RFD900 TXMOD vs Dragonlink

Hello all,

I’m a relative newbie so if it sounds like I don’t know what I’m talking about that’s because I don’t. =).

I’m looking for a long range system that has both RC and telemetry with MavLink connection to Mission Planner on a laptop.

From what I understand, the Crossfire system I’m currently using can do this, but the telemetry data to the PC isn’t consistent (maybe due to Crossfire high refresh rate).

I’m familiar with Dragonlink, and I believe it can do what I’m looking for. However, I see a lot more posts about RFD900 TXMOD in the hardware section of this forum, and I’m not entirely familiar with that system.

Can anyone explain some differences between Dragonlink and RFD900 TXMOD, and why I might want to choose one over the other? I have a RadioMaster TX16S.

Thanks.

Crossfire can do it, but it’s clunky. I’ve never been able to get it to create a stable wifi link for mission planner, however I’ve noticed it seems to work well with QGC on my iPad.

Dragon link never impressed me. I know others swear by it, but I swore at it. Admittedly the older hardware I had required me to add an external ESP32 board to get a running wifi link. Once I got it working it was stable but the external module hanging off my radio was a pain. And I didn’t like their antennas.

RFD900X can be a struggle to set up, but once you do it can really do the job. The TXMOD fits nicely in the TX16S and will create a stable link for mission planner. The newer ux receivers give more options for mounting. To me, the RFD just felt more finished than the dragon link.

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I agreed with dragonlink. It never impressed me either.
I had runaway of my vehicle just switched to dragonlink.

Now I’m really impressed with express lrs.

It has:

  1. Easy to setup and update firmware via wifi (both tx and rx)
  2. Long range for control and telemetry (if you are using 100 mWt telemetry rx as betafpv elrs)
  3. Low cost.
  4. Usually it is compatible with Crossfire antennas. You can get nice 6 dbi Longshot antenna from crossfire.

As negative side it has no two way mavlink.

Regards.

Hello Allister & Dmytro,

Thanks for the feedback. That’s helpful.

Dmytro, I have also been using ExpressLRS on some of my miniquads. I just want the two-way Mavlink, which it doesn’t provide.

Thanks,
Patrick

I would say RFD Mod+Ux receiver all day long it just works,can be a awkward setting it up but when you are up to speed with it it is a walk in the park,I have just fitted an 868Ux to a 3 inch quad and used crossfire antenna’s

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Presumably, the decision whether to use RFD or Dragonlink will depend on which functionality you predominantly need.

Dragonlink is available with 433 MHz and 868/915 MHz. With the 433 MHz variant one comes already once further than with the RFD900 as mentioned in the title of this topic.

Here you should look in the same frequency range. In the 868/915 MHz range Crossfire is also quite competitive.

If one assumes that RC control is primarily the most important, I would weight the order to Dragonlink / Crossfire / RFD. If, on the other hand, Mavlink bidirectional is primarily the most important, then rather RFD / Dragonlink / Crossfire.

Of course, you can also combine Dragonlink on 433 MHz with RFD900 for Mavlink. Or similar combinations.

What I am mainly interested in is the RC control over at least 50 km. This is possible with Dragonlink and also Crossfire. With RFD900 I am not sure. These distances go but contrary to advertising not without further out of the box.

For these or greater distances, I myself have not yet seen a system that can then also Mavlink bidirectional. Maybe someone has a tip?

RFD TXMOD set = range, RC control, Mavlink2 2-way, reliability, good/high baud rates

I’ve seen remote UAV support conducted over RFD radios

RFDesign itself specifies around 40 km max. That’s good, but not enough (for me).

And can apparently with the TXMOD only PPM with 8 channels …

EDIT: sorry, I’m not an RFD salesman, but I have been impressed

The TXMODv2 will do 16 channels PPM or SBUS, it’s not limited to 8 channels. It can even translate → PPM on transmitter end, SBUS on receiver end, for example.
You also have the option of using the Yaapu telemetry script on suitable transmitters.

