What's new
Aloft Forums

This is a sample guest message. Register a free account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members through your own private inbox!

How to Get 10 Channels with G-RX8?

hotdogx

User
Joined
Jan 3, 2019
Messages
39
Reaction score
10
I have a new Swift S1 glider that needs 10 channels. I would like to use the G-RX8 RX. What is the best way to get 10 channels using this RX? I'm also thinking I might want to add a redundant RX, so nt sure how that would change things. I've looked at RC Groups and looked at the Aloft website store, but I am confused on exactly what items I need to add to the G-RX8 to run 10 channnels. It appears there might be several ways to do this.
 

Konrad

Very Strong User
Joined
Jan 23, 2018
Messages
7,822
Reaction score
1,488
Location
San Francisco
Yes there is more than one way to do this.
What is it about the G-RX8 that you like?

I like the bigger RX8R-pro receiver
https://alofthobbies.com/frsky-rx8r-pro.html

You can gang just about any second RX for channels 9&10.

I like this RX as my redundant RX
https://alofthobbies.com/xm-plus.html

The methods below require digital servos. Are you using S-Bus servos?

You can convert your digital PWM servo to S-bus servos with one of these soldered on to each servo lead. and run everything on S-bus. That's about $100.
https://alofthobbies.com/frsky-sd1-sbus-converter.html
https://alofthobbies.com/xm-plus.html

Another is to use an S-Bus decoder on the last channels. You will need a Channel Changer.
https://alofthobbies.com/frsky-sbus-decoder.html
https://alofthobbies.com/frsky-servo-channel-changer-sbus-cppm.html
https://alofthobbies.com/xm-plus.html
 

hotdogx

User
Joined
Jan 3, 2019
Messages
39
Reaction score
10
Obviously I am an FrSky newbie. I have already programmed an electric launched glider, a simple 2 channel DLG, and a full-house DLG on my Horus X10S using G-RX6 receivers in all three gliders. For my Swift S1 glider, I like the G-RX8 because it already has the vario and altimeter built in. If I understand correctly I can plug in the FrSky SBUS and CCPM decoder to the G-RX8, and then plug the channel 9 and 10 servos into the decoder, but I still need to get the servo channel changer to assign channels to the two added servos? This gets me 10 channels, but not a redundant receiver. If I want 10 channels AND a redundant receiver, do I need the RB-20 and a second receiver such as the XM+? Or would I need a second receiver to add to the G-RX8 first (to get channels 9 & 10), then add the RB-20 and another receiver such as the XM+?
 
Joined
May 31, 2018
Messages
92
Reaction score
13
You don't need the RB20. The redundant function of the G-RX (or any RX-series rx) just needs a second receiver that has an SBUS output that you can switch off the telemetry. You plug its SBUS out in the G-RX SBUS in. So pretty much any D16 X-series will do. Preferred choices are the XM+, XSR, RXSR because they are small and SBUS only.
The XM+ cannot send telemetry. You may need to flash the XSR (or any classic X-Series) with recent firmware to disable the telemetry. The RXSR and other RX-series receivers support disabling telemetry. Not sure about the G-RX but it is unlikely you would used that as a redundant RX.

Note: You need OpenTX 2.2.X and the latest XJT firmware (2017-05-21 170317) to disable telemetry from the TX via bindopts. The latest XJT firmware may not work on non Plus X9Ds.

Edit: Clarification
 
Last edited:

Konrad

Very Strong User
Joined
Jan 23, 2018
Messages
7,822
Reaction score
1,488
Location
San Francisco
While I do use a G-RX8 receiver I much prefer the discrete Vario.
https://alofthobbies.com/frsky-high-precision-vario-fvas-02h.html

The RB-20 looks to be your best solution.
https://alofthobbies.com/frsky-rb-20.html
https://www.frsky-rc.com/product/rb-20/

You can hook up any 2 S-bus (output) receivers and you are good. I like that the RB-20 allows you to have high power distribution. (10 servos can tax the electrical bus bar on most receivers).

If I understand correctly I can plug in the FrSky SBUS and CCPM decoder to the G-RX8, and then plug the channel 9 and 10 servos into the decoder, but I still need to get the servo channel changer to assign channels to the two added servos? This gets me 10 channels, but not a redundant receiver.
Correct. To add redundancy all you need to do is add a XM+ receiver. The XM+ makes life easier as it has no telemetry output to interfere with the telemetry output of the G-RX8.

If I want 10 channels AND a redundant receiver, do I need the RB-20 and a second receiver such as the XM+? Or would I need a second receiver to add to the G-RX8 first (to get channels 9 & 10), then add the RB-20 and another receiver such as the XM+?
Several issues here. With the RB-20 you can use any 2 S-bus (output) receivers. S-bus gives you 16 channels to work with. The RB-20 takes care of the redundancy switching should it be needed.
FrSky allows you to gang 2 receivers together to get 16 channels of PWM output (Standard servo protocols).
If using the new FrSky redundancy capable receivers there is no need to use the RB-20 to get both your 10 PWM channels and RF redundancy. All you need to add a MX+ to get your redundancy.*


To PATK point he is describing only the issues with setting up redundancy. He is not addressing how to get to 10 or more channels. He brings up a good point, what TX OS are you running? I think you said you were using a Horus TX.

