Why use external telemetry module over onboard in FC?

Hey guys, I’m trying to understand the pros and cons of using onboard telemetry (with my Mateksys H743-Wing) versus external telemetry modules. For now the built in telemetry looks like a good choice to me, although I am wondering why people sometime choose external modules? A couple of points I have for external modules:

  • more powerful, can allow bigger range for signal
  • probably could be more accurate since it is dedicated device
    But I also see a lot of downsides and the biggest one is that overal build becomes more complex.
    I don’t have requirements to control communication protocol or anything like that yet. But for the context, I’m trying to build VTOL fixed wing plane that should fly on 50-60km ranges. Also, my plane will fly on non standard frequencies with custom antenna and changed firmware for the TX/RX modules.

What would be your reasons to setup external telemetry if your FC has built it?

What onboard telemetry are you talking about?


Telemetry signals don’t have to travel far, about 10cm to the Rx or SiK :slight_smile:

Don’t they need to travel to ground receiver?

the board has a built-in accelerometer, gyroscope, barometer. so i can use the OSD and pass the info through the video transmitter right?

Sure, if the data from OSD suits your needs. But whether it’s a Vtx or another device, like a Sik telemetry radio, it’s an external device.


Yes, depending on where you want to receive them either via the receiver, Vtx, or some kind of telemetry radio like SiK. Or, since you’re going for long range, something like UAVCast might be an option. But you’ll always need to send telemetry through some kind of transmitting device.

Telemetry, as it’s definition. It can provide far more info than “accelerometer, gyroscope, barometer”. So it depends on your goal of implementing telemetry.

If you are flying long range and wanna control the drone throught telemetry, then you probably need a more powerful, reliable, long range telemetry.
If you are just using this wireless tememetry to configure the apm, then short range might do the work.

I think we have to back to our purpose of the telemetry usage. So the question is what requirement of your setup of telemetry?

Yup, that makes sense to me. Probably I am using wrong terminology and kinda confuse you guys since I’m new to that stuff. OSD should suite my needs, for sure. I don’t really need to observe telemetry info much, as long as I have control over my plane.

My goal is to build ~50km range fpv fixed wing. And the main criteria for me is to have VTX and receiver working on such ranges.

I’m kinda confused why telemetry is usually comes together with what we call receiver since telemetry suppose to actually transmit data. But that becomes making sense to me as well.

It can do both with the right RC System. See here:
Yaapu Telemetry.

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Yeah this is what was probably confusing me the most. Telemetry assumes data transmit to the receiver, while same time we are talking about telemetry to be a receiver for control.

And I actually plan to work on longer range flights (~50Km), so I guess I would need something more powerful. But as I figured the telemetry data isn’t that important for me as long as plane receives control instructions and I VTX work.

The main requirement is to control my fpv fixed wing on range ~50km. Telemetry data observation isn’t as important to that moment.

Receiver (Rx) is primarily the thing that receives the command signals from your transmitter (Tx) and forwards them to your flight controller. Newer Rx/Tx technologies are able to transmit telemetry back from the flight controller via your receiver to your transmitter, so you can get live telemetry information on your transmitter’s screen and/or trigger alerts. Transmitter is the thing you hold in your hands to control your drone.

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Thanks, that makes sense! So when RC guys mention “telemetry” they usually assume that it would work in both directions right? In common telemetry module works as receiver and transmitter?

As far as I see it, the term “telemetry” describes the process of “sending data back to the pilot”. You can get minimal data through OSD, or more data either through the RC link backwards or with a dedicated telemetry link (like this for example) parallel to RC.

If it works in both directions is depending on the type of the telemetry link.
OSD is one-way down; through the RC link is depending on the protocol used, it is possible but not all links support it (Yaapu over CRSF for example doesn’t); dedicated telemetry links usually are two-way.

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Also if you are doing ~50km missions, you might want to do some research on Antenna Trackers or links over mobile cell service.

An AAT is not absolutely necessary. What is good is a higher location and sensible antennas. And of course an RC system that goes this far (from old to new with own experience: EzUHF, Dragonlink, RFD, Crossfire, ExpressLRS).


So what usually requres choosing dedicated telemetry link paralel to RC? It is like provides more power and stronger signal or something?

Yup, dedicated dirrected antena will definitelly be used for that. Although interesting point around mobile cell service, do you have any examples in mind? Would be much appreciated

In our case higher location is not always possible. So the directed antenna will be used

For the RC system. I was looking around pros and cons, and for the longer ranges they are almost always recommend DragonLink instead of Crossfire or ERS, since DragonLink systems provide longer range on same power levels from transmitter. Definitelly a question for another topic, but if you have experience for longer ranges what would you recommend?

I have already flown over 50 km with all the systems mentioned. Currently I would prefer an ExpressLRS system (Radiomaster Bandit) on 868/900 MHz to all others.