When you are considering CompanyA says 40km and CompanyB says 50km , that’s getting into the “do the tests yourself” territory. I know the RFD’s can go a lot further. The RFD radios are used by professionals in all kinds of situations (as is Dragonlink too apparently)
Is it a want or a need? What’s your likelihood of actually getting out to 50km range. I think standard RFD radios would have no trouble at all with 50km for an aircraft. If you are worried put your ground station radio up on a pole or use a yaagi, but 50km is “we do that every day of the week” for these.

Depending on your terrain and local laws, permits and so on there could be special versions if you were to contact RFD - it really depends on your requirements.

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I believe that with any RC system with Mavlink integration, the telemetry does not go much further than 30 km (my tests with Dragonlink and Crossfire). It is much better for the range if RC and telemetry are separated (so as an example Dragonlink only for RC and RFD900 only for telemetry).

I myself have had good experiences with transmitting Mavlink telemetry via UAVCast (LTE, 4g, 5g).

How many channels are transmitted with TXMOD? Is it really only possible to use PPM with 8 channels, or can SBUS also be configured? (Ok, I saw your edit, thanks for the info!).

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I know TXMOD will do at least 16 channels with PPM or SBUS. I have that configured and working.
As far as I’m aware the RC control would go as far as the telemetry - both rely on the same radio link. The RFD’s dont use a separate frequency range for RC or Telem.
I know the standard RFD gear will do easily much more than 40km. I think the specs are conservative.
Like any RC set up, it would be important to properly configure and test failsafes.

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I just checked with someone - 70km would be typical with the standard long antennas on the ground side and stubbie antennas on the air side, 1 watt and a high data rate.
180km with a yaagi on the ground.

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wow that is impressive Shawn,thank’s for that have a nice weekend

Is there any evidence for this? For example, a log and a setup description?

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Unfortunately the logs from those flights cant be made public. I do know a few people who’s job it is to do such flights and this sort of thing is common place.
I believe their setup is similar to what I use (115k baud, SBUS RC control) or possibly higher data rates in some cases.
The default settings for 57k baud is very dated and suits the common cheap telem radios.
I’m not licensed to do anything more than VLOS so I even use the RFDs on lower power than standard (27db) just to save a tiny fraction of battery power.

EDIT
Not trying to bully you into buying RFD - just imparting my experience :slight_smile:
I don’t have any experience with Dragonlink.
Best to assess the radios yourself and make your own decision - as I said be sure to set and check failsafes. It can be hard to check range with “long range” radios.

Like a lot of things in this sector - see if the manufacture can supply real, meaningful specifications and any test data.

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Thanks for the input from everyone! I don’t plan on going anywhere near 40km, so the ultra long range is not a concern for me.

I actually owned a Dragonlink about 10 years ago, so I figured I’d just buy that again, but after reading everyone’s opinions and weighing the differences, I’ve decided to give the RFD900 TX MOD a try this time around. I will let everyone know how it works out for me.

Thanks, again, all!

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Is there a chance to get a screenshot of your configuration or of “someone”?

For example, it is relatively unlikely that a 900 MHz system beats a 433 MHz system in range. In this respect I am very skeptical that a RFD900 incl. full Mavlink should reach 70 km. It seems to me that there is some exaggeration …

This radio didnt have RTS/CTS set when I took this screen shot, nor was it doing RC control. It was intended to be just a ground station radio. The Air speed and Baud rates are what I’m currently using though.
image

The TX Mod is using those same settings (plus SBUS and RTS/CTS) and it provides telemetry data via Wifi to the ground station, and we have yaapu scripts running on the Taranis and TX16S.

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As you say 433MHz could theoretically go longer distance than 868 or 915, but in reality the power and channels available in 433MHz is severely limited due to the fact that most countries use that 433 range for garage door openers and all manner of random devices.

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There is no such thing where I fly :wink:.

Fact is, there are hardly comprehensible long range reports with RFD900, but very well with Dragonlink. Also discussions / experience reports around RFD900 are hardly to be found. The system may be quite good, but unfortunately it is hardly used.

The range of a RC system is one thing. It becomes exciting, if full Mavlink is to be transmitted with the system. 70 km is certainly not an achievable range with an RFD900 stock setup. And certainly not with a TXMOD in the handheld transmitter. At least a relay on a tripod is necessary to achieve at least approximately good ranges.