Once upon a time, a few years ago, I was on a mid-range FPV flight with my old Tricopter when I found myself churning back home in a stiff headwind.
I wasn't worried, though, I had plenty of juice left in the battery. I made my way back toward home while my spotter kept an eye on the craft.
"Why are you heading that way?" He asked.
Suddenly, the video got staticy. I jerked my head over from the video screen, but couldn't immediately spot the craft.
"Where am I?" I asked.
"You've gone behind the hill!" my spotter shouted in alarm.
My heart sank. A collection of sticks attached to a leaf-shaped body somewhere in at least 30 acres of sticks and leaves. The chances of finding it were slim. The GoPro, the ArduPilot, the copter itself--probably over $1000, all quite possibly lost.
When we crested the hill I regained telemetry from the Ardupilot and we managed to home in on it, then finally located it in the top of a spindly oak by pulsing the motors. Even knowing exactly where it was it was almost invisible against the backdrop of the canopy. I tried to shake it loose by spooling the motors up, but a THUD announced that the main flight battery had come loose.
If the battery had fallen out on impact with the treetop, we would never have regained that telemetry signal. We would never have even gotten close to finding the craft. From that moment, I started searching for a device that would help me find a lost model even if the whole rest of the craft was rendered inoperable in the crash.
I think I finally found it: The $50 tBeacon, from Konstantin Sbitnev.
The tBeacon Blue version, photo from tbeacon.org
The tBeacon lets you find a downed model (or virtually anything else) with nothing but a handheld walkie-talkie.
When attatched to a model and given a source of 5v, the tBeacon will charge an attached 1s LiPo. It will sit and passively listen to a preconfigured frequency until it hears a preconfigured tone. Alternately, you can set it up on a timer. Only once one of those conditions is met will it start broadcasting.
This is great, because it means that until it triggers, it will not create any radio interference, even in the UHF band in which it operates, so it's perfectly safe for use with an LRS.
When triggered, it broadcasts 3 ways to find it:
- An RSSI coefficient. Verbally announces how strongly it heard your signal on a scale of 0-99, with 99 being the strongest.
- A proximity beacon. Tones of descending pitch and descending power, the first being at 100mw, the second at 13mw, and the third at 1.3mw. The closer you are, the more of the tones you'll be able to hear.
- If connected to a source of telemetry (such as MAVLINK or Naza) or a GPS (such as a UBLOX or NMEA) it will vocally announce its last known GPS coordinates in a preconfigured format.
So that's the theory, but how well does it actually work?
Well, here's a video where we decided to find out by having my copilot hide my hexcopter with the beacon installed.
As you can see, we were able to find it pretty easily, even at some distance. The challenging part is when you get relatively close; If I didn't already have this one, I'd buy the "green" model for $10 more.
The tBeacon Green version, photo from tbeacon.org
It has a loud buzzer and flashing LED to help close in on it when you're too close for the radio to be of much help. As is, you can see in the video that I was able to further narrow it down by removing the antenna from my radio.
This beacon is clearly designed for amateur radio operators; the default settings are obviously aimed at users of 2-meter handsets (EDIT: WRONG. That should be 70cm. Thanks to Mostly Harmless for keeping me honest). If you're not a ham, there are ways to configure it to work with a standard off-the-shelf walkie-talkie, though it's technically illegal to use this device in such a way in the US, since it's not approved by the FCC for use on FRS/GMRS channels.
My only complaint was that it was a bit hard to tell the 2's from the 3's in some of the verbal transmissions, but this didn't end up inconveniencing me too much (EDIT: after further testing, it seems that the 2's are quite distinct but the 3's are a little ambiguous. In future, if I can't tell which it is, I'll just assume it's a 3). All in all, it's a fantastic piece of equipment, and worth every penny.
Thumbnail image from tbeacon.org