Quick Answer
ELRS telemetry sends data back from your drone to your radio. You can see battery voltage, link quality and signal strength while you fly. You turn it on with a telemetry ratio, then let EdgeTX find your sensors. Once it works, you can add voice alerts that warn you before your battery gets too low.
What Telemetry Actually Shows You
A normal FPV control link only sends data one way. It goes from your radio to the drone. Telemetry adds a small return path. Now the drone can send data back too. This data shows up as numbers on your radio screen. Some of it can also show in your goggles, in the on-screen display.
The three most useful telemetry values are:
- LQ (Link Quality): a percent that shows how many packets your receiver is actually getting. 100% means a perfect link. If LQ starts to drop, your drone is losing connection. This often happens from distance or interference.
- RSSI (Received Signal Strength Indicator): a number, in decibels, for how strong the incoming signal is. Numbers closer to zero mean a stronger signal.
- Battery voltage: the live voltage of your flight battery. This tells you how much flight time is left.
Some setups also show current draw, GPS position, and warnings from your flight controller. This depends on which sensors your drone reports.
Setting the Telemetry Ratio
The telemetry ratio sets how often the drone sends data back, compared to how often your radio sends control data out. You find this setting in your radio's ELRS menu. It is often written as a ratio, like 1:2 or 1:128.
A ratio like 1:2 sends telemetry often. Your readings stay fresh, but it uses more of the link's bandwidth. A ratio like 1:128 sends telemetry rarely. This saves bandwidth for control commands, which can help range on long flights.
For normal freestyle and racing, a middle setting works well. For long-range flights, pick a higher ratio number so control data gets priority. If you are not sure, keep the default ratio. Only change it if you see lag, or if you need more range.
Discovering Sensors in EdgeTX
EdgeTX is the free, open-source software on most modern FPV radios, including most RadioMaster models. To see telemetry values, EdgeTX first needs to find what sensors your flight controller reports.
Here is the general process:
- Power on your drone and bind it to your radio.
- Go to the Telemetry screen in your radio's menu.
- Choose the option to discover new sensors. This is often called "Discover."
- Wait a few seconds while your radio lists each value it finds, such as RxBatt, RSSI, and Curr.
- Save the sensor list once discovery finishes.
If no sensors appear, check that telemetry is turned on in your flight controller's software. Some default setups turn it off. Also check your receiver's firmware version. Very old firmware may need an update first.
Building a Telemetry Screen
Once EdgeTX finds your sensors, you can build a custom screen to show them while you fly. Most radios let you place small widgets on screen. These can show numbers, bars, or simple graphs.
A good layout shows battery voltage in large text at the top. Add link quality as a bar or percent, with RSSI as a smaller number nearby. Keep the screen simple. Too many numbers can pull your focus away from your goggles.
Setting Up Voice Alerts
Voice alerts are spoken warnings your radio plays through its speaker as you fly. You do not need to look down at a screen to hear them. This is one of the most useful things telemetry adds, especially for battery voltage.
To set one up in EdgeTX:
- Go to the Special Functions or Logical Switches menu. The exact name depends on your radio.
- Create a logical switch that triggers when battery voltage drops below a chosen number, such as 3.5 volts per cell.
- Attach a special function to that switch. Set it to play a sound or a spoken phrase.
- Test it on the bench. Lower the trigger for a moment, or use a part-drained battery, to check the alert plays.
Many pilots set up two alerts. An early warning at a moderate voltage tells you to head home. A second, more urgent alert at a lower voltage tells you to land now. This works the same on a small freestyle quad or on the kind of build in our guide to long-range FPV drones.
Common Telemetry Problems
If telemetry values freeze mid-flight, this often points to a weak link or a loose wire on the telemetry pin. Check your solder joints if the problem keeps happening. Try a lower telemetry ratio if it only happens at long range.
If voltage readings look wrong, too low or too high, your flight controller may need its voltage scale set again in its own software. This is a separate setting from ELRS. You usually find it in the power or battery section of that software.