kind of black magic is used to achieve the telemetry data being sent back to the tx, but tbh I don't use the info much beyond knowing if it is getting good signal or not the rest of the info I want to know I just add to the on screen display/osd so shows up in my goggle view but in that case no real mystery since using the vtx ;)
 
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