Connect 2 telemetry devices

I would like to use 2 telemetry devices on the pixhawk.

One like a short range 433 or 868 mhz radio and one 4G (LTE) like UAV MATRIX.

The reason is that we can use the short range Radio for take off and landing and the LTE for long range monitoring the flight. We cannot use only LTE because the connection is sometimes not reliable when we fly in remote areas.

Both solutions use serial RX/TX, 57600 baud. TX from pixhawk can go to RX on both without a problem, but TX from the units cannot be tight together to RX on the pixhawk.

This way we would have reliable control and Telemetry during take off and landing and can monitor the flight for long range, even when the connection is intermittent. It would also serve as redundancy in case 1 of the units would fail.

Is there a solution for this?

Just use two serial ports, both set to MAVLink. Be careful that you are not sending conflicting commands from the connected GCS stations.

Thanks for your fast answer. That solution crossed my mind as well, I just wasn’t sure what happens if both radios send the same command, but the LTE with 200mSec delay. Will that be a problem?

Simply monitoring two downlink telemetry streams is no problem.

For control via MAVLink, you’ll probably want to do some work to ensure that only one command is sent rather than blindly doubling them.

Perhaps this topic may be of interest:

There may well be a simpler/more elegant means of MAVLink command redundancy, but I am unaware of it.

Yes, I read that as well. But that will add a companion computer and a lot of complexity. I’m a fan of KIS, keep it simple.

I will give it a try on 2 serial ports and see what happens. Actually, we would only give commands in emergency situations. We’re flying large survey missions and for example we could fly into the rain. We just want to be able to give an RTL command or cut short on the mission by skipping some way points. Worse case scenario will be the command will be received twice. :slight_smile:

Most of the time (almost always) we will be definitely out of the range of the short range radio, so the command will only be received by the LTE.

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@tridge Sorry to bother you.
I have tried to connect 2 telemetry on the plane, but it doesn’t work. I posted this in Mission planner:

But i think its likely this problem comes from arduplane. Can you give some thought please?

We have been using 2 link simultaneusly for years with no problems, trough companion.

So that mean the companion handle the incoming telemetry 1 and 2 and probably translate in to 1, correct?

I’m using 2 separate telemetry units, 2 serial inputs.

We use mavlink-router, one link is udp the other is tcp

I’m just using 2 serial ports on the pixhawk. Very simple and straightforward. I also tried updating to the latest stable release. No difference. UDP (Telemetry 1) freezes up.

Very simple and straightforward and doesn’t work :slight_smile:

Yes, unbelievable. I did some more experiments today and noticed the pixhawk stops listening to serial 1 as soon as the other serial port is connected. It keeps on sending status messages, but doesn’t respond to any incoming message.

I also tried vice versa. So connect the secondary serial port first and then connect serial 1. Same result. Serial 1 keeps silent.

If you could add a companion running mavlink-router it would be much easier to manage connections, take it in consideration if everything else fails.

Thank you very much for your replies. I really appreciate. It simply blows my mind that something so simple doesn’t work. Am I the only one who would like to have redundant telemetry?

Probably not the only one but i think not many doing it without a companion.

@Verloop ArduPilot can support several simultaneous mavlink connections for redundant control. I commonly have 2 links on my aircraft, and sometimes have 3.
The key to this is ground station support for multiple links. MissionPlanner is a bit limited for that, I use mavproxy for multi-link
I think MissionPlanner can do it though and what we need is a wiki update to show how.
ping @hwurzburg

Thanks very much for your help. Looking forward to that information.

Ive been looking at the information about MAVProxy, but i think this is not what I mean.

I think mavproxy is for multiple groundstations to control 1 airplane.

I’m using 2 serial telemetry devices on 1 pixhawk. One connected to serial 1, the other connected to serial 4.

I can only send commands from the ground control station to the telemetry device on serial 4. I can receive status information on both.

I want to be able to send commands from the gcs to the uav on either 1 of them.

that is one use, but it is not the primary use. Most common is multiple links to one aircraft, or multiple links with multiple aircraft

try the “set link” command

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