Finding a lost model via RSSI?

[wbortz]

I'm new to this stuff, but I haven't found this via googling, so I though I'd ask here.

I built a Mugi a few months ago, brushless and with an old Parkzone TX/RX set, and while it flew, it was pretty hard to control. Very tough though - the first 10 flights were all heavy impacts, and the 11'th I lost it way downwind in the jungle. Found it with the help of a theodolite app and a lot of luck, but since then I added a little lost model alarm beeper, which really helps here - in 8 foot cane grass, you can't see a model a meter away.

I've since picked up a 9XR with FrSky module, put openTX on it, and wow - my flying immediately improved! Thanks very much to all the open source authors! Amazing how much smoother the model flies with a solid control system.

Now that I have telemetry running, it occurred to me that with a directional patch antenna, I should be able to wave the transmitter around and get some sort of directional indication of a lost model, assuming the RX survived. If nothing else, I should be able to do a grid search pattern like when using an avalanche tranciever to search for buried skiiers.

Has anyone tried this? With a smartphone mounted on the TX and receiving telemetry, I could even plot approximate vectors on a map using the GPS, compass and gyros of the phone. Overkill, but at the rate I loose planes, it would be cool.

Here's a shot from the theodolite app of where my plane went down. I wandered through the jungle along that approximate line and eventually stumbled into the plane, but I got very lucky. I hear lots of stories of 100" planes lost in the grass in this spot.

last known position of Mugi

Wade

[Kilrah]

Yes I have used that approach once and it worked pretty well just looking at the RSSI bars on the radio in openTx.

[lebenj]

with another telemetry system (Hott from Graupner), i saw a guy finding is model.
it was during a glider contest. The model fall behind a small forest, inside a corn field.... nobody was thinkink he could get his glider back....
But the guy did it, quite quickly and with regular antenna.... just looking the RSSI on the TX screen, and playing with the antenna orientacion.
inside the corn field, he could ear the servos moving....

[Flaps 30]

Finding a model using the RSSI signal makes sense. This is very much like Fox hunt that is done by radio hams. You can use the normal aerial on your transmitter to search out the model. Just use the end of it as a pointer. Minimum signal=Model direction. The side of the aerial will show a maximum in the direction of the model.

Fitting a patch antenna for direction finding is good.. Even better would be something like an eight element yagi or helical aerial.

You may have to do some triangulation to work out where the model is as you get closer to it.

My models have a lost model alarm fitted which does help and has saved one of my models from being a total lose when it landed in thick undergrowth. The fault was with an aileron servo that caused it to go Earthwards.

I wonder how many of you put your address and/or phone number in/on your models? Long time back it was a normal thing to do.

[ShowMaster]

Address, name, what and risk a liability lawsuit?
My plane I just recovered from a golf course lost its lipo at 250 ft when I did a tight outside loop. The canopy and lipo went in one direction and the plane now tail heavy and no control drifted with the prevailing winds. Total round trip in 97 deg Wx was 1 mile, 2 6ft fences, and a large water filled wash.
I had to put up with bugs and worse yet, laughing golfers!
None of the onboard electronics had power but" I had my contact info in it". The new lipo and canopy did not.
I'm now in the process of fabricating a new foam canopy for a V1 SkySurfer since only v4 parts are in stock now.
I'm sure someone looking for their plane will find my battery and canopy but sadly no name on them.
Next time they'll all have contact info on them. This is my faithful er9x mods test plane and so far in 2 years the only crashes have NOT been related to the 5 different moded 9x systems tested in it.

I do have a lost plane alarm and I'm thinking of powering it with it's own 2c small lipo that is charged through a diode when the BEC is powered. This will require a ganged switch or 1 for the alarm power. Remembering to turn it on is a new worry.

I do have the Frsky GPS for but not a smart phone or portable GPS for tracking the last known position. In this case it wouldn't have helped.
So any good ideas on powering an onboard alarm that can work if main power fails and an easy way to charge it and have it power on with the BEC?
Anyone have a spare SkySurfer V1 canopy ha ha!
I need a good piece of elapor foam so I'll have to check the fields trash cans after this weekends flying. Always a good source of new foam parts on a Sunday afternoon.
SM


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[wbortz]

Finding a model using the RSSI signal makes sense. This is very much like Fox hunt that is done by radio hams. You can use the normal aerial on your transmitter to search out the model. Just use the end of it as a pointer. Minimum signal=Model direction. The side of the aerial will show a maximum in the direction of the model.

Hah - I hadn't thought of using the minimum RSSI of a normal quarter wave whip antenna - that's great, as I don't need any extra gear hanging off my TX. Might have to try a fox hunt in the yard to practice.

Keeping the battery and RX connected will be the key though. So far so good - even had a crash where the coils came right off the motor, but didn't loose my battery-esc-RX connection. Crashing less will also be good.

Edit - works great! Was flying the new Alula in 25 mph + - got blown over the back of the hill, needed more ballast. Even out of sight (but not far out of sight) behind the sand dune, I could pinpoint the direction using the point the whip trick. Easy to get within audible range of the beeper! I was also tickled that my TX started beeping warnings at me as I lost signal due to crashing behind the dune; I could tell that the model was in trouble, but it was nice to have the little reminder from the TX. The openTX, 9XR and FrSky setup is amazing!

Wade

[ShowMaster]

For tall bushes a 50 ohm resistor on a connector screwed on in place of an antenna will really reduce the range.
That or hold the tx against your chest and cradle it to absorb the rf and just turn your body. Again, the RX must have power.


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[jhsa]

Just put it in range test mode I think it recduces the range by about 30 times..

João

[Flaps 30]

That is true João. Holding the TX close to your body (horizontally) is important as your body effectively blocks signals from behind you. If the model happens to be in a tree, then as you get closer to it, you will find that the weak signal will occur when you tilt upwards.

Yup - The 50 Ohm trick is one that is used often in Fox hunts when you are close in. But the range test mode would do the same.

I wonder if you can train a gun dog to find your model as it falls out of the sky?

[tedbmoss]

I "lost" a model about 700 feet off the end of the runway. I could get a line on it with the standard 5 db antenna but could not locate it when I got close because it was not directional emough. We kept walking past the plane. I went to Fry's electronics store and bought a corner reflector and came back and found it in 5 minutes. The guys with me were impressed by the ease of locating the plane with the corner reflector, the signal just cuts off at the edges, giving a very narrow line even close to the plane.

[Kilrah]

When you're close you can switch the radio to range check mode, and work only on distance rather than trying to find the direction with the antenna