Thursday, 9 April 2015

Taranis at La Muela. Or how RSSI found my models.

Just got back from the F3F competition at La Muela in Spain. It was the 20th Anniversary event, and Pierre Rondel won the event with a flawless demonstration of controlled aggressive flying. What was interesting is that Pierre was using a 'cheapo' FrSky Taranis, having recently switched over from JR after three years as a sponsored pilot.

I was also using my Taranis, and with the help of some particularly good lift was lucky enough to win the third round. This meant that two of the first three round winners were running open source operating systems. Who would have believed this likely even just two years ago?

Winner Pierre Rondel was using a Taranis

Using RSSI to find a lost model

While La Muela can produce fabulous thermal lift, it's also capable of humungous sink. As anyone who has landed out at La Muela will testify, retrieval can be somewhat time consuming and success is never a given. This time, two of my sport models (a Wildthing, and a Gladiator) fell victim.

La Muela is a BIG place to lose a model - red circle contains two full size humans (Kevin and Andrzej)!

Fortunately, both models were equipped with FrSky X4R receivers. These tiny units support telemetry of received signal strength (RSSI). This means that it's possible to get a bearing on the receiver simply by pointing the tx in the direction of the strongest reading. Well that was the theory!

Confronted with the prospect of several hours of possibly fruitless searching, I decided to try this method, without any particular expectation of success.


In the case of the Wildthing, the telemetry ceased when the model went down, and I feared that the battery had become disconnected from the impact. Nevertheless, I decided to carry the transmitter as I set off in search of my model.

I had been descending steeply for 15 minutes when - to my great surprise - the transmitter sounded a "telemetry signal critical" warning. The signal was weak, but hey, the model was alive! I carried on descending, taking a bearing every 20 meters or so, until I was finally reunited with the model. It was well hidden from the launch point, hence the initial loss of signal.

The Gladiator was the second model to go down. This time, there was no interruption in the telemetry. However, it took me a full hour of walking on rough ground to reach the model. Most of that time was spent retracing my steps, after the RSSI told that I was on the wrong side of a particularly deep and long ravine. Once on the correct path, the transmitter once again led me to the exact spot.

I had read of other fliers using RSSI  in this way, but was impressed by the effectiveness of this technique. Without it, those models might have remained where they landed.

Wildthing impact area, well hidden from launch point (iPhone 6 pano shot.)


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