FrSKY R9M & R9MM combo - using as redundant system

[Tim Callahan]

the instructions for this package are usless for non-tec guys like me. I have no idea how the R9MM receiver is connected to the main receiver in the plane, this goes in a Kappa 35. i need a wiring diagram showing me the connections to and from the two receivers. the mini receiver has 4 ports labeled ch 1 tru 4. it also has a 5 pin plug with s bus out, s port/f port, Gnd, v-in, and inverted s port. where do all thoes ports go? the package has a 4 pin plug with a plastic female connector that could hook to the 4 ports ch 1 -4. there is a 5pin plug that could be used for the other 5 ports. but where do they all go ?? video's showing redundant systems using other receivers show using a standard 3 wire connecton from one receiver to the other that wont work here. the receiver i'm trying to connect it to (the main receiver) is a GRX8.
Can any body help ??

 

[Konrad]

It is my understanding that these Rx are not compatible. The R9MM uses the 900mHz radio frequency band and the GRX8 uses the 2.4gHz radio frequency band.

 

[Tim Callahan]

That is true, but part of the redundant package is the 900mHz plug in moduel that plugs into the back of the Taranis radio
that transmits in the 900mHz frequency, supposably to give you not only a redundant system but also the additional distance with the 900nHz frequency transmitter moduel and receiver. at least i think thats what they are advertising with this combo package (R9M & R9MM)

 

[Konrad]

No that is not how it works. When you plug in the R9M TX module you turn off the internal 2.4 gHz and use the external plugged in TX RF deck, R9M.
I don’t see any mention of using 2.4gHz hardware concurrent with 900 mHz hardware. Nor do I see any redundancy on the 900 mHz band equipment. Can you link to the documents you reference?
https://alofthobbies.com/frsky-r9-mm.html
https://alofthobbies.com/frsky-r9m-transmitter-module.html

I go into a bit more detail here.
https://forum.alofthobbies.com/inde...ombo-using-as-redundant-system.595/#post-4419

I'll try to address your concerns in that thread.

All the best,
Konrad

 

[Wayne]

You can run the 2.4 and the 90-0 systems at the sametime. Frsky also has some cool new receivers for the 900 coming out soon.

 

[Konrad]

Ok,
Why would one do that? As the 2.4 gHz doesn't reach out as far as 900 mHz.
So, the 2.4 gHz RXR series (redundant series) of receivers would be the primary and the 900mHz S.Bus output would be the redundant RX.

Is this documented anywhere?

All the best,
Konrad

 

[Wayne]

Dual frequency.

 

[Konrad]

Dual frequency.

Dual frequency bands. As it is 2.4 gHz is a multi frequency set up.

My understanding is that the higher frequency bands allow for more data transmission. Lower frequency bands allow for longer transmission distances.

If looking for redundancy you would be limited by the transmission rate of the 900 mHz band and your range would be limited to that of the 2.4gHz band, while maintaining redundancy.

All the best
Konrad

 

[Wayne]

The thinking being that if something were take out one band, the other band could be relied on. 900 is really good at getting around and even through stuff that 2.4 hates.

 

[Konrad]

Yes, the higher the frequencies the more line of sight the transmission.

As a redundancy system dual frequency bands results in having to deal with the limitations of ether band . Not a combination of the benefit of ether bands strengths.

So in this case we are limited to the distance of the 2.4 gHz band if one is to maintain redundancy.

Yes, at short range 900 mHz gives you a fighting chance to transmit through tree leaves, that line of sight problem.

 

[Wayne]

Konrad - The way FrSky redundancy works is that it uses just one receiver until that reciever starts to have issues, then it switches over to the alternate. So, let's say the 2.4 is the primary. It will work from the 2.4 until it starts to fail, then it switches over to the 900. It will then switch back to 2.4 once it is solid.

In testing the the R9 modules when they first came out (they are much better now) we found them to be rock solid driving around the many commercial buildings near our office. The receiver was down low in our parking lot and I drove around in my car with the transmitter inside the vehicle and we drove all the way over to the street light and went behind one of the 2 story office buildings over there. Still 100% locked in. No way would 2.4 still be operating. I think we were on the mid power level for the test. They talk about 900 being able to bend around hills and penetait trees, but in that testing the signal should have been shooting through many office buildings, and we were right up against the 2 story with the transmitter. I think that was a brick/stucco building, but maybe it was a wood structure..

On your next visit, lets load you up with an R9 setup for some testing. I think you will be surprised.

I'm curious how well 900 works for R/C boats. I think they would have a lot to gain also. 2.4 really does not like water much.

 

[Tim Callahan]

ok this brings me back to my original question. how does the R9MM receiver connect to the primary (GRX8) receiver ? the R9MM has a 5 hole port on one side and a 4 hole port along the other side with a pigtail that has a 4 pin female connector, and a 5 pin plug, how do i connect the two receivers ? can you give me a wiring diagram ? what about using a RX8R receiver as the main and using the GRX8 as the redundant, i know this limits me to 2.4 but remember i'm flying line of sight and don't have building or trees to deal with. my problem is the carbon Kappa35 dead spots.

 

[Konrad]

Tim,
Do you have this manual?
https://www.frsky-rc.com/wp-content/uploads/Downloads/Manual/R9 MM/R9 MM -manual.pdf

On the first page they show to bring S.bus out you need to solder the red lead of your extension harness to V_in, the black lead to GND, and the yellow or white to the pad labeled S.Bus_out. The other end of the harness would plug into the S.Bus in pins on the GRX-8 receiver with the Jr male connector.

Wayne,
Line of sight is a bit of a misnomer, inaccurate, when dealing with radio propagation, so is bending.

Most wood structures are impervious to 900 mHz. And yes moisture (water) loves to absorb 2.4 gHz radiation. This is why on high humidity day we get a lot more "telemetry loss" warnings. You should see how the 2.4 gHz signal strength dies when flying in fog.

I'll try to make time for some fun with RF stuff the next time I stop by. Now it has been 30 years since I took my last commercial FCC tests. I think the name of the ticket has changed 2 or 3 times since then!


P.S.
I think with firmware 170922 you CAN use the redundantcy feature while in PWM mode! I may have learned something new!