Litchi signal loss question

Emil Cost · Jul 7, 2016

Hi all, This is a great forum. I have a question that I can't seem to find the answer for, so I am going to reach out to you guys and probably get the answer right away. Here is my question about Litchi signal loss:

The two signal strength indicators on the top of the app are the uplink and downlink. When you get the lost signal message the downlink bars go red. The downlink strength bars make sense because the RC is measuring incoming signal strength from the Phantom. When you lose signal, does this only apply to the downlink video feed to your tablet? Can you still send commands to the Phantom, such as return to home? How can the uplink indicator measure anything if there is no downlink signal to hand shake with? My big questions is this: If I lose signal on the downlink, do I still have the ability to transmit commands to the Phantom? If I'm on a waypoint mission and I lose signal and want to bring her home, will the return to home message be sent and received after I flip over to P mode? One last question: If all else fails, if I turn off the transmitter, will the Phantom return to home, even if it's running a waypoint mission, and it never gets the P mode command?

Anyway guys, thanks for listening.

alokbhargava · Jul 7, 2016

Consider two independent channels of communication: one for Video and other for Commands. Signal lost means Command line is down and RC can no longer communicate with AC. You can set on DJI Go app as how Ac behaves in case signal is lost, you have choices: RTH, Landing or hover. If Signal is lost, no matter how you press RTH button it will not be effective, thats why we have a setting which finally stays on AC and works accordingly in case signal is lost.

If you are flying in waypoint mode, all controls are transferred to AC for execution unless you pause or stop. So turning off RC will not matter but it is not advisable to turn off RC. AC will reach last waypoint and then execute the last action like hover or return to home point etc.

With The Birds · Jul 7, 2016

Think if the signal meters more as video link and control link quality. Not sure about the standard but with pro and advanced it is very common to loose video while still having control of AC.

As long as your RTH setting is return (as opposed to hover or land) and you have set an RTH height sufficient to clear any obstacles on the direct route home you will see your AC again (assuming sufficient battery to make the flight prior to auto land on critical level). The obvious exception being if you are flying a litchi waypoint mission with LCMC set, the AC will continue to happily fly to the last waypoint and completion setting.

Turning off your AC will initiate the same behaviour as any other event or circumstance causing lost signal.

You need a connection to sent an RTH command manually.

Mark The Droner · Jul 7, 2016

There are quite a few possible scenarios and some of them can be confusing and disconcerting if you're new.

1) Everything is working perfectly.

2) You've lost video but you still have telemetry. Since you have telemetry, you can see that your control signal is still intact. So you can still control your Phantom.

3) You've lost telemetry but you still have video. This can be confusing because it will still show the previous telemetry and you might be confused and think some of it is current, but it is not. For example, it might report 65% battery when you actually have something less. You should probably come home.

4) You've lost video and telemetry. Now you have nothing but a dead screen which isn't updating. You might have control and you might not. You don't know. This is where a live tracker such as Flytrex Live 3G is really handy. If you want to initiate RTH, best bet is to turn off the power to your transmitter.

5) You've lost the control signal. But you still have video and telemetry. You should see a big red DISCONNECT on your screen. You have no control of the aircraft. It is most likely already in RTH mode. If you have it set to come home, you will likely get the control signal back as it gets closer, and you can then take control of your Phantom if you wish.

Hope this helps.

Emil Cost · Jul 8, 2016

alokbhargava said:
Consider two independent channels of communication: one for Video and other for Commands. Signal lost means Command line is down and RC can no longer communicate with AC. You can set on DJI Go app as how Ac behaves in case signal is lost, you have choices: RTH, Landing or hover. If Signal is lost, no matter how you press RTH button it will not be effective, thats why we have a setting which finally stays on AC and works accordingly in case signal is lost.

If you are flying in waypoint mode, all controls are transferred to AC for execution unless you pause or stop. So turning off RC will not matter but it is not advisable to turn off RC. AC will reach last waypoint and then execute the last action like hover or return to home point etc.

Very helpful information. I think you cleared it up for me.. thank you!

happydays · Jul 8, 2016

If you're in waypoint mode and you lose FPV, you will in all likelihood lose the telemetry metrics as well. Not contol, but telemetry. I have also seen on three occasions where FPV was lost on a waypoint mission that when the video link came back, the telemetry numbers stayed stuck. But mostly it comes back in line with the FPV.

Emil Cost · Jul 8, 2016

happydays said:
If you're in waypoint mode and you lose FPV, you will in all likelihood lose the telemetry metrics as well. Not contol, but telemetry. I have also seen on three occasions where FPV was lost on a waypoint mission that when the video link came back, the telemetry numbers stayed stuck. But mostly it comes back in line with the FPV.

Good to know... and also good to test all sorts of scenarios for the "just in case" situations. I flew a Litchi mission last night and I walked so I positioned myself in line of sight with the quad. I had perfect video transmission at over 6500 feet. Not a single dropped frame or screen freeze moment. I also have antenna reflectors that help a lot. The knowledge beforehand of how things work, as far as losing signal and how to recover, will save you big time if and when the situation arises. This forum is fantastic. I ask a question, and almost immediately, I get responses from great people like yourself. Much appreciated, and thank you!