*Advance question. I wonder if one can loop back the RF (S-bus) data from the 2nd channel expansion RX into the the primary receiver to gain one's redundancy. Assuming one has a redundancy capable RX.
 
Last edited:
Joined
May 31, 2018
Messages
92
Reaction score
13
Using an RB20 in a glider seems a bit overkill to me.

You can use the FrSky SBUS and CCPM decoder with the G-RX6 to get 10 PWM channels and yes you would need a servo channel changer to set the channel addresses. There may be a LUA script for this so you can use the TX but I have not come across it. Seems like that would be nice.

You might prefer to use the single channel SD1 SBUS convertors since they can be inline or installed at the relevant servo.
https://alofthobbies.com/frsky-sd1-sbus-converter.html

I haven't used any of these so just pointing them out.

As noted SBUS runs on 9ms refresh so digital servos only for any connected via SBUS.
 
Last edited:

Wayne

Administrator
Staff member
Joined
Nov 29, 2017
Messages
7,707
Solutions
2
Reaction score
4,374
Location
Novato, CA USA
I'm not sure how large the Swift is that you are building, but if you expect to have an amp load over 10 amps, I will suggest jumping to something like the RB-20. It is not overkill when you are flying something really large that needs the amps. A normal receiver can not supply enough current to drive big servos in big planes.

If it is the Top Model Swift that we sell, I don't think you will need the RB-20.

As stated you can use the glider 8 channel receiver, simply plug in an XM+ to the Sbus In port, and add you servos. The additional servos should be digital and can plug into one of the Sbus decoders that the guys linked above. You will need a channel changer to set what channels the decoders will be listening for.

To be clear, these are Sbus to PWM decoders that you want. You do not want an Sbus to CPPM converter.
 

Konrad

Very Strong User
Joined
Jan 23, 2018
Messages
7,822
Reaction score
1,488
Location
San Francisco
Hotdogx, I too am new to FrSky. (I've only programed about half a dozen ship). One of the advantages to FrSky is that there is more than one way to skin the cat. (Sorry about the cat). While at first this can be confusing and makes it difficult at the consumer level. It affords us at the hobby level a lot of flexibility.

I find that I spend a lot of time at the FrSky site reading the manuals.
https://www.frsky-rc.com/download/

All the best,
Konrad
 
Last edited:

hotdogx

User
Joined
Jan 3, 2019
Messages
39
Reaction score
10
I appreciate everyone's inputs. I'm happy to get better educated on the FrSky receivers and redundancy setups. I should have mentioned that I am running OpenTX 2.2.2 on my Horus X10S. So far I like the way OpenTX does things. The Swift S1 glider I have is the 1/4 scale Top Model 3.14 meter. I got it (and my radio) from Aloft. I will be using Hitec digital servos throughout. HS-5245MG on ailerons, flaps, and elevator; HS-5085MG on spoilers; D485 on rudder; and D645 on retract and tow release. I prefer to set everything up on separate channels, thus the 10 channels. I will be doing hard aerobatics but I don't expect the current draw of the Hitec digital servos to exceed 4-5 amps max (assuming use of aileron, flap, elevator, and rudder servos simultaneously). The G-RX8 manual does not state its maximum amp capability for driving servos. I have run a similar set of servos on a 1/3 scale glider using a 9 channel Spektrum RX. I have no way of knowing if the G-RX8 power bus is similar in size/capability, but in this RCG posting a guy ran the G-RX8 at 14 amps with no problem https://www.rcgroups.com/forums/showpost.php?p=39213399&postcount=1488 If his test was valid then the G-RX8 would have no problem running the digital servos in the 1/4 scale Swift.

OK, having said all that, my current understanding is I can use a G-RX8 RX; plug in an XM+ RX to the G-RX8 to get my redundancy; plug in the FrSky SBUS and CCPM decoder to the G-RX8; plug the channel 9 and 10 servos into the SBUS and CCPM decoder, and use the servo channel changer to assign channels to the two added servos (running PWM of course). I believe this gets me 10 channels with redundant receivers. Is that correct? This would be a nice setup as well as being cost effective.
 

Konrad

Very Strong User
Joined
Jan 23, 2018
Messages
7,822
Reaction score
1,488
Location
San Francisco
Yep, but the bus bar will not handle much over 5 amp at 100% duty cycle. These are the same power busses as used by most manufactures for most receivers. These were adequate when we ran analog servos. But if you put an inferred thermometer on these power busses with a full compliment of digital servos you will see that the receiver electrical bus is inadequate. Actually I think the bus bar is good for 7 to 10 amps. It is the Jr style connector that is limited to 5 amps. This is why many higher current BECs use dual Jr connectors.

P.S.
To your question on RCGoofs. This S-bus decoder allows you to pull 4 PWM channels from the S-Bus stream.
https://alofthobbies.com/frsky-sbus-decoder.html

All the best,
Konrad
 
Last edited:

Taboaco

New User
Joined
Jun 7, 2023
Messages
2
Reaction score
0
Location
USA
Is it possible to get 2 G-RX8 in redundancy and get the extra channels from de slave RX?
 

Taboaco

New User
Joined
Jun 7, 2023
Messages
2
Reaction score
0
Location
USA
Is it possible to connect in redundancy mode and use the PWM output on the slave RX to get the extra channels?
 
Top