Typhoon Relief Mission X8 lost due to RTL Fly-Away

Tridge,
As always your responses are detailed and candid, I really appreciate you taking the time to analyze these events.
We have a 1280mhz 800mw FPV Tx, but it far enough away from the GPS that it should not cause such extreme interference, I have used this configuration before with success. DragonLink is RX only. The only new RF is the RDF900 and that may be the issue since it is 1000mW and about 8" away from the GPS. I’m not sure why it would affect the gps lock the moment of takeoff in both instances.
The local crew reported a similar GPS fly away with their Sky Surfer in the same area last year, so perhaps there is interference on that band locally. It is very rural so I would think the noise floor would be low, however there is also no governmental oversight of the frequency bands, so who knows.
I see a lot of wisdom in implementing a GPS FS, and I hope to see that soon. For the Pixhawk, I would also like to have two GPS’s onboard and some algorithm that identifies a divergence between them, and allows the pilot to lock out the bad one. GPS units are so inexpensive these days, some aircraft could justify 3 GPS’s and the ability for the code to automatically lock out the one that doesn’t agree. Is there a way to measure distance to the GCS using telemetry packets, like DME? If so, it could be very useful for the Dead Reckoning code, and could provide a sanity check for the GPS data.

Thank you for fixing the bug, we will update to 2.77 and continue our work.

Mahalo!

[quote=“iskess”]We have a 1280mhz 800mw FPV Tx, but it far enough away from the GPS that it should not cause such extreme interference
[/quote]
I’d say that is your most likely source of interference. Analog FPV transmitters often put out a lot of unwanted signal well beyond the main transmission frequencies. They are not LIPD (low interference potential) devices, and instead just blanket a wide chunk of spectrum with a broadband signal.
I’d suggest you do some tests without the FPV transmitter

[quote]The only new RF is the RDF900 and that may be the issue since it is 1000mW and about 8" away from the GPS
[/quote]
The RFD900 is a 900MHz LIPD device. It is quite high power, but is narrow band. If you suspect it is a problem then you can lower its transmit power and it will still get you much more range than a 3DR radio as it has a 20dB low noise amplifier as well.

That also puzzles me. I’d do some tests to see if your ESC or motor may be emitting too much signal in the 1.5GHz band that the GPS uses. Is either your ESC or motor very close to the GPS?
On my X8 I put the GPS right out on the wing, cut into the foam to minimise drag (just make yourself a longer cable).

yep, I have some test code running for dual-GPS already. I just need a bit of time to clean it up for release.

Interesting idea! I don’t think it would work with the Si1000 on the 3DR radio or RFD900 as its timing probably isn’t accurate enough, but it may work with some other radio types in the future.
Cheers, Tridge

tridge posed in the other topic, so closing this one

Thank you Michael.

Aloha,

I wanted to write and thank everyone for helping out with the issues we had with out X8. Thank you Tridge for the quick response and info. I am grateful.

Many Mahalos!!

Chuck