Make it beep, and make sure it still beeps without a battery
The cheapest locator is a plain buzzer on the flight controller. It has to be an active buzzer, one that makes its own tone when it gets power. Betaflight only switches the buzzer pin on and off, so buzzers that need an AC or PWM signal click or stay silent. Solder it to the pads usually marked BZ+ and BZ- (sometimes B+ and B-).
In Betaflight you then want two things:
- A switch. In the Modes tab add the BEEPER mode on a spare AUX channel. When you flip it, the buzzer sounds. If DShot beacon is set up (see below), the same switch makes the motors beep while the quad is disarmed.
- Automatic alarms. In the Configuration tab, under Beeper Configuration, keep RX_LOST enabled. It beeps when the receiver loses the link and repeats until the link comes back. RX_LOST_LANDING plays SOS when the link is lost during a failsafe landing.
Oscar Liang says a buzzer works best once you are already near the quad, within something like 50 metres. The real problem is that a hard crash often ejects the LiPo, and then the buzzer has no power at all.
A self-powered buzzer fixes that. It has its own small battery that charges while the quad is powered, and it starts sounding when the main power disappears. Depending on the model it keeps going for many hours or even days. These usually have three wires. Oscar's wiring is GND to GND, 5V to B+ and B- to B-; the extra ground wire is what charges the internal battery. Betaflight setup is the same as for a plain buzzer. For long range builds Oscar calls it one of the best cheap recovery upgrades. Standalone beacons with a motion sensor also exist and need no wiring, but you have to charge them and remember to switch them on before every flight.
Test the beeper with the switch before each session. A buzzer with a cracked solder joint is only weight.
DShot beacon: the motors as a beeper
If there is no room for a buzzer, as on a tiny whoop, the ESCs can make the motors beep. This needs a DShot ESC protocol, which Bluejay, AM32, BLHeli_S and BLHeli_32 all support. In the Configuration tab, under DShot Beacon Configuration, enable RX_LOST (beep after link loss), RX_SET (beep when the BEEPER switch is on) or both, and pick one of the five tones. The beacon never runs while the quad is armed.
It is much quieter than a buzzer. Oscar says you need to be within a few metres. Running it loud for a long time can also overheat the motors and ESC. In BLHeliSuite the Beacon Strength default is 80 on a 1-255 scale and Oscar suggests not going above about 120. The Beacon Delay setting (10 minutes by default) starts the beeping on its own after the quad sits idle, which helps when you cannot reach it from the radio.
Record where it was: GPS coordinates and DVR
A GPS module helps even when GPS Rescue fails, because the last known position survives the crash. There are three places to read it:
- The telemetry screen on the radio. It works, but often shows only a few decimals.
- The OSD. Add the GPS latitude and longitude elements (
GPS LATandGPS LON) and read them back from the goggle recording. - A telemetry log on the radio's SD card. In EdgeTX, run "Discover new sensors" on the telemetry page with the quad powered so the GPS sensors appear. Then add a Special Function "SD Logs" with a switch: the arm switch, "ON", or "TELE", which logs whenever telemetry is coming in. For GPS, Oscar suggests an interval of 0.5 to 2 seconds. The CSV files go into the Logs folder on the SD card.
Paste the last coordinates into Google Maps or any map app. If you also take a point from a few seconds earlier, the line between the two shows the direction of travel. Telemetry is not instant, and a quad that was flying fast or already losing the link may lie some distance from the last logged point. EdgeTX colour radios also include a GPS Model Locator app, which appears when the model has a GPS sensor and points you to the last known position with distance and heading.
Record DVR on every flight, ideally with automatic recording turned on in the goggles. Without GPS, the last seconds of video are often all you have. Look for landmarks, work out the direction you were flying and remember that a quad can keep tumbling for a long way after the first hit. Oscar says DVR was the only reason he recovered one quad that went into the sea.
Use the radio link as a direction finder
If the receiver still has power, the control link itself can lead you to the quad. EdgeTX ships a Lua script called "Model Locator (by RSSI)" in the Apps (Tools) menu. It reads the receiver's RSSI from telemetry, for example from ExpressLRS, shows a bar and beeps faster and higher as the signal improves.
The trick is transmitter power. At high power the RSSI stays strong everywhere and tells you nothing. The script itself asks for 25 mW with dynamic power off, and Oscar starts as low as 10 mW. If there is no signal at all, raise the power one step until the receiver reconnects, then lower it again as you get closer. Turn slowly on the spot, watch the bar, walk where it gets stronger and repeat.
The script's notes also describe a more precise method. Aim the antenna tip straight away from you and turn until the signal is at its weakest, not its strongest: that is the direction of the quad. Walk some distance sideways, take a second bearing the same way, and the quad is where the two lines cross.
Without the script, the RSSI value on the telemetry screen works the same way. A number closer to zero means a stronger signal, for example -30 dBm is stronger than -70 dBm. On analog video, goggles that show video RSSI do the same job with the VTX as the beacon, and a directional patch or helical antenna makes the direction much easier to judge.
AirTag and other independent trackers
An Apple AirTag runs on its own CR2032 cell, so it keeps working if the LiPo is gone. It weighs about 12 g, which is little on a 5- or 7-inch quad and a lot on a micro. It has no GPS or cellular radio of its own. Its location is reported only when a nearby Apple device picks it up through the Find My network. Near paths and towns that can work well. In a remote field, forest or on a mountain it may report nothing.
A label with a phone number under the frame costs nothing and can help if someone else finds the quad first.
A setup worth copying
Oscar's recommendation for an expensive long range quad is a self-powered buzzer, GPS Rescue, GPS coordinate logging on the radio and DVR on every flight. A beeper alone fails when the battery ejects. GPS logging stops when the power goes. RSSI only works while the receiver is powered and in range. DVR always survives, but only gives you a rough area. Combined, they cover each other's gaps.